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Corn+Soybean Digest

Gray Leaf Spot Has Arrived

As is often the case, June rains were both a blessing and a curse for farmers. One problem stemming from the moisture is gray leaf spot that has been building in cornfields in northeast and north-central Kansas, according to Kansas State University Research and Extension (K-State) Plant Pathologist Doug Jardine.

"Rains earlier in June allowed the disease to gain a foothold in the lower canopy and it is beginning to move upward in some fields. One field in Pottawatomie County had lesions on the ear leaf, and pollination had not begun yet," he says.

Gray leaf spot lesions tend to be rectangular, Jardine says, adding that early lesions are small, brown spots with yellow haloes that gradually expand to full-sized lesions. Expanding lesions are initially tan and later turn gray on the underside of the leaf during moist conditions.

A spray calculator to assist in fungicide application decisions is available on the K-State Department of Agricultural Economics website.

Producers can put in their own data to determine whether or not a fungicide application might be profitable.

"Many fields that are planted to more resistant hybrids, especially when rotation and tillage are used, probably would not reach the breakeven level," Jardine says.

Products containing both a strobiluron and a triazole mode of action work well, he adds. Those currently registered in Kansas include Headline AMP, Quilt, Quilt Xcel and Stratego.

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