Be on the look out for first generation European corn borer
Extension Specialist, Colorado State University Extension
Adult European corn borer monitoring sites in northeastern Colorado are showing emergence and flight of the moth. For historic European corn borer moth emergence and duration of infestation data, check our pest alert website (http://northernipm.colostate.edu/) where trap counts from different locations and years are found.
First generation moths prefer taller and early planted fields for laying eggs; your non-Bt hybrid cornfields should be scouted the next 2-3 weeks. Some hybrids have useful resistance to the first brood of European corn borer, which feeds in the whorls and later enters the stalk. Control can be expected with Bt corn hybrids, except those containing only events that target corn rootworms.
European corn borer usually goes through two generations each year. The young larvae feed first on the leaf near where they hatched. As the larvae grow, they move to the whorl or leaf sheath area, and feed. When leaves emerge, the “shot hole” feeding signs in the leaves can be seen. Most of the mature larvae will bore into the stalks, feed, and finish development there. Second generation larvae cause ear damage, tunneling in the shank and feeding on silks, kernels and cobs. Signs of infestation include: dropped ears, broken shanks, stalk breakage, sawdust-like castings on leaves, and holes in the stalks.
To determine infestation levels of first generation and make management decisions, 25 plants in four locations in a cornfield should be checked for leaf infestations. Larval damage is noticed as feeding scars and shot holes in plant leaves. Chemical control of first generation corn borer is justified when 25 percent of the plants in your sample show feeding damage and show presence of larvae. Chemical control of the pest must be applied before the feeding larvae bore into the stalks.
More detailed management information including effective products, rates of application and others can be checked in the High Plains IPM Guide: http://www.highplainsIPM.org.