DuPont Pioneer and university research across 475 on-farm trials  shows corn  yield increases an average of 7 bu./acre in response to a foliar fungicide application. The average yield response is generally greater in fields with large amounts of residue on the soil surface, such as corn-following-corn, and no-till  or strip-till . Later-maturing fields can also be at greater risk to foliar disease and are more likely to benefit from a fungicide  application.
DuPont Pioneer experts recommend scouting for foliar diseases in corn just before tassel emergence. Consider the following factors when planning an application of foliar fungicide.
Many foliar pathogens survive in corn residue. The risk of foliar diseases, such as gray leaf spot and northern leaf blight, increases when corn is planted into a field that was corn the previous year.
Rainy and/or humid weather is most favorable to foliar diseases. In growing seasons when these conditions prevail, the risk for disease development increases.
History of Disease
Some field locations may have a history of greater foliar disease severity. Fields in river bottoms, low areas or surrounded by trees may be more prone to foliar corn diseases.
If the disease resistance rating is a 6 or greater, a fungicide application may not provide a yield benefit. For susceptible products with disease rating less than 4, spray if disease symptoms are present on the third leaf below the ear or above on 50% of the plants examined.
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For intermediate products with disease rating of 5, determine if disease symptoms are present on the third leaf below the ear or above on 50% of the plants examined. Also consider the above factors, spraying if the field is in an area with history of foliar disease, a corn-on-corn planting, contains 35% or more surface residue and weather is warm and humid.
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