Pacific Northwest 1998 An Online Guide to Plant Disease Control

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OSU Extension Office
 
Blueberry -- Ripe Rot (Anthracnose)
 
Cause: Colletotrichum gloeosporoides (sexual: Glomerella cingulata) and C. acutatum, fungi. This disease appears on fruit before harvest (ripe rot) and as a postharvest fruit rot, but control tactics must be implemented earlier in the season. Warm, wet conditions favor disease spread and buildup. Spores are dispersed by splashing rain or irrigation. Infection can occur any time during bloom and berry development. About 10 to 12 hours of continual leaf wetness at 52-80°F is necessary to establish infections. Berry infections remain quiescent (latent) until fruit is nearly mature. The fungus overwinters in blighted twigs and fruit trusses. Pruning and the destruction of prunings from the field did not reduce primary inoculum and has little impact on the resulting disease.

The cultivars such as Bluecrop, Blueray, Bluetta, Earliblue, Herbert, and Spartan are very susceptible while the cultivars Collins, Elliot, and Weymouth are considered resistant.

Symptoms: First, blighting of shoot tips; then, a few flowers turn brown or black. Leaf spots, when they occur, are large or small and roughly circular. As infected berries ripen, the flower end may soften and pucker. Under warm and rainy conditions, salmon-colored spore masses form on infected berries. After harvest, spore masses form rapidly on infected fruit when in cellophane-covered baskets or in plastic clamshell packs.

Note the sporulation of the fungus on the side of this berry.
 
Cultural control: A combination of cultural and chemical practices is most helpful in combating losses due to this disease.

  1. Avoid overhead irrigation or apply such that plants are not wet for extended periods of time.
  2. Lower the temperature of harvested fruit to 32°F as soon as possible after picking.
  3. Prune bushes for adequate airflow and to reduce drying time after becoming wet.
Chemical control: Apply during bloom and use along with cultural practices. Applications may be needed after bloom in especially wet years. Exclusive use of some products, such as Funginex and Indar, for mummyberry control has resulted in elevated levels of anthracnose. Although this may be an artifact of fungicide testing trials, addition of broad spectrum fungicides in an overall program is recommended.

  1. Abound at 6 to 15.5 fl oz/A. Do not apply more than 2 sequential applications or more than 3 applications per year. May be applied on the day of harvest. 4-hr reentry.
  2. Cabrio EG at 14 oz/A. Do not use more than 2 sequential applications or more than 4 applications per year. May be used at harvest. 24-hr reentry.
  3. Captan 80 WDG at 1.25 to 3.1 lb/A plus spreader sticker. May be applied up to day of harvest. Moderately effective. 72-hr reentry.
  4. 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.
  5. 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: Although Aliette is registered for use, it has been effective in only 3 of 9 trials.

Although chlorothalonil products (Bravo and Echo) are registered, their performance has been quite variable and more often ineffective than effective. Since it cannot be used after early bloom, it is not recommended for controlling this disease.

Although Indar is registered, it has not been very effective in western Oregon trials.

Biological control:
  1. Serenade MAX at 1 to 3 lb/A plus a surfactant. Active ingredient is a protein from Bacillus subtilis strain QST 713. Performance was good in Michigan when mixed with a surfactant. 4-hr reentry.
References:
Polashock, J.J., Ehlenfeldt, M.K., Stretch, A.W. and Kramer, M. 2005. Anthracnose fruit rot resistance in blueberry cultivars. Plant Disease. 89:33-38.

Verma, N., MacDonald, L. and Punja, Z. K. 2007. Environmental and host requirements for field infection of blueberry fruits by Colletotrichum acutatum in British Columbia. Plant Pathology 56:107-113.

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