Native habitat
A grove of aspens with leaves quaking in the wind or in glowing yellow fall color is an arresting site. Quaking aspens (Populus tremuloides) have one of the largest natural ranges of any tree. They grow natively across Canada and as far south as Pennsylvania, Missouri, and the western mountains reaching into Mexico. Pockets of western Montana are home to many native quaking aspens. Aspens are most common at higher elevations and in riparian areas at lower elevations. However, they also grow in some rather dry sites near ponderosa pine and Douglas-fir.

Growth patterns
Aspens grow rapidly to reach maximum heights of 50 to 60 feet. They are considered a short-lived species since they rarely live to 150 years old. As ornamentals, individual aspens commonly live for only 20 - 40 years reaching a height of 30 - 40 feet. Although their lifespan is short, aspens produce new shoots from their roots. In wet sites, aspens can produce 100 suckers per square meter. These new shoots grow into mature trees that are genetically-identical to the mother tree. This clonal reproduction results in the solid stands of aspens found in nature. Their dense, shallow root system allows them to survive in boggy areas.

Site requirements
Aspens need full sun since they are extremely intolerant of shade. They can grow in most soil types and pH may range from 5.0 to 8.0. However, they prefer well-drained soils. Higher elevation locations such as Bozeman and Butte are good for ornamental planting. Aspens are a "pioneer" tree species that can survive in many locations, but hot, dry sites are least favorable to growth.

Potential problems
Aspens are very popular among Montana homeowners. However, they are susceptible to numerous problems that can detract from their beauty in the home lawn. The natural suckering can be a problem for homeowners that want to keep aspens "within bounds." The short lifespan can be problematic and aspens become susceptible to more problems as they age. They are prone to more diseases and insects than most other trees grown in Montana.

Diseases
There are several diseases that can cause black spots on leaves or twig dieback, or both, on aspen. These include shoot and leaf blight, bacterial blight, and Cytospora and Hypoxylon canker.

BACTERIAL BLIGHT causes young leaves and the attached twigs to turn black quickly. Cankers (oval, sunken areas), also can develop on the south side of trunks and branches in trees with this disease. The disease is not usually fatal to trees, especially mature ones, but can cause stunting.

To manage bacterial blight, prune infected tree branches, making the cuts about 8 inches below the damaged area. Sterilize pruning tools after each cut in a solution of 1 part household bleach to 9 parts water. Burn or dispose of the pruned material. Rake and dispose of leaves and debris in the fall. If bacterial blight is a chronic problem in your aspen trees, begin treatment in spring when leaves start to emerge. Spray the tree 3 or 4 times, once every ten days, with Bordeaux mix or other product labeled for bacterial blight.

VENTURIA LEAF AND SHOOT BLIGHT is also a fungal disease that causes black or brown lesions that kill the leaf and shoots on aspen. Within a few days, the blackened leaf tissue turns olive green as the fungus continues to grow. In wet years, all terminal shoots may be killed, but damage does not spread to the rest of the tree. Young saplings are more prone to damage than older trees. Prune infected shoots, disinfecting pruners between cuts. Rake and remove fallen leaves to help prevent reinfection next spring.

SEPTORIA LEAF SPOT is another fungal disease in aspen. Symptoms are the brown or black mostly circular spots on the leaves. Damage does not usually extend into the stem. The fungus overwinters in dead leaves and twigs. Severe infections can result in partial defoliation of the tree, but is usually not fatal to the tree, which will generate new leaves. However, cankers can be produced that can girdle and kill stems or branches, or serve as infection courts for other diseases.

To control Septoria leaf spot, remove and dispose of fallen leaves and stems. In spring, spray trees 2 or 3 times with a Bordeaux mix or other fungicide labeled for septoria leaf spot to prevent infection. If you purchase aspen trees, ask for disease-resistant clones. Plant trees with plenty of room to allow for good air circulation, and prune with the same goal in mind.

A fourth cause of black spots on aspen leaves is WINTER DAMAGE. Environmental factors, such as cold, drought, or wind can cause damage in the winter months that does not become evident until leaves begin to form. To check for winter damage, cut a twig from the branch, and split it lengthwise. Winter damage causes the inside of the twig to be brown or black.

To minimize winter problems, do not fertilize aspens! High nitrogen fertilizers encourages rapid growth, and the new shoots often are not able to harden off before fall freezes occur. It is better to let trees grow at a slower rate than to push them to grow faster and die faster. Deep-kwater all trees (both evergreens and deciduous) in the fall after leaves of deciduous trees have turned fall color, but before the ground freezes. Water the extended root area 2-3 times farther than the branches extend, to a depth of two feet.

Cytospora and Hypoxylon cankers are common fungal diseases of fast-growing trees such as aspen. These fungi infect the branches and trunk resulting in sunker cankers and tree dieback. The pathogen mainly infects trees already stressed by drought, insects, winter injury, pruning, and similar factors. To avoid Cytospora, plant in a favorable site in a location that mimics the native range of the species. Prune only in late winter when trees are dormant. Water trees judiciously and control other pest problems.

Written by Martha Mikkelson and Sherry Lajeunesse, Plant Disease Diagnostician and Extension Urban Pest Management Specialist, Montana State University. Jan. 1998.
 

Cool, wet spring weather in spring can create ideal conditions for ANTHRACNOSE diseases on ash and maple. On ash, look for irregular, rapidly expanding, water-soaked spots on new leaves. Young lesions are greenish-brown to dark brown. Severe infections may lead to girdling and wilting of young shoot bases. Leaf drop and twig blight can occur also. Symptoms of maple anthracnose include brown to black areas that run along the leaf veins. There may be crinkling and distortion of severely infected leaves. Leaf drop and twig cankers may occur. Frost injury and leaf scorch can cause similar sysmptoms.

Anthracnose rarely kills trees. However, severe disease levels can predispose them to other disease, insect, and environmental problems. Dry weather is the best control for this disease. Raking and destroying fallen leaves and pruning severely infected branches may help somewhat.

Fungicides rarely are needed for anthracnose in Montana. However, if the disease does become a chronic problem, fungicides such as chlorothalonil and mancozeb are most effective if sprayed in early spring at bud break, followed by regular intervals during wet weather. By the time symptoms become widespread on the leaves, it is usually too late for good control.

References:
Pests of Landscape Trees and Shrubs; An Integrated Pest Management Guide. 1994. University of California. Oakland,
    CA  94608-1239. Pub. #3359. 327 pp.
Pirone, P., J. Hartman, M. Sall, and T. Pirone. 1988. Tree Maintenance. Sixth Edition. Oxford Univ. Press, New York, NY   10016. 514 pp.
Plant Health Guide. 1995. Meister Pub. Co. Willoughby, OH 44094-5992. 178 pp.
Sinclair, W., et al. 1987. Diseases of Trees and Shrubs. Cornell Univ. Press, Ithaca, N.Y. 576 pp.

Written by Sherry Lajeunesse and Martha Mikkelson, Extension Urban Pest Management Specialist and Plant Disease Diagnostician, Montana State University. Jan. 1998.
 

Juniper-Hawthorn Rust
JUNIPER-HAWTHORN RUST is a fungal disease that requires two different host species to complete its life cycle; a conifer and a deciduous host. Both must be growing close to each other for the disease to develop. In Montana, juniper is the most common conifer host. Hawthorn and serviceberry (also called juneberry and saskatoon) are common deciduous hosts. Apple is sometimes infected, but rarely. Mountain ash, pear?.

A closely related, but LESS common species of rust in Montana is CEDER-APPLE RUST. Many of our ornamental evergreens are mistakenly called "cedars", but these actually are junipers. Symptoms and management for both rust species are similar.

The fungus overwinters in reddish-brown galls up to two inches in diameter on the branches of the juniper host. In spring, the galls swell, and become covered with spikes. Later they form gelatinous, yellow-orange "sporehorns" that discharge disease spores. The spores blow in the wind to infect the secondary hosts such as hawthorn, serviceberry, or mountainash. On the broadleaf trees, pale yellow-orange spots form on leaves and fruit, and may develop numerous tentacle-like projections about 1/4 inch long.

Generally, the galls do little permanent harm to juniper trees or alternate hosts. Prune the galls from the infected trees to manage the disease in juniper. When the disease occurs chronically, preventative applications of fungicides can protect valuable alternate hosts growing near infected junipers.

References:
Pacific Northwest Plant Disease Control Handbooks. 1997. Extension Services of Oregon State University. Corvallis, OR 97331-0817.
Pirone, P., J. Hartman, M. Sall, and T. Pirone. 1988. Tree Maintenance. Sixth Edition. Oxford Univ. Press, New York, NY 10016. 514 pp.
Sinclair, W., et al. 1987. Diseases of Trees and Shrubs. Cornell Univ. Press, Ithaca, N.Y. 576 pp.

Written by Sherry Lajeunesse and Martha Mikkelson, Extension Urban Pest Management Specialist and Plant Disease Diagnostician, Montana State University, Jan. 1998.
 

MYSTERIES OF CEDAR-APPLE RUST
Many people think fungi are either boring or annoying, but any long, coffee-ladden discussion about the life style of cedar-apple rust should prove these ridiculous perceptions wrong. Think these facts over: 1) Gymnosporangium rusts reduce tree vigor, but do not kill trees outright. 2) Rusts are considered to be some of the most complex and advanced members of the fungal world. 3) Species of the fungus Gymnosporangium must reproduce via a sequence of five different spore types on two very unrelated host plants in order to survive. If you're thinking "Yeah, so what?", read on.

Some diseases, such as damping off caused by the fungus Rhizoctonia, kill seedlings outright. Others such as Gymnosporangium rusts are common and very visible on certain trees, but they only reduce tree vigor by diverting carbohydrates. As true parasites, they do not kill trees. Now, which do you think is the "smarter" fungus: the pathogen that kills its source of food or the parasite that feeds off the host without causing much growth reduction? The old addage "don't cut off the hand that feeds you" becomes pertinent here. Maybe annual herbaceous plants will be quickly replaced. However, when the target is a relatively slow-growing, long-lived species such as a cedar, it may be best to keep the food source alive, especially when life depends on cedar soup.

Plants had been battling fungal diseases for eons before fungicides were invented to help them. As you can imagine, they have developed all kinds of strategies to keep from being devastated by these killer fungi. And just like the development of the U.S. Department of Defense, the fungi developed new weapons of attack as the plants got more defensive. Rusts are considered to be at the top of the fungal totem pole in terms of being evolutionarily-advanced. One reason for this lies in their ability to secretly enter plants without tripping burgular alarms (Trojan horse theory). Once inside the plant cells, complex adaptations allow them to "tread and feed lightly" so they do not kill their host. More "primitive" pathogens do not have the ability to do this. Whether this less destructive approach of the rust parasites has slowed the natural development of host resistance is very debatable. Development of resistant plant varieties remains the most important means of controlling rust diseases as a whole. However, rusts often overcome the resistance that plant varieties have attained, attesting to the fact that the coevolution between rust fungi and their hosts is still very dynamic. So, the rusts give us an opportunity to see evolution in progress!

Rusts belong to a group of fungi that have developed very specific host relationships involving both a conifer and a rosaceous host. In other words, when you see Gymnosporangium rust on cedar or juniper, you can expect the same fungus to show up later on roseacous hosts that include either apple, crabapple, saskatoon, pear, hawthorn, or mountain ash. (The exact tree species that are infected depends on which fungal species are involved.) A cedar tree is not at all related to an apple tree, but the same rust species infects both in the course of its life cycle.

Additionally, it is important to remember that the symptoms on the two hosts look entirely different. This is because Gymnosporangium rusts produce five very different spore types, each of which grows on a different area of one of the two hosts. The structures these spore types form include large orange horn-like structures on conifer hosts in spring followed by a spore type well adapted for air-current travel to the roseaceous host. Two rusty-colored spore stages form sequentially on the upper and lower leaf surfaces respectively. The latter spore type also infects the fruit. Another "travelling" spore type is then produced. After these spores move back to the conifer host, they infect this tree again causing hard galls to form on the twigs. The rust spends the winter in the protective gall and begins this complicated cycle all over again in the spring.

The development of parasitism involves very specialized evolution in order to divert food from the host without greatly harming it. Forming a parasitic relationship with two hosts seems doubly difficult. So why would a fungus evolve such an odd dependancy on these two hosts? And what is the advantage of producing five different kinds of spores on these two hosts when other fungi seem to cause disease with just one spore type on one host? I don't claim to know all the answers. My theory is there are advantages to infecting cedars earlier in the spring and moving to apple leaves and fruit as they develop later. Since each spore type develops in a different location, this allows specialization in many niches or "spaces". Crowding is less likely to inhibit colonization of the host and differences in food sources can allow for more fungal diversity. Maybe the sporadic nature of the fungus on each host also allows less chance for host resistance development.

Gymnosporangium rusts do have a very colorful life cycle that is worthy of any philosopher's pondering. I'll admit that I am an oddball plant pathologist, but certainly in this case the question of "why does cedar-apple rust behave so strangely?" is much more intriquing than "how do I get rid of it?"
 

Cytospora Canker

Dead, sunken areas on tree trunks and branches sometimes are caused by Cytospora canker. Many deciduous trees (trees that lose their leaves in the fall) are susceptible. Common hosts are fruit trees, poplars, aspens, cottonwoods, willows, and spruce. Cankers often are associated with pruning wounds.

Long, sunken areas form on the trunk or branches. The cankered bark often is cracked or discolored with a ridge around the margin. Small, black "pimples" may be on twigs and branches or within the canker. Small branches and twigs are girdled rapidly, while larger branches and the trunk may take several years to become girdled and die.

On spruce, the lowest branches die, then branch death progresses up the tree. Dying branches first turn yellow-green, then purple, followed by needle drop. Profuse resin flows from infected branches, coats the entire surface of the bark around the cankers, and drips onto lower branches. See "Cytospora canker on spruce."

Cytospora overwinters on the bark and in the cankers. During wet weather in spring, spores form and wash to other branches by rain. These spores also can be transported by insects, pruning tools, and clothing. If the spores land on a wound, they can cause an infection. A canker will eventually develop as the fungus invades healthy bark.

To control Cytospora canker, remove and burn all cankered limbs and sprouts preferably in late winter. Avoid wounds such as lawnmower or vehicle damage. Maintain plant vigor through proper watering and fertilizing. Keep in mind that fertilizer actually can encourage Cytospora indirectly by promoting winter injury of new tissues whose growth was encouraged by the fertilizer.

Water trees deeply over the entire extended root zone area. For deciduous trees this area is 2-3 times farther than the branches extend. For conifers, water 1½ times farther than the branches. Allow the water to soak to a depth of about 3 feet. Deep water all trees in late fall, after leaves of deciduous trees have turned autumn color but before the ground freezes. Water again in spring as soon as the ground thaws. For more information on good watering practices, see the topic sheet in this series "Watering Trees and Lawns: The Pest Connection".

In most of Montana, tree fertilizers are not needed. Avoid unnecessary fertilization since it can lead to other pest problems, winter damage, contamination of groundwater, overly rapid growth, and unnecessary expenses. To determine if your trees need fertilizing, have the soil tested or look for symptoms of nutrient deficiency such as yellowing, stunted growth, or twisted, deformed foliage. For additional information, see the topic sheet in this series, "Fertilizing Trees & Shrubs: Good Practices Can Help Prevent Pest Problems".

References:
Harris, R.W. 1992. Arboriculture; Integrated Management of Landscape Trees, Shrubs, and Vines. Prentice- Hall, Inc., Englewood Cliffs, NJ. 674 pp.
Pests of Landscape Trees and Shrubs; An Integrated Pest Management Guide. 1994.
University of California. Oakland, CA 94608-1239. Pub. #3359. 327 pp.
Pirone, P., J. Hartman, M. Sall, and T. Pirone. 1988. Tree Maintenance. Sixth Edition. Oxford Univ. Press, New York, NY 10016. 514 pp.
Shigo, A.L. 1986. A New Tree Biology. Shigo and Associates, Durham, NH 03824. 595 pp.

Written by Sherry Lajeunesse and Martha Mikkelson, Extension Urban Pest Management Specialist and Plant Disease Diagnostician. January, 1998.

Diseases in Trees: How Much Can Trees Tolerate?

As summer wears on, we see more and more damage from diseases accumulating on landscape trees. How much is too much? It depends on the tree, the disease present, and the time of season. Although we do not have frequent disease problems in trees in Montana, there are many diseases that can attack trees, and they can be difficult to diagnose.

Some common symptoms that usually are less severe are powdery mildew, rusts, and sooty molds. Powdery mildew causes powdery, white accumulations on foliage. Rust fungi cause small, round spots of orange powder on deciduous tree leaves or orange galls on conifer branches. Sooty mold, a black fungus that forms on leaves and twigs in association with aphids, usually is not a serious problem either.

Most pathogens that cause brown or black spots on tree leaves are not serious, although they can cause twig dieback. In those instances, prune and dispose of the heavily-infected branches. Generally by September, leaf diseases are not very important since the tree has already stored enough nutrients and carbohydrates for winter, and the leaves are not as crucial as they were earlier in the season.

Symptoms that may indicate a serious problem are sunken, discolored areas in the bark of trunks or branches. These are called cankers. Cankers can girdle trunks and branches, causing tissue death beyond the cankered area. Wilting leaves, splitting bark, decaying wood, or deformed, streaked, or mottled foliage are other symptoms that may indicate more serious problems. If you see any of these symptoms, try to get the problem identified, and implement the appropriate control measures.

References:
North Dakota Tree Handbook. 1995. Agriculture and Natural Resources, North Dakota State Universit, Fargo, ND. 228 pp.
Pirone, P., J. Hartman, M. Sall, and T. Pirone. 1988. Tree Maintenance. Sixth Edition. Oxford Univ. Press, New York, NY 10016. 514 pp.
Sinclair, W., et al. 1987. Diseases of Trees and Shrubs. Cornell Univ. Press, Ithaca, N.Y. 576 pp.

Written by Sherry Lajeunesse and Martha Mikkelson, Extension Urban Pest Management Specialist and Plant Disease Diagnostician. January 1998.
 

See "Identifying Elm Firewood" publication - this factoid needs work
Wood from trees infected with Dutch-elm disease should be debarked before storage or buried or burned immediately after tree cutting to prevent spread of this fatal disease to healthy trees. This is because infected trees which are cut down can contain beetles carry the disease to healthy trees. The beetles fly around and feed from about April 1 to September 15, so it is especially important to get rid of all elm firewood during that period or completely debark the logs. Since burning elm firewood kills the beetle grubs and eliminates beetle breeding sites, it is the most effective method of disposal.

Debarking the wood is a good way to rid the wood of elm bark beetles, thereby limiting spread of the disease. There have been no DED problems associated with using debarked wood for firewood

Insecticides do not effectively kill beetles in the wood . Since the beetles tunnel beneath the bark, it is difficult to obtain the complete insecticide coverage of the wood that is necessary for good beetle control. In addition, burning insecticide-treated wood in an indoor fireplace is not recommended.

References:
Harris, R.W. 1992. Arboriculture; Integrated Management of Landscape Trees, Shrubs, and Vines. Prentice- Hall, Inc., Englewood Cliffs, NJ. 674 pp.
Johnson, W., and H. Lyon. 1991. Insects That Feed On Trees and Shrubs. Cornell Univ. Press, Ithaca, N.Y. 560 pp.
Sinclair, W., et al. 1987. Diseases of Trees and Shrubs. Cornell Univ. Press, Ithaca, N.Y. 576 pp.

Written by Sherry Lajeunesse, Extension Urban Pest Management Specialist. Sept., 1997
 

Iron chlorosis causes leaves to turn yellow while the leaf midrib remains green. Advanced symptoms include very pale leaves that turn brown at the tips. Iron chlorosis is a common problem, especially for plants more suited to acidic soils, which have a low pH. If the pH of the soil is too high, which is often the case with our alkaline western soils, iron chlorosis can result.

Iron chlorosis is an iron deficiency that can be caused by several other things too, such as roots that are damaged by tilling, dry soil, and sandy soil with insufficient organic matter. Tilling damage and dry soil make the roots less able to take in nutrients.

Usually adequate iron is present in the soil. However, high pH results in conversion of the iron to a form that the roots cannot absorb. Have the soil pH tested so you will know your "starting point."

You can try to gradually lower the soil pH although this may take a long time. Try adding 1-2 inches of compost to the soil every few years, or add sulphur or peat moss. Plants also can be mulched with conifer needles which will leach some acids into the soil.

Short-term solutions include foliar application of iron chelate which is available from most garden supply stores. Try spraying 1 tbsp. iron chelate/gallon water on the tree leaves in early summer. You should see improvement in leaf color within 2 weeks. However, you will have to reapply the iron chelate as symptoms reappear.

Select trees and shrubs adapted to the soil type, climate, and other conditions in your yard to save problems in the long term. If soil is "improved" so certain plants can be grown, you must maintain the improvements each year. Plants growing under "foreign" conditions are under continual stress, resulting in more pest and environmental problems.

References:
Evans, G., and A. Epps. 1994. Choosing Trees and Shrubs for Montana Landscapes. Extension Publication EB 123, Montana State Univ.- Bozeman. Bozeman, MT 59717. 61 pp.
Pests of Landscape Trees and Shrubs; An Integrated Pest Management Guide. 1994. University of California. Oakland, CA 94608-1239. Pub. #3359. 327 pp.
Pirone, P., J. Hartman, M. Sall, and T. Pirone. 1988. Tree Maintenance. Sixth Edition. Oxford Univ. Press, New York, NY 10016. 514 pp.
Sinclair, W., et al. 1987. Diseases of Trees and Shrubs. Cornell Univ. Press, Ithaca, N.Y. 576 pp.

Written by Sherry Lajeunesse, Extension Urban Pest Management Specialist. Sept., 1997
 

DIEBACK of ornamental junipers is noticeable nearly every year across Montana. Both wet and dry condition can be the culprits. In general, junipers are adapted to dry, barren, rocky or sandy soils (which provide excellent drainage and aeration) and full sun. They do not fare well when planted in heavy clay, waterlogged soils, or are heavily mulched with bark and/or black plastic.

Some Montana conditions exceed junipers' tolerance for drought, however. For example, they continuously lose water through transpiration during winter months and cannot replace lost moisture in frozen ground. Therefore, they can suffer drought stress even in winter. Junipers planted near building foundations receive less moisture than shrubs out in the open. It is important to monitor soil moisture in such areas by using a Paul Brown probe or similar means. Deep water these junipers when the soil becomes too dry.

Water junipers so the moisture soaks at least one foot deep several times a year, especially in late fall just before the ground freezes. Water again in the spring as soon as the ground thaws. Avoid watering in late summer until time for the final watering in fall to give the shrubs time to "harden off" for winter.
 

JUNIPER TWIG BLIGHT is a second cause of juniper dieback. This disease usually is a problem of seedlings and nursery stock. Shrubs and trees older than five years rarely are seriously affected.

I

Symptoms

1. Dieback occurs on tips of branches that are the diameter of a pencil or smaller. Infected foliage becomes pale, then reddish brown, then turns brown or ash-gray after death.

2. Scrape away the bark until you reach living wood. A sharp line between discolored dead wood and healthy wood is a strong sign that Phomopsis is the problem.

3. Look at the base of the ash-gray scale needles for small, black fruiting bodies. The fruiting bodies form the spores that cause new infections. In wet weather, spores ooze from the fruiting bodies and splash onto new foliage. The spores are produced year round and infect yellowish-green juvenile foliage. The darker green mature foliage is resistant to infection.
 

Look-alike symptoms

Two other fungi can cause twig blight in juniper: Kabatina juniperi and Cercospora sequoiae var. juniperi. The distribution and severity of the two diseases is not yet known. The symptoms are identical for the Phomopsis and Kabatina twig blights, but the Cercospora twig blight is different.
 

Favorable conditions

Most severely-diseased plantings result from overly-wet conditions. Junipers have two flushes of growth under natural conditions, one in spring and another in summer. Pruning also stimulates new growth. When this growth coincides with wet, warm weather or frequent overhead sprinkler irrigation, severe twig blight can occur. Junipers growing in poorly drained, shaded and overwatered sites are most susceptible. Under such conditions, the entire shrub may die.
 

Control

1. Do not buy plants that have dead or dying twigs.

2. Plant junipers where air circulation will allow the foliage to dry quickly after dews, rain, or sprinkler irrigation.

3. Do not crowd plants. Avoid sprinkler irrigation if possible.

4. Plant resistant varieties.

5. Prune out infected branches during dry weather.

6. Apply fungicides such as Clearys 3336, Fore, or Kocide whenever new growth begins and conditions are wet.

7. Where twig blight has been a problem, protect spring and fall growth with a fungicide. Fungicides are not needed during dry weather.
 

Resistant Varieties

There are varieties of juniper which are resistant to juniper twig blight, and the whole issue can be avoided by planting these varieties. Ask your nursery or Extension agent for variety recommendations.

Chinese juniper (Juniperus chinensi)

'Fimina',' Iowa', 'Keteleeri', 'Pfitzeriana Aurea', 'Robusta', 'var.sargentii, var. sargentii glauca, 'Shoosmith'

Common juniper (J. communis )

'Aureo-spica', 'Depressa', 'Hispanica', 'Hulkjaerhus', 'Prostrata aurea', 'Repanda', 'Saxatilis', 'Suecica'

Creeping juniper ( J. horizontalis )

'Plumosa', 'Plumosa aurea', 'Procumbens'

Savin juniper ( J. sabina )

'Broadmoor', 'Knap Hill', 'Skandia'

Western red cedar (J. squamata )

campbellii, fargesii, prostrata, pumila

Rocky Mountain Juniper ( J. scopulorum)

'Silver King'

Eastern Redcedar ( J. virginiana)

'Tripartita'
 

References:

Evans, G., and A. Epps. 1994. Choosing Trees and Shrubs for Montana Landscapes. Extension Publication EB 123, Montana State Univ.- Bozeman. Bozeman, MT 59717. 61 pp.

Michigan Horticultural Extension. Twig blight of juniper. http://www.dlcwest.com/~createdforyou/juniper2.html

Moorman, G.W. 1997. Juniper twig blight. Plant Disease Facts. Pennsylvania State University. http://www.cas.psu.edu/docs/CASDEPT/PLANT/ext/jtwigblt.html

Pirone, P., J. Hartman, M. Sall, and T. Pirone. 1988. Tree Maintenance. Sixth Edition. Oxford Univ. Press, New York, NY 10016. 514 pp.

Sinclair, W., et al. 1987. Diseases of Trees and Shrubs. Cornell Univ. Press, Ithaca, N.Y. 576 pp.
 

Written by Sherry Lajeunesse and Martha Mikkelson, Extension Urban Pest Management Specialist and Plant Disease Diagnostician. February, 1998.
 

Leaf Scorch (Environmental)
 

Symptoms of leaf scorch due to environmental causes include browning of the leaf margins and\or yellowing or darkening of tissues between the main leaf veins. As the condition progresses, entire leaves may dry up, turn brown and become brittle. Leaves sometimes wilt rapidly and may remain pale green in color, even when dried out. Damage usually is more noticeable on the windward or southern side of trees. Plants may lose many leaves prematurely during late summer and have some twig dieback.
 

Leaf scorch can be caused by adverse environmental conditions, such as soil compaction, transplant shock, nutrient deficiency, drought, salt toxicity, and weed killer injury. Leaf scorch is common in Montana due to cold soils and slow root growth. The loss of leaves is seldom fatal, but favorable conditions should be corrected if possible to prevent decline or death of the tree. Stressed plants are susceptible to secondary problems such as attack by insects or diseases.
 

Prune sprouts and diseased branches to prevent leaf scorch. Maintain plant vigor through proper watering and fertilizing. Water deeply to encourage deep root systems that enable trees to withstand environmental stress such as drought and winter desiccation.
 

Check soil moisture at least 12 inches down. If the soil is rather dry, water trees slowly and deeply, allowing water to penetrate at least two feet. Deep-water the entire area under the canopy, one and one-half to three times farther than the branches. Because 95% of the roots of most trees are found in the top 18 inches of soil in this extended area. Sufficient moisture will help keep the trees vigorous enough to withstand pest attacks, as well as help prevent winter injury. It is very important to deep-water trees and shrubs at least twice a year, especially in areas where the water table is far below the soil surface or on sites exposed to wind; water every fall, after leaves turn autumn color, but before the ground freezes (perhaps at the same time fall fertilizers are applied if needed), and again in spring, as soon as the ground thaws to replenish dehydrated roots.
 

Avoid frequent, light waterings, and watering only at the base of the tree trunk. Trees suffering from drought can be selectively pruned to reduce transpiration, which is the loss of water due to evaporation through the leaves. Drought occurs when transpiration exceeds the plant's ability to supply water through the roots. Prior to planting, reduce foliage of transplants by pruning to minimize early injury due to water stress.
 

To determine if trees need fertilizing, have the soil tested and supply any missing nutrients. Avoid overfertilization, which can also harm trees and ornamentals. In most of Montana, additional tree fertilizers are not needed, especially when planted in turf areas that receive fertilizers. Unless trees are showing symptoms of nutrient deficience, such as chlorosis, stunted growth, or deformed foliage, refrain from fertilizing them unless soil tests indicate otherwise.
 

Compacted soil can be loosened over time by the annual use of core aerators, which remove a plug of soil up to four inches long, and then adding an inch or so of finished compost. The compost will soon work its way down into the soil, loosening it over time. Using dark-colored permanent mulches under the entire canopy area can help prevent compaction once soil is loosened.
 

When using herbicides near trees, do not allow mist to settle onto trees, and avoid spraying under the dripline since roots can take up many herbicides. Apply pesticides only on windless days to avoid problems with drift.
 

References:
 

Harris, R.W. 1992. Arboriculture; Integrated Management of Landscape Trees, Shrubs, and Vines. Prentice- Hall, Inc., Englewood Cliffs, NJ. 674 pp.

North Dakota Tree Handbook. 1995. Agriculture and Natural Resources, North Dakota State University, Fargo, ND. 228 pp.

Pirone, P., J. Hartman, M. Sall, and T. Pirone. 1988. Tree Maintenance. Sixth Edition. Oxford Univ. Press, New York, NY 10016. 514 pp.
 

Written by Sherry Lajeunesse and Martha Mikkelson, Extension Urban Pest Management Specialist and Plant Disease Diagnositician. February, 1998.
 

Powdery Mildew
 

Patches of white or grayish powder on garden plants, lawns, shade trees, or shrubs are probably powdery mildew. Powdery mildew is a fungal disease found throughout North America. It can cause severe problems in irrigated areas. Powdery mildew can attack a wide variety of turf plants, garden vegetables, and landscape trees and shrubs. The degree of damage varies with the plant and environmental conditions. In some cases, yield is lost or plants might die. In other species of plant, yield is not affected and damage is negligible.
 

In gardens and orchards, powdery mildew is common on peas, cucumbers, squash, strawberries, raspberries, apples, and cherries. On garden plants, look for patches of grayish-white powder on either the upper or lower surfaces of leaves or on various parts of the plants. As soon as diseased garden plants are discovered, prune out and destroy the infected parts. Disinfect pruning tools in a bleach solution of one part household bleach to four parts water after each cut. If the infestations are severe, remove and destroy entire plants that are infected.
 

In addition to pruning, fungicidal soap, which is manufactured by several companies, can help to control the disease. Fungicidal soaps are safe for both humans and the environment and are made from highly refined fatty acids, a form of soap. Another option is to spray once a week with a solution of one teaspoon baking soda dissolved in one quart of water. Antitranspirants, such as Wilt-pruf or VaporGard, have also been shown to prevent powdery mildew when applied every two or three weeks. Sulfur-based fungicides applied every 7-10 days will also help prevent spread of powdery mildew to healthy plants. Be sure to spray the undersides of leaves as well as the upper surfaces when using any of these sprays.
 

To manage powdery mildew in fruit trees, follow the same methods just discussed. In areas where powdery mildew is a chronic and severe problem in fruit trees, a preventative spraying program should begin in spring, with weekly applications of a fungicide such as lime sulphur to prevent establishment of the disease.
 

Shade trees and ornamentals are usually not severely damaged by powdery mildew. Many times all that is needed for trees and ornamentals is pruning and cleanup of fallen leaves and debris in the fall, unless the infestation is serious.
 

Powdery mildew in lawns is seldom serious enough to warrant chemical control. In shady areas that might be more prone to infection, shade tolerant grasses such as creeping red fescue can be planted. Raise the mowing height for grasses in shady areas that are prone to powdery mildew infection, and avoid over- or under-application of nitrogen. Organic fertilizers or slow-release formulations of lawn fertilizers are good choices. Watering lawns in the morning gives the plants the rest of the day to dry off, discouraging establishment of diseases, including powdery mildew. The longer plants remain wet, the more susceptible they are to infection by diseases. Do not work around plants when they are wet, as the disease spores can easily be transported to other plants on your clothes, hands, and tools under these conditions. Thin plants to allow air circulation and penetration of sunlight.
 

References:
 

Agrios, G.N. 1988. Plant Pathology. Third edition. Academic Press, San Diego, CA. 803 pp.

Flint, M.L. 1990. Pests of the Garden and Small Farm. University of California. Oakland, CA 94608-1239. Pub. #3332. 276 pp.

Howard, R., J. Garland, and W. Seaman. 1994. Diseases and Pests of Vegetable Crops in Canada, An llustrated Compendium. The Canadian Phytopathological Society and the Entomological Society of Canada, Ottawa, Ont. Canada K2A 1Y8. 554 pp.

Pacific Northwest Plant Disease Control Handbooks. 1997. Extension Services of Oregon State University. Corvallis, OR 97331-0817.
 

Written by Sherry Lajeunesse, Extension Urban Pest Management Specialist. Sept., 1997
 

Pruning Diseased Wood from Trees and Ornamentals
 

Late winter or early spring is a good time to inspect trees and ornamentals for symptoms of disease and to prune out any diseased plant material you find. Pruning is one of the best ways to keep the disease from spreading to other parts of the tree or to healthy trees. It is usually best to prune when woody plants are still in dormant stages to reduce problems from diseases and insects. Also, before leaves are formed it is easier to see symptoms of diseased wood.
 

Some of the more common problems you might find are black knot in plum and chokecherry; blight (including fire blight) which can occur in apple, crabapple, saskatoon berry, mountain ash, and raspberry; canker, which can be found in most trees and shrubs; and rusts, which can be found in apple, crabapple, juniper, cedar, and saskatoon berry.
 

The symptoms associated with these diseases include:

- swellings and knots that are black and hard (black knot);

- twigs that appear blackened as though scorched by fire, sometimes curled into a 'shepherd's crook' on the tip (blight or fire blight);

- purplish to chocolate brown spots or bands;

- tissues which crack open and expose the wood underneath, or sunken, elongated areas which are often cracked or discolored (canker).
 

In the case of conifers, needles can turn yellow-green then purple, then drop. Heavy resin can flow from infected conifer branches, coating the surface of the bark around cankers and dripping onto lower branches. Galls that are brown, warty or decayed can also indicate diseases, as can pronounced swellings, or large numbers of smaller branches called witches' brooms.
 

To prune the diseased material, cut off the infected area along with at least eight inches of healthy tissue. Sterilize your pruning tools between each cut by dipping them in a solution of household bleach diluted one part bleach to nine parts water, leaving the tool in the solution for 15 seconds. When you are finished pruning, disinfect the tools a final time, then coat the metal parts with a light oil. Be aware that your hands, gloves, clothing, and gardening tools can also spread the pathogens, especially when foliage is wet. Burn or bury the diseased plant material to destroy the pathogens as soon as possible and do your pruning in dry weather to minimize the spread of the diseases. Not all symptoms you find will be caused by pathogens; some can be caused by environmental or physical damage, such as sunscorch, winter injury, or dog urine. If you are not sure, or need help with the pruning process, contact your county Extension agent.
 

References:

Agrios, G.N. 1988. Plant Pathology. Third edition. Academic Press, San Diego, CA. 803 pp.

Harris, R.W. 1992. Arboriculture; Integrated Management of Landscape Trees, Shrubs, and Vines. Prentice- Hall, Inc., Englewood Cliffs, NJ. 674 pp.

Ellis, B.W. and F. Marshall. 1991. The Organic Gardner's Handbook of Natural Insect and Disease Control: A Complete Problem-Solving Guide to Keeping Your Garden and Yard Healthy Without Chemicals. Rodale Press, Emmaus, Pennsylvania. 418 pp.
 

Written by Sherry Lajeunesse, Extension Urban Pest Management Specialist. Sept., 1997
 

Slime Fluxing
 
 

Foul-smelling, slimy, weeping wounds on trees could be a conditions known as slime flux. The condition is caused when bacteria grow in fluids seeping from cracks or wounds in trees, or from crotch areas where fluids can accumulate. It is associated with a condition called wetwood that affects inner portions of the tree. Many species of tree can be affected, but slime flux and wetwood are most commonly found in elms and poplars, including the cottonwoods. It can also affect aspen, fir, maples (including box elder), white pine, mountain ash, paper birch, and others.
 

Usually, slime flux and wetwood in landscape trees is unimportant except for the undesirable appearance of the dark fluids seeping down the trunk of the tree. Severe infestations can sometimes cause foliage on upper branches to wilt and branches to die back. It does not result in tree mortality, however.
 

It is fortunate the damage is not severe, because there are no known cures. Drain tubes can be installed by tree care professionals for cosmetic purposes, allowing the fluids to drop to the ground rather than running down the side of the tree. Note: drilling holes in trees with this condition can spread the condition to other portions of the tree. For the most part, there is little you can do, or should do.
 

References:
 

Harris, R.W. 1992. Arboriculture; Integrated Management of Landscape Trees, Shrubs, and Vines. Prentice- Hall, Inc., Englewood Cliffs, NJ. 674 pp.

Pirone, P., J. Hartman, M. Sall, and T. Pirone. 1988. Tree Maintenance. Sixth Edition. Oxford Univ. Press, New York, NY 10016. 514 pp.

Sinclair, W., et al. 1987. Diseases of Trees and Shrubs. Cornell Univ. Press, Ithaca, N.Y. 576 pp.
 

Written by Sherry Lajeunesse, Extension Urban Pest Management Specialist. Sept., 1997
 

Spruce Dieback
 
 

The vast majority of damage we see on spruce trees in Montana is not caused by diseases, but rather by environmental causes such as drought and freeze damage. The damage may not become apparent for many months, which often results in misdiagnosis. Symptoms are usually dieback that begins from the needle tips and moves back toward the branch, in a rather uniform pattern. Sometime whole branches or portions of the tree may be killed. Color varies from brown to yellow to reddish-brown.
 

Heavy fall moisture can result in flushes of growth susceptible to winter damage. In addition, warm periods during winter, including chinooks, can cause spruce needles to loose moisture through transpiration and because the ground is frozen, roots can not absorb more moisture from the soil. Drying out (desiccation) of tissues can result.
 

Trees that go into winter under dry conditions also account for much of the damage we see every year. Most tree roots, of even the tallest trees, are in the upper 18 inches of soil, meaning that trees can become drought-stressed much more quickly in both winter and summer than we would suppose. Without a deep watering that soaks into the ground at least two feet in late fall, just before the ground freezes, the tree is very susceptible to drying out, resulting in dead needles and branches the following spring or summer. Windy, sub-zero temperatures increase moisture lost through transpiration, making the problem even worse.
 

To help prevent dieback, stop watering all your trees, including spruce trees, after midsummer. Then give them all one final deep watering after deciduous trees have changed to autumn color, but before the ground freezes. Water the entire area under and around the tree half again beyond the dripline of the evergreen trees. For example, if the branches extend six feet from the tree trunk, water at least nine feet around the trunk. (Roots of deciduous trees extend 2-3 times farther than the branches, so water that extended area for those trees.) Allow the water to soak down a minimum of two feet. A good, deep watering again in spring, as soon as the ground thaws can provide the tree with important moisture it may have lost during winter. In years when fertilizer is needed by the tree, you may wish to apply a appropriate granular product, then follow with this deep fall watering.
 
 

Fertilizing trees can also result in similar problems, especially to the flush of new growth that results. In most parts of Montana, trees need no fertilizing. This is particularly true in turf areas that receive occasional applications of fertilizer. In areas where soil tests show nutrients ARE lacking, fertilizing only once every 3-4 years is usually sufficient. If you do not conduct a soil test, do not apply fertilizers unless trees are showing symptoms of nutrient deficiency. Avoid annual applications of tree fertilizer. When fertilizers are necessary, apply them in fall, before the leaves of deciduous tree turn autumn color, but before the ground freezes, then apply your deep fall watering to help carry the fertilizers into the root zone. Research has shown that in spring trees use nutrients they stored the autumn before; spring-applied fertilizers will not be absorbed until early summer, about the time deciduous trees are fully leafed. If you wish to make tree fertilizer applications in spring, wait until this time.
 

In areas with heavy clay soil or very shallow water tables, another cause of dieback can be soils saturated with water, leading to oxygen starvation of the roots. If needles three or more years old are dying, the problem is not too serious. If new growth is affected, chances of recovery are not as good. Deep sampling of soils with a soil probe in these areas can help determine if drainage improvement is needed.
 

To prevent dieback in areas where heavy soils are not a problem, stop watering spruce trees after midsummer, until one final deep watering after deciduous trees have changed to autumn color, but before the ground freezes. Water the entire area under and around the tree half again beyond the dripline of the evergreen trees. For example, if the branches extend six feet from the tree trunk, water at least nine feet around the trunk. Allow the water to soak down a minimum of two feet. A good, deep watering again in spring, as soon as the ground thaws can provide the tree with important moisture it may have lost during winter. In years when fertilizer is needed by the tree, you may wish to apply a appropriate granular product, then follow with this deep fall watering.
 

References:
 

Harris, R.W. 1992. Arboriculture; Integrated Management of Landscape Trees, Shrubs, and Vines. Prentice- Hall, Inc., Englewood Cliffs, NJ. 674 pp.

Lajeunesse, S., G. Johnson, and J. Jacobsen. 1997. Proactive Pest Management; Using landscape design and plant vigor to manage weeds, insects, and diseases. Montana State Univ., Extension Service, Video No. 38. Bozeman, Montana. 23 min.

North Dakota Tree Handbook. 1995. Agriculture and Natural Resources, North Dakota State University, Fargo, ND. 228 pp.

Shigo, A.L. 1986. A New Tree Biology. Shigo and Associates, Durham, NH 03824. 595 pp.

Sinclair, W., et al. 1987. Diseases of Trees and Shrubs. Cornell Univ. Press, Ithaca, N.Y. 576 pp.
 

Written by Sherry Lajeunesse, Extension Urban Pest Management Specialist. Sept., 1997
 

Sunscald on Trees
 
 

Sunscald may sound like something that happens in hot weather, but on trees and ornamentals it is a cold-weather problem, occurring in winter and early spring. Tender bark on a southern surface warms much more from winter sun than the bark on the northern surface. The temperature of dark-colored bark in particular is raised considerably by the sun's rays. If a chilling breeze comes along or a cloud suddenly covers the sun, the mercury falls rapidly. The sudden drop in temperature can make the plant cells rupture, causing damage to the bark. Damage that occurred in winter might not be apparent until spring. Sunscald is particularly noticeable on young trees planted where daytime heat is high, such as beside a wall that reflects the sun's heat, or on the south side of the trunk. In warm weather, light-colored mulches can also reflect heat onto tree trunks. As a result parts of a tree, or even the entire tree, can be damaged. This is especially true for young trees. Bacteria or insects may enter the damaged bark and cause further problems.
 

Sunscald on trees can be prevented by wrapping the trunks with a commercially available tree wrap or with burlap or agricultural fleece. You can also guard against sunscald by painting the bark of young trees with white interior latex paint mixed with water 1:1, in the fall. The light color reflects the sun's rays and prevents sudden temperature changes. Using dark-colored mulching material that will absorb the sun's heat, rather than reflecting it onto the tree's trunk.
 
 

References:
 

North Dakota Tree Handbook. 1995. Agriculture and Natural Resources, North Dakota State University, Fargo, ND. 228 pp.

Pests of Landscape Trees and Shrubs; An Integrated Pest Management Guide. 1994. University of California. Oakland, CA 94608-1239. Pub. #3359. 327 pp.

Pirone, P., J. Hartman, M. Sall, and T. Pirone. 1988. Tree Maintenance. Sixth Edition. Oxford Univ. Press, New York, NY 10016. 514 pp.
 

Written by Sherry Lajeunesse, Extension Urban Pest Management Specialist. Sept., 1997
 
 

TREES - FRUIT

Apple Scab

need photos, otherwise ok
 

Apple scab is a fungal disease that occurs most commonly during cool, moist summers. In other areas such as the northeastern United States, apple scab is much more common and more severe than in Montana. The disease is more common in western Montana than in eastern Montana.
 

Fungus: Venturia inequalis
 

Hosts:

Apple and flowering crabapple are susceptible to scab. The fungus that causes pear scab is closely related to the apple scab fungus, but does not infect apple or crabapple and vice versa..
 

Symptoms:

Symptoms occur on both the leaves and the fruit. Look for leaf spots that are pale yellow when young, but then become olive-green and then nearly black in color. The margins of these spots are feathery and indistinct. The spots can darken to nearly black. Severely-infected leaves may curl and crack. On fruit, small, dark, raised areas appear first. Later, the skin ruptures and the exposed fruit tissue has a brown or black velvety appearance. As these spots enlarge and age, the center turns brown and corky. Fruit becomes distorted and young fruit drops.
 

Disease cycle and favorable conditions:

The disease spores spend the winter in fallen leaves and in the soil. In early spring, wind blows the spores to new host trees. During damp periods, new leaves become infected easily. The longer the leaves are wet, the more severe the infection will be. Once the disease has infected the tree, damage to the crop may be minimized but not cured.
 

Controls:

When the weather is favorable or there have been past problems with apple scab, preventative spray programs must begin as soon as leaf growth appears. This is because spores readily infect leaves from the time of cluster bud break until the leaves are fully expanded. Preventative spray programs entail regular application of a fungicide throughout the season. Fungicides such as captan, Funginex, mancozeb, and wettable sulfur are effective. When using any pesticide, whether it is natural or synthetic, be sure to read and follow label instructions carefully to ensure personal safety, and safety to others and the environment.
 

Resistant varieties:

A much easier way to deal with apple scab is to plant scab resistant varieties. There are numerous crabapples and apples that are resistant to apple scab and need no spraying for disease control.
 

Crabapple Varieties - Susceptible to Apple Scab
 

Almey Hopa Red Silver Van Eseltine

American Beauty Pink Perfection Royal Ruby Vanguard

Barbara Ann Radiant Royalty

Dorothea Red Jade Spring Snow
 

Crabapple varieties - Good to excellent resistance to apple scab

Adams Harvest Gold Robinson

Bob White Liset Sentinel

Centurion Madonna Snowdrift

Donald Wyman Molten Lava Sugar Tyme

Christmas Holly Prairifire

Source: Apple Scab and Flowering Crabapples, http://www.ipm.iastate.edu/ipm/hortnews/1991/6-5-1991/scab.html Richard Jauron, Department of Horticulture, Iowa State University, Ames, Iowa.)
 

The following is a list of some apple cultivars for western Montana. Only cultivars rated as "very hardy" are recommended for eastern Montana. The list is adapted from ratings compiled by Nancy Callan (Western Agricultural Research Center, Corvallis).
 

FB* RUST SCAB MILDEW HARDY

RIPENS AUGUST:

Lodi S - - - -

Geneva Early S S S - -

Quinte - - - - H

Julyred S - S - H

Jerseymac S - S - -

State Fair S - - - H

Redfree MR R R - -
 

RIPENS SEPT.:

Wealthy S - - - H

Prima MR R R R -

Novamac R R R S -

Chehalis - - R - -

Gala S - - - T

McIntosh MR - S - H
 

RIPENS OCT:

Sweet Sixteen MS - - - H

Macoun - - - - H

Spartan R - R - -

Cortland - - - - H

Delicious - - - - -

Empire - - - - -

Priscilla R R R S T

Johnathan - - - S T

Johnafree R R R S -

Honeycrisp - - - - H

Nova Easygro R R R R -

SirPrize S S R R -

MacFree R R R S -

Liberty MR R R S -

Freedom R R R R -

*FB = Fire Blight
 

More on apple scab - make LINK to Cornell University Apple Scab Home Page

http://ppathw3.cals.cornell.edu/profiles/applescab/pa2200t0.html

References:

Flint, M.L. 1990. Pests of the Garden and Small Farm. University of California. Oakland, CA 94608- 1239. Pub. #3332. 276 pp.

Gilkeson, L., and P. Michalak. 1994. Controlling Pests and Diseases. Rodale Press, Emmaus, PA 18098. 159 pp.

Pacific Northwest Plant Disease Control Handbooks. 1997. Extension Services of Oregon State University. Corvallis, OR 97331-0817.

Pest Alert, SDSU Cooperative Extension Service, July 15, 1995, Vol. 4 No. 7
 

Written by Sherry Lajeunesse and Martha Mikkelson, Extension Urban Pest Management Specialist and Plant Disease Diagnostician, 1998.
 

Fire Blight
 

Cause

Fire blight is caused by the bacterium Erwinia amylovora.
 

Hosts

Fire blight is a bacterial disease that attacks many trees and shrubs in the Rose family. (Make table)These include apple, crabapple, pear, mountainash, flowering almond, hawthorn, and cotoneaster during wet weather. Raspberry, rose, serviceberry (saskatoon), and spirea sometimes are infected as well. However, the strain of bacterium that infects raspberry does not infect apple and vice versa.
 

Origins of fire blight

Fire blight is native to North America and likely occurred on native plants such as crabapple, hawthorn, and mountain ash. The disease probably spread to susceptible cultivated apples, pears, and woody ornamentals planted by the early American pioneers. As the settlers moved west, so did fire blight. By the early 1900's, fire blight was a serious threat wherever apples and pears were grown.

It is interesting to note that stringent quarantine laws in countries such as Germany have been largely successful in keeping the disease rare in Europe. Also of interest is this little-known fact: In 1885, Joseph Arthur proved that fire blight was caused by a bacterium and for this he earned the first Doctor of Science degree awarded in America.
 

Symptoms

Symptoms include blossoms and young leaves that suddenly turn brown and wilt. Later, the twigs may appear scorched by fire, and may curl into a characteristic "shepherd's crook". Severe infections ultimately can be fatal. The leaves on infected branches often remain on the trees all summer and well into the winter. Fire blight also produces cankers on branches and twigs. These cankers consist of discolored areas that are slightly sunken and tend to crack around the edges.
 

Disease spread

The cankers may produce a slimy, bacterial ooze that contains millions of bacterial cells. Flies, bees, ants, aphids, and beetles can spread these bacteria from blossom to blossom and from tree to tree. The disease also can spread by rain, wind and pruning shears.

Most fire blight bacteria survive from one season to the next in hold-over cankers on infected trees. Infections occurring during bloom and during the prolonged cool, moist periods mostly come from the bacteria in the cankers. Other minor sources include hail, insects, and wind.
 

Favorable conditions

Hope for dry weather during blossom time. Higher temperature and lack of free moisture on the blossoms stops the activity of the bacteria. Fire blight most commonly develops in the late spring to early summer. Temperatures between 65 F and 86 F and plentiful rain with alternating periods of sunshine are necessary for disease to occur.
 

Economic damage

Fire blight is the most damaging disease of apples and pears in North America. Losses from the disease cost growers millions of dollars annually. Fire blight damages the current years crop as well as causes permanent damage to orchards.
 

Cultural control

Avoid heavy, early-season fertilization that results in profuse succulent new growth. It is especially important to keep watersprouts (new shoots growing from the base of tree) pruned. Watersprouts are very susceptible to the bacteria and infection can progress rapidly into the tree base causing loss of the whole tree.

Once fire blight has infected a tree or shrub, eradication is the only way to control it. During the dormant period, prune out the infected plant material, cutting at least six inches below the diseased wood. Disinfect pruners between each cut by dipping them in a solution of one part household bleach to nine parts water for ten seconds. Burn the diseased prunings.

Prevent problems by planting resistant varieties, or spray existing plants with an antibiotic such as Agristrep, every five to ten days during bloom. The addition of Regulaid as an adjuvant will increase absorption of the streptomycin. Excessive fertilization, especially with nitrogen, can make plants susceptible to fire blight. Fertilize only when soil tests show a nutrient deficiency. Rapid growth can make the tree or shrub susceptible to other problems as well; steady growth is best.
 

Control with Antibiotics

In very early spring, spray with a dormant oil plus copper-based fungicide before the buds begin to swell. Antibiotic sprays are only effective during flowering and in the summer. Mid-season sprays generally are not cost effective except after hail storms or other damage occurs.

When properly timed, antibiotic applications during bloom are effective. However, rain and temperatures between 65 F and 86 F are necessary for infection and disease spread. If blossom infection is well controlled, fire blight is often not a significant problem later.

Streptomycin (Agristrep) is the most effective antibiotic, except in areas where streptomycin-resistant strains of the bacterium have developed. Where streptomycin is not effective, copper-based bactericides, oxytetracycline, and flumequine are possible alternatives. Because of their limited systemic and curative action, bactericides are applied as protectants two or three times during the bloom period. Apply more often when it rains!

Repeated use of all antibiotic materials could lead to antibiotic resistance in fire blight bacteria. Resistance to both antibiotics and copper compounds has been found in fire blight bacterial populations in Washington and elsewhere. Resistance is not known to occur in Montana yet.
 

Biological control

Biological control of fire blight also is under study. Applications of antagonistic bacteria such as Pseudomonas fluorescens strain A506 and Erwinia herbicola strain C9 have been fairly effective in Oregon-based studies. Plant Health Technologies, a subsidiary of J.R. Simplot Co., is evaluating these organisms and plans to pursue EPA approval if results continue to be good. Development and approval processes move slowly, however, and a commercial biocontrol product probably won't be available before 1996 or later (check into this!)
 

Resistant varieties

Apple breeding programs have provided new cultivars with greater resistance to a number of diseases, including fire blight, apple scab, powdery mildew, and rust.
 

The following is a list of some apple cultivars for western Montana. Only cultivars rated as "very hardy" are recommended for eastern Montana. The list is adapted from ratings compiled by Nancy Callan (Western Agricultural Research Center, Corvallis).
 

FB* RUST SCAB MILDEW HARDY

RIPENS AUGUST:

Lodi S - - - -

Geneva Early S S S - -

Quinte - - - - H

Julyred S - S - H

Jerseymac S - S - -

State Fair S - - - H

Redfree MR R R - -
 

RIPENS SEPT.:

Wealthy S - - - H

Prima MR R R R -

Novamac R R R S -

Chehalis - - R - -

Gala S - - - T

McIntosh MR - S - H
 

RIPENS OCT:

Sweet Sixteen MS - - - H

Macoun - - - - H

Spartan R - R - -

Cortland - - - - H

Delicious - - - - -

Empire - - - - -

Priscilla R R R S T

Johnathan - - - S T

Johnafree R R R S -

Honeycrisp - - - - H

Nova Easygro R R R R -

SirPrize S S R R -

MacFree R R R S -

Liberty MR R R S -

Freedom R R R R -

*FB = Fire Blight
 

References:
 

Brown, Bill. Pest Alert. 1995. Colorado State University, Vol. 12, No. 1.

Brown, Bill. Pest Alert. 1995. Colorado State University, Vol. 12, No. 4.

Brown, Bill. Pest Alert. 1995. Colorado State University, Vol. 12, No. 5.

Pacific Northwest Plant Disease Control Handbooks. 1997. Extension Services of Oregon State University. Corvallis, OR 97331-0817.

Pests of Landscape Trees and Shrubs; An Integrated Pest Management Guide. 1994. University of California. Oakland, CA 94608-1239. Pub. #3359. 327 pp.

Plant Health Guide. 1995. Meister Pub. Co. Willoughby, OH 44094-5992. 178 pp.

Sinclair, W., et al. 1987. Diseases of Trees and Shrubs. Cornell Univ. Press, Ithaca, N.Y. 576 pp.

Watkins, J.E. 1992. Fire blight of apple, pear, and woody ornamentals. NebGuide, G92-1120-A.

Written by Sherry Lajeunesse and Martha Mikkelson, Extension Urban Pest Management Specialist and Plant Disease Diagnostician. January 1998.
 
 

VEGETABLES AND SMALL FRUITS
 

Damping-Off

Damping-off is a fungal disease commonly infecting seedlings planted in wet, cold soil. This disease is caused by fungi that rot the seedling stem right at the soil line. As a result, the infected seedlings can wilt and die literally overnight. Damping-off also can kill seedlings before they break through the soil. After a few weeks of growth, plant stems toughen and become resistant to damping-off fungi.

It is important to plant seeds when soil temperatures are favorable for plant growth. Optimal temperatures for growth vary with plant species. For example, spinach and pea seeds germinate and grow in cooler soils (at least 40 F) whereas corn and bean seeds require warmer soils (at least 55 -60 F). When starting plants indoors, grow in well-drained soil with plenty of light and air circulation. Avoid crowding of plants, low light, and heavy nitrogen fertilizers. A thin layer of sand or perlite that keeps stems dry at the soil line also can help. Plant seeds treated with a fungicide in areas where damping-off disease is common.

In greenhouses, funigicides containing a combination of thiophanate-methyl and metalaxyl such as DrenchPak (W.A. Cleary ) protect against the different fungi causing damping-off. Several biological fungicides recently have come on the market that are used as seed treatments, pre-plant applications, sidedressing, soil drenches, or foliar spraying. Examples include Promote Plus and Mycostop.

If, in spite of all your precautions, you find your garden seedlings toppled over one morning, all you can do is re-plant as soon as possible. Careful site preparation, good cultural care, and proper watering can all help prevent problems with damping-off.

References:

Cleary, W.A. 'Technical Information" 1-800-524-1662.

Flint, M.L. 1990. Pests of the Garden and Small Farm. University of California. Oakland, CA 94608-1239. Pub. #3332. 276 pp.

Gilkeson, L., and P. Michalak. 1994. Controlling Pests and Diseases. Rodale Press, Emmaus, PA 18098. 159 pp.

Howard, R., J. Garland, and W. Seaman. 1994. Diseases and Pests of Vegetable Crops in Canada, An Ilustrated Compendium. The Canadian Phytopathological Society and the Entomological Society of Canada, Ottawa, Ont. Canada K2A 1Y8. 554 pp.
 

Written by Sherry Lajeunesse and Martha Mikkelson, Extension Urban Pest Management Specialist and Plant Disease Diagnostician. January 1998.
 

Late Blight of Potato and Tomato
 

LATE BLIGHT is the most destructive disease of potatoes throughout the world. This disease was responsible for the Great Potato Famine in Ireland in the 1840's in which at least 1 million people died and another 1.5 million immigrated to the United States. The disease was first found in Montana in 1995. Late blight has the potential to devastate commercial potato crops in Montana when favorable weather conditions exist. It can spread rapidly in both commercial potato and tomato operations and in private gardens.
 

Because new strains of the late blight fungus are very aggressive and resistant to the very effective fungicide metylaxyl, late blight is a very real threat to seed potato producers in Montana. It is important for home gardeners to watch for the disease and to take potato plants with suspicious symptoms to their county Extension agent and be prepared to quickly destroy plants if the disease is confirmed.
 

Late blight infects crops and weeds in the family Solanaceae, including potato, tomato, and weeds such as the nightshades. Symptoms usually appear first on older leaves soon after flowering, following warm and wet or humid weather. Dark green, water-soaked areas at leaf tips spread inward and become dark brown and brittle in one or two days. On undersides of these leaves a cottony film may be visible around the edges of the lesions. Lesions obliterate the pattern of leaf veination. (Another form of blight, early blight, does not obliterate patterns of leaf veination.) Potatoes near the soil surface can develop lesions that are irregular and sunken; the lesions usually appear in and around the eyes. Affected tissue is granular and reddish in appearance an can penetrate up to one inch into the tuber. If you suspect late blight, it is very important to report it immediately to your county Extension agent, listed in the phone book under county government, or to the Montana Department of Agriculture.
 

To control late blight;

1.) Never plant table stock potatoes. Plant only Montana certified seed potatoes or certified seed potato stock. If you do buy out-of-state potatoes, buy only potatoes that are certified disease-free. This is required by law. Do not personally transport potatoes into Montana from other states since they can harbor the disease.

2) Avoid highly susceptible varieties such as Bintje, Norchip, Norland, Norgold, Norkotah, Red Pontiac, Russet Burbank, Sangre, Shepody and Warba. If available, plant resistant varieties such as Brador, Chieftain, Desiree, Dorita, Epicure, Kennebec, Nooksac, and Sebago.
 

3) Plant potatoes in a different part of the garden each year, but not close to tomatoes or in shaded areas.
 

4) Plant tomatoes against a south wall where they can be protected from the rain by the overhanging eaves or by a temporary lean-to. For tomatoes grown in the open, be prepared to erect a temporary shelter of polyethylene or similar material above them to keep the rain off. Do not enclose the plants completely or the high humidity will encourage the disease.
 

5) Do not overfertilize or overwater. Dense, lush foliage stays wet longer and is more likely to become infected.
 

6) Water the ground only. Don't use sprinklers on either potatoes or tomatoes.
 

7) Monitor your garden on a regular basis and quickly remove any suspicious leaves or shoots. Put them in a sealed plastic bag, keep them cool, and take them to your county extension office.

8) For potatoes to be stored, remove tops two weeks before digging the tubers. Harvest in dry weather.
 

9) Harvest all the tubers so that there are no "volunteer" plants that emerge the next year.
 

10) Do NOT compost diseased potato residue!
 

Fungicides:

Careful use of fungicides will help to ensure success in the battle against late blight. If you live in areas where seed potatoes are grown commercially, use preventative applications of fungicides such as maneb or chlorothalonil. Otherwise, no preventative fungicide treatments are recommended in home gardens. Because the disease is also spread by tomatoes, plant only tomatoes grown in Montana or certified to be free of late blight. Destroy and bury cull potatoes, diseased plants, and volunteer potato and tomato plants.
 

The product that you use must contain one of the following ingredients: chlorothalonil, copper oxychloride, tribasic copper sulphate, copper hydroxide, maneb, or zineb.
 

For best results, the first spray must be applied before any infections appear. For potatoes, start spraying when the plants are about six inches high. For tomatoes, start as soon as they are planted out.
 

The fungicide must be reapplied every 5 to 10 days. Read the label for rates of application and days to harvest limitations.
 

Spraying can be suspended during warm, dry weather in mid-summer but start once again before the onset of fall rains.
 

These funigicides are not systemic so residues can be washed off with warm water and a little detergent. Rinse in cold water and dry.
 
 
 

Timing of symptom development

Contrary to the disease name, the early blight symptoms are more likely to begin after flowering.
 

Symptoms

Symptoms usually develop after flowering - not "early" as the disease name implies. Circular or irregular dark spots develop on older leaves. As these spots enlarge, they develop concentric rings, giving a target effect. There is usually a chlorotic (yellowish) zone around the spots that fades into the normal green of the leaves. Early blight can cause tuber rot on potato, but this is rare.
 

Favorable conditions

Early blight can occur over a wider range of weather conditions than can late blight. Warm weather with heavy dews or rain generally are favorable. Early blight is more severe when the plants are under stress from poor nutrition (especially low nitrogen), drought, or other pests.
 

Year-to year survival of disease

Early blight is caused by a fungus that overwinters in potato plant debris or tubers, soil, and in other members of the same plant family, such as peppers and tomatoes.
 

Control

- Plant potatoes or tomatoes in the same area of the garden only once in every 4 years.

- Maintain nitrogen fertility at optimum levels.

- When blight first appears on the lower leaves, remove and destroy affected leaves. Then, begin a a thorough spray program with fungicides containing such active ingredients as chlorothalonil, mancozeb 80% WP, or maneb. Apply according to label directions, repeating applications every 7 - 10 days.

- Minimize harvest injury to tubers.

- Store tubers at 38 - 40 F after curing.
 
 
 
 
 
 
 
 

BLACKLEG is a bacterial disease that can infect potato stems and tubers.
 

Symptoms

The first symptoms often begin at flowering. Yellowish leaves that wilt during hot temperatures are common. The lower stem may be gray to inky black. Tubers may or may not be affected. Tuber infection usually begins at the stem end and appear as a creamy, odorless, soft decay that is sharply separated from the healthy tissue by a dark brown to black line. When other organisms move in, the rot can become very smelly.

Disease spread

The bacteria usually spread via infected seed tubers or plant residue, insects, water, rain splash, and equipment.
 

Favorable conditions

Wet soil and cool temperatures
 

Controls

1. Buy certified disease-free seed

2. Ideally, plant small whole seed. If you must cut the seed before planting, sterile the knife in rubbing alcohol between cuts. Planting in a warm, moist soil will promote growth and stimulate wound healing.

3. Plant in moist, well-drained soil when temperatures are 10 C or higher.

4. Do not overwater!

Allow tubers to mature before harvest.

Store freshly dug tubers at 12 C for 7 to 10 days to cure them. Then lower the temperature to 2 to 5 C. Maintain relative humidity at 90% with adequate air circulation

5. Do not wash tubers between harvest and storage.
 

Resistant cultivars

Russet Burbank has some resistance; all other commonly-planted cultivars are susceptible.

Once a plant is infected, control is difficult. Prevention is best. Sometimes treatment with fixed copper fungicides can be effective. Purchase only certified seed potatoes to avoid problems with blackleg, phytophthora and other problems. Avoid over-watering and mechanical damage to plants. Limit early nutrient supply to keep top growth within reason.
 

VERTICILLIUM WILT (pronounced Vert-uh-sill-ee-um) is a fourth potato disease you might encounter.
 

Symptoms

Symptoms include lower leaves and stems that die early on scattered plants. Areas between leaf veins often turn yellow then brown. Often only one stem or one side of the plant wilt, especially on hot days or when the soil is dry. Plants may recover at night or during wet, warm weather. When the stem at ground level is cut diagonally, the vascular rings may be brown.
 

Favorable conditions
 

Disease spread

Verticillium wilt is spread by infected or contaminated seed pieces and by infested soil, farm machinery, and irrigation water. The fungi involved can survive for many years in the soil. Other crops and weeds can harbor the fungi - even without symptoms. The fungus grows inside the water-conducting vessels and blocks water movement, thereby causing wilt.
 

Control:

Maintain vigorous plants by proper fertilization and watering.

Plant potatoes and tomatoes in the same spot only once every four years.
 
 

The symptoms of this disease begin to appear late in the season, when older, lower leaves become yellow, curl and roll, and show tipburn, then die. The inside of the plant stem turns yellow or brown. This disease is caused by a fungus. Again, prevention is the best management tool, although applications of a sulphur fungicide every 7-10 days will help in control. To prevent the disease, plant resistant varieties, and do not plant in areas where other infected plants have grown.
 

PREVENTION OF POTATO DISEASES: To prevent many of the potato diseases, rotate crops in the potato family on a 4-year cycle (minimum) in your garden plot. Rotate garden crops, with a minimum 4 year rotation cycle, planting all crops in the same family as potato in a different part of the garden each year. For more information on rotating garden crops and on plant families, see the fact sheet in this series "Rotating Garden Crops to Prevent Disease". Clean up garden debris well in the fall and do not compost diseased plant material.
 

References:

Agriculture and Agri-Food Canada, Province of British Columbia. 1994. Late Blight of Potato and Tomato. QP #17011.

Flint, M.L. 1990. Pests of the Garden and Small Farm. University of California.

Oakland, CA 94608-1239. Pub. #3332. 276 pp.

Howard, R., J. Garland, and W. Seaman. 1994. Diseases and Pests of Vegetable Crops in Canada, An llustrated Compendium. The Canadian Phytopathological Society and the Entomological Society of Canada, Ottawa, Ont. Canada K2A 1Y8. 554 pp.

Pacific Northwest Plant Disease Control Handbooks. 1997. Extension Services of Oregon State University. Corvallis, OR 97331-0817.
 

Written by Sherry Lajeunesse and Martha Mikkelson, Extension Urban Pest Management Specialist and Plant Disease Diagnostician. February, 1998.
 

Raspberries: Cane Blight & Verticillium Wilt
 
 

Two common disease problems on raspberries are cane blight and verticillium wilt. CANE BLIGHT causes canes to wilt and die while loaded with fruit. Late in the season, brownish-purple areas appear on cut or injured parts of the cane. These discolored areas spread down the cane and encircle it. Cane blight cannot be cured. Remove and burn all affected stalks.

The second disease is VERTICILLIUM WILT. This disease causes lower leaves to develop an off-green or yellowish-bronze tinge in June or early July. The leaves curl upward, then turn brown and fall off, beginning at the base of canes and progressing upward. Sometimes a sudden wilt occurs in hot, dry weather. Canes show blue or purple streaks. Red raspberry is more resistant, symptoms show up later in the season, and discolored leaves turn upward. It is difficult to see cane streaks in red raspberries because of the natural color in them. Infected plants eventually die. Remove and destroy infected and surrounding plants. For future plantings, avoid heavy, poorly drained soils, and buy disease-free stock. Avoid planting new plants in soils which were formerly planted to other plant hosts of verticillium wilt.
 

References:
 

Flint, M.L. 1990. Pests of the Garden and Small Farm. University of California. Oakland, CA 94608-1239. Pub. #3332. 276 pp.

The Organic Gardener's Handbook of Natural Insect and Disease Control. 1992. B. Ellis and F. Bradley, Eds. Rodale Press, Emmaus, PA 18098. 534 pp.

Pacific Northwest Plant Disease Control Handbooks. 1997. Extension Services of Oregon State University. Corvallis, OR 97331-0817.
 

Written by Sherry Lajeunesse, Extension Urban Pest Management Specialist. Sept., 1997
 

Rotating Crops to Prevent Disease
 
 

The annual cycle for many disease organisms is to attack the crop in the summer, survive the winter as spores in the soil or in plant litter, then attack the new planting the following year. So if you plant the same crop in the same spot year after year, the pathogen populations can continue to build and the disease will become an increasingly serious problem. You can break the cycle by moving the susceptible plant to another spot. Over time, many pathogens die back, and then it is safe to plant the original crop in that spot again. This is the idea behind rotating crops to prevent plant diseases.
 

The first step in planning crop rotation is to make a list of the crops you intend to plant. Most diseases tend to attack plants within in the same botanical family, so group your crops together in these botanical groups. Our common vegetables usually belong to one of ten families. Tomatoes, potatoes, peppers, and eggplants are in the Nightshade Family (Solanaceae); cabbage, radishes, turnips, broccoli, cauliflower, and brussels sprouts are in the cabbage family (Cruciferae), and are also called cole crops. Spinach is in the family Chenopodiaceae, and lettuce and other salad greens are in the Lettuce Family (Compositae). Peas, beans, and lentils are in the Legume Family (Leguminosae), and carrots, parsley, and dill are in the Umbelliferae Family. Cucumbers, the squashes, and melons are in the Melon Family (Cucurbitaceae), and onions, leeks, garlic, and chives are in the Lily Family (Liliaceae). Corn is in the family Gramineae, and strawberries are in the Rose Family.
 

The second step is to divide your garden into the same number of sections as the number of plant families you will have. For example, if you have six plant families, divide your garden into six sections. It works best if all the sections are the same size to ensure each section of soil is rotated from year to year.
 

Step three is to assign a plant family to each section, making notes of the assignment on a permanent map of your garden. (It is difficult to remember the order of rotation after two or three years without permanent records.) In each subsequent year, move each plant family to the next section in the garden, always following the same order. If you have 6 groups of plants, 5 years will pass before the same crop is planted in the same section of ground. A cycle of at least 4 years is most effective.
 

Crop rotation works best for controlling soilborne diseases that attack only a few species of plants. Most of the diseases caused by soilborne fungi are particularly easy to control this way. Added bonuses of crop rotation include control of certain insect pests and prevention nutrient depletion in the soil in particular spots in your garden.
 

References:
 

Controlling Pests and Diseases; Rodale's Successful Organic Gardening. 1994. Rodale Press, Emmaus, Pennsylvania 18098. 422 pp.

Ellis, B.W. and F. Marshall. 1991. The Organic Gardner's Handbook of Natural Insect and Disease Control: A Complete Problem-Solving Guide to Keeping Your Garden and Yard Healthy Without Chemicals. Rodale Press, Emmaus, Pennsylvania. 418 pp.

Flint, M.L. 1990. Pests of the Garden and Small Farm. University of California.

Oakland, CA 94608-1239. Pub. #3332. 276 pp.
 

Written by Sherry Lajeunesse, Extension Urban Pest Management Specialist. Sept., 1997
 

Tomato Problems Common in Montana
 
 

From a plant disease's point of view, years with cool, wet weather are very good years. Some of the more common tomato diseases we see in Montana include septoria leaf spot, early blight, and a variety of symptoms that are caused by environmental factors rather than a disease organism.
 

SEPTORIA LEAF SPOT, also known as SEPTORIA BLIGHT, is caused by a fungus that produces brown, somewhat circular spots that appear first on the lower leaves, then begin moving up the plant. The spots are quite small, ranging in size from 1/16" to 1/8" in diameter. As the spots mature, they sometimes become gray or white, surrounded by a dark margin.
 

To help control septoria leaf spot, stake plants to improve air circulation and to encourage quick drying of moisture on plant surfaces. Water only at the base of the plant, to avoid wetting the foliage. Remove weeds, which can harbor the disease, and remove badly infected leaves from the plant and destroy them. Clean up and remove all plant debris in the fall to minimize re-infection next year. Little is known about varieties that are resistant to this disease.
 

After discovering the disease, apply fungicides containing chlorothalonil, such as Ortho's Multi-Purpose Fungicide or Daconil 2787. Fungicides with the active ingredient maneb will also help, but do not apply within 5 days of harvest.
 

Another problem we see is EARLY BLIGHT, another fungal disease. This disease will also attack potatoes. Symptoms of early blight can be found on leaves, stems, and fruit. Small, irregular brown spots appear on older leaves first, enlarging until they are 1/4 to ½ inch in diameter. Dark rings of velvety spores commonly form in a bull's eye pattern inside the lesions. The surrounding tissue turns yellow. Often, the entire leaf turns yellow if the infection is severe. Dark, leathery spots may appear on the fruit.
 

High soil fertility reduces the severity of early blight, so keep plants properly fertilized and growing vigorously, and control weeds that might harbor the disease. When purchasing

tomato plants, ask for varieties that are resistant.
 

If you find early blight, begin applying fungicides that contain the active ingredient chlorothalonil, such as Ortho Multi-Purpose Fungicide or Bravo. Fungicides that contain mancozeb or maneb will also work, such as Dithane or Maneb.
 

Most of the non-pest problems we see in tomatoes are caused by environmental factors such as COLD, WET WEATHER, symptoms of which include rolled and deformed leaves, especially the lower ones, and yellowing leaves with reddish veins. There is not much to be done about these problems, obviously. Another condition, called OEDEMA, is caused by water-logged soil and high humidity. This can result in whitish-tan raised areas that have a corky texture. Improving drainage, if possible, might help. SUNSCALD and SCORCH are two other examples of environmentally caused symptoms.
 
 

Because tomatoes can also spread late blight, a very serious disease of potatoes, it is extremely important to plant only Montana-grown or certified late blight-free tomatoes. The Great Potato Famine in Ireland in the 1850s was caused by late blight. For more information on late blight in potatoes, see the fact sheet in this series "Potato Diseases".
 

References:
 

Controlling Vegetable Pests; Environmentally Friendly Gardening. 1991. C. Putnam, Projec t Ed. Ortho Books, Chevron Chem. Co., San Ramon, CA 94583. 160 pp.

Flint, M.L. 1990. Pests of the Garden and Small Farm. University of California. Oakland, CA 94608-1239. Pub. #3332. 276 pp.

Howard, R., J. Garland, and W. Seaman. 1994. Diseases and Pests of Vegetable Crops in Canada, An lllustrated Compendium. The Canadian Phytopathological Society and the Entomological Society of Canada, Ottawa, Ont. Canada K2A 1Y8. 554 pp.

Pacific Northwest Plant Disease Control Handbooks. 1997. Extension Services of Oregon State University. Corvallis, OR 97331-0817.
 

Written by Sherry Lajeunesse, Extension Urban Pest Management Specialist. Sept., 1997
 

LAWNS

Fairy Rings
 

One of the first parts of the lawn to green up in the spring are the circular fungal infections called fairy rings. While fairy rings are not particularly attractive, they are not terribly damaging to lawns, and most people just learn to live with them. One reason is that there are no easy ways to get rid of them. One difficult way is to dig up the entire infested area to 2 feet deep and at least 1 foot beyond the outer edges of the ring. If you choose this method, dispose of the infected soil, taking care not to spill any on healthy lawn.

Because fairy rings do not really destroy turf, most people just ignore them. There are some techniques for minimizing the rings, however. Remove and discard the mushrooms that usually develop around the edge of the rings. Fairy rings grow well in dry, low fertility lawns. Spiking the fairy ring area with a spading fork every few days and watering it well sometimes works. Encourage beneficial soil microbes by the application of organic fertilizers and by topdressing with humus builders such as finished compost, or commercial products like Lawn Restore or Vitabuild. Supplemental nitrogen can help compensate for temporary nitrogen tie-up by beneficial microbes.

A remedy I have heard about is to wait for a full moon, set a comfortable lawn chair out, and with a 6-pack of your favorite beverage try and catch the fairy that is responsible for the rings; the theory goes, even if you don't catch the culprit, by the time your beverage is gone, you won't care about the rings anymore. This remedy is said to be ineffective, but enjoyable.
 

References:
 

Shurtleff, M., W. Thomas, and R. Randell. 1987. Controlling Turfgrass Pests. Prentice-Hall, Inc. Englewood Cliffs, NJ 07362. 449 pp.

Turfgrass Compendium. The American Phytopathological Society Disease Compendia Series, St. Paul, Minnesota. 126 pp.

Watschke, T., P. Dernoeden, and D. Shetlar. 1995. Managing Turfgrass Pests. Lewis Publishers, Boca Raton, FL 33431. 361 pp.
 

Written by Sherry Lajeunesse, Extension Urban Pest Management Specialist. Sept., 1997
 

Lawn & Turf Grasses with Endophyte-Induced

Pest Resistance
 

Endophytes are naturally-occurring fungi that live inside the tissues of certain grass species. They benefit the grass by producing toxins that repel and kill many grass-feeding insects and provide resistance against certain diseases. They also make grasses more vigorous, more tolerant of heat and drought, and more competitive against weeds. In return, the grass provides the nourishment and the environment the fungi need to survive.
 

These beneficial fungi have been added to many lawn and turfgrass varieties in recent years, and many of these varieties are now commercially available. If you are reseeding lawns or turf in the fall or establishing new turfgrass areas, you may want to consider the benefits of purchasing grass seed with endophytes.
 

Some of the insect pests that are controlled or reduced by endophytes include cutworms, sod webworms, aphids, and most insects that feed on the crown and lower stem of grasses. Endophytes are also found in the root system, but have variable effects on root-feeding pests such as grubs: sometimes they help, sometimes they do not. Endophyte-induced resistance to diseases has not been well documented at this time. It has been reported that dollar spot, leaf spot, stem rust, and brown patch might be reduced by endophyte inoculation.
 

Not all turf varieties can be inoculated with endophytes, but new ones are expected to be available soon. Tall fescue, perennial ryegrass, and fine fescue are some of the grass species for which endophyte-inoculated varieties are commercially available. Unfortunately, endophytes that can survive in Kentucky bluegrass have not yet been found, but researchers hope to soon discover a strain that will work.
 

A caution when considering the use of endophyte-inoculated grass is that the toxins produced by endophytes can be toxic to livestock that graze the plants. Do not plant endophyte-inoculated grass where horses or other livestock might eat it. The toxins are harmless to humans and non-grazing animals.
 

When purchasing grass seed that contains endophytes, check the lot numbers to make sure the seed is fresh because the endophytes may die after storage of two years or less. The grass seed may still be viable, but the fungi may not be.
 

References:

Danneberger, T.K. 1993. Turfgrass Ecology and Management. G.I.E. Inc., Cleveland, OH. 201 pp.

Handbook of Integrated Pest Management for Turf and Ornamentals. 1994. Leslie, A.R., ed. U.S.

Environmental Protection Agency. Lewis Pub., Boca Raton, FL. 660 pp.

The IPM Practitioner. Bio-Integral Resource Center. Berkeley, CA 94707.
 

Written by Sherry Lajeunesse, Extension Urban Pest Management Specialist. Sept., 1997
 

Melting-Out

Irregularly-shaped dead patches in your lawn could be from a fungal disease called melting-out. Melting-out is one phase manifested by the leaf, crown and root rots that are the most common and serious group of diseases attacking lawn and turf grasses in the US.
 

When the fungi attack the leaf portions of grass, the symptoms are small dark brown, reddish-brown, or purplish spots which appear on the grass blades from early spring to late fall. The spots increase rapidly in size, become round or oblong, and the centers gradual fade to an ash white or straw color. Sometimes, the spots are described as "eye-spots". Leaf infections are sometimes so severe that the blade is girdled and drops, sometimes entire grass plants are killed.
 

These fungi can be very destructive during wet, humid weather or in areas where the turf is sprinkled frequently, especially in late afternoon and early evening. The more often grass is wet and the longer it remains wet, the greater will be the chance of disease.
 

With the arrival of relatively dry weather, the fungi may attack the roots of diseased plants. These symptoms usually appear first in warm to hot weather as a reddish-brown decay of the root tissues. Sometimes the color turns chocolate-brown to black. Such plants lack vigor and often wilt during mid-day, even when soil moisture is abundant. The lawn may have a drouth-injured appearance, then gradually turn brown and begin thinning out. As the disease progresses, large irregular areas are yellowed, then become straw-colored and die out. This is called the melting-out phase. In some instances the entire lawn can be lost. Once the fungi that cause melting out disease become established in a lawn they cannot be eradicated and remain an ever-present problem.
 

To manage melting-out disease, mow bluegrasses, fescues, and ryegrasses at the recommended maximum height. Avoid close clipping at all times. Mow the grass so that no more than 1/3 of the grass height is removed at one time.
 

If dense thatch more than one-half inch thick has formed, reduce or remove it with a power rake in the spring or early fall. These machines can be rented at most large garden supply centers. Application of sufficient, but not heavy amounts of slow-release available nitrogen can also help. Too much nitrogen can be detrimental and can leach into the ground water. Soil tests can determine proper amounts. Proper watering practices will also help manage melting-out disease. For information on good watering practices, see the fact sheet in this series, "Watering of Lawns and Trees".
 

When planting new lawn or turf, buy only top-quality, disease-free seed, sod, springs or plugs from a reputable dealer. Select locally adapted, disease-resistant grasses or combinations (blends and mixtures). Your county Extension agent can recommend grass species to grow.
 

References:
 

Shurtleff, M., W. Thomas, and R. Randell. 1987. Controlling Turfgrass Pests. Prentice-

Hall, Inc. Englewood Cliffs, NJ 07362. 449 pp.

Smiley, R., P. Dernoeden, and B. Clark. 1992. Compendium of Turfgrass Diseases. 1992. The American Phytopathological Society Disease Compendia Series. APS Press, St. Paul, MN 55121. 98 pp.

Watschke, T., P. Dernoeden, and D. Shetlar. 1995. Managing Turfgrass Pests. Lewis Publishers, Boca Raton, FL 33431. 361 pp.
 

Written by Sherry Lajeunesse, Extension Urban Pest Management Specialist. Sept., 1997
 

Snow Mold
 
 

Snow mold can be a problem during cold, wet autumn and spring weather and under the snow in winter. As snow melts, patches of grey, white or pink fuzzy mold appear on the grass. The grass blades may turn yellow or brown. Circular to irregular patches of turf may die and occasionally form large areas of dead grass.
 

Turf is most at risk when snow falls on unfrozen, wet ground. Heavy snow accumulation that lasts late into spring allows the disease more time to develop. Excessive nitrogen fertilizer forces the turf to grow late into autumn and so the turf does not "harden-off" for winter and is more susceptible to these fungi.
 

To manage snow mold, use slow-release nitrogen fertilizers earlier in the season, reduce fertilizer application and irrigation in late summer to allow the turf to harden off. For the last mowing of the season, adjust mower cutting height to about two inches, so grass does not 'mat' under snow. Rake up fallen leaves and other moisture-holding debris. In the spring, break up piles of snow, if feasible, to speed melting. Pick up grass clippings and manage thatch, keeping thatch layers less than 3/4" thick. If soils are compacted, aeration and improving drainage may help. When the lawn has dried in spring, use a stiff broom to break up the patches of mold.
 

In home lawns, chemical control is rarely required. If chemicals are used, apply flowable sulfur fungicide or other labeled fungicide to the infected areas every three to five days until the symptoms disappear.
 
 

References:
 

Watschke, T., P. Dernoeden, and D. Shetlar. 1995. Managing Turfgrass Pests. Lewis Publishers, Boca Raton, FL 33431. 361 pp.

Turfgrass Compendium. The American Phytopathological Society Disease Compendia Series, St. Paul, Minnesota. 126 pp.

Shurtleff, M., et al. 1987. Controlling Turfgrass Pests. Prentice-Hall, Englewood Cliffs,

N.J. 449 pp.
 

Written by Sherry Lajeunesse, Extension Urban Pest Management Sprecialist. 1997.
 
 
 
 

GENERAL PLANT DISEASE TOPICS

Sanitation - Proactive Plant Disease Management
 
 

Many plant diseases spend the winter in foliage and plant material left from the summer. A good way to reduce winter survival of the disease organisms is to remove old plant material and compost it or dispose of it. Composting healthy plant material can recycle the nutrients and organic matter it contains, feeding your soil.
 

Debris should be burned, buried, or hot-composted if it comes from areas where disease was a problem last season, such as debris from rose bushes infected with blackspot, or vegetable beds where powdery mildew caused problems. High temperatures are essential to kill the disease organisms, so make sure your compost pile reaches internal temperatures of 140- 160F to kill the disease organisms if you choose to compost materials that come from problem areas. Do not compost plant material infected with viral diseases; place these materials in sealed containers and dispose of them in your trash. After working with diseased plant material, sterilize tools in solution of one part household bleach mixed with nine parts of water to avoid transporting the pathogens to another part of your yard.
 

Removal of old raspberry canes is also a good idea because they can serve as a harborage for diseases such as anthracnose. These sanitation measures can help keep your yard and garden disease-free.
 

References:
 

Pirone, P., J. Hartman, M. Sall, and T. Pirone. 1988. Tree Maintenance. Sixth Edition. Oxford Univ. Press, New York, NY 10016. 514 pp.

Controlling Vegetable Pests; Environmentally Friendly Gardening. 1991. C. Putnam, Project Ed. Ortho Books, Chevron Chem. Co., San Ramon, CA 94583. 160 pp.

Ellis, B.W. and F. Marshall. 1991. The Organic Gardner's Handbook of Natural Insect and Disease Control: A Complete Problem-Solving Guide to Keeping Your Garden and Yard Healthy Without Chemicals. Rodale Press, Emmaus, Pennsylvania. 418 pp.
 

Written by Sherry Lajeunesse, Extension Urban Pest Management Specialist. Sept., 1997
 

Symptoms of Common Plant Diseases
 
 

Symptoms of our more common yard and garden plant diseases in Montana fall into eight broad catagories: 1) blights, 2) cankers, 3) galls, 4) leaf blisters or curls, 5) mildews, 6) rots, 7) rusts, and 8) wilts.
 

BLIGHTS: Symptoms include sudden withering and death of leaves and branches, or in the case of blossoms, wilting and discoloration. Conspicuous spots or irregular dead areas on leaves and twigs which cause foliage to distort and drop prematurely could be a blight. Damage from blights can be minor, as in the case of some anthracnose blights, to serious, as in the case of fireblight.
 

CANKER: symptoms usually form on woody stems and may be sunken areas, cracks, or raised areas of dead or abnormal tissue. Sometimes the cankers ooze conspicuously, or in the case of evergreens, drip sap onto the branches beneath. Cankers can sometimes be one of the symptoms manifested by another disease.
 

GALLS: are swollen masses of abnormal tissue that range in size from small to quite large. Certain insects can also cause galls. Cut a gall open and search for signs of an insect inside- if you find none, the gall is probably caused by a disease.
 

LEAF BLISTERS are yellow bumps on the upper surfaces of the leaves with gray depressions on the lower surfaces. LEAF CURL DISEASES cause new leaves to be pale or reddish with the midrib deformed. The leaves pucker and curl as they expand. Certain insects cause similar symptoms, but on closer inspection, if insects are the cause the insects themselves or other signs of their presence can be seen.
 

MILDEWS are usually one of two types. Downy mildew is usually a white to purple, fuzzy growth, usually on the undersides of leaves and along stems. It turns black with age. Powdery mildew is a white to grayish powdery growth on the upper surfaces of leaves.
 

ROT DISEASES cause decay of roots, stems, wood, flowers, and fruit. They can be soft and squishy or hard and dry, and color can be either light or dark.
 

RUST DISEASES typically produce symptoms that include a powdery tan to rust-colored coating or soft tentacles.
 

WILT DISEASES cause permanent wilting, often followed by death of part or all of the plant.
 

Most symptoms you find in your yard or garden will be caused by insects or environmental problems such as water stress or nutrient deficiencies, so try to rule out these possibilities first. If you have yard and garden reference books, you can often identify the disease based on the categories of symptoms listed above. The species of plant on which the symptoms occur will also help identify the problem as most diseases are quite specific in the kinds of plants they will attack. If you need additional assistance with identification, your county Extension agent can help.
 

References:
 

Agrios, G.N. 1988. Plant Pathology. Third edition. Academic Press, San Diego, CA. 803 pp.

Howard, R., J. Garland, and W. Seaman. 1994. Diseases and Pests of Vegetable Crops in Canada, An llustrated Compendium. The Canadian Phytopathological Society and the Entomological Society of Canada, Ottawa, Ont. Canada K2A 1Y8. 554 pp.

Sinclair, W., et al. 1987. Diseases of Trees and Shrubs. Cornell Univ. Press, Ithaca, N.Y. 576 pp.

Turfgrass Compendium. The American Phytopathological Society Disease Compendia Series, St. Paul, Minnesota. 126 pp.
 

Written by Sherry Lajeunesse, Extension Urban Pest Management Specialist. Sept., 1997
 
 

Common scab - potato

Fusarium dry rot - potato

Fusarium, verticillium wilt - potato, tomato

White mold - bean, sunflower, petunia, etc.

How to recognize plant diseases:

Patterns, symptom types, detective work, etc.

Fungicides for plant diseases: what's available, etc.

Plant Disease control methods: General (Master Gardener)

How to prevent disease in your garden (Master Gardener)

Growing aspens in Montana

A plant for every season

Dwarf conifers of note

Growing viburnums

Growing native plants

Small shrubs for Montana

How to plant a tree

Composting

Greenhouse disease control

What size tree should I buy?

Fruit for the small yard

Space-saving garden techniques

Preventing deer damage

Seeding a lawn

Sodding a lawn

Common causes of dead patches in lawns

Tree wraps

Get more out of the water you use on your lawn

Fertilizing lawns

Xeroscaping

The threat of noxious weeds in wildflower seed mixes

Biocontrols for the yard and garden

Attracting birds and butterflies to your garden

Trapping rainwater for use on the yard and garden

Attributes of different turfgrasses (drought, sun, cold, mowing, traffic, etc.)

Kid's gardens:

Growing orchids

Plant diseases that have changed world history

Month-by-month garden to-do list

Vines for Montana

Gardening book titles

Public gardens and arboretums to visit

Native grasses