Pacific Northwest 1998 An Online Guide to Plant Disease Control

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OSU Extension Office
 
Blueberry -- Botrytis Blight
 
Cause: Botrytis cinerea, a fungus that survives as sclerotia (resistant survival structure) and dormant mycelium on dead twigs of bushes and prunings. It also overwinters as a saprophyte on dead organic matter in or on the soil surface. In spring, these tissues produce vast numbers of spores during wet periods. Spores spread primarily by wind but also by splashing water. Cultivars that tend to retain floral structures a long time apparently are more susceptible.
Symptoms: During wet springs, blueberry blossoms take on a brown, water-soaked appearance and die. Blossoms may be covered with dense grayish powdery masses of Botrytis spores. Infections may move through the blossoms rapidly and often destroy the entire floral structure. The disease also can move from blossoms back into fruit-producing wood. On young leaves, pale brown lesions form. Fruit may shrivel and be covered with the characteristic gray sporulation after harvest.

Infected succulent twigs are at first brown to black and later bleach to tan or gray. Twigs blight from the tip toward the base. Black sclerotia can be found near the tip of blighted twigs. Symptoms can be seen after winter injury and/or before floral budbreak. The disease is easily confused with bacterial blight and/or the shoot blight stage of mummyberry if there is no sporulation.

Symptoms are similar to Pseudomonas and Mummyberry. Look for the gray sporulation.

Infected blossoms take on a brown, water-soaked appearance and die.

Sporulation of Botrytis can be seen on this blighted shoot tip.
 
Cultural control:

  1. Annually prune to remove infected twigs and to open canopy for good air circulation.
  2. Space plants for good air circulation and quick drying.
  3. Adjust timing and/or frequency of overhead irrigation to keep aboveground portions of the plant dry.
  4. Avoid late-season fertilization.
  5. Practice good weed control.
Chemical control: Apply fungicide from prebloom through the end of bloom. Alternate or tank-mix chemicals to avoid problems with resistant strains.

  1. Captan 80 WDG at 1.25 to 3.1 lb/A. May be applied up to day of harvest. Moderately effective alone. 72-hr reentry.
  2. CaptEvate 68 WDG at 3.5 to 4.7 lb/A Do not apply more than 2 consecutive application or more than 21 lb/A/season. Can be used day of harvest. 48-hr reentry.
  3. Elevate 50 WDG at 1.5 lb/A. Do not use more than 6 lb/A/season. Can be used up to and including the day of harvest. 12-hr reentry.
  4. Iprodione 4L AG at 1 to 2 pint/A can be applied up to and on the day of harvest. Alternate with other fungicides and limit to two (2) applications in order to delay or prevent buildup of resistant fungi. 24-hr reentry.
  5. Pristine at 18.5 to 23 oz/A. Do not use more than 2 consecutive applications or more than 4 times/year. Can be used day of harvest. 12-hr reentry.
  6. Switch 62.5 WG at 11 to 14 oz/A. May be used up to and including the day of harvest. Do not apply more than twice sequentially or use more than 56 oz/A/season. 12-hr reentry.
  7. Ziram 76 DF at 3 lb/A. Do not apply after 3 weeks from full bloom. Moderate to poor control ranking. 48-hr reentry.
Notes: The commercial efficacy of Messenger (a bacterial protein) is unknown in the PNW and is not recommended.

Use of propiconazole (Orbit) for mummyberry control has been associated with an increase in Botrytis severity.

References:
Smith, B. J. 1998. Botrytis blossom blight of southern blueberries: Cultivar susceptibility and effect of chemical treatments. Plant Disease 82:924-927.
Content edited by: Jay W. Pscheidt on January 1, 2009
 
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