How to Handle Southern Root-Knot Nematodes
Arkansas Research Arms Soybean Farmers Against Southern Root-Knot Nematodes
By Laura Temple
Soil harbors countless beneficial microorganisms that help plants thrive. But it also harbors plant-killers. In Arkansas and other areas of the Mid-South, the southern root-knot nematode decimates soybeans.
“Nematodes are tiny, non-segmented round worms,” explains Dr. Travis Faske, professor and Extension plant pathologist with the University of Arkansas. “Just a few species are plant-parasitic, meaning they feed on and damage crops. But the southern root-knot is the number one plant-parasitic nematode in Arkansas.”
This nematode can cause dead spots in soybean fields with 50 to 100% yield reduction. Faske leads ongoing research funded by the Arkansas Soybean Promotion Board to identify management options to help soybean farmers fight southern root-knot and other nematode problems.
“Most nematode management strategies focus on soybean cyst nematode, which can be a problem in the Mid-South,” he says. “We focus on southern root-knot nematode.”
The Arkansas video collection from the SCN Coalition’s “Let’s Talk Todes” series features Faske discussing southern root-knot nematodes. Part of their challenge is that all the primary crops grown in the region – soybeans, cotton, corn, grain sorghum and rice – serve has hosts for the nematode and are susceptible to damage. Peanuts are the only non-host crop grown in the region, though the prolonged flooding of rice can drown them and reduce populations in those fields.
How do farmers know if they have these nematodes in their fields?
They aren’t visible to the naked eye, and in soybeans symptoms show up late in the season, usually under the heat and stressful conditions in August. The Arkansas Soybean Promotion Board funds free soil assays to Arkansas farmers as part of this project so they know where they need to protect against these pests.
“Nearly every soybean-growing county in Arkansas has southern root-knot nematodes,” Faske says. “While they aren’t in every field, soil testing tells farmers where they need management strategies. Tests also allow us to monitor their spread.”
Consistent Efficacy Ratings
In response to the challenges of southern root-knot nematodes, many control options have been developed. Faske evaluates seed-applied nematicides, biologicals, soybean cultivars and combinations of these options. His results help farmers decide how to manage fields with known southern root-knot nematode pressure. In addition, this project includes determining the impact of reniform nematodes, another plant-parasitic species that is spreading in the Mid-South.
“We’ve been doing this research for more than a decade,” Faske says. “But several seed-applied nematicides have been developed over that time, soybean breeding continues to develop new cultivar lines and other biological and foliar plant growth treatments claim to impact nematodes. Farmers what to know how well these treatments work, and we try to answer that question.”
Resistance to southern root-knot nematodes or effectiveness controlling them can be subjective. Faske and his team evaluate every option they can find to provide a consistent measure of effectiveness. His trial plots now cover 13 acres in cooperating farmers’ fields with known heavy southern root-knot nematode pressure. The team monitors soybean roots to rate the percent of galls, or knots, this nematode creates on them.
“The galls each hold a female nematode that is stealing water and nutrients from the soybean to reproduce,” he explains. “When soybeans experience stress from hot, dry Arkansas weather, they can’t overcome that competition for resources with the nematodes and die early.”
The percentage of soybean roots with galls objectively shows the degree of variety resistance or the effectiveness of seed-applied nematicides. All trials are taken to yield, as well. Faske shares results with farmers through University of Arkansas Research and Extension publications and blog posts.
Those southern root-knot nematode ratings help farmers stay profitable, according to Doug Hartz, a professional farm manager based in Stuttgart and member of the Arkansas Soybean Promotion Board.
“One of the farmers I work with who operates one of our client’s properties was ready to stop renting this farm because of the well-below-average soybeans yields it produced,” Hartz says. “The farm had known southern root-knot nematode pressure. Although the farmer chose varieties rated resistant by suppliers, the soybeans weren’t performing in the field.”
Hartz connected with Faske’s team and offered a field as a trial location in 2016. And since then, the farmer chooses varieties based on gall ratings and yield data from Faske’s trials.
“Soybean yields on that farm have increased 20% or more by using Faske’s data,” Hartz says. “The cooperation between the farmer, landowner and researcher allowed us to get more accurate in-field ratings to manage southern root-knot nematode, and reinforces the value of independent research. That demonstrates exactly what the Arkansas Soybean Promotion Board tries to do with checkoff investments. We support research that keeps farmers on the leading edge.”
To learn more about the Arkansas Soybean Promotion Board's checkoff-funded research, watch the full Field to Film: Featured Research video series here.
For more on this study, click here or visit the Soybean Research Information Network to learn about other soybean research projects.