Cause Nematodes are a big problem in the production areas of California but have not been investigated as a problem in the Pacific Northwest. Soil types, that are sandier, generally result in more nematode injury at lower population levels. Host ranges are wide for many of these nematodes making crop rotation impractical.
In the PNW, root-lesion nematodes, Pratylenchus spp., are common followed by root-knot nematodes, Meloidogyne spp. Pratylenchus spp. are migratory endoparasites that feed inside roots, tunneling inside and moving back into soil and to new roots at will. They tend to cause simple growth reductions of tops and roots. No symptoms may occur other than that plants appear smaller than expected. This type of damage is difficult to diagnose unless the soil is examined for nematodes, because it could be due to a nutrient problem or some other cause.
Meloidogyne spp. are sedentary endoparasites that tunnel into the roots, establishing permanent feeding sites from which they do not move. They may protrude from roots as they grow. The result can be a reduced root system, changes in root structure due to much swelling and galling, hairy-root conditions due to stimulation of lateral branching of the root system, and reduced tops.