Cause Ditylenchus destructor, a nematode that lives in soil and can be carried in bulbs. The disease has been found in a few dahlia cultivars: Brandaris, Pop Harris, Oakleigh Champion, Gold Rose, K.S. Snowball, Mary Elizabeth, and Kidd Climax. Probably all cultivars are susceptible. The nematode has occurred infrequently, probably from the introduction of infested dahlia tubers.
Symptoms No aboveground symptoms or unusual growth behaviors are associated with affected plants. The cortex of most affected roots usually is roughened in some manner. Roughening greatly hinders an early detection of superficial necrosis that may be the result of any initial infection. Any area with unusually transverse longitudinal cracking, or showing evidence of cortex flaking or sloughing, should be regarded with suspicion. In advanced stages, infected tissues discolor brown to black. The progressive breakdown is a dry granular type. Apparently the infection will progress slowly in storage until the root is nearly destroyed.
Sampling Sampling specifically for this nematode before planting dahlias probably is not necessary unless there has been a history of potato-rot symptoms in the area. Soil samples alone should be sufficient. If this nematode is suspected in dahlias, submit both tubers and soil for testing.
- Select clean planting stock. Purchase from a reliable nursery.
- Destroy infected bulbs and debris.
- Use at least a 2-year rotation.
- Do not plant in infested soil.
Chemical control Preplant soil fumigation.
- Telone II is registered at various rates depending on planting depth and soil type. See label for details. 5-day reentry. Restricted-use pesticide.
Reference Jensen, H.H., Smithson, H.R., and Loring, L.B. 1958. Potato-rot nematode, Ditylenchus destructor Thorne, 1945, found in dahlia roots. Plant Disease Rept 42:1357-1358.