Control of Root-Knot Nematodes in the Home Vegetable Garden

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Nematodes–especially root-knot nematodes–cause major losses in vegetable crops in commercial farms, greenhouses, and home gardens in North Carolina. Root-knot nematodes are microscopic roundworms that can pierce the roots of certain plant species and lay their eggs inside the roots. This gives the roots a “knotty” appearance (Figure 1 and Figure 2) and results in a wilted or stunted appearance of the whole plant. Meloidogyne incognito, the southern root-knot nematode, is most common in North Carolina, but other species have been found recently. These pests occur in about two-thirds of the fields used for crops in the state.

Although many spring-planted vegetables such as beets, carrot, English pea, lettuce, potato, radish, and others are susceptible to root-knot nematode, they can be grown in infested soil and suffer only minor damage because nematodes are inactive at low soil temperatures (60°F). However, these same vegetables can suffer extensive damage when planted in the late spring, summer, or fall when soil temperatures are more suitable for nematode activity (70–85°F). Other common garden vegetables grown during mid- to late summer, such as tomato, pepper, cucumber, squash, eggplant, and okra also are highly susceptible to root-knot nematode.

Plants growing in nematode-infested soils usually are unthrifty, stunted, yellowish, and have galled and decayed roots. Plants with infected roots are more susceptible to other diseases caused by fungi and bacteria and tend to stop producing early. Root-knot nematode problems can be detected by examining the roots of vegetables for the conspicuous root galls (swellings) as soon as harvest is completed or through a soil assay. Crop losses due to these nematodes can be greatly reduced by using available control practices. However, control steps must be taken before planting or seeding. Once the nematodes are inside the roots, effective treatments are not available. This publication describes ways to minimize nematode problems by employing one to several control measures. The most reliable control of root-knot nematodes can be achieved by integrating two or more of the tactics described herein. Combining an effective rotational scheme, resistant varieties, and selected cultural practices gives excellent control with little added cost.

Inga Meadows
Charles Averre
Harry Duncan
Kenneth Baker
North Carolina Cooperative Extension