Pacific Northwest 1998 An Online Guide to Plant Disease Control

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OSU Extension Office
 
Wheat -- Eyespot (Foot Rot, Strawbreaker)
See Also: Wheat -- Common Root Rot ; and Wheat -- Crown Rot (Foot Rot, Seedling Blight, Dryland Root
 
Cause: The fungus, Pseudocercosporella herpotrichoides (sexual stage: Tapesia yallindae and T. acuformis), survives on infected crop residue in soil and causes disease on barley, oats, rye, and grasses as well as wheat. It is prevalent in the prairies of the Columbia Basin, the Willamette and Grande Ronde valleys of Oregon, and Powder and Bear Lake counties of Idaho. Because cool temperatures, wetter soils, and high humidity favor the disease, the amount of disease in a field is affected by planting date, winter temperatures, and the amount of disease in the last wheat crop. Tilling winter wheat in spring, like harrowing for weed control or shank application of fertilizer, increases the amount of foot rot damage. Applying more nitrogen than recommended also increases disease incidence.
Symptoms: A disease called sharp eyespot, caused by Rhizoctonia cerealis, is often confused with strawbreaker foot rot. Distinguishing between eyespot and sharp eyespot is important in making decisions about fungicide applications.

The diagnostic symptom of eyespot is elliptical (eye-shaped) spots on leaf sheaths. Lesions are white to light brown at first, then turn dark. Later, the stem's base is attacked, and gray fungus may grow in the center of the infected area, whose margins are indistinct. Stems shrivel at the base and and plants may lodge. Diseased tillers may mature early, producing white heads. Otherwise, heads are small and fill poorly under moisture stress and high temperatures.

The symptoms of sharp eyespot are also elongated, eye-shaped lesions. However, sharp eyespot lesions are bordered by a dark brown edge that sharply delineates the infected area from surrounding tissue. Centers of sharp eyespot lesions often are covered with white fungal growth, and centers fall out, leaving a characteristic hole.

Note the lesions on the culms.

Eyespot on the left plant and Fusarium sp. on plants on the right side of the picture.

Sharp eyespot due to Rhizoctonia sp.
 
Scouting: Chemical applications are recommended for susceptible cultivars when 10% or more of stems sampled are infected with eyespot. When sampling, examine at least 50 stems per field (more is better), and take them from across all the field, not just near the road. Be careful not to count lesions of sharp eyespot. Check fields several times during the potential application period (late February or March); the disease may increase after the earlier check.

Fields of susceptible cultivars with 10% or more stems with eyespot lesions usually respond to chemical treatment by yielding 20% more than if left untreated. To determine whether a chemical application is cost-effective, multiply 20% by your yield potential, times the price you expect to get for the wheat. This gives you a conservative estimate of the potential investment return on your fungicide. For example, if yield potential is 30 bu/A, applying fungicide may save 6 bu (30 x 0.2). At $3/bu, the return is $18, less the cost of the fungicide.
Cultivar Resistance: The soft white wheat cultivars 'Coda', 'Foote', 'Gene', 'Hyak', 'Madsen', 'Temple', and 'Weatherford' have moderate resistance to eyespot.
Cultural control:
  1. Late-fall seeding can substantially reduce disease severity.
  2. Minimal till and no-till practices reduce disease incidence com-pared to conventional tillage (moldboard plow, disk, harrow).
  3. Plant spring wheat or barley in areas with a history of severe disease.
  4. Rotating to legumes, or spring cereals for 3 or more years reduces the inoculum available to infect the next wheat crop.
Chemical control: Apply fungicides as soon as 10% of stems are affected. Apply when the fungicide spray can easily penetrate to the crown area of the plant. Do not apply after stems begin elongating or after the foliage closes between rows, because leaves protect the crown area from the spray. In most areas, best spray time is late February or in March. Apply any chemical only in combination with cultural controls, above.
  1. Quilt at 14 fl oz plus half the rate recommended of another EPA registered fungicide such as Topsin M. Apply at tillering but before elongation has occurred. Do not feed treated forage or cut green crop for hay or silage. Preharvest interval is 45 days. 12-hr reentry.
  2. Tilt at 4 fl oz/A plus half the rate recommended of another EPA registered fungicide in not less than 15 gal/A water (ground) or 5 gal/A water (air). Apply at tillering but before elongation. Do not apply within 30 days of harvest for forage, 40 days for grain and straw and 45 days for hay. 12-hr reentry.
  3. Topsin M WSB at 1 lb/A on fall-seeded wheat. Apply at tillering but before elongation. Apply only once per season. Do not cut hay within 90 days of application. Do not graze livestock in treated fields. If fungal resistance is suspected, tank-mix at 0.4 lb/A with another fungicide with a different mode of action. 12-hr reentry.
References:
  1. Wiese, M.V. 1987. Compendium of Wheat Diseases, 2nd ed. St. Paul, MN: APS Press.
Content edited by: Richard Smiley and Cynthia M. Ocamb on January 1, 2009
 
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