The eggs of the golden nematode, a tiny worm that feeds only on potato roots, may lie dormant in soil for decades, never hatching until touched by a substance exuded from the root of the potato plant.

Thus alerted to the presence of food, the egg resumes development and, in days, hatches a worm that will begin eating the root and damaging the crop.

Agricultural researchers have known this for 50 years, but they have not been able to turn their knowledge into a remedy for nematode infestations. Now, however, a U.S. Department of Agriculture nematode specialist, Bill B. Brodie, has isolated the substance exuded by the potato plant and is searching for the chemical or chemicals in it that act as the "hatching factor."

Brodie, based at the Agricultural Research Service's laboratory at Cornell University, said that if the chemical can be purified and synthesized, it should be possible to spray fallow fields, tricking the nematodes into hatching into a world in which they would promptly starve. Then it would be safe to plant potatoes.

James L. Riopel, Brodie's collaborator at the University of Virginia in Charlottesville, forecasts that once the mechanism is established for the golden nematode, it should be easier to tackle other nematode species that behave the same way with other crops.

The soybean cyst nematode, one of the worst offenders, costs U.S. farmers an estimated $255 million a year in lost crops. There are at least 2,500 species of plant-eating nematodes.