Nematodes are very tiny, microscopic worms that mostly live in soils, although foliar nematodes live in leaves. While some species harm plant roots, others are beneficial by attacking and killing pests.
Root-knot nematodes (Meloidogyne spp.) are tiny creatures that feed on the roots of plants and can cause various types of damage. These microscopic worms cause gall growth or swelling to occur. Once plant roots are affected by nematodes, they become weak and fungi and bacteria cause even further damage.
Symptoms: Typical root symptoms indicating nematode attack are root knots or galls, root lesions, excessive root branching, injured root tips and stunted root systems. Symptoms on the above-ground plant parts indicating root infection include poor growth, yellowing or bronzing of the foliage, loss of leaves, stem die back and failure to respond to fertilizer due to root damage. Eventually, the entire plant will die. Nematode-damaged plants usually show poor quality over a period of several years before death. Nematodes can pierce the roots of certain plant species and lay their eggs inside the roots. This gives the roots a “knotty” appearance and results in a wilted or stunted appearance of the whole plant. Root-knot nematode problems can be detected by examining the roots for the conspicuous root galls (swellings). You can also send samples of root and soil to a nematode-testing lab for evaluation.
Photos: Scott Bauer,
Spread: Parasitic nematodes are readily spread by any physical means that can move soil particles about—equipment, tools, shoes, birds, insects, dust, wind and water. In addition, the movement of nematode-infested plants or plant parts will spread the parasites.
Cultural control: Avoid planting highly susceptible plants. Ornamental plants such as azaleas, camellias, yaupon holly, nandina, oleander and others are resistant. Use only nematode-free nursery stock for planting. In most countries, government nursery inspectors will condemn and destroy any nursery stock showing evidence of nematode infestation. In nursery operations, use benches raised off the ground and pot plants only into pasteurized soil mixes. Keep containers, bins, benches and flats clean. Fumigate outdoor growing fields where nursery stock will be grown. Rotate crops to control certain nematodes. Where the crop value is too low to justify large-scale soil fumigation, crop rotation is the only practical method of nematode control. Use cover crops that reduce nematode damage. Cover crops can improve soil structure and fertility, decrease soil erosion, be used as animal feed, and suppress weeds, insects and pathogens. Examples of cover crops that have been shown to suppress nematodes include cowpea, rapeseed, velvet bean and sudangrass.
