If the drought persists, Idaho farmers could have a tougher time with weeds, says an expert in the field.

"If plants are very drought-stressed, I tell the grower not to expect much in the way of performance from the herbicide," Don Morishita said. He is a weed specialist for the University of Idaho Cooperative Extension Service in Twin Falls.Morishita said cuticles on leaves of drought-stressed weeds often thicken, making it more difficult for herbicide to penetrate. Photosynthesis also slows, and with it movement of herbicides through the plant.

Reduced metabolism also can cause herbicide injury to a drought-stressed crop unable to break the herbicides down rapidly.

He said farmers should consider applying herbicides as early as possible to take advantage of spring rain.

Researchers at Utah State University have found that the weed kochia, a particular problem in Idaho crops, is fairly drought-tolerant. It becomes more competitive under drought conditions.

On the other side, wild oats become less competitive when there is little water.