Cause Tylenchorhynchus claytoni. The nematode has been found in Oregon azalea and rhododendron plantings, primarily in nursery stock. Rhododendron indicum 'Formosa' was found to be tolerant of the nematode, but R. obtusum 'Hershey Red' was stunted. The nematode attacks the feeder roots. Stunt nematodes are migratory ectoparasites and found only in soil. Therefore, send only a soil sample for nematode analysis. Samples may be taken any time of the year in a greenhouse environment.
Symptoms General stunting, poor root system, yellowing (off-color) of tops may be observed. Affected areas in a field planting are often circular.
Cultural control
- Good horticultural management (such as proper fertility and watering) will aid the plant's ability to tolerate high nematode numbers.
- Use a soilless potting media for greenhouse grown crops.
Chemical control Preplant soil fumigation the fall before spring planting.
- Basamid G. Avoid application when soil is over 90°F. Do not apply within 3 to 4 feet of growing plants. 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 52 to 103 fl oz/1,000 ft of row using a single chisel per row on mineral soils. 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.5-day reentry. Restricted-use pesticide.
- Vapam HL at 37.5 to 75 gal per treated acre in enough water to soak at least 2-inches deep. May be drenched on beds or rows preplant followed by a method to seal or cover the treated area. Can also be used to treat soilless media. See label for details specific to your application. Restricted-use pesticide.
Reference Benson, D. M. and Barker, K.R. 1985. Nematodes-a threat to ornamental plants in the nursery and landscape. Plant Disease 69:97-100.