The good news is that by now if disease symptoms are still below the ear leaf, you're likely not going to see much if any yield reduction due to foliar diseases. That's the word form Dave Nanda, genetics and technology consultant for Seed Consultants, Inc.
Even two weeks ago at a farmer meeting near Batesville, Nanda told farmers that if symptoms were minimal, there was likely no economic reason to try to spray. Part of his reasoning is that corn is currently around $3 per bushel. It would take at least 20 bushels of corn just to cover fungicide and application costs. If corn was $5 per bushel, the math would be different. However, you would still need to weigh the time of the season and amount of grain fill which has already occurred.
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Diseases spotted in some fields this summer include gray leaf spot, northern corn leaf blight and a few lesions of other diseases. Susceptible hybrids have generally more lesions than non-susceptible hybrids. Until and unless the ear leaf is infected by lesions which grow and grow together, leading to early death of the plant, major yield loss isn't likely, Nanda says.
The places where he recommended spraying fungicides earlier in the season, directly after pollination, were largely in corn after corn fields where the hybrid was fairly susceptible to disease. Corn after corn provides the best chance for infection earlier in the season because there is generally more disease inoculum still remaining there from the previous season, he notes. It overwinters in residue, and doesn't have to blow into the field to begin new infections.
While there were diseases spotted early, most did not develop to severe levels in fields that were corn following soybeans or corn after another crop besides corn, Nanda concludes.
For more corn news, corn crop scouting information and corn diseases to watch for, follow Tom Bechman's column, Corn Illustrated Weekly, published every Tuesday.