LSU AgCenter nematode specialist Charles Overstreet has found variable soil textures can affect nematode damage to soybeans, results similar to findings in cotton. His experiments over the past three years, primarily at the LSU AgCenter Northeast Research Station in St. Joseph, also has analyzed nematicide performance against nematodes in soybeans.

“We’ve been looking at site-specific applications of nematicides on cotton for a number of years with great results,” said Overstreet. “But we didn’t have information on whether these same nematicides would work well in soybean production systems, and now we know they do.”

One part of the study looked at different soil textures in the same fields and how they affected nematode populations and the health of the plant. The results consistently showed greater nematode plant damage in lighter, coarser soils and minimal damage in finer clay soils, just as the researchers had anticipated.

Using a Veris machine that records electrical conductivity in soils, researchers have been able to make maps of variable soil textures. The results help predict which areas of the field are likely to be damaged by nematodes and those that won’t.

“Once we found over 200,000 reniform nematodes in a pint of soil from a cotton field,” said Overstreet. “We can find heavy populations of nematodes in clay soils and still not show any damage, yet the same level of nematodes in lighter soil really clobbers the plants.”

Overstreet said he believes lighter soils are susceptible to drought, increasing plant chances for disease or pathogenicity, while heavier soils have more nutrient and water-holding capacity. Lighter soils show the best results when using the nematicide Telone to combat nematode populations, according to Overstreet.

As was found in cotton tests, researchers achieved good soybean yields when the fumigant was applied to lighter soils, but there was hardly any response from soybeans in heavier clay soils.

“Even though nematodes were present in high levels in both soil textures, that’s exactly what we saw in cotton,” Overstreet said. “Telone is expensive, so we can use this information to make more cost-effective management decisions, spraying only where there’s going to be a benefit.”

Southern root knot and reniform nematodes have caused problems in both cotton and soybeans. Researchers were surprised to discover newer soybean varieties didn’t show the nematode symptoms or damage that had been present in cotton.

“This year, I set up root knot and reniform resistant varieties in multiple soil textures,” said Overstreet. “We want to know how much of the variety component is impacted in these heavier soils.”

Grain sorghum is not grown much in Louisiana because it is not profitable. But, because it has high drought tolerance and can grow in almost any soil, Overstreet is studying nematode-resistant varieties, just in case it ever is used as an alternative.

“We’re not showing a lot of damage to grain sorghum from the nematodes,” said Overstreet. “It does help keep the populations down, but the problem is it wasn’t always an economic option.”

These studies have enhanced knowledge about nematodes in soybeans, grain sorghum and other row crops. Overstreet appreciates the opportunity to discover more.

“It’s a hotbed of nematodes here at the station, nothing that wouldn’t be found on a typical farm field,” he said. “It has exactly what I was looking for – variable soil texture.”

Randy LaBauve