Southern Root-Knot Nematode In Soybean: Risks And Control Options

SARAH CATO 

LONOKE, ARKANSAS

Although most crop pests attack from above ground, some of the most damaging threats – nematodes – lurk beneath the soil.

Nematodes are microscopic, unsegmented roundworms. Some nematodes infect plants and are called plant-parasitic or -pathogenic. The southern root-knot nematode, scientific name Meloidogyne incognita, is the most damaging – and most common – nematode species in Arkansas soybeans.

Southern root-knot nematodes damage plants by invading the root system and developing specialized feeding sites that rob plants of nutrients and water. As a result of this infection, they cause knot-like swellings, or galls, to form on infected plants. Galls become a part of the root, whereas nodules are attached to the root system.

“The southern root-knot nematode is the most yield-limiting, plant-pathogenic nematode that affects soybean production in the Mid-South,” said Travis Faske, extension plant pathologist for the University of Arkansas System Division of Agriculture. “It’s found in nearly all soybean producing counties in Arkansas and can cause significant grain yield losses when a susceptible variety is planted in a field with a high population density of root-knot nematodes.”

But how can growers control them? It starts with knowing your fields, Faske said.

“The foundation of any nematode control program is the identification of the types of nematodes present and an estimation of their relative population density,” he said. “The most effective way to do this is through soil samples assayed by a nematology laboratory.”

The Division of Agriculture runs the Arkansas Nematode Diagnostic Laboratory near Hope, which offers soil nematode assay for a small fee to any Arkansas producer. With the information from soil samples, producers can make site-specific management decisions to prevent widespread damage. This Arkansas Soybean Promotion Board is working in partnership with the Division of Agriculture to provide these assays to soybean producers for free. Those interested can contact their local county agent.

Crop rotation and resistant varieties

“Crop rotation can be a very useful nematode management strategy,” Faske said. “But it’s important we match the cropping sequence to the nematode species we’re dealing with.”

For southern root-knot nematode specifically, Faske said planting peanuts or sesames can effectively lower the nematode density but corn, grain sorghum, cotton and vegetable crops will likely make the situation worse. Rice is a host, but growing rice in a flooded field for two months will significantly reduce nematode densities in the soil.

In addition to crop rotation, resistant soybean varieties are another tool for producers to manage root-knot nematode populations.

“Resistant varieties offer an advantage to producers struggling with nematode populations by reducing galling and increasing grain yield,” Faske said.

Screening varieties

Each year, Faske and his team run trials assessing the commercially available soybean varieties that are marketed as suitable for production in fields where southern root-knot nematodes are present.

“This year we tested 44 varieties that are marketed to growers for root-knot nematode-infested fields,” Faske said. “We tested these varieties in a field with a high population density of southern root-knot nematode, a density that would be considered severe for soybean production in Arkansas. This puts the most stress on the soybean to perform under the most stressful conditions.”

The trials test the susceptibility of each variety to southern root-knot nematode as well as yield performance.

“This really is one of the most important trials we do each year in our program,” Faske said. “There are no other programs that I’m aware of that provide susceptibility and yield data of commercially available soybean varieties for Mid-South farmers.”  

Ensuring that varieties marketed as suitable for root-knot nematode fields actually are resistant, and testing their yield performance provides growers with valuable, science-based information when making planting decisions, Faske said.

“Some of these varieties are marketed as being suitable for production in a southern root-knot nematode field. They are not,” he said. “This research provides an unbiased assessment of soybean varieties marketed as ‘moderately resistant’ or ‘other’ in a comparison trial. If your favorite brand is not in this test it is because there is no resistance to southern root-knot nematode in their portfolio or they did not send us seed to test.”

The results of this trial are available on the Division of Agriculture plant disease website and the Arkansas Row Crops blog. Funding for the trials is provided by the Arkansas Soybean Promotion Board. ∆

SARAH CATO: University of Arkansas