If you're walking fields to get a handle on what yields might be like, you will see things on leaves or stalks that initially may concern you. But especially at this stage in the season many things you see on leaves and stalks and even ears may be of little or no consequence for yield.
One is damage by a nuisance insect called leaf miner. "We can find evidence that it has fed on leaves, but it's not a big deal," says Danny Greene, owner of Greene Crop Consulting, Franklin, Ind.
"This insect scrapes off tissue on leaves, but it's only a small amount and is usually nothing more than a nuisance."
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In contrast, disease lesions, which usually involve discoloring of the leaf from tan to yellow to brown as tissue deteriorates and finally dies, can be an issue. Speckled brown and yellow spots or small rectangles on leaves are signs of disease.
At this point in the season, however, they're not a concern unless there are several lesions on the ear leaf. At this late date, spraying may not be economical anyway, says Dave Nanda, consultant for genetics and technology with Seed Consultants, Inc.
"You have to factor in the price of corn when figuring if it pays to spray," he says. "When corn is $3 per bushel, the economics are a whole lot different than when corn is $5 per bushel."
Now it may take up to 10 or more bushels per acre yield increase from a fungicide application just to break even, he notes. If the disease hasn't broken and spread to ear leaves and above in dramatic fashion by now, that type of yield gain by stopping the fungus is not likely, Nanda says.
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Under $5 corn which only needs about a 6 bushel payoff, there may have been situation earlier in the season where it might have paid. But corn isn't $5 per bushel and it isn't still early in the season.
The only exception may be fields of corn planted after corn. Nanda found some of those fields had enough infection to justify treatment earlier in the season, he notes.