Root-Knot Nematodes

Garden pest · Meloidogyne spp.

Description

Root-knot nematodes are microscopic roundworms that live in soil and feed inside plant roots. Several species in the genus Meloidogyne attack vegetables, ornamentals, and other garden plants. Juveniles enter young roots and establish feeding sites that cause the surrounding tissue to swell into characteristic knots, or galls. Damaged roots absorb water and nutrients less effectively, so plants may grow slowly, yellow, or wilt during warm weather even when the soil is moist. Severe infestations can reduce flowering and harvests, especially in sandy soils and warm climates. The nematodes spread in infested soil, transplants, and water that moves soil from one place to another. Their eggs can remain in soil or infected roots between crops. Root-knot nematodes do not usually kill an established plant quickly; instead, damage builds as their populations increase over a growing season.

Symptoms

• Galls or swellings
• Stunted growth
• Yellowing leaves
• Wilting

How to Identify

Lift a struggling plant gently and wash soil from its roots. Look for firm, irregular swellings that are part of the root itself, often on fine or branching roots. Above ground, uneven growth, yellowing, and daytime wilting are clues but are not diagnostic: drought, poor nutrition, and root disease can look similar. Root rot usually leaves roots dark, soft, or decayed rather than firm and knotted. On legumes, beneficial nitrogen-fixing nodules are generally distinct bumps that can be detached from the root; root-knot galls are integrated into it. For a definite identification, submit roots and surrounding soil to a plant diagnostic laboratory.

Prevention

Start with healthy transplants and clean potting mix; inspect roots before planting. Avoid moving soil from affected beds on tools, shoes, or plants, and clean equipment after working there. Remove infected roots after harvest rather than leaving them in the bed. Where available, choose varieties labeled resistant to root-knot nematodes; resistance may apply to particular nematode species, so check local guidance. Rotate susceptible crops with crops confirmed to be poor hosts for the species in your garden. Because these nematodes have many hosts, rotation without a suitable crop may offer little benefit. Manage weeds that can harbor them. Add organic matter and keep plants adequately watered and nourished to help them tolerate damage, although these measures will not eliminate the pest.

Treatment

There is no reliable way to cure roots that already have galls. First, keep affected plants evenly watered and mulched to reduce stress; remove badly affected annuals, including their roots, when practical. Do not move their soil to clean beds. For the next planting, use resistant varieties or a suitable nonhost crop. In a sunny, hot season, soil solarization can reduce nematode numbers in an empty bed: moisten the soil, cover it tightly with clear plastic, and leave it covered for about four to six weeks during the hottest weather. Results depend on climate and soil depth, and nematodes may survive below the heated layer. Replant with clean transplants and avoid disturbing untreated soil. Commercial nematicides may be available for certain crops and locations, but they can be hazardous and are often restricted to licensed applicators. Consult a local extension service before considering one.

Plants Affected

Arborio Rice, Arrowroot, Banana, Basmati Rice, Bhutanese Red Rice, Bitter Melon, Black-eyed Pea, Bottle Gourd, Carrot, Cassava, Chayote, Fig, Ginger, Guar Bean, Indica Rice, Jasmine Rice, Lablab Bean, Lima Bean, Okra, Plantain, Purple Rice, Rice, Ridge Gourd, Sushi Rice, Sweet Potato, Turmeric, Ube, White Rice, Winged Bean, Yam, Yardlong Bean

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