Pacific Northwest 1998 An Online Guide to Plant Disease Control

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OSU Extension Office
 
Azalea -- Leaf and Flower Gall
 
Cause: Exobasidium vaccinii, a fungus that is believed to overwinter as spores adhering to bark and bud scales and to cause infection with the opening of buds in spring. Older leaves are resistant to infection. Infection is dependent on high humidity and moisture during bud break. Occurrence in the Willamette Valley has been quite variable from severe for a few years, back to back, to hardly noticeable for several years in a row. Hosts of this fungus include Camellia, huckleberry, Kalmia, kinnikinnick, Leucothoe, madrone, Pieriss, and salal.
Symptoms: Either all or part of a leaf may become thickened, fleshy, and covered with a white bloom of spores. At first, diseased leaves are succulent and white, but they later turn into hard, brown, gall-like bodies. Galls are composed of fungus-infected plant tissue.

The strange looking tissue in the center is galled leaf tissue.

Note the healthy leaves on top and the galled leaves in the middle.

Whole leaves to small parts of leaves can be affected.

 
Cultural control:

  1. Remove and destroy galls before they turn white.
  2. Reduce greenhouse humidity.
  3. Select less susceptible cultivars.
Chemical control: Apply the first spray before budbreak in spring and the second spray 2 to 3 weeks later. Some references call for regular applications until all galls have dried up. Symptom reduction is then seen the following spring.

  1. Bayleton 50 T&O at 5.5 oz/275 gal water. Landscape only, not for use on plants for sale.12-hr reentry.
  2. Copper-based fungicides may discolor foliage and blooms.
    1. Bordeaux 6-2-100.
    2. Champ Formula 2 at 0.6 pint/100 gal water. 24-hr reentry.
    3. Copper-Count-N at 1 quart/100 gal water. 12-hr reentry.
    4. Nu-Cop 50 DF at 1 lb/100 gal water. 24-hr reentry.
    5. Lilly Miller Microcop at 1.5 Tbsp/1 gal water.
  3. Mancozeb-based products. 24-hr reentry.
    1. Fore 80 WP at 1.5 lb/100 gal water plus a spreader-sticker.
    2. Pentathlon DF at 1 to 2 lb/A or per 100 gal water.
    3. Protect DF at 1 to 2 lb/100 gal water plus 2 to 4 oz spreader-sticker.
  4. Strike 50 WDG at 2 oz/100 gal for outdoor use. In the greenhouse, use 1 oz/100 gal in winter and 2 oz/100 gal in summer. 12-hr reentry.

Content edited by: Jay W. Pscheidt on January 1, 2009
 
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