How to get ahead of nematodes in cotton

In Delta Farm Press

by Patrick Shepard, Delta Farm Press

Louisiana witnessed a shift from root-knot to reniform nematodes in the late 1980s and 1990s. “We conducted nematode survey work in cotton in the mid-1990s, and found that 50 percent of the fields had reniform and only 25 percent had root-knot,” says Louisiana State University AgCenter plant pathologist Charles Overstreet.

“However, we’re now moving slightly back in the other direction because we’re rotating more with corn; we’re now finding a mixture of both reniform and root-knot in cotton fields. Corn is a host for root-knot, but not reniform, so yearly rotation helps manage reniform nematodes. Many Louisiana growers now plant one year with cotton and one with corn.”

In addition to yearly rotation, some Louisiana cotton growers plant root-knot-nematode-resistant cotton varieties in fields where a root-knot problem has been identified. “For example, some of the newer Phytogen varieties contain two genes that help control root-knot,” Overstreet says. “Phytogen 427 offers pretty strong resistance to root-knot.”

Planting resistant varieties helps control root-knot, but high levels of nematodes might also require using a nematicide. “In Louisiana, the most popular nematicide seed treatment is Avicta Complete Cotton,” Overstreet says. “Avicta Complete Cotton controls both root-knot and reniform nematodes when populations are low to moderate. A newer nematicide tool is Velum Total, which is applied in-furrow. In fields with very high levels of nematodes, growers might want to use both a seed treatment and an in-furrow treatment, providing dual methods of control.

“We also use a little Telone, a fumigant that is put out a week to 10 days ahead of planting, or it can be applied in the fall. We especially use the product in a site-specific manner where you just treat areas instead of the whole field.

Louisiana witnessed a shift from root-knot to reniform nematodes in the late 1980s and 1990s. “We conducted nematode survey work in cotton in the mid-1990s, and found that 50 percent of the fields had reniform and only 25 percent had root-knot,” says Louisiana State University AgCenter plant pathologist Charles Overstreet.

“However, we’re now moving slightly back in the other direction because we’re rotating more with corn; we’re now finding a mixture of both reniform and root-knot in cotton fields. Corn is a host for root-knot, but not reniform, so yearly rotation helps manage reniform nematodes. Many Louisiana growers now plant one year with cotton and one with corn.”

In addition to yearly rotation, some Louisiana cotton growers plant root-knot-nematode-resistant cotton varieties in fields where a root-knot problem has been identified. “For example, some of the newer Phytogen varieties contain two genes that help control root-knot,” Overstreet says. “Phytogen 427 offers pretty strong resistance to root-knot.”

Planting resistant varieties helps control root-knot, but high levels of nematodes might also require using a nematicide. “In Louisiana, the most popular nematicide seed treatment is Avicta Complete Cotton,” Overstreet says. “Avicta Complete Cotton controls both root-knot and reniform nematodes when populations are low to moderate. A newer nematicide tool is Velum Total, which is applied in-furrow. In fields with very high levels of nematodes, growers might want to use both a seed treatment and an in-furrow treatment, providing dual methods of control.

“We also use a little Telone, a fumigant that is put out a week to 10 days ahead of planting, or it can be applied in the fall. We especially use the product in a site-specific manner where you just treat areas instead of the whole field.

“We have used Veris EC soil mapping data to help us identify management zones in a field based on soil texture where you’re likely to have nematode damage. You might not have to use Telone in other zones where the soil is a little heavier or has a clay content deeper in the soil profile.

“If you don’t know where to use site-specific in a field with variable soil textures, I recommend putting out several 6- or 12-row Telone strips in a field to see where you get a response and where you don’t.

“Additionally, when using site-specific, you need to be sure you have a problem field. So sample to see what levels of nematodes are present. If possible, divide a field into EC zones so you sample within a similar soil type rather than across the whole field.”

Root-knot nematodes favor a coarse textured soil like sandy soils; reniform thrives best in a silt loam soil. “Cotton sustains more damage in sandy soils that don’t have the water-holding capacity or nutrient-holding capacity to withstand root stress caused by nematodes,” Overstreet adds. “Low levels of nematodes can cause a lot of injury in sandy soils, while it takes a lot more to cause injury in some of the heavier soils.”

Go to Delta Farm Press to see how Tennessee and Mississippi are dealing with nematode management.

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