Nematodes on Tomato Roots

Many tomato varieties are highly susceptible to nematodes.

Tomatoes are easy to grow and very popular. Unfortunately, they are often plagued by a host of garden pests, which can make an easy-to-grow vegetable more trouble than it may be worth. Tomatoes are a favorite food of the nematode. Nematodes thrive in the same soil conditions as tomatoes and live in the root system. They are minute (about 0.5 millimeters in length), worm-like animals that feed on the root juice of plants. Their presence causes root knots, or "galls," to form, which prevent nutrients from reaching the plant.

Nematodes

The University of Missouri Extension identifies nematodes as the most damaging pest in the home garden. Endoparasitic nematodes spend their lives within plants. Under a microscope, they look like tiny worms. Their eggs move through the soil to invade the roots near the tip. The females are spherical-shaped.

Symptoms

The nematodes' presence in the root system is an infection, and the roots respond by forming galls. Galls may be mistaken for nodules, which are an indication of beneficial bacteria, and commonly attached to the side of the root. If you pull out the plant and inspect its roots, the galls are immediately recognizable. The size of the galls will indicate the degree of infestation: large galls signal a severe nematode problem. Other symptoms include stunting, yellowing and wilting and death in hot weather. Infected plants may wilt readily even when the soil moisture is adequate.

Soil

The Department of Plant Industries of Queensland, Australia explains that nematodes are aquatic creatures. They require a water film around soil particles before they can move, and, unfortunately, the soil moisture that is optimum for plant growth also supports nematodes. The greatest damage occurs in warm sandy soils. Hot, dry soil is inhospitable to nematodes; under those conditions they will desiccate and die.

Treatment

Commercial tomato growers have access to nematicide, a highly toxic pesticide that home gardeners do not have access to. Crop rotation and soil cultivation eliminate available food for nematodes by controlling weeds and eliminating their favorite foods. Planting resistant varieties of tomatoes, certain grasses and onions (all of which are resistant) will keep them at bay. The University of Florida Extension recommends planting grasses or brassicas after a tomato harvest, followed by onions, followed by leaving an area fallow, especially during a hot, dry season.

Prevention

Prevention is the best medicine for the home gardener. Nematodes are often introduced to your soil from outside. Inspect any new plants for nematode infestation: look for galls before you plant. If you have had nematodes in the past but have avoided a certain garden patch for a while, have your soil tested for nematodes before planting. Avoid moving infested soil, whether on your shoes or on garden tools and burn all tomato roots at the end of the season. Add organic matter to your soil in the form of compost or manure. It will provide plants with the strength and nutrients they need to fend off a nematode attack.

References

• Queenland Government, Australia: Tomato root knot nematodes: Biology and control
• AVRDC: Root-Knot Nematode on Tomato
• University of Florida Extension: Nematode Management in Tomatoes, Peppers and Eggplant
• University of Missouri Extension: Managing Nematodes in Gardens