Southwestern Corn Borer Second Flight Well Under Way

July 23, 1999
The second flight of southwestern corn borer moths has been under way since mid-July in southern Illinois. Ron Hines, Senior Research Specialist, Dixon Springs Agricultural Center, has been monitoring flights of this insect pest with pheromone traps in Massac and Pope counties. For the weekly monitoring period that ended on July 14, moth captures were 120 and 212 for the southern and northern traps, respectively. The number of moths collected in the southernmost pheromone trap through July 20, was 161 moths. As reported in an earlier issue of the Bulletin, depending on summer temperatures, two to three generations may occur annually in southern Illinois.

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. 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 larval instars.

Scouting for the second generation of southwestern corn borers should begin about 2 weeks prior to tasseling and continue for 2 weeks after pollination is complete. Producers should look for egg masses and larvae on the leaves or behind leaf sheaths. A rescue treatment may be justified when 20 to 25 percent of the plants are infested with eggs or newly hatched larvae behind leaf sheaths. This very simple threshold is suggested only as a starting point. Low commodity prices and the cost of the insecticide rescue treatment must obviously be factored into the decision-making process. Once larvae have tunneled into stalk tissue, rescue treatments are no longer an option. Insecticides that are labeled for use against the second generation of southwestern corn borer include Ambush 2E* (6.4 to 12.8 ounces of product per acre), Lorsban 4E (1.5 to 2 pints of product per acre), Lorsban 15G (6.5 pounds of product per acre), Penncap-M* (2 to 4 pints of product per acre), Pounce 1.5G* (6.7 to 13.3 pounds of product per acre), Pounce 3.2EC* (4 to 8 ounces of product per acre), and Warrior T* or 1E* (2.56 to 3.84 ounces of product per acre). (Products followed by an asterisk are restricted for use to certified applicators.)--Mike Gray, Kevin Steffey

Author: Kevin Steffey Mike Gray