Kerry Siders, IPM agent for Hockley, Lamb and Cochran Counties, in his weekly crop update, cautions corn producers to be alert for diseases developing on late-planted acreage.
Siders says disease likely will develop late, and disease that came in on earlier planted corn will provide spores for these later infections.
Ronald French, Extension Plant Pathologist in Amarillo, explains the process: “Once a pathogen is established in a field (and produces spores), it may be necessary to spray mixed mode of action chemistries. A triazole, such as Tilt, will target the actively growing fungus, while a strobilurin will target the spore’s ability to establish by reducing its energy source prior to penetration and colonization of tissue.”
French also recommends growers use a hybrid resistant to the important diseases. “Corn hybrids are ranked (for disease resistance) from 1 to 9, 9 to 1, 1 to 5, or 5 to 1, depending on the seed company. Because last year Goss’s wilt occurred throughout the High Plains and parts of the South Plains, there might have been a push for resistant hybrids for Goss’s wilt or for crop or field rotation, but resistance to rusts and northern leaf blight may not have been at the top of the list.”
French says producers should base spray decisions on disease presence in the field, where it’s located in the canopy, and whether the corn hybrid is susceptible, moderately susceptible, or resistant.
“Usually, sprays applied past tasseling may not be warranted.” Fungicides applied at tasseling probably last for two weeks. Anything past two weeks is residual, so it covers later growth stages.”
Siders adds that as corn producers move into August they should be ready to take action on corn disease infections.