Scott Ebelhor knows a thing or two about corn and soybean diseases. He grew up on the Kentucky side of the Ohio River on a family farm. Now he manages Beck's Superior Hybrids practical farm research plots at Fort Branch. That area of the world is known for high humidity and is predisposed to diseases on crops, especially to leaf diseases.
Last year wasn't necessarily one of those years. Yet Ebelhor tells crowds at Becks winter meetings all over Indiana that the principle of diseases development and subsequent disease management still held true even in the hot, dry 2007 season.
"It takes three thing in a triangle to have a disease problem that requires treatment for economic benefit," Ebelhor says. "You need the pathogen, of course, and the host. But you also need environmental conditions that are favorable for the development of disease. If you don't have weather conditions favoring disease, then the triangle isn't complete, and you're not going to see the disease pressure from most foliar and other plant diseases as you would in a year that features more rainfall and especially higher levels of humidity."
Moisture and enough humidity to foster disease development were the missing ingredients in many areas last year, especially in the early and mid-season period. Trials where fungicides were sprayed on corn where disease symptoms weren't apparent tended to show little if any yield benefit, and seldom any economic benefit after the cost of treatment and application were included.
Ebelhor specifically studied spraying fungicides on soybeans at the R2 reproductive stage and R4 reproductive stage in plots last summer at his location. The R4 stage is more advanced in terms of pod and crop development. He notes that some rain fell between the R2 and R4 application stage. That completed the triangle for some organisms, introducing more moisture and making the environment more favorable for development of certain diseases.
He wasn't surprised to find that the application at the R4 stage paid off in terms of more yield benefit to go against the cost of the fungicide and its application than the same fungicide sprayed at the R2 stage of soybean development. If conditions had remained the same from R2 to R4, without the rainfall and increase in humidity, it's possible that there may not have been a bigger payoff to the fungicide for the alter application, compared to the earlier one, he notes.
Dave Nanda, consultant for Corn Illustrated, a Farm Progress special project, says that it's always wisest to assess conditions before deciding whether to spray a fungicide or not. Like Ebelhor, he agrees that if all three legs of the triangle are not in place, then the likelihood of serious disease is minimal, at least for the time being. At the same time, that probably means that the likelihood of a net plus payback for applying the fungicide is also unlikely.