Three Diseases of Wheat in Illinois
|Frederic L. Kolb
Professor of Plant Breeding
Department of Crop Sciences
Many different pathogens infect wheat in Illinois, but which diseases are economically important varies from year to year. Three wheat diseases will be discussed: barley yellow dwarf virus (BYDV), stripe rust, and Fusarium head blight (or head scab).
Barley yellow dwarf virus is vectored by aphids. Aphids feed on the plants and introduce the virus into the plants. Infection may occur either in the fall or in the spring. Fall infection produces more stunting and results in greater yield loss than spring infection. Spring infections often result in yellowing and reddening on the upper leaves, but generally produce little stunting. There are some differences among wheat varieties in the level of the tolerance to BYDV; however, the best control methods are seed treatment or foliar-applied insecticides to control the aphid vectors of BYDV. Gaucho® and Cruiser® are effective seed treatment insecticides. Warrior® foliar insecticide applied either in the fall or in the spring is also an effective way to control aphids. The difficult question is “When are these treatments economically beneficial?” This question is difficult to answer because the number of aphids varies from year to year and the percentage of aphids carrying the virus fluctuates from year to year and even from fall to spring of the same season. BYDV was particularly severe in parts of southern Illinois in 2006.
Stripe rust, as the name indicates, is first observed as well-defined stripes of lesions running lengthwise along the leaves. Stripe rust was not severe in Illinois in 2006, but was moderately severe in parts of Illinois in 2005. Prior to 2000 stripe rust was seldom observed in Illinois, but it has been more common in Illinois in the last several years. In recent years new races of stripe rust seem to be more adapted to higher temperatures. Varieties differ in resistance to stripe rust so variety selection is important in preventing losses due to stripe rust. A number of foliar-applied fungicides are also effective in controlling stripe rust.
Fusarium head blight, or head scab, is an important wheat disease because it can result in huge economic losses in years when it is severe. Infection takes place when rainy weather (with long periods of high relative humidity) occurs during, or just after, flowering. Infection is especially likely when warm nights coincide with the rainy weather. Losses from head scab are due to reduced yield and test weight, but also because the fungus produces a mycotoxin, deoxynivalenol (DON). Producers suffer discounts for lower test weight and high DON levels, and millers cannot use wheat with high DON levels for milling. Varieties differ in level of resistance to head scab. Producers should use head scab resistance as one criterion for variety selection. Producers should also plant varieties differing in maturity because this spreads the risk of infection since the varieties flower at different times. Also, for the past several years Folicur® fungicide has been available for application to control head scab under a Section 18 permit. Producers should use a combination of pest management methods to control head scab since no one method is likely to eliminate losses from head scab when environmental conditions favor infection.