Growing resistance to chemical herbicides.

Herbicide resistance in weeds, one of the most vexing issues of modern agriculture, is about to get worse, cautions Robert G. Harvey, professor of agronomy, University of Wisconsin-Madison. He maintains that the phasing out of the broad-acting triazine family of herbicides and their replacement by more weed-specific chemicals is almost certain to lead to greater resistance to chemical herbicides.

The triazines--organic chemical herbicides first introduced in the 1950s--have been among the most widely used and effective in the world. However, the fact that they persist in the environment and are water-soluble has posed problems of surface and ground water contamination. The compounds also have been implicated as potential carcinogens. As a result, their use increasingly has been restricted, and industry gradually is phasing out what once were considered the wonder chemicals of modern farming.

Filling their place will be a new family of chemical compounds that, while potentially safer, act far more selectively on weeds. The danger that poses, Harvey notes, is that herbicide-resistant...