Are rootworm larvae eating your corn?

When I am asked when corn rootworm eggs will hatch and larvae will begin to feed on corn roots, I answer "June 6," however, we continue to be warmer than usual. Rootworm eggs will hatch when approximately 500 air heat units, base 50, have been accumulated. As you can see from the Degree Days report at the end of this issue, we had accumulated 440 to 500 degree days, base 50, by May 31. This means that the eggs have hatched and larvae are beginning to feed on corn roots.

Corn rootworms can injure corn roots.

Very young larvae are difficult to find for two reasons. First, they are small and extremely hard to separate from soil efficiently. Second, when they initially attack corn they are small enough to burrow completely inside roots. During the week beginning June 8, larvae should be able to be found more easily and root injury should begin to be apparent. Now is the time to begin sampling for larvae and looking for root injury.

There is another reason the week of June 8 is important in corn rootworm larval management. If postemergence insecticide treatments to protect corn roots are planned, applications should begin during this week. Prior to this week, little feeding will have occurred. By the end of the week, most of the eggs will have hatched and the majority of the larvae will be present during the residual life of an insecticide applied at this time.

This article originally appeared on page 99 of the IC-480(13) -- June 8, 1998 issue.

Updated 06/07/1998 - 1:00pm