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Issue No. 7, Article 4/May 8, 2009

Wheat Scab Alert and Results of 2008 Illinois Wheat Fungicide Trials

According to the Fusarium Head Blight Risk Assessment Tool on May 5, wheat fields in portions of southern and central Illinois are under high and medium risk of Fusarium head blight (scab). Some fields in southern Illinois should be at or near heading and flowering. Wheat is susceptible to scab from flowering through kernel development, but it is important to make any fungicide applications for protection against scab at early flowering (Feekes growth stage 10.5.1). Only triazole-type fungicides (Folicur, Prosaro, Caramba, and others) should be applied for control of scab. It is important to follow manufacturer's instructions regarding rates, timing, and spray volume. Products that contain a strobilurin-type fungicide (Headline, Quadris, Quilt, Stratego, Twinline, and others) should never be applied for control of scab. Strobilurin fungicides applied at heading or flowering can actually increase the deoxynivalenol (DON) contamination in grain. DON is a toxin that the scab fungus (Fusarium graminearum) produces (see "Management of Fusarium Head Blight of Wheat" in issue 5 of the Bulletin, April 24, 2009).

Fusarium head blight risk from May 5. Red areas indicate high risk, yellow areas indicate medium risk, and green areas indicate low risk. Current maps are available at www.wheatscab.psu.edu.

When applied correctly and at the appropriate timing (Feekes 10.5.1), foliar fungicides can reduce scab and DON. Fungicides applied with this timing can also protect against late infections of foliar pathogens that can cause foliar blights and rust. Wheat fungicide trials were conducted at five locations in Illinois in 2008 (Table 1), with a range of diseases and disease pressure found. In general, when disease pressure was high, the foliar fungicides applied did a good job of reducing disease and preserving yield. When disease pressure was low, fungicides had little effect on yield.

--Carl Bradley

Carl A. Bradley

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