Meloidogyne species The Root-Knot Nematodes   Damage to Corn.   Because of the world-wide distribution of the root-knot nematodes and the damage they are known to cause,  these nematodes must be ranked as important disease producers in corn. Biology.   There are at least 6 Meloidogyne species which affect corn roots. The female is usually pear-shaped, with a fragile white cuticle, and may be up to 2 mm in diameter. Ecology.   Root-Knot nematodes are distributed world-wide. Symptoms.   Symptoms of corn infection by Meloidogyne spp. vary with the species, but generally include stunting and chlorosis.  Numerous root galls are noted in infected plants,  proliferation of fibrous roots may also be present. Damage to other crops.   Tomato plants are also damaged by root-knot nematodes. Control.   Good control of some species has been obtained with chemicals- with fumigants generally giving better control than granular nematicides.