Root Rot Nematodes

Root-rot nematodes are from the genus Meloidogyne, and thrive in hot climates with short winters. They are not host-specific, and infect the roots of a wide host range, including flowers and vegetable crops (tomato, green pepper, corn, grains, and so forth). They are sedentary endoparasites—living and feeding from within their hosts.

Females lay their eggs in a gelatinous mass on a root gall surface; ensuring a protective, moist environment in which the eggs develop. The first molt occurs within the egg (J1 stage). After the eggs hatch, the second-stage juveniles (J2) are motile. They leave the egg; penetrate the root with their stylets, just behind the root cap; and secrete a liquid that stimulates growth hormones in the cells, causing them to divide and swell. This forms root galls that become permanent feeding sites. After molting through two more juvenile stages, (J3 and J4), reproductively mature females lay a new batch of eggs. This lifecycle occurs over the course of several weeks, so, in the right environmental conditions, plants can become infected very quickly. If the galls become separated from the roots, the eggs can exist in the soil for years, until the right conditions and a suitable host are available.

Galls on carrot from root-rot nematode. Photo by Claudia Nischwitz.
Copyright, ASPnet.

Above ground, plants exhibit symptoms that are similar to any disease that harms the root system, including stunted growth, wilting, and yellowed leaves. Reduced crop yield also results. To help with diagnosis, it is necessary to have the soil analyzed and to check the roots for galls, if at all possible.

For management tips, see the Integrated Pest Management (IPM) site. Since the eggs can remain in the soil for years, management is difficult. The solution is prevention – using resistant plant varieties; rotating crops so the nematodes cannot continue their lifecycles from season to season; leaving soil fallow periodically; amending the soil to keep it healthy; planting when nematodes are less active; and keeping infected plants or material from contaminating uninfected areas. Soil solarization, the process of heating the top 8 - 12 inches of the soil, can temporarily reduce the nematode population. Currently no chemical or soil fumigants are available to the home gardener.