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Control measures
When facing the threat of cercospora or other disease pressure, growers should look for corn hybrids or bean varieties with disease resistance or tolerance. “Some soybean varieties have good resistance to frogeye leaf spot,” he says. “Varieties with the RCS3 gene hold up effectively.
“In corn, there are no hybrids with complete resistance, but there are some with some tolerance. Growers should also scout and monitor their fields,” he says. “If you have conditions that promote disease (wet weather, high relative humidity, etc.), you need to look at spraying a fungicide.
“Continuous corn is always a risk because cercospera overwinters in the residue in those fields,” Bradley points out.
Of course, the price of corn or soybeans may dictate whether the extra $15+/acre cost is warranted, he says, noting that “corn at $4.50-5 (or higher) would probably be sprayed more openly than corn at under $3.”
LaFoe doesn’t mind the cost if he can boost yields. “I think it’s a good investment to put down a fungicide on corn and beans, especially if we see the wet spring weather,” he says.
Meanwhile, the Fungicide Resistance Action Committee (FRAC), an international committee that evaluates fungicides' likelihood of developing resistance, has determined that strobilurin fungicides have been deemed high risk for fungal pathogens developing resistance to them. "Plant pathogenic fungi developing resistance to strobilurin fungicides is not new," says Bradley. "This has already occurred in potatoes and other crop and disease systems where multiple fungicide applications occur during the growing season."
Late November 2010
