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Blueberry Pests – Nematodes

Nematodes are unsegmented roundworms that may be found in nearly every habitat on earth. Some species are free-living in soil or freshwater or marine systems, while others are parasites of plants or animals, including man. Free-living species and insect parasites may be beneficial, but plant and animal parasites are often serious pests. Nearly 3,000 species have been described as parasites of plants.

The dominant plant-parasitic nematodes found on blueberries in the Pacific Northwest include root-lesion (Pratylenchus spp.), dagger (Xiphinema spp.) and stubby-root (Paratrichodorus spp.). Adult root-lesion nematodes are 0.02 inches long, stubby-root nematodes are 0.04 inches long, and dagger nematodes are 0.09 inches long, so they are rarely visible to growers. Special laboratory procedures are required to isolate nematodes from soil or roots and correct identifications must be made by trained professionals.

All plant parasitic nematodes feed by puncturing plant cells with their stylet (a structure resembling a hollow needle) and sucking out the material within the plant cell. Dagger and stubby-root nematodes feed as ectoparasites with their bodies remaining outside the root and only their stylets penetrating the cells of the roots.

Dagger nematodes may cause damage directly to roots if present in high numbers, but are most important as vectors for the tomato ringspot virus. Blueberry plants infected with tomato ringspot virus will display malformed (strap-shaped) and chlorotic leaves and necrotic, circular lesions on stems (see Diseases Virus and Virus-like Diseases). Small populations of these nematodes can cause serious loss where the virus is present, spreading it from plant to plant and from infected weeds to blueberry plants.

Stubby-root nematodes have been shown to seriously damage blueberry cuttings by severely stunting the root system.

Although damage to healthy, established blueberry plants has not been documented, nematodes can stunt the growth of young blueberry plants. Larger plants may be susceptible to damage if also stressed by other factors that limit root growth.

Root-lesion nematodes feed as migratory endopara