Adult corn borer moths began to emerge around the last week of May this season. Crop scouts in S…

By Kalona News

Adult corn borer moths began to emerge around the last week of May this season. Crop scouts in Southern Iowa began to see a few egg masses in the taller corn fields the second week of June. The peak egg laying period, which is now over, occurred during the third week of June. Our abnormally cool temperatures and hard rains were not favorable for egg laying and larva survival.

Corn borer female moths seek out the tallest corn fields to lay their eggs. Since corn planting was so stretched out this spring, corn borer moths may have concentrated in those few early planted corn fields. Now is the time to be checking these early planted corn fields for live larva. Look for cream colored small larva, 1/8”-3/8” long in the whorl of the infested corn plants. Shot-holes in the center whorl leaves will also be present. Each larva which survives past 3/8” in length has the potential to move down the stalk and bore into it. Insecticide treatments are no longer effective after the larva bores into the stalk.

It is estimated that each borer which tunnels into the stalk can reduce the yield from 5% to 6%. As the price of corn decreases, the economic insecticide treatment threshold increases. The USDA projected fall harvest price is being estimated at around $1.50 per bushel. Expected yields of 125 bushels and 150 bushels per acre would require an average of 1.7 to 1.4 larva per plant respectively, to provide an economic return with an insecticide treatment cost of $15 per acre. Individual producer costs will vary.

There are several publications on European Corn Borer management that can be obtained from your Washington County ISU Extension office. Call 319-653-4811 for more information.