WSU Whatcom County Extension

Integrated Pest Management for Blueberries

Anthracnose

Anthracnose Fruit Rot (Ripe Rot)

(Colletotrichum gloeosporioides and C. acutatum)

Diseases

 

Anthracnose

Symptoms

Anthracnose fruit rot or ripe rot can cause various symptoms to blueberry plants, which can cause a loss in yield and transfer infection to ripening fruit. Shoot tip blighting, black flowers, and leaf spots are all symptoms. This is a pre- and post-harvest disease and can be serious under warm and wet conditions. Infected fruit show softening and puckering at the flower end. Salmon-colored spore masses may also be seen in warm and wet conditions. After harvest, spore masses form and infection spreads quickly, especially on fresh fruit in enclosed packages.

 

Life History

The pathogen over-winters on stems, leaves, and flower buds both on the plant and in prunings. In the spring, the fungus produces spores, which get splashed onto flowers and developing fruit by rain and overhead irrigation. At least twelve hours of continuous leaf wetness at temperatures between 52°F and 80°F (12°C and 27°C) is required for new infections to occur.

 

Monitoring

In the spring, look for orange spore masses on last year’s fruiting stems. Look for blighted shoot tips and flowers turning black or brown. When fruit are beginning to ripen, look for sunken, shriveled berries. Riper fruit may show the orange spores.  In areas with a history of anthracnose infection, scout in more areas.

 

Thresholds and Management

Threshold varies according to end product usage and processor. Processors of IQF fruit have zero tolerance for anthracnose infected berries. Talk to your buyer for their threshold.

Prune to allow for adequate air movement. This will help the plants dry faster to avoid the twelve hours of leaf wetness the disease needs to take hold. Always irrigate early in the morning, especially when overhead irrigating, to allow the plants to dry during the day. If possible, avoid overhead irrigation altogether. After harvest cool fruit as soon as possible, as cooler temperatures slows down the rot. Spores have the ability to travel on innate objects, such as machinery and harvesting equipment, therefore avoid introducing anthracnose to your farm through infested flats and totes. Also, do not take the harvester from an infected field to a non-infected field.

Some cultivars are more resistant to Anthracnose than others. Select a resistant variety over a susceptible one.

 

References

British Columbia Ministry of Agriculture and Lands, Pest Management, Blueberry Anthracnose
http://www.agf.gov.bc.ca/cropprot/blueberry.htm

Michigan State University, Michigan Blueberry Facts, Anthracnose
http://www.blueberries.msu.edu/anthracnose.htm

Michigan State University Extension, Blueberry Fruit Rot Identification Guide
http://web2.msue.msu.edu/bulletins/Bulletin/PDF/E2847.pdf

 

 

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WSU Whatcom County Extension • 1000 N. Forest St., Bellingham, WA 98225 • (360) 778-5800 • whatcom@wsu.edu