Cotton Nematode Management

By Wade Parker

Many growers have noticed large problem spots or streaks in their cotton fields. The plants start turning yellow, bronze, brown, and start to shed their leaves. This problem is usually  two issues, some type of leaf spot disease or nematodes. In some situations, it is both.

Let’s discuss nematodes. Nematodes damage cotton by attacking the young tap and secondary roots. Their feeding stimulates the production of galls. These galls interfere with the roots’ ability to absorb water and nutrients. Root galls are the only distinctive symptoms of root knot nematode injury on cotton plants. Above ground, infested plants have a nonspecific poor growth appearance.

The only true way to determine whether you have nematodes or not, is to soil sample. Not only does sampling determine if you have nematodes, it also determines what species are present. It is very important to determine the species so proper management can be implemented. The time to sample is now!! This time of  year we always concentrate on defoliating cotton, blasting peanuts, and getting harvesting equipment ready. Nematode sampling gets put on the back burner.

Nematode Sampling Procedure

Nematodes are highly detectable in early fall. They are undetectable during the winter and early spring but often increase to a very high population density in the early fall when living roots are present. Make sure your sample is representative of the field. Collect soil from around the field rather than from only one or two spots. Nematodes samples should be taken at the 6″-8″ level in the root zone of the plant. Once samples have been taken, keep them in a cool dry place. Do not waste time or forget about them, bring them into the Extension Office ASAP.

Management

Once you know what species and the severity of a nematode population, there are a few options available. Crop rotation is very effective. For example, rotating cotton with peanuts will reduce the southern root knot nematode population. There are a few cotton varieties available that are tolerant or resistance to nematodes. These varieties should only be planted where a known nematode population exists, as the yield potential of these varieties is still being researched. There are also a few chemical treatments that either suppress or control nematode populations.

This image shows a small patch of unhealthy, nematode infested cotton. Notice the healthy cotton bordering the problem area. Nematode populations are usually higher in sandy or lighter areas of the field.

Even though it maybe hard to see, these roots have small galls on the ends and in the middle parts of the roots. This plant also does not have a healthy tap root.

This is a close-up version of above ground symptoms of nematode infested plants.

Source:uga.edu