Growers face nematode threats

Until the ’80s, soybean cyst nematode (SCN) was the main parasitic nematode concern Southern soybean growers faced.

Decades later, they are experiencing additional threats from lesion, reniform and southern root-knot (SRK) nematode, says University of Arkansas System Division of Agriculture Plant Pathologist Travis Faske. As a result, The SCN Coalition has expanded its educational outreach to other parasitic nematodes soybean growers face.

Like SCN, anything that moves the soil moves other parasitic nematodes. “That’s why it’s important to detect what nematodes are in your soil,” Faske says. “Growers in Arkansas can utilize free sampling supported by the soybean checkoff to determine what nematodes are present, and at what population densities.”

Faske says the Coalition’s “What’s your number?” tagline rings as true for Southern soybean growers as those in the heart of the Corn Belt. “Through soil sampling, it’s been determined SRK is the most common nematode threat in Arkansas,” he says. “The Cotton Belt is associated with the highest population densities and distribution of SRK.

“Soils in the northern U.S. soybean-growing areas are too cold for SRK, but almost every crop that is grown in Arkansas, besides peanuts, is a host for SRK, which makes it a challenge to manage,” adds Faske.

Faske recommends soybean growers test soil every three to five years to determine which nematode(s) are present and to see if population densities have changed. “There are a few soybean varieties available that offer resistance to SRK,” he says. “Seed-applied nematicides are also popular. If a grower has an option of having peanuts in their program, it’s good to add that into the rotation, or an SRK-resistant cotton variety.”

Scout fields for visual symptoms

Unlike SCN, in which foliar symptoms are typically absent or mild until nematode numbers develop to high levels, soybean growers can tell there is an issue brewing if a field is infested with SRK. “Within a green field, a bull’s-eye will become visible if high populations of SRK are present,” explains Faske. “Plants will turn yellow, be stunted and prematurely die. That’s when a grower recognizes they have a problem that needs to be investigated.”

During the growing season, Faske says the telltale symptom that SRK has infested fields is to dig up a plant and look at the root system. “When soybean roots are developing, the second-stage juvenile migrates up to the root system to establish a feeding site,” he says. “While the SCN adult females break through the root surface and attach to the exterior of the root, SRK enters and stays in the root and causes it to swell, which is called a gall.