April's Ag Advice by April Borders The European corn borer is one of the major corn pests for us. Not only do we have to deal with the first generation but we also have to deal with a second generation. Recent surveys of the light traps that are used in our area have indicated relatively high numbers of first-generation corn borer moths. This makes it imperative that farmers start scouting their corn for the corn borers.
According to SDSU Extension Entomologist Mike Catangui, the numbers are not at record highs, but enough corn borer moths have emerged from their over-wintering sites (corn stubble from the previous year's corn crop) to cause serious infestations of corn borer larvae.
Traps at the Southeast Research Farm near Beresford recorded a peak number of more than 150 moths on June 13. Last year around this same time the number caught at this site was greater than 400 moths. This was a record for this location since trapping of corn borers began in 1996.
Catangui's research plots at the Southeast Research Farm near Beresford currently show infestations levels similar to the outbreak years of 1996 and 1997 when an average of 14 bushels per acre was lost to the insect. The worst yield loss was recorded last year at about 32 bushels per acre.
We are currently worried about the first brood of the bivoltine corn borer. The first generation larvae are found feeding on the leaves of corn in mid-to-late whorl stages. They chew small holes on the leaves creating a "buckshot" effect. As the worm grows it leaves this area and begins to tunnel in leaf midribs and sheaths. After reaching approximately 1/2 inch in length (third instar) it tunnels into the stalk usually at one of the lower nodes, and feeds until full grown (fifth instar).
All non-Bt corn will need to be scouted. The Bt corn with the gene for resistance against corn rootworms will need to be inspected because it is not resistant to corn borers. Once the corn borers are inside the stalk, any attempt to spray for them will be ineffective so spraying, if needed, must be accomplished soon.
Spraying with an insecticide is recommended if one out of four (25 percent) of the corn plants show signs of corn borer infestations such as "shot holes" on the leaves, larvae in the whorl, and egg masses on the underside of leaves. This economic threshold assumes four live larva per plant, $2.00 per bushel corn market value, and $10 per acre insecticide-plus-application cost.
Insecticides labeled for use against the European corn borer larvae include Ambush, Asana XL, Baythroid, Capture 2EC, DiPel, DiPel ES, Furadan 4F, Intrepid 2F, Lorsban 4E, Lorsban 15G, Mustang, Mustang MAX, Nufos 4E, Penncap-M, Pounce 3.2EC, Pounce 1.5G, Sevin XLR Plus, Tracer, and Warrior. Always read and follow label directions.
For more information on the European corn borer and its control contact the Extension Office at 677-7111.