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Nematode study uses electrical mapping

Electrical conductivity mapping has been useful to find soil textures to provide precision applications of fertilizer and irrigation water, but can it be used to treat pests? Scientists at Louisiana State University believe it can and are finding surprising results battling root knot nematodes in cotton.

“Nematodes can be a very detrimental pest to cotton in our areas, and because of the expense of treatments and the damage they cause, we needed a way to treat them in the most economical way,” says Dennis Burns, assistant Extension county agent at LSU’s Agricultural Center in Tensas Parish. Burns has been associated with the project since 2004.

“It’s frustrating — you can’t just treat a field from one end to the other. If you put [nematicide] in the right place, you get good results, or lose money in the wrong place.”

The scientists knew nematodes tend to be found in areas with lighter sand textures, but are much less prevalent in clay areas. The problem was finding the susceptible areas, which meant understanding the soil texture of the whole field. A bigger problem was the fact that many textures can be found in Louisiana fields, especially closer to the Mississippi River Delta. To differentiate between the textures, the researchers used USDA soil maps and producers’ knowledge of their fields, but the biggest tool was electrical conductivity mapping, which provided in-depth maps of the soil profile.

“We got into it initially to see if we could identify where the nematodes were occurring in the field. We were thinking we could map the areas of the field where nematodes could occur and eliminate part of the field where it is too heavy for the nematodes,” says Charles Overstreet, an LSU nematologist, Baton Rouge. Overstreet has been leader of the project since 2001.

Key Points

• EC mapping helps locate soil types that are prone to nematode infestations.

• Researchers use EC results to set up test strips for nematicide studies.

• Soil texture maps can help predict where root knot nematodes will be present.

Unexpected results

Using a Veris machine, researchers mapped university and producers’ fields, creating between three and 10 zones in each, depending on soil profiles. Samples were taken in each zone to find accurate nematode populations. They found that nematode populations didn’t always correlate with soil texture, and areas with higher nematode populations didn’t always show as much damage, especially in clay.

“I assumed if you had a high level of nematodes, you’d see more damage. That’s not what we got,” Overstreet says.

Nematicide trials with Telone-treated seed led to even more unexpected results. Researchers found that high populations didn’t always show any response to nematicides.

“We could identify root knot nematodes, but couldn’t find a response in the Telone. We couldn’t show any favorable response to any nematicide,” Overstreet says.

The lower populations in lighter textures tended to respond better to nematicide, but to find the areas that had the best response, test strips were spread across the field, crossing as many textures as possible. Each strip was between 10 and 12 rows wide, planted with Telone-treated seed, with nontreated control strips between each verification strip. Strips that didn’t have desirable results received further Telone applications.

Results corresponded to the initial mapping.

“With our soil types in Louisiana, the results are the same as other states, South Carolina or Georgia, and they see the same pattern: Almost always, the lighter zones are going to need nematicide, but the heavier zones won’t,” Overstreet says.

“For heavier soils, seed treatments are fine, but in lighter soils, seed treatments aren’t as strong.”

For producers who want better control over root knot nematodes, Overstreet recommends mapping the soil profile, with at least three to five zones in the field and samples pulled from each zone. Test strips should be part of the management plan, but they should cross as many zones as possible.

“If you have heavy clay, don’t bother pulling samples from the clay, just pull from the lighter parts of the field,” Overstreet says.

“Once you have an idea of where the nematodes are located, decide where you are going to treat, then put three to four strips in the field to find out where the response is.”

Overstreet plans to continue the research at least for the next few years, putting a new focus on the textures to see how the zones might change in crop rotations, especially between cotton and corn rotations.

Brazil writes from Clermont, Fla.

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THE SOIL'S ILLS: Gene Burris of the LSU AgCenter (right) has been helping Tensas Parish, La., farmer Jeff Lee use electrical conductivity to do battle with nematodes.

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GALLING SITUATION: Root knot nematodes create galls on the roots and rob cotton plants of their nutrients.

This article published in the March, 2010 edition of MID-SOUTH FARMER.

All rights reserved. Copyright Farm Progress Cos. 2010.