What will at least a week of much cooler, much less humid weather due to diseases that were building in parts of the Corn Belt? The only way to know is to go out in the fields and keep a careful eye on what's happening. Pathologists can guess, but guessing won't pay your bills.
Before the rainy, humid spell gave way to a cool reprieve last week, alarm bells were sounding from consultants in some areas, including northeast Indiana. Apparently some corn was sprayed with fungicide already in Allen County, Ind., last week. Crops consultants were reporting finding lesions of some key corn diseases, including gray leaf spot, with even a few of the lesions above the ear leaf.
Once lesions move up in a plant, major yield impact is more likely. The earlier it happens in a season, the more likely it is. However, fungicides can't be applied until certain stages of growth, based on specific instructions on the labels of individual products. Applying too early or too late may lead to developmental problems, which could affect ear development and final yield, even if it's only by a small amount.
But now, even if you saw disease symptoms last week, you may want to wait before sending the aerial applicator up over your fields. Dave Nanda, a crops consultant, Indianapolis, Ind., knows firsthand that conditions can change. He would scout frequently, but not pull the trigger yet unless conditions are very severe.
In 2010 he scouted a field that was susceptible to gray leaf spot in late June. It was all he could do to refrain from telling the farmer to schedule spraying. Gray leaf spot lesions were developing on lower leaves, and moving up the plant. It was warm, humid and the disease was progressing.
Then the weather turned very cool and persisted through much of July. Of course, that may not happen this time. But last year, with a cool July, Nanda found no more disease around August 1 then he did on June 25! The farmer didn't spray, and believes he saved the expense without harming yield. Some gray leaf spot came in alter, but by then, final yield was already established, at least in that field.
So put on your walking shoes and be quick to scout, slower to call in the plane, experts suggest.