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Flights for Second Generations of Corn Borers Are Under Way

July 13, 2001
Gary Bretthauer, unit educator, Kendall County Extension, reported shot-hole damage to 30% of the corn plants in a field scouted this week. Each damaged plant had at least one larva, some still on the leaves, but most in the stalks. Gary has received similar reports from producers in the area. Ron Hines, research agronomist at the University of Illinois Dixon Springs Ag Center and an ever- vigilant observer of corn borer activity, has reported the beginning of captures of European and southwestern corn borer adults in his traps in Massac and Pulaski counties. The numbers of European corn borer adults Ron has captured were low as of July 10. However, he reported 75 southwestern corn borer adults in one type of trap on July 10 in Massac County. Randy McElroy reported low numbers of ECB egg masses in fields in Hamilton county.

The flight of the moths that will lay eggs for the second generation of southwestern corn borers this year seems to be a bit ahead of schedule. As the next few weeks unfold, we will be better prepared to determine the potential for infestations of the second generation of both of these pests. So keep tabs on the moth flights, and be prepared to scout and treat if necessary. Knowing what egg masses and larvae look like will aid your scouting efforts.

Southwestern corn borer female moths may oviposit eggs singly or in small clutches of up to five eggs on either the upper or lower surface of a corn leaf. Females lay most of their eggs in the ear zone. The eggs are oval, flattened, and cream colored when first deposited. When eggs are laid in masses, they overlap like fish scales, similar to the eggs of European corn borers. Within 48 hours after they are laid, three pink to red transverse bars become visible on southwestern corn borer eggs. Southwestern corn borer larvae have indistinct bands across their bodies, from which very fine hairs (setae) project. Tubercles (small bumps) become very apparent on fourth and fifth instars.

Small larvae of the second generation usually can be found between or under the husk layers of the primary or secondary ears, on ear shoots, and behind leaf sheaths. When larvae reach the third instar, they bore into the stalk and begin tunneling. They also may tunnel inside ear shanks, and occasionally they can be found feeding on kernels in the ear.

Scouting for the second generation of southwestern corn borers should intensify for at least 2 weeks after pollination is complete and should continue throughout July. Look for egg masses and larvae on the leaves or behind leaf sheaths. A rescue treatment may be justified when 20% to 25% of the plants are infested with eggs or newly hatched larvae behind leaf sheaths. If the percentage of plants infested is not enough to justify treatment, scout again in 3 to 5 days, then consider treatment if the sum of the two counts is more than 25%. These simple guidelines are suggested only as starting points. Low commodity prices and the cost of the insecticide rescue treatment must be factored into the decision-making process. After larvae tunnel into stalk tissue, rescue treatments are not a control option.

Insecticides that are labeled for use against the second generation of southwestern corn borer include *Ambush (6.4 to 12.8 oz of product per acre), *Asana XL (5.8 to 9.6 oz of product per acre), *Capture 2EC (2.1 to 6.4 oz of product per acre), Lorsban 4E (2 to 3 pt of product per acre), *Pounce 3.2EC (4 to 8 oz of product per acre), and *Warrior T or 1E (2.56 to 3.84 oz of product per acre). Use of products preceded by an asterisk is restricted to certified applicators.--Susan Ratcliffe, Kevin Steffey, and Mike Gray

Author: Kevin Steffey Mike Gray Susan Ratcliffe

The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

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