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Early insects may start showing up in corn

Posted Friday, May 27, 2011, at 3:09 PM

Some corn planting is still going on in the area in addition to some replanting of corn. What effect will this late planting have on potential insect problems? First, black cutworm moth captures indicates the potential for damage to corn especially in late planted corn. The intensive capture data indicates that some cutting may now be occurring but the potential for heavy cutting exists for the latter half of May. Corn plants are susceptible to black cutworm damage up to the 5-leaf stage of plant growth. Considering current field conditions where wet soils have delayed corn planting, it is likely that situations will develop where seedling corn plants will be exposed to relatively large black cutworm larvae in those areas where intensive captures of black cutworm moths have been reported. Scout all corn fields for the presence of black cutworm larvae on a weekly basis until corn reaches the 5-leaf stage, especially those fields that are planted late.

The traditional economic threshold for black cutworm cutting in field corn is 4-6% cutting above ground and 2-3% cutting below ground. A couple of years ago, entomologists at Iowa State developed a pest model that indicated as the corn price exceeds $5 - $6 per bushel, the economic threshold may be lowered to 2% for both above and below ground cutting. Based on a review of the Iowa State calculations, Missouri pest management recommendations for cutting were modified in 2011 to follow the economic threshold of 2% or more seedling cutting of either type. Remember that most feeding damage to corn by black cutworm larvae will typically occur within 7-10 days following emergence.

Farmers also need to pay attention to seed-applied insecticide and Bt corn labels to determine management strategies. Seed-applied insecticides and some varieties of Bt corn provides only suppression and not control. Suppression is fine under ideal environmental conditions and moderate infestation levels; however, under environmental stresses and/or heavy pressure, the efficacy of these products labeled for suppression may not be sufficient. Certain hybrids potentially may be overwhelmed by large infestations of black cutworms.

Wireworms are typically not a problem. As soil temperatures increase, wireworm larvae typically begin to move deeper into the soil and away from the seed. However, if planting has occurred and seedlings are subjected to prolonged periods of cool and wet soil conditions, increased levels of root injury by white grubs and feeding on below-ground potions of the stem may occur by wireworms. Any corn fields that are coming out of grass, such as pasture, may have an increased risk of wireworm damage.



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As our local University of Missouri Agronomy Extension Specialist, Crook has been writing a column for the print edition Agriculture page for the past three years and we will now be sharing it on our web version. Crook has a bachelor and masters degree in agronomy from University of Missouri and received his doctorate in Agronomy from Kansas State University. He was in soybean variety development research for 22 years for various seed companies and has been Saline County's agronomy specialist for 10 years.
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