Nematodes & Tomato Plants

• Nematodes, also called roundworms, are a microscopic type of worm that can infest tomatoes. They are parasitic worms, and eat the roots and leaves, doing damage to the tomato plants and reducing crop yields. They damage they cause also makes tomato plants vulnerable to secondary infections of fungus, bacteria or viruses.

Root Gall

• Meloidogyne nematodes, or "root knot" nematodes, feed on the roots of tomato plants. Nematodes lay their eggs in the tomato's roots, and by the end of the growing season there can be enough nematodes to severely damage the plant. The infection of nematodes causes swellings, or "galls," on the roots of the plant. Symptoms of root knot nematode infestation, aside from the galls, include stunted growth, yellowed leaves, fewer tomatoes produced, smaller tomatoes produced and rotted roots. Infected plants will usually be found grouped together, rather than as part of a decline over the whole field.

Resistant Varieties

• There are several varieties of tomato plant that are resistant to root knot nematodes. Planting them in infected soil will lower nematode populations to under dangerous levels, according to the University of Arkansas Division of Agriculture. Nematode resistant tomato varieties include anahu, atkinson, big beef, champion, empire, monte carlo, nemared, nemato, red october, sugar snack, super beefsteak and winter red. The "N" on packets of tomato seeds, usually seen in "VFN," means that that species is nematode resistant.

Root Lesions

• Pratylenchus nematodes infect the root systems of tomato plants as well. They cause tears, or lesions, in the roots of the tomato plants that they infect, causing damage to them and impairing growth. The lesions caused by these nematodes have turned brown.

African Marigolds, Tomatoes and Nematodes

• Planting African marigolds two weeks before planting tomatoes has been shown to reduce root lesion nematode damage by 99 percent, according to Martin Guerena, agricultural specialist for the National Center for Appropriate Technology. This is because these flowers produce polythienyls, which are chemicals that suppress root lesion nematodes, as well as other species.

Soil Additives

• Soil that has had ground parts of the neem tree or chinaberry tree added to it inhibits the infection of tomato plants by root knot nematodes. Farmers in India have used products of the neem tree as natural pesticides for hundreds of years. Soil that is just 1 percent "neem cake" showed a 67 to 90 percent reduction in the number of both root knot nematodes and root lesion nematodes.