FUNGAL DISEASES: LOWER STEMS AND ROOTS
 
 

BARE PATCH OR RHIZOCTONIA ROOT ROT
 

Scientific name: Rhizoctonia solani

Hosts: Barley is most susceptible, but bare patch also can affect spring and winter wheat and oats (2).

Symptoms:

spear tip symptom - on plant

field symptoms, #1

field symptoms, #2

- Yellowing and stunting of plants shortly after crop emergence

- Plants have much shortened, discolored, or nonexistent root systems.

- Secondary roots may appear "nubbed off" near the crown line with necrotic spearpoint-like foot from 1/8 to 1/4 inches long (1).

Lab diagnosis: Rinse roots in running water for several hours. Do not chlorox. Plate onto Rhizotonia selective media or water agar. WARNING: Rhizoctonia solani is difficult to isolate later in the season.

Look-alike symptoms:

- Common root, crown, and foot rot (Common root rot)

- Dryland root, crown, and foot rot (Fusarium foot rot)

- Pythium root rot (more common in wet years)

- Take-all (1)

Favorable conditions:

- Seeding spring grain 1 - 2 days after application of non-selective herbicides such as glyphosate;

- Bare patch typically is most severe in fields with heavy volunteer wheat or barley.

- Bare patch may be more severe in the location of former chaff rows where heavy volunteer arose (2).

Pattern in field: Bare patch may be more severe in the chaff rows where volunteer from the previous year's winter wheat was more extensive (1).

Infestation levels:

Life cycle: Seeding directly into small grains that have sprayed with glyphosate within two days prior to seeding can increase potential for bare patch. Dr. James Cook (Washington State University) feels that the volunteer is serving as a source on which the pathogen increases. The inoculum load on the volunteer is very high just before the volunteer is destroyed. Spraying the volunteer two weeks before seeding will result in a reduced inoculum density (1).

History in MT and US: Bare patch is very common in Oregon, Washington, and Australia. In Montana, the disease is less common, but may occur when favorable conditions exist (2).

Crop losses:

Controls:

Cultural controls:

- Spraying the volunteer with glyphosate two or more weeks before seeding will result in a reduced inoculum density (1).

- Following the above with light tillage can reduce levels of bare patch (1,2).

Resistant varieties:

Biological controls:

Chemical controls:

References: 1) Riesselman, J. Root rot in spring grains, Chemical fallow and root diseases, Montana Crop Health Report, July 14, 1989. 2) Riesselman, J. Bare patch of cereals, Montana Crop Health Report, April 20, 1990, No. 1.
 
 
 
 

COMMON ROOT, CROWN, AND FOOT ROT or COMMON ROOT ROT

Pictures of common root rot:

healthy plant (left) vs. syptomatic plant (right)

diseased root system - Cheyenne winter wheat, Chester, MT, June 1979

condia of common root rot
 

Scientific name: Cochliobolus sativus (Ito &Kurib.) Drechsl. ex Dastur = Perf., Bipolaris sorkiniana = Imperf. (Helminthosporum sativum) (2).

Hosts: Wheat, barley, and many native grasses (10)

Symptoms of Common root, crown, and foot rot (Common root rot):

- Infections may occur at any stage of plant growth.

- The most obvious symptoms during late fall and early spring are brown spots or elongated blotches on roots, subcrown internodes, crowns, and lower leaf sheaths. These vary in length, ranging from less than 1/8 to over 1 inch. In contrast, healthy crowns will be white in color (7).

- On leaves and stems, the disease causes wilting, stunting, and chlorosis (7). Common root rot also causes chocolate-brown leaf spots especially on lower leaves (1).

- After heading, white heads without kernels or with shrivelled kernels may develop. Stems may appear white (1).

- Lodging may occur.

- In humid or irrigated areas, the pathogen may infect heads and cause black point on seed (1).

Field diagnosis: Remove suspected seedlings, wash free of soil, and examine for the presence of dark brown lesions and nonfunctional roots with few or no new roots initiating from the crown. Split the crowns at the base of stems with a sharp knife or a razor blade to detect rot (7).

Look-alike symptoms:

1) Fusarium foot rot (dryland root rot). Symptoms are similar to those of dryland root, crown, and foot rot (Fusarium culmorum and F. graminearum). Dryland (Fusarium spp.) and common (Bipolaris spp.) root rot are often grouped together as a disease complex. However, Fusarium commonly infects wheat later in the season than does C. sativus (common root rot) (10).

2) Take-all. Take-all also causes white heads. However, crowns and main roots of plants infected with take-all generally are shiny blue-black in color and have more root rot than with common root rot, resulting in stubbed off roots with take-all. Plants infected with take-all can usually be pulled from the soil much easier than healthy plants or ones with common root rot (1).

3) Fusarium scab (head blight) Scab causes causes whole or partial heads to appear white. Generally, stems don't turn white and the diagnostic salmon or orange color is present at the base of the spikelets when scab is present.

4) Frost injury

5) Hail injury

6) Heat canker

7) Wet soil/weather stress (5)

Favorable conditions: The common root rot fungi are considered to be weakly virulent pathogens. They cause the most damage when plants are under stress from adverse environmental conditions (10). Therefore, damage due to common root rot can vary widely from year to year in a given location.

Damage is most severe in plants under stress. Stresses that have been shown to increase common root rot severity include (13):

- drought

- flooding

- high salinity

- plants with mechanically damaged leaves

- deep planting

- plants with few tillers

- Occurence is most common in low rainfall dryland winter wheat areas.

- High fall soil temperatures and low fall soil moisture and windy weather can contribute. - Injury can be severe when hot weather follows cool, wet weather (5, 11).

Pattern in field:

- Symptoms may occur in low areas where infection was favored by early high moisture.

- Symptoms may be most noticeable on exposed slopes of the field where moisture is most limiting later in the season (5).

- Individual fields affected by root and crown rot contain scattered pockets of dead and dying plants.

Infestation levels:

- Common root rot impairs the roots and crown resulting in fewer tillers and heads. Reduced yield and lower grain quality result (9, 11). When early injury is evident, stand loss and weakened plants often occur. The disease causes losses in seedling vigor and impairs root and crown function (9). Plants with aedquate soil moisture may compensate for root rot infection with production of additional roots. If soil is dry, the plants will depend entirely on decayed roots for moisture uptake (5).

- If a plant stand consists of healthy plants mixed with light-moderately diseased plants, the healthy plants may compensate for the reduced stand by yielding more than normal due to reduced competition for water and nutrients.

- The disease is most severe when infection occurs in the seedling stage. Plants may be killed outright. This is the "seedling blight" or "post emergence damping-off" phase of the disease (11).

- Severe root rot at other growth stages also can cause plant death. This usually occurs during heading or early grain filling stages (11).

- In the spring when deciding whether to destroy infected crops, consider the following: the estimated yield, soil moisture for replacement crops, other cropping options, partial field loss, government programs, soil erosion, and effect on rotations (7).

Life cycle: The fungi survive as thick-walled, resistant conidia in soil on old barley and wheat stubble and straw. Cochliobolus sativus spores can persist longer in the soil than many other soilborne diseases. Some C. sativus spores remain viable in the soil after 8 to 10 years. Because of this and the fact that many native grasses can support the disease, common root rot cannot be eliminated entirely from a field (although levels can be reduced through rotations) (12).

Infections may occur at any stage of plant growth (1, 9).

The fungi responsible for the root diseases of wheat all live in the top 4-6 inches of soil. the occurrence of C. sativus and Fusarium spp., mainly on the subcrown internodes and on crown roots near where they emerge from the tiller bases may be due to the presence of the inoculum very near the soil surface (6).

Multiple infections of root rot pathogens are necessary for severe disease to occur (more spores = more lesions if environment is favorable) (11).

History in MT and US: Common root rot is a problem mainly in the Great Plains of the US (6). Common root rot occurs throughout MT, ND, and the Pacific Northwest. The disease is present in wide areas of MT (1).

Crop losses:

- Common root rot impairs the roots and crown resulting in fewer tillers and heads. Reduced yield and lower grain quality result (9, 11).

- When common root rot is severe, plants may be killed. This usually occurs during heading or early grain filling stages (11).

- Common root rot was reported to cost to MT growers was over 20 million dollars in lost grain production annually in 1979 (17).

- To evaluate the seriousness of common root rot in Montana, soil fumigation was used in fields in Big Sandy and Glasgow to eliminate the disease in 1979. On the average, the plants in fumigated plots yielded 30% more than those in the non-fumigated plots. Fumigation is not a practical disease control method, but it does show the limiting effects of common root rot on yield potential (17).

- Root rot complexes are estimated to cause 3-4% and 5.7% wheat yield losses annually respectively in North America and the Canadian Prairies (3, 6). Stack (9) cites losses to common root rot as 5% on spring wheat and 10% on barley on a long-term basis in the Northern Great Plains.

- In Saskatchewan field trials, losses in 6 of the most susceptible and 6 of the most resistant spring wheat varieties averaged 8.1% and 4.1% respectively (12).

- In individual fields, losses can be greater than 30% in some years (9).

Controls: Good rotation is the best method for management of common root rot. Variety choice and fungicide seed treatment also are important (8).

Cultural controls:

Rotations and fallow:

- Crop rotations to non-host plants provide the best control of common root rot (11).

- Rotate 2 or more years out of wheat and barley and into a non-host (oats or any broad-leaved crop).

- The best rotation crops seem to be forage legumes, hay crops, flax, and corn (11).

- Long term rotations (3 - 4 years) will provide the best control (8, 11).

- Fallow also will reduce the common root rot fungus population (8).

- Control weeds in summer fallow to decrease the potential of moisture stress (7).-

Tillage:

- Deep tillage does NOT reduce the level of common root rot (8).

- Some reduction of common root rot severity has been seen under minimum and no-tillage practices (8, 11)

Seeding:

- Large, heavy seed produces the most vigorous plants which are better able to resist the effects of root rot (11).

- Seed infected with C. sativus or Fusarium will yield weakened plants that are less able to resist common root rot (11).

- Seed later when the soil temperature at the 3-in depth is 55 F or lower(1).

- Plant seeds in a firm seedbed (7).

- Plant seeds shallowly in warmer soils (7).

Soil fertility:

- Adequate nitrogen and potassium appear to reduce the severity of common root rot, probably because plants are more vigorous and less affected by pathogens (11).

- Excessive nitrogen can increase root rot severity in wheat and barley (11).

- Some reports indicate that ammonium forms of nitrogen reduce root rot relative to nitrate forms of nitrogen (11).

- Adequate chloride levels (greater than 60 lbs) have been shown to increase plant tolerance to root rot in some locations but not in others (11).

Resistant varieties:

- Varieties of wheat, durum, and barley vary in their susceptibility to common root rot. No varieties are immune to infection, but some are more tolerant to the disease than others (9, 11). In Saskatchewan field trials, losses in 6 of the most susceptible and 6 of the most resistant spring wheat varieties averaged 8.1% and 4.1% respectively (12).

- Many of the most reistant lines are of relatively recent origin. Amidon has relatively high resistance whereas Len is quite susceptible to common root rot (12).

- Planting varieties adapted to your area and planting tolerant varieties can aid in control.

- Varieties with greater tillering capabilities can partially compensate for stand loss (5).

Biological controls:

Chemical controls: Fungicide seed treatments can reduce disease when the infected seed is the source of inoculum. However, in the Northern Great Plains, inoculum already is present in most fields. In general, seed treatments can reduce common root rot severity, but this has not consistantly been accompanied by a higher yield response. This is due mainly to increased yield of healthy plants mixed in a diseased stand (14).

Seed treatments would be most valuable in the following situation: continuous wheat or barley; where short rotations between susceptible crops occur, and in soils or areas where moisture stress is likely (11).

In field trials conducted in North Dakota from 1983 to 1990, the effect of 8 fungicides on common root rot severity and yield of wheat and barley were tested (9). As the table below shows, difenoconazole and triadimenol provided the best controls.
 
Material Trade Name Formulation Rate Wheat Barley
Difenoconazole Dividend 3 FS 20 mg/kg +9% +4%
Triadimenol Baytan 30 F 100 mg/kg +7% +8%
Nuarimol N/A 3.3%EC 75 mg/kg +5% +2%
Imazilil Fungaflor 10%EC/6.5%L 100mg/kg +4% -3%
Maneb DB-Green 50%FL 740 mg/kg +1% N/A
Carboxin/Thiram Vitavax 200 17%FL 450 mg/kg -2% 0%
Flutriafol N/A 2.5%FL 100 mg/kg -9% +2%
Propaconizole Tilt 3 FS 1.125 SL -14% -5% 
a, bYield difference relative to non-treated control plants

Other reports indicate that iImazilil seed treatment provides the best control of common root rot. Imazilil is sold as Flo Pro IMZ flowable, Agsco Double R, and Nuzone 10 ME. In these reports, carboxin gave poor control and tridimenol (Baytan 30) gave fair control) (2).

Field experiments with chloride fertilizers (KCl and CaCl2) have sometimes reduced common root rot severity, but most have resulted in little effect on yield, lower plant nitrate and protein concentrations, and increased test weights (14, 15, 16).

References:

1) Pacific Northwest Plant Disease Control Handbook , 1990, 1994.

2) Gustafson "Disease Advisory" Spring 1993.

3) Wiese, M.V. 1977. "Common (dry land) root and foot rot and associated leaf and seedling diseases" Compendium of Wheat Diseases. APS Press, St. Paul, MN, p. 52-53.

4) NDSU Pest Report, "Discolored wheat heads" July 31, 1992, No. 14.

5) Guide to Herbicide Injury Symptoms in Small Grains. Second Edition. 1992. Agri-Growth Research, Inc., Hollandale, MN, pp. 77-78.

6) Cook, R.J. Veseth, R.J. 1991. Wheat Health Management. APS Press, St. Paul, MN, p. 46.

7) Watkins, J.E. et al. 1992. "Root and crown rot - winterkill complex of winter wheat" NebGuide. Cooperative Extension, University of Nebraska-Lincoln, G92-1097-A.

8) Lamey H.A and McMullen, M.P. 1993. "Crop rotations for managing plant diseases" North Dakota Extension Service. Bulletin PP-705.

9) Stack, R.W. 1991. Effect of fungicidal seed treatments on common root rot of spring wheat and barley. Proc. First Internat. Workshop on Common Root Rot of Cereals. Saskatoon, Sask., Agriculture Canada, pp. 87 - 91.

10) Hill, J.P. and Blunt, D.L. 1994. Wheat seedling responses to root infection by Cochliobolus sativus and Fusarium acuminatum. Plant Disease, Vol. 78 No. 12, pp. 1150-1152.

11) Stack, R.W. and McMullen, M. 1988. Root and crown rots of small grains. NDSU Extension Service, Bulletin PP-785 (Rev.).

12) Stack, R.W. 1994. Susceptibility of hard red spring wheats to common root rot. Crop Science, v. 34 (1), pp. 276 - 278.

13) Duczek, L.J. 1993. The effect of soil salinity on common root rot of spring wheat and barley. Canadian Journal of Plant Science, v. 73 (1), pp. 323 - 330.

14) Shefelbine, P.A., Mathre, D.E., and Carlson, G. 1986. Effects of chloride fertilizers and systemic fungicide seed treatment on common root rot on barley. Plant Disease, v. 70 (7), pp. 639 - 642.

15) Windels, C.E., Lamb, J.A., and Cymbaluk, T.E. 1991. Common root rot and yield responses in spring wheat from chloride application to sil in northwestern Minnesota. Plant Disease, v. 76 (9), pp. 908 - 911.

16) Goos, R.J. Johnson, B.E., and Stack, R.W. 1989. Effect of potassium chloride, imazilil, and method of imazilil application on barley infected with common root rot. Can. J. Plant Sci. v. 69, pp. 437 - 444.

17) Grey, W., Mathre, D., and Riesselman, J. 1979. Common root rot of cereal grains, Montana Plant Health Report, December, 15, 1979, Number 7.
 
 
 

DRY SEED DECAY
 

Scientific name: Penicillium spp. (2)and other soil-inhabiting fungi

Hosts: Winter wheat

Symptoms of dry seed decay : Seeds may decay in the soil or seedlings may become blighted and killed below the soil surface.

Look-alike symptoms:Winterkill , Bare Patch

Favorable conditions: Any soil condition that prevents rapid germination and emergence increases the possibility of seed decay. Seeding winter wheat into dry soil increases dry seed decay incidence. If wheat is seeded into dry soil with the expectation of following moisture to stimulate germination, problems can occur. Light showers that dry out germinated seeds can cause poor stands if additional moisture does not occur.

Pattern in field: Stands are thin and uneven or lacking plants in small to large areas.

Infestation levels:

Life cycle: Penicillium and Aspergillis are not true wheat pathogens, but they can rot seed planted in a warm, very dry seedbed. They are the same fungi responsible for moldy grain in storage. They can grow on grain when the relative humidity of the air is as low as 80% or even lower. In a way, dusting wheat into a dry seedbed is like putting it into storage in soil where is may eventually mold and die (5).

History in MT and US: Historically, dry seed decay has been most severe when winter wheat was seeded and did not germinate for several weeks. This is not uncommon, especially in the northern part of MT's winter wheat producing region (4). Dry seed decay is most common in the northern and drier areas of Montana.

Crop losses: Decreased stand emergence.

Cultural controls:

- Seed when soil conditions are conducive for rapid germination and wheat emergence.

- Seed when soils are cooler.

Resistant varieties:

Biological controls:

Chemical controls:

- Imazilil (Flo Pro IMZ) gives the best control of dry seed decay.

- Captan, difenconazole (Dividend), maneb, and thiram also are effective in reducing dry seed decay (4).

- Carboxin and PCNB give poor control (3).

References: 1) D. Mathre et al. 1991. "Dry seed decay of winter wheat" Montguide MT 9109 (AG). 2) Pacific Northwest Plant Disease Handbook, 1994. 3) Gustafson's Disease Advisory, Spring 1993. 4). Riesselman, J.R. 1994. "Dust seeding winter wheat". Montana Crop Health Report. Sept. 2, 1994, No. 11. 5) Cook, R.J and Veseth, R.J. 1991. Wheat Health Management. APS Press, St. Paul, MN, p. 42.
 
 
 
 

DRYLAND ROOT, CROWN, AND FOOT ROT or FUSARIUM FOOT ROT
 

Scientific name: Fusarium spp. (3) Fusarium culmorum and Fusarium graminearum (2).

F. culmorum (along with Cochliobolis sativis) is predominant in lower temperature areas such as the northern Great Plains and much of the inland northwest.

F. graminearum dominates in the warmest wheat-growing areas, such as the Corn Belt, the Southeast, and the south central Great Plains (5).

Hosts: Winter and spring wheat, barley (5)

Symptoms of Fusarium foot rot:

1) In late fall and early spring, the most visible symptoms are uniformly brown roots and a discolored subcrown internode chocolate brown discoloration of lower stem extending 4-5 inches up the plant.

2) The above pattern increases until boot stage. Then, the lower stem extending above the first nodes may be streaked or uniformly brown.

3) White heads devoid of kernels or with shrivelled kernels may be produced. Lodging may occur.

Look-alike symptoms:

1) Symptoms are similar to those of common root, crown, and foot rot. In fact, dryland (Fusarium) and common (Bipolaris) root rot are often grouped together as a disease complex.

2) Take-all also causes white heads. However, crowns and main roots of plants infected with take-all generally are shiny blue-black in color and have more root rot than with common root rot, resulting in stubbed off roots with take-all. Plants infected with take-all can usually be pulled from the soil much easier than healthy plants or ones with common root rot.

Favorable conditions:

- Damage is most severe in stressed plants. Drought stress is a common cause.

- Occurence is most common in low rainfall dryland winter wheat areas.

- High fall soil temperatures and low fall soil moisture can contribute.

- Fields with high levels of residue from previous years are more susceptible.

- Spring wheat generally is not affected (1).

Pattern in field:

- Droughty areas of fields such as sandy areas or hilltops.

- Stressed areas of fields

Infestation levels: The development of Fusarium foot rot depends on infected plants being water-stressed. Once water-stressed and diseased, a good rain will not allow for recovery since the water transport systems have already broken down. Plants NOT under water stress can become infected but the disease does not progress up the stem.

Life cycle: The fungi survive in soil on old stubble and straw. Infections may occur at any stage of plant growth. Foot rot fungi survive as thick-walled spores known as chlamydospores. F. culmorum chlamydospores are very hardy and can live for many years in the soil.

F. culmorum also uses infested residue as a food base and energy source to attack the next crop. If the field is left fallow and the residue allowed to rot, the chlamydospores formed in the stubble are simply freed into the soil, where they wait ready to infect the next wheat crop or other susceptible plants in the field (5).

The fungi responsible for the root diseases of wheat all live in the top 4-6 inches of soil. The occurrence of C. sativus and Fusarium spp., mainly on the subcrown internodes and on crown roots near where they emerge from the tiller bases may be due to the presence of the inoculum very near the soil surface (6).

Fusarium foot rot is important in dry soils and can grow on and within wheat plants under conditions that are too dry for other fungi to growth under and certainly too dry for growth and possibly even for metabolism by wheat. Although wheat is remarkably resistant to these Fusarium fungi, it becomes fully susceptible under water stress (5).

History in MT and US: Fusarium foot rot is common especially in dryland acreage in central and eastern Montana when conditions are favorable for disease development. For example, in 1994 in the Golden Triangle, there was virtually no precipitation during the growing season after early June. Under these conditions, Fusarium foot rot was common in fields throughout the area and intensified drought effects (7). Fusarium foot rot is a problem mainly in the Great Plains of the United States (5).

Crop losses:

Cultural controls:

- Seed when the soil temperature at the 3-in depth is 55 F or lower.

- Plant seeds shallowly in warmer soils.

- Rotate 2 or more years out of wheat, barley, or oats (6).

- Burying residue deeply and reducing the seeding rate are helpful.

- Fertilize to achieve vigorous root and shoot growth, but avoid excessive nitrogen that promotes excessive vegetative growth. This will increase transpiration and accelerate water stress when soil moisture is limiting. Nitrogen should be applied at rates to achieve realistic yield potential for a given environment (6)

- Stress avoidance is important.

Resistant varieties:

Susceptible varieties: Neeley primarily; incidence appears lighter in other varieties.

Biological controls:

Chemical controls:

Use one of the following seed treatments:

- Imazilil (sold as NuZone (Wilbur-Ellis), Double-R (AGSCO), and Flo-Pro IMZ

- Difenconazole (sold as Dividend (CIBA) gives good control of root rot and some of the smut diseases.

- Vitavax Extra (Gustafson, Inc.) is a premix of Vitavax is suggested since imazilil does not control the smut diseases.

Effect of imazilil seed treatment on Pondera spring wheat (Bozeman, 1991, Don Mathre and Bob Johnston, Plant Pathology, MSU)(6).

Treatment Yield (bu/A)

Imazilil - inoculated 36.8*

Non-treated - inoculated 28.8

Non-treated - non-inoculated 41.6*

*statistically different (P=0.05)

Plots treated with Imazalil seed treatment in 1987 had a noticeable reduction in the percentage of white heads due to Fusarium foot rot (1).

References: 1) Riesselman, J. Fusarium in drought-stressed wheat. Montana Crop Health Report, July 1, 1988. 2) MCHR 8/10/87 3) MCHR 7/13/87 4) Pacific Northwest Plant Disease Control Handbook , 1990, 1994. 5) Cook, R.J. Veseth, R.J. 1991. Wheat Health Management. APS Press, St. Paul, MN, p. 46, 54. 6) Jacobsen, B. Whiteheads and dryland foot rot. Montana Crop Health Report, July ?, 1994. 7) Martha Bamford, personal observation
 
 
 

EYESPOT and STRAWBREAKER and FOOT ROT
 

Scientific name: Pseudocercosporella herpotrichoides

Hosts: Winter wheat. Spring wheat, spring barley, rye, oats, and legumes are less susceptible (3).

Symptoms of eyespot (strawbreaker):

field symptoms - in Oregon

- First symptoms are white to tan eye-shaped spots with brown margins on the leaf sheaths and stems near the soil line (5).

- Later, the base of the stem is attacked, and gray fungus growth forms in the center of the infected area. Lesion margins are indistinct.

- The stems shrivel at the base and may fall over in irregular tangles.

- Heads are reduced in size and fill poorly under moisture stress and high temperatures. - Affected plants mature early and produce white heads (5).

- Lodging is common (5).
 

Look-alike symptoms:

- Sharp eyespot disease (Rhizoctonia cerealis) is often confused with Strawbreaker foot rot. The symptoms of the former are also elongated, eye-shaped lesions. However, these lesions are bordered by a dark brown edge with a sharp, distinct margin. Sharp eyespot lesion centers are often covered with white fungal growth, and the centers fall out exposing the culm.

- Wheat stem sawfly (also causes lodging).

Favorable conditions:

- Cool, moist climates

- Tillage of winter wheat in the spring (such as harrowing for wheat control or shank application of fertilizers) increases the amount of foot rot damage.

- Excess nitrogen increases disease severity.

- Continuously-cropped winter wheat, high soil moisture, dense canopy, high humidity near soil surface (5);

- Mild winters and prolonged cool springs

- Spring frosts.

Pattern in field:

Infestation levels:

Life cycle: The fungus overwinters on infected crop residue in the soil.

History in MT and US:

- Strawbreaker is more prevalent in the Great Lakes region and the Pacific Northwest (4).

- Generally, strawbreaker is not common in Montana. However, the disease occasionally has been identified in winter wheat grown in mountain valleys and a few wetter areas east of the divide (e.g. July 1980) (1, 2). In 1987, strawbreaker caused up to 25% lodging in Southeastern Montana (2), but this is considered to be somewhat of a "fluke" (2).

Crop losses:

- Heads are reduced in size and fill poorly under moisture stress and high temperatures.

- Losses due to lodging can be severe. In 1987, strawbreaker caused up to 25% lodging in Southeastern Montana (2).

Cultural controls:

- To reduce the chances of water stress, fertilize only enough for the attainable yield as set by the available water and no more (5).

- Minimum tillage and no-till can reduce disease incidence relative to conventional tillage. correct??

- Plant spring wheat or barley in severely infected areas.

- Rotation to spring wheat, barley, and legumes for 3 years can reduce inoculum levels.

- Late fall seeding reduces disease incidence.

Resistant varieties:

Biological controls:

Chemical controls: Since strawbreaker is so rare in Montana, fungicides are not recommended here. However, in areas of the United States where the disease is common, fungicide applications in early spring are useful. Some resistance has developed to benzimidizole fungicides (Benlate, Mertect, Topsin M) in some areas of the Pacific Northwest.

References: 1) MPHR 7/30/80 2) Riesselman, J. Strawbreaker. Montana Crop Health Report, July 27, 1987 3) Pacific Northwest Plant Disease Control Handbook. 1994. 4) Wiese, M.V. 1977. "Foot rot or eyespot" Compendium of Wheat Diseases. APS Press, St. Paul, MN, p. 46-47. 5) Riesselman, J. Strawbreaker in Montana. Montana Plant Health Report, July 30, 1980, Number 9.
 
 
 
 

PYTHIUM ROOT ROT

Picture of pythium root rot:

field shot
 

Scientific name: Pythium spp. (root rot)

Hosts: Wheat, barley, and oats

Symptoms:

1) Wheat seeds infected with Pythium usually can be recognized by soil adhering to the embryo end. The sticky threads (hyphae) of Pythium hold the soil onto the seed in the region of the embryo, where the infection occurs (3).

2) Mild infections may cause reductions in plant population, tillering, and maturation.

3) Adult plants may be stunted and/or chlorotic as if deficient for nitrogen.

4) Total plant collapse and decay can occur.

5) Heads may contain shrivelled grain.

6) All these symptoms often occur uniformly across the field, are subtle, and are difficult to recognize and diagnose.

7) Severe infections cause general root rot.

Lab diagnosis: On agar media, it may be difficult to tell pathogens from saprophytes. Instead use light microscope. Take roots and one-cell thick sheaths from lower crown area. Stain with cotton blue + lactophenol. Look for thick-walled oospores and coenocytic hyphae (no septa).

Look-alike symptoms:

Favorable conditions:

-More common in heavy, poorly-drained soils, but also in well-drained soils with good moisture. Chemical fallow situations (cooler, wetter soils). The lower the pH - down to about 5.0 - the more the infection. This may be related to less competition from other microbes, especially bacteria at lower pH's (3).

-Pythium infection of wheat embryoes is more common if the seed is placed into dry soil and water is then added (as in dusting in seed and then irrigating), than if seed is placed into soil that has been wet for at least a few days before sowing. The difference probably is caused by competition from the associated soil microorganisms. Most microorganisms are dead or stressed in dry soil and require several days to resume normal activity after soil is wetted. On the other hand Pythium germinates and grows more rapidly and thereby gains an advantage over its competitors in dry soil freshly rewetted. When soil has been wet for several days, the other microbes are active and "hungry". The gobble up a greater share of the nutrients leaking from the germinating seeds and roots so that Pythium gets a smaller share (3).

-Pythium root rot is more severe in low fertility fields or fields low in P (3). Early fall planting can increase infection rates (3).

Patterns in field: Symptoms often occur uniformly across the field, are subtle, and are difficult to recognize and diagnose. Areas of the field that are wetter, poorly drained, high in clay content, and lower in pH may have more disease (3).

Infestation levels: The amount of Pythium infection that occurs in wheat depends on soil moisture and clay content of the soil. Infection generally increases as soil moisture and clay content increases (3).

Life cycle: Pythium spp. reside in the soil and in old root residue. The fungi begin their parasitic invasion of wheat seeds in soil by infecting the embryo within 24-48 hours after planting. Pythium colonizing the embryo of a germinating wheat seed is ideally positioned to live on sugars and other nutrients form the seed as they solubilize enzymatically. The fungus then moves from within the endosperm to the shoot and roots. Also, it continues to parasitize the emerged seedling by remaining in the seed region and initiating new infections at the root tips. The fungus is very skillful as an invader and destroyer of root hairs and young roots. These roots are critical to nutrient uptake by the plant before tillers and associated crown roots develop (3). The infection rate can be as high as 60-70%, but the seedlings rarely are killed. Instead, they remain stunted and produce small leaves- symptoms that may go unnoticed, since the plants appear normal except for their small size (3).

History in MT and US: The disease is more important in areas of the US with higher rainfall.

Pythium damage is probably more limiting at stands and seedling vigor of wheat during more years and over a greater area of North America than any other disease (3).

Crop losses:

Cultural controls: Plant early to allow rapid seed germination and seedling establishment. Use high quality seed.

Resistant varieties:

Biological controls:

Chemical controls: Metylaxyl seed treatment gave 14% yield increase in 7 barley varieties (Mathre and Johnston, 1970's). Apron seed treatment is registered for use on cereals.

References: 1) Lipps, P.E. 1988. Wheat disease control in Ohio. Dept. of Plant Path. Ohio State Univ. 2) Pacific Northwest Plant Disease Control Handbook, 1994. 3) Cook, R.J. Veseth, R.J. 1991. Wheat Health Management. APS Press, St. Paul, MN, p. 46.
 
 
 
 

SHARP EYESPOT

Scientific name: Rhizoctonia cerealis

Hosts: Winter wheat, barley, and oats

Symptoms of sharp eyespot:

symptoms - on lower stems

Look-alike symptoms:

Favorable conditions:

Distribution of infestation:

Infestation levels:

Life cycle:

History in MT and US:

Crop losses:

Controls:

Cultural controls:

Resistant varieties:

Biological controls:

Chemical controls:

References:
 
 
 
 

TAKE-ALL

Pictures of take-all:

petri plate culture of take-all

runner hyphae, wheat roots

Bob Johston in field - wheat infected with take-all, Lind, WA, 1971

biocontrol comparisons - wheat infected with take-all

aerial view of field - take-all patches, Opheim, MT, 7.24.85
 

Scientific name: Gaeummannomyces graminis f.sp. tritici

Hosts: Spring and winter wheat and turfgrasses are susceptible to take-all. Barley is susceptible, but less so than wheat. Rye, oats, and some triticale are resistant to take-all (6).

Symptoms of take-all:

root symptoms - #1

root symptoms - #2

ABOVEGROUND SYMPTOMS:

- Plants are stunted, mature early, and have white, empty heads.

- Some tillers may not head.

- Plants may turn gray as a result of secondary fungal infection.

More information (M-TA-SYM1)

BELOWGROUND SYMPTOMS:

- Plants pull up easily or break off at the soil line.

- In severely-infected plants, the stem near soil level becomes coal-black under the leaf sheaths.

- Individual roots may develop light to dark brown or black lesions and may have necrotic tips.

- In advanced stages, roots may turn coal black in color and are black on the interior when scraped (6).

Lab diagnosis: Dark brown "runner" hyphae of the fungus many or may not be observed on the root surface, because G. graminis frequently penetrates young roots and grows between the cortex and stele. The presence or absence of runner hyphae may not be a good diagnostic character of disease in all cases because the fungus grows over the surface of the cortex of resistant rye and oat roots without causing disease (6).

FUNGAL ISOLATION AND CULTURE:

1) Sterilize roots in 0.1% AgNO3 (silver nitrate).

2) Plate onto Take-all selective media (SM-GGT3) (7).

Media preparation information (D-TA-LD1)

Look-alike symptoms:

1) Common root rot:

- The crown and roots of plants infected with common root rot are dark-brown in color (not coal black as with take-all).

- Plants infected with common root rot usually do not pull out of the soil as easily as those infected with take-all.

2) Fusarium foot rot

3) Nitrogen deficiency

On young plants, aboveground symptoms are characteristic of a general nutrient stress.

4) White heads also can be caused by:

a) Frost injury

b) Wheat stem maggot

c) Cephalosporium stripe

Many conditions that favor take-all also favor Cephalosporium stripe. Both fungi are soilborne, survive on wheat residue, infect roots, and are favored by continuous wheat production, high soil moisture, and early planting (8) .

d) Sharp eyespot

e) Hessian fly

f) Strawbreaker

Favorable conditions:

- Almost all Montana fields have take-all organisms present. In some fields take-all is present in high amounts.

- Continuous-cropped spring wheat, and also winter wheat.

- High moisture situations (irrigated acreage and high precipitation areas such as NW Montana). The incidence of take-all is highest during excessively wet years.

- Take-all is more severe in fields with greater than 7.0 pH (3).

- Early fall planting can increase infection rates (3).

- Take-all is more severe in low fertility fields or fields low in phosphorus (3). Few diseases respond as dramatically to nutrition as take-all. Disease severity is increased by a deficiency of any of the essential mineral nutrients. Nitrate forms of nitrogen increase take-all whereas ammoniacal forms decrease the disease.

- Take-all often is more severe in fields where quackgrass (Agropyron repens) and/or downy brome (Bromus tectorum) have been problems in recent years. These weeds may compete strongly with wheat for nutrients (6).

- Also, other weeds and volunteer wheat can harbor the take-all fungus, increasing its populations and inoculum potential (9).

- Hot, dry weather can cause infected plants to ripen prematurely. This is because plants transpire more rapidly than the decayed root system can resupply with water.

- Survival of the take-all fungus is much lower in 1-5 months of warm, moist soil than in 1-5 months of cool, moist or warm, dry soil (9). ("Warm" = 21 - 29 C, "Cool" = 35 C.) However, in most years in Montana, the combination of high summer rainfall and high temperatures are not common enough for this phenomen to have a major effect on the occurance of take-all as they might in a state such as Kansas.

- Shading of the soil by surface residue can lower soil temperatures and allow survival of high take-all fungus populations (9, Kansas report).

- Generally, take-all often is more severe in no-till fields. This may be due to survival of take-all on plant residue (3) and shading effects of the residue in keeping soil temperatures lower (9). Conditions are even more favorable if wheat is under continuous production under no-tillage (3).

- Although many of the conditions that favor take-all also favor Cephalosporium stripe, the presence of one disease has not been shown to increase the severity of the other (synergism). Instead, there may a slight antagonism between the fungi causing these two diseases (8). More information (CS-FC1)

Pattern in field: Grain losses of up to 10-15% from reduced root capacities and killed or aborted tillers may go undetected in the field. Wheat fields severely infected with the take-all fungus may have an uneven appearance in height by the time of heading, although significant levels of infection frequently go undetected. Whiteheads (prematurely ripened, poorly filled, or empty seed heads) produced on severely-infected plants may be scattered throughout the stand or may occur in circular to irregularly-shaped areas in the field (6).

Infestation levels: Take-all causes the greatest losses when plants are infected at the 2-3 leaf stages. Infection of only every 10th plant can be potentially severe if the fungus colonizes these plants well and then moves down the row (5). If infected during jointing or later, the diseased plants often are of uneven height, poorly tillered, and have small heads. These plants will be found in patches in the field (5).

Life cycle: The fact that take-all is favored by wet soil does not mean that it is important only in wet areas. The disease can begin with only a few weeks or a few days of suitably moist soil. Most wheat is exposed to soil ideally moist for take-all development during the early stages of plant development. This is when the impact of root disease on tiller and head formation is greatest. In addition, high residue levels on the soil surface keep the soil wet longer.

The take-all fungus survives as mycelium in soil in the old roots and tiller bases of past wheat (and barley) crops. The fungus uses these plant remains as a food base for survival and to support its growth onto new roots of the new crop. However, the take-all fungus is a good parasite ("predator"), but a poor saprophyte ("scavenger"). As other soil microorganisms decompose the host residue, the viability of G. graminis var. tritici decreases (9). These facts have important implications in management practices (see Take-all - Cultural Controls).

Infection of the new crop begins by infection of the seminal roots, when the plants are at the 2-3 leaf stage. Infection of only every 10th plant can be potentially severe if the fungus colonizes these plants well and then moves down the row (5).

History in MT and US:

- Take-all was first described in Australia 150 years ago (6).

- The disease was first diagnosed in Montana in 1980. Since then, take-all has infected over 250,000 acres in MT causing yield losses of up to 40%.

- Almost all Montana fields have take-all organisms present - in high amounts in some fields. The disease is most severe in irrigated fields throughout the state and in high precipition acreage such as in NW Montana.

- Generally, take-all is not found in dryland wheat in Montana. An exeption to this occurred in 1993, which was an excessively wet year throughout the state. During 1993, take-all was found commonly in dryland fields at low to moderate levels.

Crop losses:

- Yield losses may be up to 40%.

- More common are grain losses of up to 10-15% from reduced root capacities and killed or aborted tillers. Losses at these levels may go undetected in the field or be attributed to other causes (6).

Control: Take-all is controlled primarily by management practices such as crop rotations, acidyfying soil pH, and tillage (6). See below for more detail.

Cultural controls:

CROP ROTATION:

Where take-all has decreased yields in recent years, avoid planting wheat unless a long-term monoculture is planned (4). Rotate out of wheat or barley into alfalfa for one year usually sufficient to reduce inoculum in field. Some crop rotations increase take-all severity in wheat while other rotations decrease the disease. Alfalfa is a crop that increases take-all while oats and lupine decrease take-all in subsequent wheat crops. More information (M-TA-CC3). Do not follow wheat after legume crops that were heavily infested with cheatgrass.

MOISTURE:

High moisture can increase take-all severity (6).

PLANTING DATE:

Later seeding dates of winter wheat can decrease take-all severity (6).

TILLAGE:

- Plow under residue.

- A firm seedbed can reduce take-all severity. Use of press wheels on experimental grain drills to firm the soil after seeding increased manganese tissue concentrations and markedly reduced take-all. More Information (M-TA-CC2)

NUTRITION:

- Few diseases respond to nutrition as dramatically as does take-all. Disease severity is increased by a deficiency in any of the major nutrients.

- Specific forms of nutrients have different effects on take-all severity. Ammoniacal forms of nitrogen (NH4) decrease take-all while nitrate forms of nitrogen (NO3) increase this disease (6). More Information (M-TA-CC4)

- Maintain a good level of nitrogen. The use of ammoniacal forms of nitrogen, slow-release nitrogen, and chloride fertilizers are reported to decrease damage (4).

- Chloride fertilization can decrease take-all severity (6).

- Fertilization with manure can increase take-all (6).

HERBICIDES:

In susceptible fields, Take-all severity often increases in the season after glyphosate (Roundup) application. More Information (M-TA-CC1)

Resistant varieties: High levels of genetic resistance do not exist, although a limited range of tolerance is present in some wheat lines. Varieties with lower nutrient requirements and greater efficiency of storing nutrients may have greater resistance to take-all (6).

Biological controls: There is a phenomenon known as "take-all decline." After approximately 7 years of continuous wheat production, antagonistic organisms build up in the soil and help control take-all. 1993 field trials of potential biocontrols were conducted by Dr. Don Mathre. Orlando found 2 biocontrol fungi (unidentified because haven't sporulated in culture). By 7/93, controls and biocontrol + Take-all plot looked similar.

Chemical controls: Tridimefol (Baytan 30) seed treatment provides good control. Other seed treatments including carboxin (Vitavex), imazalil (Flo-Pro-IMZ), captan, and maneb gave poor control of take-all.

Post Farm trials: A conducive soil was inoculated with 5 g oat kernel inoculum per row (small amount) in 1993. High levels of disease resulted. A Rhone-Poulenc fungicide is controlling the disease well.

References:

2) MCHR 7/27/87

3) Lipps, P.E. 1988. Wheat disease control in Ohio. Dept. of Plant Path. Ohio State Univ.

4) Pacific Northwest Plant Disease Control Handbook, 1994.

5) Cook, R.J. Veseth, R.J. 1991. Wheat Health Management. APS Press, St. Paul, MN, p. 46. 6) Huber, D.M. and McCay-Buis, T.S. 1993. A multiple component analysis of the take-all disease of cereals. Plant Disease. Vol. 77 No. 5, pp. 437-447.

7) Media book, Take-all selective media, Mathre lab, 517 Leon Johnson Hall.

8) Bockus, W.W., Davis, M.A., and Todd, T.C. 1994. Grain yield responses of winter wheat coinoculated with Cephalosporium graminearum and Gaeumannomyces graminis var. tritici. Plant Disease, Vol. 78 No. 1, pp. 11-14.

9) W. W. Bockus, Davis, M.A., and Norman, B.L. 1994. Effect of soil shading by surface residues during summer fallow on take-all of winter wheat. Plant Disease, Vol. 78 No. 1, pp. 50-54.