Macon LaFoe knows it’s not if his soybeans and corn will face big pressure from cercospora,but the proverbial when. However, fungicide treatments can KO the disease and could also produce higher yields.

Cercospora is nasty fungus that comes in several variations, which can prevent beans from maturing properly and cause gray leaf spot in corn. Left uncontrolled, the disease can ruin leaves, thwart ears, lead to lodging of weak stalks on corn and decrease soybean yields 25% or more.

Timely fungicide treatments will help prevent or control the disease. LaFoe has had success in using fungicides in both corn and beans on his Oak Ridge, LA, farm. That’s been through periodic, as-needed sprays.

Even though University of Illinois and University of Tennessee research indicates the fungus that causes cercospora, frogeye leaf spot and other diseases has shown resistance to strobilurin fungicides in a Tennessee field, LaFoe will continue treatments when they’re needed. The resistance has not been documented beyond Tennessee.

LaFoe’s corn and bean acres are on former cotton ground that was mostly disease-free. Not enough corn has been produced to generate severe disease problems.

“We nearly always spray soybeans with a strobilurin fungicide because of the potential for soybean rust and other diseases,” he says. “We typically don’t have as much disease pressure on corn. But the more corn we grow, the more disease we’re likely to see.”

His rotation is about two-thirds corn and one-third soybeans. Corn yields are 190-220 bu. under irrigation. Beans push 60 bu. There’s also some wheat on the 2,500-acre farm. All crops faced pressure in 2009 due to an extra dry spring and early summer that turned to extra wet weather in late summer and early fall.

“We didn’t spray much corn because it was so dry and we didn’t foresee much disease pressure,” LaFoe says. “That wasn’t an ordinary year. We usually see a wetter, cooler spring. And that often promotes disease problems.”

In those years, he applies fungicides to beans and corn and doesn’t mind the $14-15/acre cost it involves.

“We usually use one or two programs,” he says. “We either apply 10 oz. of Stratego or 14 oz. of Quilt. They provide good control for us on cercospora infestations.”

 “We’ve found that the quality of our beans has improved with fungicide treatments,” LaFoe points out. “From what we’ve seen in corn test plots, there’s a chance we can improve our corn yields, as well.”

The corn test plots, conducted in conjunction with Bayer CropScience, involved a check plot, a plot treated with 10 oz. of Stratego and a plot with a 12-oz. Stratego application.

“With the 10-oz. rate, we saw a 1-bu./acre higher yield than with the check,” says LaFoe. “But with the 12-oz. treatment we saw a 10-12-bu. improvement in yields.