WSU Whatcom County Extension

Integrated Pest Management for Blueberries

Botrytis

Botrytis Blossom and Twig Blight (Botrytis cinerea)

Diseases

 

Botrytis

 

Symptoms

Botrytis is a serious fungal disease of blueberries in Northwestern Washington, and can cause damage on stems, blossoms and fruit, especially during wet springs. Infected blossoms show symptoms similar to frost damage, turning brown after a period of high humidity. Under ideal conditions, gray mycelium and spores may be produced on infected blossoms. Botrytis can grow from the infected flower cluster into the stem to cause dieback of the stem. Stem infection can also occur through wounds or areas of frost damage. Branch tips are silver and brittle. Botrytis can also infect green stems causing girdling and eventual die-back. Botrytis causes fruit rot, although the symptoms may not be visible until after harvest. Fruit infected during development will have a decreased shelf live; fresh market fruit packed in closed containers may be unmarketable.

 

Life History

Botrytis overwinters in infected stems of bushes and in plant debris at the soil line. Copious amounts of spores can be produced during wet springs. Spores are dispersed through wind movement and water splashes. Dead tissues on bushes offer opportunities for colonization. Blossoms present during spore dispersal are vulnerable to Botrytis infection, especially when humid conditions are prominent.

 

Botrytis

 

Monitoring

During dormancy, beginning in December, visit 20 bushes per site and inspect 10 shoots per bush for dieback at five sites. Monitor again at 3-5% bloom. Many conditions can cause dieback in previous year’s growth. During bloom stage, look for blighted blossoms and infected stems and record infection level. Look for infected fruit during ripening stages.  

 

Thresholds and Management

Consider treatment when twigs are found infected.  No threshold exists for fruit botrytis.

Branch tips killed by low winter temperatures are easily infected. Remove infected plant material and reduce humidity in the canopy by a regular thinning. If the disease is present in every field it will be hard to eliminate but can be reduced. Apply fungicides during bloom and fruit ripening. Avoid excessive use of nitrogen fertilizer in the spring because the Botrytis fungus will readily infect succulent green growth. Older parts of the plants are rarely attacked. Cool berries rapidly after harvest.

Resources

Michigan State University, Michigan Blueberry Facts, Botrytis Blight
http://www.blueberries.msu.edu/botrytis.htm

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

Oregon State University Extension, An Online Guide to Plant Disease Control, Blueberry-Botrytis Blight
http://plant-disease.ippc.orst.edu/ShowDisease.aspx?RecordID=177

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