Western bean cutworms are damaging corn again in northwestern Iowa for the second consecutive year. This insect traditionally has not been a problem in Iowa, but significant yield loss did occur in some fields during 2000 and early indications are that more economic damage is expected in 2001. On August 7, Tony Weis (Vohs Seeds, Holstein, IA) reported some corn hybrids that have nearly five larvae per plant. More typically there was less than one up to just over two per plant. Infestations were the worst on later silking hybrids. He noted that although many of the larvae were buried in the ear, there were some that tended to be around the husk and in the silks. Paul Kassel, extension crops specialist, found 1/2- to 3/4-inch-long larvae in Osceola County on August 10 at a density of one larva per four plants.
This insect is difficult to control because the larvae enter the silks were chemical control is ineffective. Proper management requires scouting for the eggs and newly hatched larvae and then using properly timed insecticides. Fields that have not been sprayed by now are probably too late to get any benefit from an insecticide application. Unfortunately, Bt corn does not provide any control of this insect.
This article originally appeared on page web of the IC-486(21) -- August 20, 2001 issue.