Early Arrival Of Corn Insects Poses Problems

URBANA, ILL.

 Mike Roegge, University of Illinois Extension, Adams/Brown Unit, reports that over the past week he had captured the first corn earworm (CEW) of the season, and seen the first European Corn Borer (ECB) larvae in non GMO corn as well. It sure seems early in the season for these pests, but none the less, they’re here now. For those producers with Bt corn, your corn is (mostly) protected, but your refuge acres aren’t. Likewise, for those who grow non GMO corn these insects could cause problems.

   Normally, corn earworm is a problem later in the summer when they can infest ears and open the ear up for disease concerns as well as other insects. But there have been times when the populations of CEW are so high so early in the season that they'll attack and feed on the vegetative parts of the corn plant when ears are not available.

   ECB also damage vegetative parts of corn plants, and if populations are high enough, can cause economic damage. Producers should scout non GMO corn fields for the presence of both these insects. Young ECB will leave “scratches” or pin hole feeding on the surface of the corn leaf. As the larvae continue to grow, they’ll tunnel into the mid rib and eventually the stalk. Once they’ve entered the stalk, there is no opportunity to control them. Depending upon temperatures it usually takes about 10-14 days between first instar and third instar (at which time the larvae will enter the stalk).

   To determine if treatment should occur, scout your fields to determine infestation levels. Scout the field by examining 25 plants in at least 5 areas of the field. Estimate percent infestation and pull the whorls of several plants to determine number of and size of the borer. Using the web site below, enter that information, as well as expected yield and price and cost of control. For instance, lets say you found 40% of the corn plants infested with an average of one second instar larvae per plant. The expected survival rate of the borer is 50 percent, the cost of control is $12 per acre and the expected loss is 5 percent (early whorl stage). The expected yield is 200 bu/acre and the expected price is $4.25. After inputting these figures into the calculator, you’ll find a negative return.

http://ipm.illinois.edu/decision/corn_borer_first.html rst.html

   But use the figures from your field to determine the need for treatment. Scouting may pay big dividends. And while you're scouting, don't forget to use this time to determine how well your weed control program is working, as well as appraise the overall quality of your field. It's becoming pretty obvious that some corn fields are having a rough time of it. Δ