Corn Leaf Diseases and Fungicide Recommendations

July 12, 2010 at 9:38 am

Gray leaf spot has been confirmed in corn fields throughout the Midwest (Indiana, Kentucky and Ohio). Disease severity varies throughout fields as well as within a field; hybrids that are susceptible to gray leaf spot are more likely to show sypmtoms. Weather has not been our friend this year and the recent warm and humid weather has helped to bring about gray leaf spot in corn fields.

Gray leaf spot can cause yield loss, but severity depends on the number of lesions and how far up in the canopy they occur as the plant enters tasseling and pollination. If lesions have reached the ear leaf or higher during the two weeks before and after tasseling, yield loss could occur. If the disease appears later in the season, economic impact and yield loss will be minimal.

Before deciding on a fungicide application, the first thing a grower should do is review hybrid susceptibility to gray leaf spot. Hybrids vary in their susceptibility to foliar diseases of corn, and hybrids susceptible to diseases such as gray leaf spot are at a greater risk of disease development than hybrids with moderate or high levels of disease resistance.

Strobilurin and strobilurin/triazole premix fungicides are most effective at preventing yield loss when applied in response to disease presence, and at the tasseling to early silking (VT-R1) growth stage.

There are two things to keep in mind prior to making a fungicide application:

1) university researchers have not seen consistent yield benefits from foliar fungicide applications in corn.

2) all corn fields are showing some level of disease, but the decision to spray should be based on the type of disease present, as well as the factors discussed above. A few lesions on a corn leaf will not justify a fungicide application

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