Tomato root knot nematodes can make a gardener's life miserable. Unfortunately, there is little that can be done for existing plants once these creatures have taken hold. If you takes steps to prevent the nematodes in the first place, your tomato plants can be healthy and nematode-free.
Tomato root knot nematodes are minuscule worms that cannot be seen without a microscope. More than 50 kinds of nematodes exist and live in soil all over the world, affecting different kinds of plants. Many of them are harmless, but root knot nematodes are particularly fond of tomato plants.
Female root knot nematodes lay eggs on the surfaces of tomato roots. When the larvae hatch, they burrow into the roots to feed on their juices. As they do, they excrete an irritating solution that causes massive swelling in the roots. These swellings are referred to as knots or galls, and if there are enough of them close together, they may fuse to form one large swelling that looks like a sausage. The roots of severely infected tomato plants have a difficult time taking up the nutrients tomato plants need from the soil.
Root knot nematodes cannot be seen on a tomato plant without digging up and examining the roots. Because all the action happens below ground, gardeners may begin making a diagnosis of root knot nematodes on their tomatoes by noting what happens above ground. Affected plants will look comparatively small and sickly, and may at first appear to have nutrient deficiencies. Because severe knotting on the roots prevents tomato plants from uptake of nutrients, even if they are abundant in soil, poor growth is the result. Gardeners can then dig up the roots of affected plants for examination. Gardeners may also send samples to a laboratory for testing to find out exactly which nematodes have invaded their tomatoes. A local county extension office may be able to run tests or suggest a testing facility.
Root knot nematodes may infest tomatoes without a gardener's knowledge. If the population is small enough, they may not actually cause a noticeable problem. However, by the time a problem has become noticeable, affected tomato plants are usually beyond saving. Any corrective efforts made on a gardener's part should be addressed toward making the garden more suitable for nematode-free tomatoes in coming seasons.
Solarization (using a plastic tarp to heat the soil) is effective, but requires a few months to work effectively. Depending on a gardener's setup, this may be more time than you wish to leave a portion of the garden go unproductive. To solarize, remove all plants from a patch of soil and then water it. Lay a black plastic tarp over the soil to absorb the heat of the sun and heat the soil. Once soil hits 120 degrees F, nematodes in the first 2 inches of soil will be killed.
Incorporating green manure (tilling under of living mulch) and other organic materials such as compost and manure can also help to control the growth of the nematode population in a garden. Rotation of tomatoes, potatoes, peppers and other plants in the Solanaceae family is essential for root knot nematode infection prevention.