Root-knot nematodes are plant parasitic microscopic roundworms. Root-knot nematodes are one of the most destructive plant-parasitic nematodes and can cause extreme agricultural damage. Plants that are especially vulnerable to root-knot nematodes include tomatoes, eggplant, watermelon, soybeans and bell peppers. A root-knot nematodes life cycle includes 6 stages: an egg state, 4 immature stages, and an adult stage.