MISSISSIPPI STATE -- Weeds and a strange animal that lives in the soil and feeds on roots are under attack by Mississippi State University researchers trying to give every advantage to the state's soybean producers.

Gary Lawrence, a nematologist with the Mississippi Agricultural and Forestry Experiment Station, is working on the control of nematodes -- microscopic, worm-like animals in the soil that feed on the roots of plants.

Dan Poston is a MAFES researcher working on weed control, specifically the fine-tuning of early-production weed control systems. Along with several others, these men are helping soybean farmers increase yields, lower inputs and produce better crops. Funding from the Mississippi Soybean Promotion Board supports these efforts.

"Nematodes are a significant problem in soybean production," Lawrence said. "The three major species of nematodes that are a problem in Mississippi are the root knot, the reniform and the soybean cyst."

Nematodes feed off the nutrients the plant is producing for yields. Lawrence said the best defense against them is a resistant plant variety. Different varieties of soybeans have resistance to various nematodes, but no variety has resistance to all nematodes.

The next best defense is rotating the affected crop with a non-host crop. Soybeans are most often rotated with cotton, but cotton is extremely susceptible to the common reniform and root-knot nematode. Fields infected with these nematodes must be treated differently.

"The final method for nematode control is chemical," Lawrence said. "Producers who use a nematicide can generally increase yields five bushels or more. Depending on soybean's price and the cost of the chemical application, they can sometimes break even using this treatment."

Nematicides are granular pesticides placed into the furrow with the seed at planting.

"You can't see the nematodes, so you don't know if you're killing them," Lawrence said. "I suggest producers leave some rows without nematicide to see the difference."

Lawrence said a nematicide does not affect nematodes between the rows.

"The nematicide will reduce nematodes early in the season and give the plant a chance to grow without nematodes. When the nematicide degrades in the soil, the nematodes will reestablish, but by then, the plant should be larger and more able to thrive," Lawrence said.

Some cotton producers make a second application of nematicide, but the best solution for soybeans seems to be a 1:1 rotation with a non-host crop.

"Producers can introduce corn into the rotation, but since cotton is the main crop, no one wants to stay away from cotton for more than one year," Lawrence said.

While nematodes are invisible attackers, weeds are obvious. Weeds serve as hosts for some nematodes, so even when growing a resistant soybean variety, the presence of weeds can limit the success of that variety.

Poston, who works from the Delta Research and Extension Center in Stoneville, said early soybean production changed producers' weed control needs.

"Our major problems are no longer in-season weed control but preplant," Poston said. "We're doing a lot of work looking at ways to control annual grasses at harvest and the economics of burn-down prior to planting."

Poston said researchers are trying to determine if spending an extra $8 to $10 an acre on a residual herbicide will pay off in better weed protection. Producers now apply burn-down herbicides in late February to early March and start planting by late March. A residual may keep producers from having to spray again until four to six weeks into the growing season.

MSU has fine-tuned the timing for burn-down herbicide applications and recommends adding a residual herbicide to the mix. Three-way mixes that attack glyphosate-resistant weeds also are recommended.

Poston said growers have been slow to adopt the practice of adding a residual grass herbicide to the tank mix because of cost, but he expects new products and generic chemicals on the market to lower prices soon.

The other issue being studied is how to control weeds that appear before harvest.

"We're trying to look at in-season residuals to eliminate weeds at harvest, and harvest aids applied prior to the combine going out into the field," Poston said. "We're looking at a multiple approach to managing late-season weed resurgence during the growing season."

Poston is also working on weeds developing resistance to glyphosate. His group is looking at chemical control, plant biology, germination patterns, and the impact of temperature and light on germination as they try to develop control strategies for weeds that have developed resistance.

Contact: Dr. Gary Lawrence, (662) 325-2811