European corn borer moths are showing in all light trap locations in Colorado, reports Assefa Gebre-Amlak, a Colorado State University Extension regional pest control specialist.

However, this is the first generation for the season, and scouting for eggs may not be practical, he adds. Infestation is best determined by examining plants for feeding and live larvae, Gebre-Amlak says.

Corn is still small in the northern region of the state and borer larval damage is not expected at this stage (less than 16 inches long with extended leaves) due to a chemical called Dimboa. However, as corn develops most varieties lose their resistance to larval feeding, he notes.

First generation borers usually prefer taller plants for egg laying, so the earliest planted fields are the most likely to have higher egg numbers. Non-Bt corn fields need to be scouted if the corn is above 16 inches in extended leaf height.

Locations of moth finds include Burlington, Eckley, Kirk, Haxtum and Wauneta, with the highest counts found in Yuma County

To determine infestation levels, Gebre-Amlak advises producers to check at least 50 plants in four-five different field locations, being sure the move into the field at least 100 feet from the border.To determine numbers of live larvae, pull the whorl from each symptomatic plant and carefully unwrap leaves. Chemical control of first generation borers is recommended when 25% of the plants have feeding damage and live larvae, he says. Control measures must be taken before the larvae bore into the stalk for effectiveness.

Timely and accurate scouting is the key to managing European corn borer in standard (non-Bt) corn hybrids. Conditions vary from field to field and each should be scouted to make accurate control decisions, he says.