Corn Rootworm Problem

The Corn Rootworm Problem

Corn rootworms are among the most serious insect pests of corn in the United States. The larvae feed on corn roots from early June until late July. They eat small roots, scar large roots, and tunnel inside large roots and other supporting root structures. In years when weather stress occurs and root regrowth is poor, damaged plants may topple over. Crop losses and control costs attributed to the management of corn rootworms approach $1 billion annually. The major species are:

western corn rootworm (WCR)
northern corn rootworm (NCR)
Mexican corn rootworm (MCR)
southern corn rootworm (SCR)

Most growers rely on crop rotation and soil insecticides to manage corn rootworm. Rotating from corn to soybean (and/or sorghum in Texas) has helped to control crop loss because rootworm adults do not lay eggs in soybean in most areas of the country and rootworm larvae cannot survive on soybean roots. Because eggs are not laid in soybean in most areas, corn can be planted after soybean without concern for rootworm larvae. When eggs are laid in corn one year, the larvae that hatch in soybean fields the next year starve to death. Soil insecticides are used to protect roots from larvae feeding damage. Another strategy has been to use foliar applied insecticides in controlling adult beetles to prevent damage to corn ears and to reduce the number of eggs laid that could cause economic damage the following year.

Many management strategies used today are being re-examined:

Although soil insecticides protect corn from serious larval damage, they do not manage rootworm populations.
Beetles move back and forth among fields so that even if a farmer tries to control adult populations, beetles from a neighboring field can re-infest his or her field.
Conventional insecticides are under close scrutiny by recent EPA regulatory reviews because of the Food Quality Protection Act.
Crop rotation is no longer an effective management strategy in some areas. A small percentage of NCR eggs that are laid in the fall remain dormant in the soil and hatch the second year when corn is again the crop. Also, in parts of the eastern Corn Belt, development of a "variant" of WCR that lays eggs in soybeans has rendered crop rotation ineffective.
Populations of WCR in portions of Nebraska are resistant to carbaryl and methyl parathion resulting in poor control of adults in these areas.
Insecticides are sometimes harmful to non-target organisms.