Nematodes, also known as eelworms, make important contributions to garden soil's composition. Many of the minuscule, sightless, eel-shaped organisms are beneficial, preying on insect pest larvae and even other, detrimental nematodes. The bad sorts, like root knot and stubby root nematodes, pierce the roots of vegetable plants to suck out nutrients or to lay their eggs inside, causing knots to form. More than one species of the parasitic worms may be present in a garden area.
At first, symptoms can mimic those of overwatering -- plants appear stunted and foliage turns yellow. Wilting in the midday sun often seems more severe than usual, and fruit production will decline. The plants' roots may be heavily damaged before above-ground symptoms become apparent. Nematode-infested root systems are subsequently more susceptible to fungal infections, such as fusarium and verticillium wilt, that sometimes inhabit the garden soil. If your vegetable plants exhibit any of these signs, pull a plant up and inspect the root system. If you see knobby growths or the deep roots have disintegrated, leaving only a tangle of surface roots, destructive nematodes have probably been at work.
Widely planted home garden vegetables such as tomatoes, bell peppers, hot peppers, cucumbers and sweet potatoes are often targeted by the mooching nematodes. In gardens with sandy, moist soils in warm climates, the vegetable plants become even more attractive to the eelworms. Then, because plants with damaged roots quickly suffer water stress under these conditions, they deteriorate. Root knot nematode-resistant pepper varieties have been developed. "Charleston Belle" and "Carolina Wonder" are notable bell pepper examples, while "Carolina Cayenne," a hot pepper, also resists these pests. Any vegetable plants that carry a "VFN" classification have been developed to avoid nematodes, as well as fusarium and verticillium wilt. Main season tomato varieties that bear this seal include "Better Boy," "Celebrity," "Champion" and "Champion II."
Natural Nematode Management
Uniquely among the vegetables susceptible to nematode attack, tomatoes can be protected by companion planting with asparagus, which emits a natural nematocide. Marigolds and dahlias reportedly discourage the tiny nuisances when they're interplanted with garden vegetables. If a nematode infestation remains confined, crop rotation may be enough to deter the problem. Soil solarization -- placing plastic sheets over the surface and allowing the summer sun to raise the soil temperature to a level that kills the nematodes -- is another natural remedy you can try.
For severe infestations that do not respond to natural treatments, remove the root systems of suspect plants and seal them in double plastic bags, along with some of the soil. Contact your county cooperative extension office to find out where to get your plant specimens tested. Complete soil fumigation may be necessary to control your nematode problem, but this can only be done by a professional who's certified to use the pesticides required.
- Sunset Magazine: Nematodes
- Carrots Love Tomatoes; Louise Riotte
- University of California Integrated Pest Management: Nematodes
- University of California, Marin Master Gardeners: The Case of the Curious Pest
- Vertical Vegetables & Fruit; Rhonda Massingham Hart
- Jupiterimages/Photos.com/Getty Images