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Issue No. 11, Article 2/June 5, 2009

Update on a Wheat Disease Survey in Illinois

The high levels of rainfall received in Illinois this spring have created favorable conditions for wheat diseases. A survey was initiated last week to determine the impact of diseases on wheat fields in the state. Nine counties in southern Illinois have been surveyed so far (Clay, Gallatin, Jefferson, Pope, Randolph, Saline, Washington, Wayne, and White), with preliminary results presented in Table 1. A more complete picture of how diseases impacted the 2009 wheat crop will be available once the survey is complete.

Leaf blotch caused by the Stagonospora nodorum/Septoria tritici complex is present on the flag leaves throughout southern Illinois fields, with average incidence ranging from 76% to 100% of flag leaves affected. Leaf rust has been found in only a very small portion of the fields surveyed so far, with 0% to 56% of leaves affected, at very low severity levels. Head scab (Fusarium head blight) has been present in every field surveyed so far, with average incidence ranging from 17% to 100% of the heads affected. Glume blotch also can be found in every field; average incidence ranges from 50% to 92% of the heads affected.

Leaf blotch caused by the Stagonospora nodorum/Septoria tritici complex.

Fusarium head blight (head scab) causing bleaching of the wheat heads.

Wheat head affected by glume blotch

What can I do now? Most wheat fields in Illinois are now past the stage of applying any disease control treatments. A few fields in northern Illinois may have not yet reached the early flowering stage (Feekes growth stage 10.5.1). Some fungicides can be applied at that stage to give protection against head scab and foliar diseases. The current map on the Fusarium head blight risk assessment tool website (www.wheatscab.psu.edu) shows low risk of head scab in northern Illinois.

In fields with high levels of head scab, it is important to increase the fan speed on the combine at harvest. A higher fan speed will blow more of the scabby kernels out the back of the combine, which may reduce any discounts applied at the elevator for low test weight and high deoxynivalenol (DON) contamination.

What can I do next year to manage head scab? The best practices for managing head scab are done prior to planting, such as choosing a variety that has some resistance to the disease. Information about the level of head scab resistance in some wheat varieties is available at vt.cropsci.illinois.edu/wheat.html. Another management step is deciding where to plant winter wheat. When planting into a field with a lot of corn stubble on the soil surface, the risk of head scab will increase, as it is likely that the stubble will already be infested with the fungus that causes head scab (Fusarium graminearum, aka Gibberella zeae). The final step in managing head scab is to apply a fungicide if conditions have been favorable for developing the disease.--Carl A. Bradley

Carl A. Bradley

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