Parasitic worms could damage soybean yields

Soybean prices have been in the doldrums and another problem could impact profits. Soybean plants have no natural defense against root knot nematodes, a plant parasitic round worm that is so small it’s measured in micrometers, University of Arkansas System Division of Agriculture science writer Fred Miller told Talk Business & Politics.

The worms can impact soybean yields, especially in high yield fields, he said. These worms have existed in the sandy soils in eastern Arkansas for hundreds of years. Many of those fields were traditionally used to grow cotton and the worms didn’t have an impact on the plant, Miller said. As cotton prices have dropped in recent years, many farmers have converted these fields into soybeans fields, he said.

“We don’t have good resistance in soybean varieties, he said.

John Rupe, professor of plant pathology for the University of Arkansas System Division of Agriculture, coordinated a research effort of scientists from the UA Division of Agriculture, Mississippi State University and Louisiana State University to study a way to deal with the issue. The researchers’ areas of expertise included plant pathology and nematology, soil science and agricultural economics.

The research drew on existing research data and employed the latest technology and time-tested scientific methodology to test nematode control strategies on cooperating farms in all three states, Rupe said. They used replicated test strips in soybean fields, including control strips in which no control strategy was used.

Crop rotation was not tested, Rupe said, because root knot nematodes thrive in such a wide range of plant hosts that there are few options among rotation crops that would help reduce the pest populations. Peanuts are a good rotation crop in the fields, but it’s not a practical.

“There are no high-yield soybean varieties with good resistance to root knot nematode,” Rupe said. “So we focused on nematicide soil applications and seed treatments.”

The research has shown that the most effective control strategy for root knot nematodes is a nematicide chemical called Telone II. It’s a preplant fumigant that must be injected into the soil about two weeks before planting, Rupe said. Telone is expensive because it has to be injected into the soil, and it has to be done before planting because it can damage the plant.

Agriculture economist Robert Stark is working out the economics of cost versus return, Rupe said, and those numbers will figure into recommendations the division is developing for soybean growers. Fields in eastern Arkansas have highly variable soil structures, especially in the Delta, and this can impact costs, he said.

Land within a single field can vary from sandy soils to more densely packed silt loams and clays, where nematode populations are lower or even nonexistent, Rupe said.

Soil structure in test fields was analyzed and mapped using electrical conductivity sensors from Veris Technologies, Rupe said. Finer, more compacted soils conduct electricity more efficiently than coarser, looser sandy soils. The soil texture maps generated by this system identify sandy areas in a field where root knot nematodes occur in higher populations, he added.