For Del Unger, the question about whether or not to use fungicides is an easy one. He applies fungicides on all of his corn, no matter what the hybrid is, no matter if he's seen any signs of disease yet or not.
Unger, Carlisle, says there are two reasons for that. One, they're after least cost per bushel, not least cost per acre. And following continuous corn most of the time, they figure that it pays to apply the fungicide, even if it adds to the total input bill.
Second, before the environmentalists get too charged up, there's very few seasons when he wouldn't need it. That's because he says he and his family farm in a bowl. Most of what they farm lays very near the Wabash River in southwestern Indiana. Because the land is so close to a major waterway and the riverbottom ground lies flat for many miles coming out from the river, the bowl effect allows for lots of foggy mornings and hazy nights, even in a normal year, in their part of the world. That typically means conditions are right for diseases, often heavy disease pressure. So rather than take a chance, they just plan on spraying from the start.
However, if you don't live in a bowl with lots of bottom ground, and if you don't have much continuous corn, where disease inoculum can build up, and you don't grow susceptible hybrids to gray leaf spot or other diseases, then Dave Nanda, agronomic consultant and director of genetics and technology for Seed Consultants, Inc., says the best approach is likely to scout fields. Don't pull the trigger on applying a fungicide unless you see sure signs of foliar disease in the field.
And if you do see signs, often lesions, try to identify which disease it is. Depending upon where you live, it could be gray leaf spot, northern corn blight, southern corn blight or another disease. Then note how far up the stalk the symptoms appear. The closer the symptoms get to the ear leaf, and the earlier in the season it is, the more likely that a fungicide application will pay, Nanda notes.
Be alert to weather changes. A couple of years ago he found signs of disease early in a farmer's field, and marked it for possible spraying. But the weather shifted into a dry, cool mode, and six weeks later the disease was no worse than before. The farmer didn't spray, and the field turned out good yields.