Alabama Corn: Nematodes Are Silent Yield Thieves

    Southern Root Knot Nematode. Photo from DAFF Archives,

    Corn nematodes in Alabama are a problem many growers are not aware of. The nematodes feed on roots, and cause symptoms similar to those of soil fertility disorders.

    Alabama Cooperative Extension System Entomologist and Plant Pathologist, Dr. Austin Hagan, said nematodes can cause slow corn seedling growth and plant discoloration.

    “We have problems with nematodes in corn each year,” he said. “They were a particular problem in corn in the spring of 2016. Cooler weather, in addition to nematode feeding on the roots under conditions that were not ideal for corn, caused slow-growing seedlings.”

    Cotton Root-Knot Nematode on Corn

    “Root-knot nematode is one of the most common pests in Alabama corn,” Hagan said. “The particular race that goes to cotton also hits corn. Anywhere in the state where producers have experienced issues with cotton root-knot nematodes in cotton, will likely see yield losses to this nematode in corn.”

    Like most nematodes, root-knot nematodes prefer sandy or sandy loam soils. These nematodes are found in North Alabama in clay soils as producers shift toward continuous corn production.

    The reproduction rate of root-knot nematodes in corn and cotton is equally high. Hagan said this indicates both plants are good hosts.

    “The yield losses seen in rotation studies suggest in continuous corn situations, or in corn planted behind cotton, producers could see a yield loss of nearly 30 percent.” Hagan said. “While this is on the extreme end, more recent trials show a four to five percent yield loss for every 100 juveniles found in a fall soil sample.”

    In studies run by Alabama Extension professionals thus far, no known resistance to root-knot nematode has been found.

    Stubby Root Nematode on Corn

    Stubby root nematode has become more prevalent in the past few years. Producers may see patchy, stunted areas in corn, easily confused with fertility and pH issues.

    “The host range includes many of our field crops, but the highest rate of reproduction is in corn,” Hagan said.

    Peanuts, grain sorghum and soybeans are hosts, but corn is the most favorite host. Stubby root nematodes prefer sandy soils. While there have not been specific studies to determine the yield impact of stubby root nematodes on corn, Hagan said there is no doubt these nematodes are capable of damage to corn on a comparable scale to root-knot nematodes.

    The threshold for treatment is as low as 10 nematodes per 100 cc’s of soil, but may be as high as 40 nematodes per 100 cc’s. Numbers appear to be higher in the spring and remain the same, or even decrease throughout the growing season.

    Lesion Nematode on Corn

    Lesion nematodes, like root-knot and stubby root nematodes, prefer sandy soils and have a broad host range. These migratory endoparasites can cause particularly heavy damage to peanut pods.

    The damage threshold is near 200 nematodes per cc of soil.

    Corn Nematode Control Options

    “There are not a lot of control options for nematodes in corn,” Hagan said. “The most effective means for control is management through crop rotation, and the second option is to use a nematicide.”

    The best crop to manage cotton root-knot nematode in cotton and corn is peanuts. Hagan said even one year of peanuts pushes the population back to a point where producers may not need a nematicide.

    There are also root-knot resistant soybean varieties. Sesame and sunn hemp are both rotation options if producers are looking for a summer cover crop.

    In-furrow nematicides in infested fields boost yields up to 30 bushels per acre. Treatment of fields with no nematode population have no known yield boost.

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