Root Knot Nematodes are microscopic, unsegmented worms that injure root tips by causing knots or galls in plant tissue when their feeding releases toxins and bacteria. In addition, they can cause roots to branch excessively or galls to form on leaves with or without twisting or distortion. The plants most commonly attacked by root knot nematodes are carrots, corn, tomatoes, okra, peppers, lettuce, onions, rye, alfalfa and chrysanthemums. Galls caused by root knot nematodes can be identified because they split open easily and the decayed tissue is obvious. Other signs of root knot nematodes are that the infested plant will appear wilted and its growth stunted as the galls reduce water and nutrient uptake.
Root knot nematodes can be controlled with least-toxic methods through plant rotation, by using a high quality compost, solarizing the soil (moisten the garden soil and cover it with clear plastic mulch during the summer months - the heat generated will kill the nematodes) and by the planting of marigolds or mustard as a cover crop.