Pest Profiles: Root-Knot Nematode

Root-knot nematodes can damage young roots but innovative products like tolerant seed varieties and seed treatments can minimize injury.

Root-knot nematodes (RKN) are aptly named. As they feed on vulnerable plant roots, sizable galls or “knots” develop on the root system. As RKN populations in a field rise, root galling increases. They negatively impact yields, too. Root-knot nematodes are a scourge to soybeans in the southern U.S. They are a threat to cotton producers in sandy coastal plains along the Atlantic. And they’ve proven to be one of the most damaging cotton pests for Alabama producers. Losses in cotton have been estimated from 10 to more than 75 percent, depending on a range of factors including soil type, weather conditions and also the quality of the cultivar.

Underground Parasites

These soil-borne microorganisms invade plant roots, seeking to establish the crop's vascular system as a specialized feeding site. When they succeed, the cellular makeup of the plant changes, and large knots develop around the feeding site and nematode itself. When infestations become advanced, cotton leaves in particular display what appear to be the symptoms of potassium (K) deficiency, such as interveinal chlorosis and leaf scorching. Often, growers fail to realize that these symptoms are not caused by low K in the soil but by root-knot nematodes outcompeting cotton plants for valuable nutrients. An examination of plant roots will reveal the galling and root swell of a nematode infestation.

Another important characteristic to note is that RKNs often thrive on weed hosts including pigweed, lambsquarter and Johnsongrass. Female RKNs can deposit up to 500 eggs in a gelatinous matrix within the feeding site on the plant root. This is a central means by which RKNs can overwinter.

Control Nematodes and Protect Crops

There are a couple of proven ways to control nematodes. The first is to look for and plant tolerant varieties. Stoneville® cotton seed includes two varieties with tolerance to RKN. ST 5458B2RF is a mid-maturing variety that offers exceptional yield potential across the Cotton Belt. ST 4288B2RF is an earlier maturing variety widely adapted for the West, Southwest, Mid-South, Southeast and Mid-Atlantic cotton geographies. With outstanding seedling vigor and consistent stand establishment, ST 4288B2F can produce excellent yields and fiber quality even in the face of moderate to heavy nematode pressure. Note: Remember that tolerance is not resistance. Resistance means that the plant suppresses the nematode’s ability to reproduce. Tolerance means that the plant can cope with a degree of nematode damage while still producing quality yields.

Seed treatments are another effective way to help minimize nematode damage. Poncho®/VOTiVO® seed treatment combines the most-trusted seed-applied insecticide with the most revolutionary, complete nematode protection on the seed. Labeled for cotton, corn and soybeans, Poncho/VOTiVO employs an innovative biological mode of action to protect vulnerable root systems from parasitic nematodes. This unique bacteria strain actually lives and grows with young roots, creating a living barrier around them that repels predatory RKN.

There are several plant-parasitic species of root-knot nematodes. Talk to your regional Crop Science agronomist or contact your local Crop Science US representative about controlling nematodes on your farm.

Works Cited

  • Riedel, Richard M., and Sally A. Miller and Randall C. Row. "Root Knot Nematode." Ohio State University Extension. Ohio State University. N.d. Web. 28 Sept. 2011. ohioline.osu.edu
  • Mitkowski, Nathaniel A., and George S. Abawi. “Root-knot nematode.” Apsnet.org. The American Phytopathological Society. 2011. Web. 27 Sept. 2011. http://www.apsnet.org/edcenter/intropp/lessons/Nematodes/Pages/RootknotNematode.aspx
  • Westphal, Andreas, and Lijuan Xing. “Diseases of Soybean.” Purdue Extension: Botany. Purdue University Cooperative Extension Service. N.d. Web. 29 Sept. 2011. www.ces.purdue.edu
  • Roberson, Roy. “Root-knot nematodes gaining ground.” SoutheastFarmPress.com. Penton Media, Inc. 9 Jan. 2008. Web. 29 Sept. 2011. http://southeastfarmpress.com/root-knot-nematodes-gaining-ground
  • The Bayer CropScience Family of Sites. Bayer CropScience. Web. 27 Sept. 2011.

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