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NMSU Farmington Nightshade Research Gives Pinto Beans a Fighting Chance

FARMINGTON, N.M. -- A New Mexico State University nightshade research project in San Juan County is helping pinto bean growers hold their own against the annual weed that used to infiltrate and overtake their fields.


Nightshade can put a stranglehold on bean plants if left uncontrolled, said Rick Arnold, weed scientist at NMSU's Agricultural Science Center at Farmington.

"Nightshade creates a problem because it germinates all summer long from the middle of May up to August in the pinto bean fields, and it competes very heartily with pinto beans," Arnold said.

The weed sometimes grows higher than the bean plant, creating a canopy of shade over the beans that reduces sunlight and plant growth. Nightshade can quickly overrun a bean field, and its berries clog harvesting machinery.

I've seen fields where the nightshade was so thick that the grower had to basically throw the crop away, Arnold said. I've also seen it so bad that, after every fourth or fifth combine load, the grower would have to stop his combine and wash out the sticky juice from nightshade berries.

Each nightshade berry holds about 20 seeds, compounding a bean grower's troubles.

Arnold has spent the past several years testing combinations of herbicides to battle nightshade species. He began testing a postemergence herbicide with the active ingredient imazethapyr several years ago, and discovered an economical nightshade control for growers at about $25 per acre.

It's well worth the investment because when growers don't use it, I've reported yield reductions of up to 80 percent, he said.

Arnold's success with the herbicide led to approval from state agriculture department and Navajo tribal authorities to use the chemical on area bean fields, thereby saving the crop and a substantial local industry.

A major bean producer in the region is the Navajo Agricultural Products Industry (NAPI). A NAPI pinto bean cleaning and packing plant operates just a few miles down the road from the science center. The people at NAPI were ecstatic over the idea of controlling black nightshade once it comes up, he said. It's just a real bad weed.

Arnold is now expanding his research by testing imazethapyr in combination with other herbicides either postemergence or as a sequential treatment.