Root knot nematodes (RKN) can give farmers headaches in multiple different crops. They can be particularly problematic in vegetable crops because of their high value. RKN’s can be difficult to diagnose when looking at the above ground portions of the plants. Usually their symptoms mimic water or nutrient stress. The photo below shows a row of tomatoes that are wilted in some spots even though they are being watered properly.
The two photos below show the effects of RKN on the roots. You can see a single root knot in the first picture and a severe infestation in the second picture.
RKN cause stress to the plants by inhibiting their ability to take up water and nutrients. This particular nematode burrows into the root as a juvenile and causes a physiological response in the plant that makes the roots swell around them. The nematode feeds on the root as it matures within it. Below is a badly infected root.
RKN are best controlled preemptively. Fumigation is the most common practice, though there are a number of cultural methods that can be done like proper crop rotation and thorough tillage. Soil samples may be taken to look for nematodes (different than standard nutrient test), however juvenile RKN can be difficult to find in such a sample. A root sample should be submitted if RKN is suspected. The table below shows the fumigation options available to vegetable producers.
This table along with more info on nematode control in vegetables can be found on pages 228-231 of the SE Vegetable Crop Handbook.