Don't Ignore Japanese Beetles in Corn Fields

Silk clipping is silk clipping, however it happens! Tom J. Bechman

Published on: Jun 30, 2006

Ask a farmer what insect he's worried about for clipping corn silks, and if he's concerned at all, it's likely due to rootworm beetles. If beetles are numerous enough and clip silks short enough and long enough, they can cause poor pollination.

However, rootworm beetles aren't the only potential corn silk clippers to be aware of these days. Japanese beetles will also clip corn silks, even though they prefer other food stuffs, including grapes and some flowers, more. Just think of these large, bronze-colored beetles as 'equal-opportunity' feeders. Translated, if it's there and they don't have anything they like better to eat, they will feed upon it. So they bear watching in cornfields.

Learn about how to scout for Japanese beetle and other silk-clipping insects, including corn rootworm beetles, in Purdue University's Corn & Soybean Field Guide, '06 edition. Japanese beetles in corn are discussed and pictured on page 75. They also can eat and skeletonize leaves, and the beetle adult pictured on page 75 in color is busy chewing on a corn leaf. However, this damage usually is insignificant.

See rootworm beetles in action clipping silks on page 73. Most of the damage in Indiana is caused by western corn rootworm beetles, but their southern and northern cousins are also pictured in the Guide.

What's important to treatment decisions, entomologists say, is not which pest is causing damage, but the amount and timing of damage. If silks are clipped back to 1/2 inch or less on 50% or more of the corn plants, by whichever insect, and adult insects are still present, then treatment may be warranted. Exact treatment recommendations and several insecticide choices are listed in the Field Guide.

Part of the key to preventing loss at pollination time is to inspect fields carefully once pollination begins. Don't over react and pull the treatment trigger too soon- remember that just like in soybeans, Japanese beetles can look worse than the damage they create, since they are relatively large, ugly insects. Go by silks, not number of Japanese beetles.

Yet don't wait too late until damage is done, insect numbs are waning, and the only reason to spray would be to make you feel better, out of revenge, played out on the last insects remaining!