Columbia lance nematodes are much different than the two more commonly occurring pests. It is a migratory endoparasite, and it feeds in an entirely different manner than root-knot and reniform nematodes, Mueller says.

“We’re not likely to find resistance to Columbia lance nematodes. It’s going to be tough to rotate around and generally is a very difficult pest for farmers who find it in their soils,” the South Carolina researcher adds.

In the Upper Southeast in 2012, there is likely to be a significant increase in peanut production and a less dramatic increase in cotton. That could be really good news for growers battling nematode problems.

None of the three most common nematodes found in cotton (root-knot, reniform and Columbia lance) feed on peanut root systems. Sting nematodes, a fourth species that occurs in cotton in the Southeast may or may not feed on peanuts, depending on where the population occurs.

The flip side of rotation is soybeans. Every nematode that goes to cotton also feeds extensively on soybeans. “If you rotate cotton and soybeans, all you are doing is creating more problems,” Mueller says.

Corn is a mixed bag with nematodes. Growers need to know precisely which nematodes are causing the problem, if they are rotating cotton and corn. If Southern root-knot is the primary nematode, corn in the rotation won’t do any good.

If reniform nematodes are the big problem, corn is a good solution and may provide two years of control for one year of corn in the rotation, Mueller says.

How much reduction in nematodes can be achieved by crop rotation is subject to many, many crop and soil conditions and often comes down to a field by field analysis by the grower or his or her crop consultant.

In a seven-year series of tests in the Southeast, USDA researchers found an increase of 26 percent in yield for cotton and 10 percent greater in peanuts, versus growing either crop in a continuous rotation.

Using other tools, like resistant varieties in combination with nematicides would clearly increase yields even more in some situations.

In the USDA tests, which were conducted primarily in Georgia, using chemical treatments had little impact on cotton yields, but increased peanut yields by 22 percent above the yield gain achieved by rotating the two crops.

Determining how many nematodes it takes to cause yield damage to crops is a bit like shooting a BB gun at a hummingbird — it’s an elusive target to say the least.