in
wheat
Picture of crinkle joint:
Hosts:
Symptoms:
- Plants growing sideways
- Distorted plants with lower nodes bent at up to 90 degree angles (1)
Look-alike symptoms:
- Hail injury
- Banvel injury can mimic crinkle joint. Banvel injury occurs when sprayed with higher than recommended rates or when applied too late (past jointing).
Favorable conditions: This physiological disorder occurs when normal upward growth of wheat is restricted.
- Cold wet weather
- Heavy, wet late spring snows
Pattern in field: Stands may be uneven (1).
Infestation levels:
History in MT and US: Crinkle joint is fairly common in Montana when favorable conditions exist.
Crop losses:
Cultural controls:
Resistant varieties: Crinkle joint seems to be more common in tall varieties. Norstar and Roughrider are very prone.
Chemical controls:
References: 1) Riesselman, J. Crinkle joint. Montana Crop Health
Report, May 12, 1989. 2) Riesselman, J. Crinkle Joint, Montana Crop Health
Report, June 16, 1989.
Picture of melanism:
Hosts: Wheat, barley
Symptoms:
- Parts of stems may turn purple (1).
- When melanism occurs on glumes it causes dark purple to black steaks or blotches on the glumes.
- The awns and peduncle show no symptoms.
- A dark purple to purple-brown ring or collar forms at each joint. Often the leaf sheath much be peeled away to see this symptom.
- The purple rings at the joints are diagnostic for this genetic disorder (10).
Cause: Under abnormal stress conditions, plants may produce purple anthocyanin pigments (3). Anthocyanin production likely is a genetic response to various stresses (1).
Look-alike symptoms:
- Black chaff: melanism that occurs on the glumes is more uniformly black than in the case of black chaff (4).
Favorable conditions:
- Melanism may occur in certain varieties in response to stresses such as low temperature or drought (1).
- The combination of hot and humid weather
Pattern in field:
Infestation levels:
Life cycle:
History in MT and US:
Crop losses: Melanism has not cuased any noticeable losses in hard red spring wheat varieties Amidon or Butte in North Dakota (4).
Controls:
Resistant varieties: Traditionally, melanism has been associated with certain genes for stem rust resistance (4). The spring wheat variety Newana often produces purple stems early in the spring when under environmental stress (2). Late in the summer, Amidon spring wheat stems tend to turn purple in a genetic response to stress (1, 2). Other varieties can develop purple stems as well but this melanism seems to be most common in the above varieties in Montana.
References: 1) NDSU Pest Report, "Purple stems on wheat",
July 31, 1992, No. 14. 2) Riesselman, J. Purpling in spring wheat. Montana
Crop Health Report, August 7, 1992, No. 10. 3) Riesselman, J. Spring wheat
problems. Montana Crop Health Report, August 26, 1989, No. 10. 4) McMullen,
M. Black chaff and false black chaff of wheat. NDSU Extension Service,
Bulletin PP-749 (Revised), November, 1989.
PHYSIOLOGIC LEAF SPOT or PINTO SPOT
Hosts: Winter wheat and spring wheat
Symptoms of physiologic leaf spot:
leaf
symptoms - Redwin winter wheat
- Symptoms first appear during late spring (Feekes scale 3-5).
- The oldest leaves of susceptible cultivars begin showing spots first and then symptoms progress to successively younger leaves after they emerge. Affected leaves become chlorotic and die prematurely.
- Characteristics of spots may vary depending on age of the lesion, wheat variety, weather, and other factors. The first symptom is often a tiny brown spot or fleck on the lower leaves. Spots may or may not be surrounded by a chlorotic halo. Spots then enlarge into brown necrotic areas or oval to irregular shapes, with or without chlorotic halos.
- The disease often increases in severity on lower leaves and simultaneously becomes established on younger leaves. When severe, older leaves are killed prematurely and up to 60% of the flag leaf may become necrotic.
******Reference 3 has good photographs*******
Look-alike symptoms:
1) Tan spot
4) Some minor-element deficiencies. Physiological leaf spot, tan spot, and Septoria leaf blotch are each suppressed by crop rotation, selection of resistant cultivars, and delayed seeding. Excessive nitrogen reduces the severity of both physiologic leaf spot and tan spot, but increases Septoria leaf blotch incidence.
Physiologic leaf spot often is misidentified as Septoria leaf blotch or tan spot even though fruiting structures are not present and cannot be induced by clinical methods (3). The following practices reduce tan spot and Septoria leaf blotch while having no effect on Physiological leaf spot:
1) Tan spot and Septoria leaf blotch damage can be reduced by avoiding dense plant canopies early in seedling development, and by reducing primary inoculum through burning or burying of residue from previously infected wheat crops.
2) Use of foliar fungicides also can control tan spot and Septoria leaf blotch (2).
3) Avoidance of excessive nitrogen fertilizers can reduce Septoria leaf blotch damage.
Favorable conditions: The following practices favor physiologic leaf spot:
1) use of susceptible varieties,
2) continuous wheat croppiing,
3) conservation tillage or no-till situations,
4) early winter wheat seeding dates, and
5) inadequate nitrogen application (2).
Pattern in field: When physiologic leaf spot occurs on leaves in the upper plant canopy, the field appears drought stressed. Such regions of the field become dull and have a brownish tint compared to nearby less affected stands (3).
Infestation levels: Damage due to physiologic leaf spot typically is minor, but damage has been moderate to severe since 1989. In many fields in eastern Oregon and Washington, physiologic leaf spot caused chlorosis and necrosis in up to 60% of the flag leaf area and caused early death of lower leaves during an especially severe epidemic in 1990 (2).
Cause: Physiologic leaf spot may result from a chloride deficiency. It is possible that chloride may affect physiological processes such as water relations, photosynthesis, or kernel development to minimize damage caused by physiologic leaf spot. Chloride is important in photosynthesis and osmotic relations of guard cells in leaves. Chloride apparently affects a wide range of developmental processes, including rate of spikelet formation, and maturation, and volume and weight of kernels. Chloride fertilizers may increase grain yields by prolonging photosynthetic activity. (2).
Calcium is an essential nutrient in plants that protects the roots from low pH, toxic ions, salinity, and ion imbalance. Calcium delays senescence and reduces membrane damage and leakiness. Calcium deficiency has been associated with reduced cold hardiness, increased risk of magnesium toxicity, and reduced growth of meristem tissues. Even though this nutrient is well known for improving plant resistance to diseases caused by soilborne pathogens, there is not much evidence that calcium plays an important role in controlling foliar diseases in natural soils (2).
History in MT and US: Physiologic leaf spot has occurred in semiarid regions of the Pacific Northwest for over three decades. The disease typically is minor but has been moderate to severe since 1989 (2). Physiologic leaf spot occurs sporadically in locations throughout Montana.
Crop losses: Yield reductions of 20% or more have been observed (1). In an unusually severe epidemic in eastern OR and WA in 1990, physiologic leaf spot reduced grain production by 10% (2). Don Mathre (MSU) estimates a 4 bu/acre yield increase by switching to a good non-pinto spot variety (conversation, 7/93).
Controls: The severity of physiologic leaf spot can be reduced by the management of wheat cultivar selection, crop rotation, planting date, and plant nutrition (2). See below for details.
Cultural controls: Field observations suggest that physiologic leaf spot is more severe in conservation tillage than in low-residue tillage systems. Leaf spot was more severe in annual wheat than in rotations of wheat with summer fallow or with peas (2). Later seeding dates of winter wheat significantly reduced leaf spot severity (2).
Resistant varieties: Tiber is resistant. Redwin, Kestral and perhaps Winridge are particularly susceptible.
Biological controls: None available.
Chemical controls: Unlike tan spot and septoria leaf blotch, fungicides do not control physiologic leaf spot (2). The problem may result from a chloride deficiency. Use 20 lb/acre potash (potassium chloride (KCl)) ($3-4/acre) or switch to a more resistant variety. Foliar application of urea+calcium chloride reduced leaf spot severity and increased grain yield. Leaf spot severity was not affected by the application of soil-applied nitrogen, the burning or leaving of stubble from previous wheat crops, or the application of diclofop-methyl herbicide.
References: 1) PNW Plant Disease Control Handbook, 1994. 2) Smiley,
R.D. et al. 1993. Influence of crop management practices on physiologic
leaf spot of winter wheat. Plant Disease. Vol. 77 No. 8, pp. 803-810. 3)
Smiley, R.W. 1993. Physiologic leaf spot of wheat. Plant Disease. Vo. 77.
No. 5, pp. 521-527.
Hosts: Wheat, barley, and oats (1)
Symptoms: Sleepy wheat syndrome causes small grain plants to exihit prostrate growth herbicide application. Initial symptoms generally appear within 3 to 5 days of application. Under normal conditions, the plants resume upright posture 5 to 14 days after the symptoms are noted (1).
Look-alike symptoms:Drought injury
Favorable conditions: Sandoz Agro, Inc. (the manufacturers of Banvel and Banvel SGF) does not fully understand what dicamba does inside a small grain plant or all the causes of sleepy wheat. Sleepy wheat is not uncommon, but even long time users may have never seen symptoms. However, under certain conditions, dicamba affects the cell walls of cereals causing a loss of some of the internal cellular water pressure (turgor pressure) allowing the cells to become flaccid (1).
Pattern in field: Normal upright leaves and tillers are mixed with leaves and tillers that are "askew" so that rows do not appear uniformly upright. In more serious cases, the plants may lay flat on the ground (1).
Infestation levels:
Life cycle: Initial symptoms generally appear within 3 to 5 days of application. Under normal conditions, the plants resume upright posture 5 to 14 days after the symptoms are noted. Small grains are most susceptible when they are growing rapidly. Rapid growth probably increases uptake and temporarily overloads the plants ability to metabolize Banvel or Banvel SGF. Surfactant can increase the severity of sleepy wheat syndrome. The prostrate grain effect is not related to Banvel or Banvel SGF rates or tank mixes (1).
History in MT and US: Sleepy wheat syndrome is not unique to Banvel and Banvel SGF. It is also observed with sulfonylureas, phenoxy, and bromoxynil products. Banvel and Banvel SGF are powerful plant growth regulators. Sleepy wheat is not uncommon, but even long time users may have never seen symptoms since dicamba only occasionally affects the cell walls of cereals (1).
Crop losses: Sandoz Agro, Inc. has observed the sleepy wheat syndrome and documented plant growth through harvest. Multiple observations and yield records in University and SANDOZ replicated trials show no yield reduction under normal growing conditions (1).
Cultural controls: Plants are most susceptible when they are growing rapidly (1).
Resistant varieties:
Chemical controls: Surfactant can increase the severity of sleepy wheat syndrome. The prostrate grain effect is not related to Banvel or Banvel SGF rates or tank mixes (1).
References: 1) "Prostrate cereal grains or sleepy wheat syndrome
- Development information from product development" Sandoz Agro, Inc. Western
Region, May 1993.
Picture of temperature banding:
Hosts: wheat, barley
Symptoms:
- Leaves may have bands altering between green and yellow, damaged tissue.
- Leaves may have scorched areas at the point where the leaf naturally bends downwards.
- In severe cases, the newly emerged leaves form corkscrews and die (1).
Look-alike symptoms:
Favorable conditions: High daytime temperatures that encourage rapid growth followed by low nighttime temperatures.
Pattern in field: Depending on severity, field appearance may range from a light silver cast to severe browning and scorching (1).
Infestation levels: As long as the growing point remains below the damaged tissue, plants will recover with little or no long term effects on yield potential (1).
History in MT and US: Temperature banding occurs sporadically throughout Montana when environmental conditions
Crop losses:
Controls:
Cultural controls:
Resistant varieties: Some varieties appear to be more sensitive to temperature banding. In 1992, the soft white winter wheat Stephens had more visible damage in Gallatin Co. than other soft white and hard red winter wheat varieties (1).
Biological controls: None available.
Chemical controls: None available.
References: 1) Riesselman, J. 1992. Hot days, cold nights blamed for burnt wheat. Montana Crop Health Report, May 15, 1992, No. 4.
