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Late freeze may have put corn at risk to insects
Kansas
The stress of a late freeze may have left this year's corn crop unusually vulnerable to insect damage, warns a Kansas State University entomologist.
Regular scouting for a variety of early-season pests could be vital to economic returns, said Randy Higgins, field crop insect specialist for K-State Research and Extension.
"If the growing point remains intact and injury is scattered, post- emergence treatment may not be necessary. In other cases, however, it could be quite beneficial," Higgins said.
Cutworms, especially black cutworms, generally cause economic damage during the first weeks just after emergence, he said. Populations tend to be heaviest in eastern Kansas where a producer has killed a living cover of spring weeds, a lot of residue is present, and/or corn is following soybeans.
Small cutworms initially feed on one side of the leaf, creating "windows." Later, they cut notches or holes. Large larvae can cut off the entire plant or damage the upper portion enough that leaves wilt.
"Rescue treatments may be justified if 3 to 5 percent of plants at the two-leaf stage are being cut and many small worms are present, indicating more damage is likely. An even lower threshold might be justified if cool weather persists, since the plants won't be able to 'grow away' from the damage," Higgins said.
K-State Research and Extension's publication "Corn Insect Management 2005" lists several post-emergence controls for cutworms: Chlorpyrifos, cyfluthrin, esfenvalerate, gamma-cyhalothrin, lambda-cyhalothrin, permethrin and zeta-cypermethrin. That publication, which also includes the trade names under which those controls are sold, is available at any local Extension office or on the Web at www.oznet.ksu.edu/library/entml2/MF810.PDF.
"Sprays generally are more effective if the leaf surface is moist to wet at the time of application," Higgins said.
Flea beetles sometimes cause injury to young plants up to about the fourth leaf stage. The damage is most severe when cool to cold temperatures have slowed plant growth.
"Border treatments may solve the problem," the entomologist said. "On two-leaf corn, populations at or above four to five flea beetles per plant are usually required to justify the expense of post-emergence sprays. We list nine treatments in our recommendations--those with the same active ingredients as the controls for cutworms, plus carbaryl and microencapsulated methyl parathion."
In recent years, southern corn leaf beetles have been an early-season corn pest in eastern Kansas.
"This drab, grayish-to-brownish beetle is hard to detect. It's only three-sixteenths to one-fifth of an inch long. It blends well with the soil, often lies motionless, and sometimes has its back covered with soil particles," Higgins said. But, damaged plants can look as if they have been chipped into pieces or fragments. Injured leaves sometimes become trapped, so they can't unfurl properly.
"We don't have a calculated threshold for the pest yet, but producers need to take action if their stand appears to be threatened," he said.
The retail products labeled for southern corn leaf beetle control contain one of these active ingredients: bifenthrin, carbofuran, chloropyrifos, cyfluthrin, lambda- cyhalothrin, or zeta-cypermethrin.
Chinch bugs commonly threaten sorghum, but occasionally injure young corn plants, too.
"Fortunately, corn usually has achieved enough size by the time the chinch bugs move in that border treatments may be all that's required," Higgins said. "Using drop nozzles and directing the spray so it hits the base of the plant and the bugs themselves can help improve chances of achieving control."
The insecticides recommended in K-State's 2005 guide include formulations of bifenthrin, carbaryl, carbofuran, chlorpyrifos, cyfluthrin, esfenvalerate, gamma-cyhalothrin, lambda-cyhalothrin and zeta-cypermethrin.
Date: 5/26/05
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