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Corn Fungicide Decisions Involve Economics

Corn Fungicide Decisions Involve Economics
Calculations as to whether to spray fungicides much different at $3 corn than $5 corn.

The farmer pulled three stalks and showed them to a crops consultant. Brown silks were beginning to form but there was likely still time to treat if it was necessary. He brought one stalk of each hybrid in the field. Since he put one hybrid in half the planter and one in the other, both hybrids extended across the field.

One had more gray leaf spot lesions than the other, although both had a noticeable amount. The lower couple sets of leaves had considerable speckling with lesions. However, there was one small lesion on the ear leaf on one hybrid and none on the ear leaf of the main ear on the other hybrid.

Would you spray or not?

Look for lesions: If you don't know what gray leaf spot lesions look like, this is a good year to find them. Whether it's a year to spray fungicide or not is a different question.

Here was the agronomist's logic. It was a borderline call since the corn was already at brown silk. It was safe to spray without risking any ear deformation at that point, but was it necessary? That depends upon what weather conditions would do from then on, and prices of corn and costs of treatment.

Related: Farmers Making Fungicide Decisions On Corn

The weather is anybody's guess. The pattern that has set up is on the cool, wet side. Cool weather does not favor gray leaf spot – it prefers warm weather. Cooler weather favors northern corn leaf blight, but no lesions of it were found on the leaves, and the farmer hadn't noticed it in the field. If weather remains on the cool side, the gray lead spot may remain a minor factor.

Second, corn could be $3 to $3.50 per bushel at harvest, not $5 to $5.50 as it was a couple years ago. Cost of treatment including application is $30 to $40 per acre, depending on choice of product and cost of aerial service.

"With the current situation you would need an increase of 10 bushels or more per acre to break even, and close to $125 per acre to actually see much reward for spraying," says Dave Nanda, consultant for Seed Consultants, Inc.

Since ear leaves are still fairly clean and given the stage of development of the crop, it would be unlikely to expect to see that much benefit.

Related: Keep an Eye Out for Foliar Diseases in Corn

If corn was still $5 or higher and it only took 6 or so bushels to break even, it might be worth considering, Nanda adds.

The idea to treat one hybrid and not the other doesn't fly since the two are both spread across the field. He makes the case for picking hybrids with similar disease resistance packages if you're going to plant two hybrids so you don't wind up in situations like this one.

The farmer chose not to spray. Nanda believes that given the facts, it was the right call.

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