By Charles Overstreet (Nematologist)
Both the Southern root-knot and reniform nematodes are beginning to show damage to cotton in Louisiana this year. Fields which have high levels of either nematode early on are the ones that are showing these symptoms.
The typical symptoms of nematode injury are short, stunted plants in either small to large areas within a field. Root-knot nematodes may be visible on the roots because they form galls on the roots in association with their feeding. Reniform is not easily visible without some magnification and cannot usually be identified in the field. Root-knot nematodes are almost always associated with sandy, coarse textured soils while reniform nematode is found in both coarse and fine textured soils.
Since many of our producers are rotating corn with cotton, be particularly aware that corn is a very good host for root-knot nematode and doesn’t reduce populations of this nematode very much. Corn is a great rotation crop to reduce the reniform nematode. However, populations of this nematode may be so high in many fields that it would take at least two years in corn to adequately reduce the populations to an acceptable level. Both of these nematodes may cause problems after only one year of corn.
Soybean is another popular crop that may be included in a rotation with cotton. Most soybean varieties are susceptible to reniform and Southern root-knot nematodes. Rotation of cotton behind soybean can result in severe damage as well.
Unfortunately, there is not a lot that you do if you are seeing nematode problems showing up now. Try to avoid any additional stress such as drought may be of some benefit. Remember these fields in the future and try to incorporate some rotation plan that may be helpful.