Laurence D. Chandler
United States Department of Agriculture
Agricultural Research Service
Red River Valley Agricultural Research Center
P.0. Box 5677; Fargo, North Dakota 58105 USA
Telephone: 701/239-1371; FAX: 701/239-1395; e-mail: chandle@fargo.ars.usda.gov

Several western corn rootworm, Diabrotica virgifera virgifera LeConte, management strategies are currently available for grower use. Soil insecticides applied at planting for control of larvae, insecticides applied as larval "rescue" treatments, foliar insecticides targeted at reducing adult feeding damage (silk clipping), and crop rotation continue to prove beneficial. Of the four techniques listed above, crop rotation strategies have proven generally more effective in managing rootworm populations. Rotating maize, Zea mays L., with a non-host crop can effectively reduce western corn rootworm populations within the field. Although some western corn rootworm populations in the United States have developed behavioral traits to overcome the rotation strategy, it continues to be widely used and highly effective throughout a wide portion of the "Corn Belt". Soil and foliar insecticides do not always provide rootworm population management. Soil insecticides applied in a band at planting protect the seed zone and the immediate area under the band from rootworm larval feeding. However, numerous larvae survive outside the insecticide band. Thus, large numbers of adults continue to be produced. These insects then lay large number of eggs which upon hatching can damage the preceding years maize crop. Population management is not always achieved. Foliar insecticides often are applied to reduce adult rootworm feeding damage on maize reproductive parts. These applications are made to protect the crop and do not always result in population reductions that will limit the number of eggs/larvae available to feed on next years crop. Again, population management is not achieved.

Adult rootworm control can, however, prove to be an effective population management strategy if reducing egg laying capabilities are considered. Carefully timed application of various toxicants can suppress beetle populations in the current growing season to levels that effectively reduce the number of eggs laid. A significant reduction in egg numbers will result in fewer larvae and less root feeding during the next growing season, which will substantially reduce rootworm populations and eliminate economic loss potential. This strategy works best in continuous cropped maize. Effective adult population management is labor intensive and requires a great degree of knowledge of pest biology and ecology, crop phenology, weather related effects, and economics. Considerable effort is needed to effectively develop and carry out an adult control program that will effectively lower corn rootworm populations to levels below which provide economic damage.

This presentation will provide a step by step guide to implementing an adult corn rootworm management program. A discussion on adult behavior, sampling/scouting techniques, female beetle reproductive status, and effective insecticides/semiochemical baits will be provided. Information on new technologies targeted at adults will also be provided.