An unusual disease problem on vinca (periwinkle) arrived in the Plant Disease Clinic least week. Stems of young vinca seedlings in plugs developed water-soaked areas above the soil line, and the tops of these seedlings fell over at the water-soaked point. This description sounds superficially like classic damping-off, in which soil-inhabiting fungi such as Pythium attack the roots and lower stem of seedlings, causing withering and collapse. The difference is that these vinca showed no problems at the soil line or in the roots; the affected areas were an inch or more above the soil line. After a day or two in a moist chamber, the affected stems were covered with Botrytis cinerea, a ubiquitous fungus in greenhouses that commonly colonizes dead tissue and attacks live plants through wounds, especially under prolonged high-humidity periods. Dr. Chuck Powell of Ohio State University, an authority on greenhouse diseases, indicated that he has seen this Botrytis blight on vinca several times during the past two years. Dr. Powell recommends spraying Daconil 2787 or Chipco 26019 to control the problem. These fungicides should be used in preference to Ornalin, which can cause phytotoxicity problems, or Cleary's 3336, which is subject to resistance by certain strains of B. cinerea.
This article originally appeared in the May 6, 1992 issue, p. 75.