Pacific Northwest 1998 An Online Guide to Plant Disease Control

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OSU Extension Office
 
Poinsettia -- Gray Mold
See Also: Greenhouse Plants, Ornamental -- Gray Mold
 
Cause: Botrytis cinerea, a fungus. The disease is especially severe on double cultivars and in cold, moist greenhouses. It can occur on all stages of development and on all plant parts.
Symptoms: Tan to brown lesions form on leaves, stems, and bracts. Long tan cankers can form on stems. Infected bracts of red poinsettias may turn purple. Lesions are often noticed first on the edges of young leaves and bracts, turning darker as they expand. Latex may exude from the undersides of lesions. Affected parts become covered with a mass of gray spores.

This stem canker is caused by Botrytis cinerea.

 
Cultural control:

  1. Space plants to allow good air circulation and get light to lower leaves.
  2. Maintain night temperature above 60oF.
  3. Provide good air movement at night.
  4. Heat and vent to expel moist air to reduce humidity.
  5. Remove dead plant debris.
Chemical control: Use foliar sprays with cultural controls. Tank-mix and/or alternate products with different modes of action to prevent the build up of resistant fungi.

  1. 26 GT Fungicide at 1 to 2.5 quarts/A. 12-hr reentry.
  2. AllBan Flo at 10 to 14.5 fl oz/100 gal water. 12-hr reentry.
  3. Daconil Weather Stik at 1.4 pints/100 gal water. Do not use when bracts are forming. 12-hr reentry.
  4. Decree 50 WDG at 0.75 to 1.5 lb/A. Do not apply more than twice sequentially. Test on plants, especially bracts, before wide scale use. 12-hr reentry.
  5. Exotherm Termil at 1 can/1000 sq ft of greenhouse. It ignites to form a vapor that condenses back on the plants. Do not use during bloom or after bract formation. See label for details. 24-hr reentry with no ventilation or 12-hr reentry with ventilation..
  6. Mancozeb-based products can be used as mixing partners and provide some protection. 24-hr reentry.
    1. Fore 80 WP at 1.5 lb/100 gal water plus a spreader-sticker.
    2. Pentathlon DF at 1.5 lb/100 gal water.
    3. Protect DF at 1 to 2 lb/100 gal water plus 2 to 4 oz spreader-sticker.
  7. Phyton 27 at 1.5 to 2 oz/10 gal water. 24-hr reentry.
  8. OHP 26 GT-O at 1 to 2.5 quarts/100 gal water. Limit to two applications per year to aid resistance management. 12-hr reentry.
  9. Spectro 90 WDG (chlorothalonil plus thiophanate methyl) at 1 to 2 lb/100 gal water. 12-hr reentry.
  10. Terraguard SC at 4 to 8 fl oz/100 gal water. 12-hr reentry.
Content edited by: Jay W. Pscheidt on January 1, 2009
 
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