Individually, a perennial weed called nutsedge and a microscopic worm known as root-knot nematode can cause substantial grief for southern New Mexico chile growers. In combination, they bring more than double the trouble. This is a telling example of the need for multidisciplinary research to solve some of agriculture's most complex problems.

Stephen Thomas, a nematologist with NMSU's Agricultural Experiment Station, has studied how the root-knot nematodes damage chile plant roots and decrease yields in sandy soils.

The power of collaboration: Jill Schroeder, Stephen Thomas and Ian Ray, all NMSU Agricultrual Experiment Station scientists, team up to get root-knot nematodes and nutsedge weeds under control in southern New Mexico chile fields.

"It seemed that the nutsedge weeds were becoming more and more of a problem in my research plots, making it harder to just study the effects of the nematodes on the chile," he says.

About 10 years ago, he turned to weed scientist Jill Schroeder for help. Together, the two have worked to figure out the relationship between the two pests.

"From our studies, we found that when purple and yellow nutsedges are present in a field, they increase the numbers of root-knot nematodes present in the soil," Thomas says. "This means there are more nematodes available to invade and damage the chile crop."

The nematodes actually seem to thrive in the nutsedge tubers, safe from pesticides. At the same time, when the researchers increased nematode levels to as much as four times the normal amount found in area fields, the nutsedge plants remained healthy and even produced more tubers.

"This means a worst case scenario for the chile farmer, because the nutsedges and the root-knot nematodes are both increasing happily at the expense of the crop," Thomas adds.

When they ran out of ideas for controlling the weeds and nematodes in chile fields, the researchers started looking for new, environmentally safe strategies to stop the pests. That's when they sought help from Ian Ray, an NMSU alfalfa breeder.

"The three of us began discussing how we might try to manage the two pests in combination," Schroeder says. "Ian was aware of some root-knot nematode resistant alfalfa varieties that we might look at as rotational crop alternatives."

Ray also had observed that nutsedge densities were lower in thick alfalfa stands compared with thinning stands. He says alfalfa often works well as a "smother" crop, because it grows fast, is cut frequently, has a strong root system and can shade out weeds.

One goal of the study is to capitalize on alfalfa's ability to reduce nutsedge numbers. With fewer nutsedge plants to feed on, the nematodes will either have to feed on the alfalfa roots or starve.

Safe harbor: Nutsedge tubers give root-knot nematodes a place to hide from pesticides.

"This is where growing a root-knot nematode resistant variety fits in," Ray says. "If the farmer grows a resistant alfalfa variety, then the nematodes will have no food source because they can't feed on the alfalfa and there will be less nutsedge to feed on."

If all goes as planned, both nutsedge and root-knot nematode numbers should decline.

The researchers are comparing a nematode-susceptible variety, Doña Ana, with a resistant variety, Magna 8, at two seeding rates. A high rate mimics a vigorous, competitive crop, while a low rate mimics a field that's beginning to decline.

They're working on the third season of the trial.

"Where we are seeing the lowest populations of the two nutsedges is in the root-knot resistant, high-density alfalfa plots," Schroeder says. "So far, this fits with our theory."

It's too soon to know if the root-knot nematodes will be weeded out, too, Thomas says. The ultimate test will come in the fourth year of the study, when the scientists rotate the research field back to chile to see if both pests are controlled.

The researchers emphasized that the results will be applicable to control of root-knot nematodes and nutsedge on light or sandy soils.

The research, funded through the state's Chile Improvement Project, has given the scientists an excellent opportunity to collaborate.

"So often, each discipline is just looking at one aspect of a problem," Schroeder says. "When we're all working together, we're considering the problem in a more realistic way as it occurs in the field."