Cause Paratrichodorus renifer. Stubby-root nematodes are migratory ectoparasites, and therefore found only in soil. This nematode is commonly found in blueberry plantings throughout the PNW but more frequently in Washington and British Columbia. This nematode has been shown to seriously damage blueberry cuttings by severely stunting the young root system. In microplot experiments, this nematode caused 40% yield loss of blueberry 'Chippewa.'
Symptoms Roots are extremely short with yellow to brownish cast; plants are stunted. Root tips become darker, stubby, and more branched.
Sampling These nematodes are found only in soil. Before planting, take soil samples with sufficient lead-time to implement management procedures if necessary. Fall sampling prior to fumigation for blueberries to be planted the following spring is an excellent strategy. The best way to collect soil samples is with a soil probe inserted to a depth of 12-18 inches. Remove the top few inches of mulch before putting the subsample into the bucket. Each probe-full of soil constitutes one subsample. Collect at least 20 to 30 subsamples for every 1 to 4 acres. Fields larger than four acres should be divided into sections, with separate nematode samples taken from each section. The subsamples should be drawn from sites chosen randomly throughout the field, usually by walking in a "W" pattern, and then mixed together in a clean bucket. Areas with different soil types or cropping histories should be sampled separately.
Cultural control
- Plant in fields with low population densities.
- Fallow the year prior to planting. Diligently control broadleaf weeds during the fallow year to eliminate possible hosts.
- Remove diseased plants and fumigate infested area.
Chemical control At this time there are no products with proven postplant efficacy registered for use on blueberry. Preplant assessment of nematode levels is necessary to determine if preplant fumigation is required. Soil fumigation allows young blueberry plants to become well established while nematode populations are low.
- Basamid G. Avoid application when soil is over 90°F. Do not apply within 3 to 4 feet of growing plants or closer than the drip line of larger plants. Do not harvest within one year of application. 5-day reentry Restricted-use pesticide.
- Dominus at 10 to 40 gal/A. Apply as a shank injection to an entire field or raised beds when soil temperatures are above 60°F but not greater than 90°F. 5-day reentry.
- Telone II at 27 to 35 gal/A broadcast on mineral soils in the fall before spring planting. Leave the soil undisturbed for at least 7 days after application. A longer interval, such as 2-3 weeks, is required if soils are cold or wet, or the site will be replanted with deep rooted trees, shrubs or vines. Odor indicates fumigant presence; do not plant until odor leaves the soil. Do not treat extremely heavy soils. 5-day reentry. Restricted-use pesticide.
Biological control
- MeloCon WG (Paecilomyces lilacinus strain 251) at 2 to 4 lb/A plus a soil wetting agent can be applied to established plants, although it might be better used when applied to plants just before planting. Stable for only days at room temperature, weeks in the refrigerator or for a year if frozen. Unknown efficacy in the PNW. 4-hr reentry. O
References Zasada, I.A., Pinkerton, J.N. and Forge, T.A. 2010. Plant-parasitic nematodes associated with highbush blueberries (Vaccinium corymbosum) in the Pacific Northwest of North America. International Journal of Fruit Science 10:123-133.
Forge, T.A., Koch, C., Pinkerton, J.N., and Zasada, I.A. 2009. First report of Paratrichodorus renifer, a nematode parasite of highbush blueberry. Phytopathology 99:S35.