Nematodes are microscopic, eel-like roundworms. The most troublesome species in the garden are those that live and feed within plant roots most of their lives and those that live freely in the soil and feed on plant roots.
Although California has many different species of root-feeding nematodes, the most damaging ones to gardens are the root knot nematodes, Meloidogyne species. Root knot nematodes attack a wide range of plants, including many common vegetables, fruit trees, and ornamentals. They are difficult to control, and they can spread easily from garden to garden in soil on tools and boots or on infested plants.
A number of other nematode species also can damage home garden and landscape plants including the ring nematode (Criconemoides xenoplax), root lesion nematodes (Pratylenchus species), the sugarbeet cyst nematode (Heterodera schachtii), the citrus nematode (Tylenchulus semipenetrans), the stem and bulb nematode (Ditylenchus dipsaci), and others." (E. J. Perry, A. T. Ploeg, 2010)University of California Statewide IPM Program
Root-knot nematodes begin their lives as eggs that rapidly develop into J1 (first-stage juvenile) nematodes. The J1 stage resides entirely inside the translucent egg case, where it molts into a J2 nematode. The motile J2 stage is the only stage that can initiate infections. J2s attack growing root tips and enter roots intercellularly, behind the root cap. They move to the area of cell elongation where they initiate a feeding site by injecting esophageal gland secretions into root cells. These nematode secretions cause dramatic physiological changes in the parasitized cells, transforming them into giant-cells. If the nematode dies, so will the giant-cells upon which it feeds. Mitkowski, N.A. and G.S. Abawi. 2003. Root-knot nematodes. The Plant Health Instructor. DOI:10.1094/PHI-I-2003-0917-01
Recommended controls for nematodes
Each control will have its own set of parameters that will be best suited for individual environments. Certain controls may only be available for commercial application.
Commercial farmers are required to reference their own state laws to ascertain if the recommended controls fall within compliance of their states regulatory guidelines.
MECHANICAL AND PHYSICAL CONTROLS
Management of nematodes is difficult. The most reliable practices are preventive, including sanitation and choice of plant varieties. You can reduce existing infestations through fallowing, crop rotation, and soil solarization. However, these methods reduce nematodes primarily in the top foot or so of the soil, so they are effective only for about a year. They are suitable primarily for annual plants or to help young woody plants establish. Once nematodes infest an area or crop, try to minimize damage by adjusting planting dates to cooler times of the season when nematodes are less active. Try to provide optimal conditions for plant growth including sufficient irrigation and soil amendments to make plants more tolerant to nematode infestation.