Corn, dry bean producers should watch for cutworms
Corn and dry bean producers should monitor their crops for western bean cutworms, said University of Nebraska-Lincoln Extension educator Ron Seymour.
"Western bean cutworm can be a really devastating pest in either corn or dry bean production," said Seymour, who focuses on insect pest management in Adams County. "If you're not looking for it and treating it in an appropriate window, you might not be able to control it at all, he said.
Seymour said that there really aren't any cultural practices that control western bean cutworm. Producers need to monitor populations in order to decide on control measures. In corn, they should look for eggs right before the plants tassel. They will appear on top of the uppermost leaf, that is, the flag leaf. The eggs are readily visible, he said. Producers should choose five or six locations in the field and check 20 or 25 plants at each location.
When the price of field corn is $3 or less and 8 percent or less of the plants are infested with eggs, spraying will probably provide economic benefit. If corn values are above that, a 5 or 6 percent infestation might very well pay off.
Insecticide application should occur when most of the larvae are out on the plant where they are susceptible. Once they get in the ear tip, it's really hard to control them, Seymour said. He said producers have about a seven-day window. When 95 percent of the field is tasseled, he said, that's the time to spray.
In dry beans, foliage makes it difficult to see the eggs, so producers should use pheromone traps to find the moths. If 700 to 1,000 moths accumulate in a trap during a two-week period, spraying might be a questionable choice. More than 1,000 moths indicate a need to spray. The time to spray is about two to three weeks after the peak of the moth flight.
Most products work well, with the exception of insecticides using Bacillus thuringiensis as the active ingredient. Larval survival is also relatively high in corn plants that express the Bt toxin, although Bt corn hybrids containing the Cry1F toxin (Herculex I) are labeled for western bean cutworm and work well. Although synthetic pyrethroid insecticides appear to force larvae out of protected areas, those products can contribute to an increase in spider mite infestations. Producers should scout for spider mites before applying any of these compounds.
Seymour recommends that people look on the UNL Entomology website (http://entomology.unl.edu/pmguides/wbcutwrm.htm) or go to their local Extension office for more information about chemical controls.