The southern root-knot nematode has been a long-term problem for cotton producers in Louisiana. This nematode tends to be found in sandy soils and is very prevalent in production fields near rivers or bayous in our state. Although reniform nematode is the dominant nematode in Louisiana cotton today, root-knot was the most important pest up until about the mid-1980s. Reniform seems to outcompete root-knot and may completely dominant fields where both pests are present.
[Image: root-knot galling]
[Image: cotton showing severe stunting]
[Image: combination of root-knot nematode and fusarium wilt]
Root-knot nematode produces severe damage to cotton. Since it is a soil microorganism, roots are the part of the plant that it attacks. Like most plant-parasitic nematodes, root-knot must feed on a live plant host. Some nematodes such as root-knot produce very specialized feeding structures in the roots of the host plant. These changes in the plant cells produce swelling of the area around the nematode, resulting in galls or knots that are clearly visible on the roots. These galls make identification of the root-knot nematode fairly easy on cotton since nothing else produces these distinct symptoms. Although root-knot nematode is often in only the sandiest areas of a field, it is usually not uniformly distributed in a field and tends to be clustered.
Corn is a popular rotation crop for cotton and does work well in reducing reniform nematode. However, corn is a poor rotation crop when it comes to root-knot nematode and often leaves damaging populations waiting for the next crop such as cotton. There does seem to be a trend toward a resurgence of root-knot nematode in fields planted with corn and where reniform has previously dominated for many years. Producers really need to be careful with rotations and understand exactly which nematode they are managing with the rotation crop.