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Flights for Second Generations of Corn Borers Are Under Way

July 14, 2000
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 both European and southwestern corn borer adults in his traps in Massac and Pope counties. The numbers of European corn borer adults Ron has captured were very low as of July 11. However, he reported captures of as many as 300 southwestern corn borer adults in one type of trap on July 11. His data suggest that folks in southern counties may be in for a real struggle with southwestern corn borers this year. On the other hand, European corn borers continue to be most noticeable by their relative absence. As the next few weeks unfold, we should get a better handle on the potential for infestations of the second generation of both of these pests.

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. A comparison of moth captures this year with last year's moth captures in southern Illinois also indicates considerably larger numbers. So keep tabs on the moth flights, and be prepared to scout, and treat if necessary. Knowing what both 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 2E (6.4 to 12.8 oz of product per acre), *Capture 2EC (2.1 to 6.4 oz of product per acre), Lorsban 4E (1 1/2 to 2 pt of product per acre), Lorsban 15G (6.5 lb of product per acre), *Penncap-M (2 to 4 pt of product per acre), *Pounce 1.5G (6.7 to 13.3 lb of product per acre), *Pounce 3.2EC (4 to 8 oz of product per acre), and *Warrior T (2.56 to 3.84 oz of product per acre). Use of products preceded by an asterisk is restricted to certified applicators.--Kevin Steffey and Mike Gray

Author: Kevin Steffey Mike Gray


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

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