If time still permits, take a handful of wheat seed and plant baits about 1 meter square on the tops of the knolls as soon as possible. Check the root zone a few days before planting corn. No thresholds have been established for this insect in field crops yet. If you can till up your soil a few days before planting, you will bring the grubs up to the surface, where some will die from being exposed to the elements or will be eaten by predators. Also, think about planting soybeans in the grub infested field instead of corn.
Soybeans appear to be more tolerant to grub feeding than corn or wheat.
Schaafsma recommends, if you are planting corn into that field, there are some treatments you can use to help protect your seed. His research done last year found that an in-furrow rootworm insecticide like Counter or Force, or the seed treatment DL Plus gave some protection against grubs during corn emergence. We did not test these treatments in combination but expect that control would be improved if the in-furrow insecticide was combined with the seed treatment. Postemergent applications of a sulfonylurea herbicide on corn already treated with a soil applied organo-phosphate like Counter, Lorsban, Thimet and Cygard may cause foliar and root injury to your crop. Sulfonylurea herbicides registered on corn include Accent, Ultim, Ultimax, Elim EP, PeakPlus, Broadstrike Dual, Striker, Fieldstar.