A new, genetically modified (GM) corn, if approved in time for spring 2003 planting, should make that season the biggest yet for GM corn. In 2001, U.S. farmers grew GM corn on about a quarter of the land planted to corn.

The new corn, Monsanto's YieldGard Rootworm corn, produces its own Bt (Bacillus thuringiensis), a natural bacterial insecticide, to kill corn rootworms. The corn rootworm triggers more insecticide use than any other single pest in U.S. agriculture.

To address concerns about corn rootworms' developing resistance to the plant-produced insecticide, Wade French, an Agricultural Research Service entomologist at Brookings, S.D., and colleagues are working with Monsanto to develop the concept of mixing conventional and GM corn seeds. The U.S. Environmental Protection Agency is reviewing Monsanto's application for approval to sell the GM seed. Based on continuing research, the EPA, ARS and Monsanto would determine whether seed sold in a mixture may be a viable commercial alternative the company could eventually consider.

In a five-year cooperative research and development agreement that was renewed recently, the researchers have found the seed mix offered superior corn rootworm control to that of a conventional insecticide and may slow down the development of resistance to Bt.

Plants growing from the conventional seeds in the mix would serve as a refuge, to ensure there are some rootworm beetles not exposed to Bt available to mate with those that are.

This new GM corn has become more important since the corn rootworm has become the first pest ever to evolve a way of foiling crop rotations. The rootworms either rotate the fields they lay eggs in or extend their egg-hatching time to match crop rotations.