Pacific Northwest 1998 An Online Guide to Plant Disease Control

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OSU Extension Office
 
Phlox -- Nematode, Stem
 
Cause: The nematode, Ditylenchus dipsaci, enters through natural openings, such as stomata, of young shoots and through wounds. It lives and feeds inside of the stem, moves upward as the shoot grows, and can exist underneath the seed coat of seeds. The nematode can infect many hosts. Movement and reproduction rates are high at temperatures between 69 and 77°F. The nematode can be spread via contaminated soil or media, water, garden tools, shoes, and infested seed. The larval stage of this nematode has the capability to survive several years in a dry state, termed anabiosis. The problem has been diagnosed a few times by the OSU Plant Clinic.
Symptoms: Abnormal growth is a common symptom. Leaves may be curled and/or wrinkled but normal width or be spindly to thread-like. Stems may be swollen near the tops while basal buds exhibit a stimulated growth. Plants can be stunted, fail to bloom, and die prematurely. Phlox varieties are not equally susceptible, and some varieties seem to be immune.

Notice the necrotic leaves and twisted stems.

Under a microscope these leaves would been teeming with foliar nematodes.

 
Cultural control:
  1. Use clean plant material for propagation.
  2. Infested plants should be immediately removed and destroyed.
  3. In the landscape, the soil should be replaced or sterilized before planting susceptible hosts back in the same site.
Chemical control: No chemicals are labeled to treat greenhouse plants infected with stem and foliar nematodes. Basamid G is labeled for the treatment of potting soils, seed and propagating beds, and soil media before planting, but not labeled for treatment once ornamental plants are planted in the soil or media.
References:
Pirone, P. P. 1978. Diseases and pests of ornamental plants, 5th ed. John Wiley & Sons, New York, NY. 566 pp.
Content edited by: Warren Copes on January 1, 2010
 
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