Many Mid-South producers may be “missing the big picture” regarding nematode-related crop losses, says Tom Allen, assistant Extension and research professor at the Delta Research and Extension Center, Stoneville, Miss.

 “We’ve got a lot of nematodes in our soybean fields,” he said at the annual meeting of the Mississippi Agricultural Consultants Association. “And unlike the Midwest, which has predominantly soybean cyst nematodes, we have several species in Mississippi that can cause yield reductions.”

Those causing the most crop losses, he says, are primarily reniform and root knot, while soybean cyst nematode is not near as prevalent throughout the state.

“While reniform nematodes get more attention in cotton, they can also be a soybean problem,” he says. “They favor a fairly specific set of soil characteristics — they like soils with a greater silt content, whereas root knot nematodes prefer sandier soils.”

Pull a plant up in a reniform-infested field and you may not see characteristics such as those from root knot nematodes, which typically produce galls on the roots, he says. “You need a microscope to see reniform nematodes.”

The key to detecting and determining the extent of the problem, Allen says, is soil sampling.

“It’s the only way to tell what you have in the soil. I know it’s not cheap — but in the long run sending a sample to a diagnostic laboratory will help you a lot. There are a number of seed treatment nematicide products available that are outstanding on reniform nematodes in the right situation. If you have a low to moderate reniform problem, they can be quite effective, but if you have 50,000 nematodes per pint of soil, it’s going to be like shooting a BB at an M-1 tank — you’re not going to get much protection.”

The soybean cyst nematode is a problem only in soybeans or related leguminous hosts, Allen notes.

“With large SCN populations, yield losses can be extensive,” he says. “In some cases, you can pull up a soybean plant, look at the root, and not think that nematodes are the culprit causing shorter soybean plants. It can be difficult to determine that there is a SCN problem; for one thing, you need a really good hand lens to see the nematodes on the root itself. Even so, it is still best to send off a soil sample for analysis.”

Root knot nematodes can cause extensive losses in cotton, Allen says, depending on the level of infestation. There are currently no varieties with resistance to the pest, although some are less susceptible and can produce good yields even with fairly high levels of root knot nematodes.

“When you encompass all these nematode issues, one of the best management strategies is rotation to a non-host crop,” he says. “However, in some cases you need to know which particular nematode is present before you can make a rotational choice.”