Root Knot Nematodes and Southern Blight in Soybeans

— Written by Andrea Gibbs | August 23, 2024 (Updated: Aug. 23, 2024, 9:45 a.m.)

Folks,

I have seen a lot of southern root knot nematode (RKN) damage in soybeans over the past month or so! In most cases I am also seeing southern blight in the areas damaged by nematodes. The nematodes have wounded the plants creating an environment for additional pathogens to thrive. Southern blight does not cause significant yield loss and it cannot be controlled with a fungicide.

Fields infected with high root knot nematode populations will have patches of non-uniform stunting, yellowing, and plants that are dead/dying prematurely. If you think you may have an issue with root knot nematodes, pull up some plants and inspect the roots. If you have high populations of root knot you will see galls on the roots.

Now is the time to take nematode samples if you suspect that you have a problem. You want to take the samples before Thanksgiving, as they move deeper into the soil profile as the temperatures cool down. Sampling supplies are available at the Extension office. It is important that you take nematode samples so you can determine what types of nematodes you have so you can plan for the following crop.

Nematodes only move about five feet in a year so if they are spreading, they are hitching a ride on your equipment. If you have nematodes make note what fields you have issues with and plow them last! The best thing you can do is clean your equipment with a 10% bleach solution. If you can't/don't have time at least knock the big chunks of soil off of your equipment before moving to the next field!

Corn, cotton, soybeans, and snap beans are all hosts of root knot nematodes. Wheat is not a host. The best thing you can do is select a resistant variety. Adding RKN resistant varieties into your rotation can help reduce populations as long as the variety is resistant to the species of RKN you have. Southern RKN races 1 and 3 are present in NC. It is important to take nematode samples to ensure that you are selecting the variety with the correct resistance!

If you need assistance sampling don't hesitate to call!