WSU Whatcom County Extension

Integrated Pest Management for Blueberries

Phomopsis Canker

(Phomopsis vaccinii)

Diseases

 

Phomopsis

 

Symptoms

This fungal pest is usually associated with warmer climates and is not considered a major pest in the Pacific Northwest. Phomopsis canker causes dieback of flowers, twigs and shoots. Cankers are seen on 1-, 2-, and 3-year old stems; they are seen as elongated, flattened cankers and become covered with small, pinpoint-sized fruiting bodies that produce spores. Infected stems will wilt during he summer and the leaves turn color earlier, causing a red flagging (similar to Godronia canker).

 

 

Life History

Phomopsis overwinters in the stems of blueberries. Spores are produced from bud break until August with most sporulation occurring during bloom. Spores are dispersed by rainwater and splashing. The fungus is active from bud swell until after harvest. Warm, wet conditions are most conducive for spore germination. Infection usually occurs at injury sites, especially those caused by winter damage, frost injury or mechanical wounding.

Phomopsis Canker Sporulating

Symptoms begin to appear during fruit set through harvest. Bushes infected with Phomopsis canker are obviously flagged. Often the wilting of the stems happens quickly and foliage appears bright orange. Upon inspection of flagged stems, cankers can be seen just above the junction of the stem and root crown or adjoining branch. Tissue around the canker can appear silvery and speckled with black dots. Phomospis fungus can also cause tip dieback, attacking two to six inches of the new growth. Foliage will wither and discolor along with the stems. Small black spore bodies may also be seen on the dieback. If given proper conditions, tip infections can spread down the cane in following years.

 

Monitoring

Begin scouting fields for bushes with flagged, orange branches after bloom and through harvest. Pay particular attention to fields that have experienced winter injury or varieties susceptible to frost damage. During other pest monitoring activities that include tip monitoring, make note tip dieback resembles Phomopsis infection. Twig blight by Phomopsis is rare in the Pacific Northwest; many other organisms such as bacterial blight and Godronia canker, and abiotic factors such as frost damage can cause similar twig damage.

Visit ten to twenty bushes at each site to monitor for tip dieback. Inspect at least five tips per bush for symptoms. Look for small black fruiting bodies. If the symptoms are commonly found, send samples to diagnostic labs for identification.

 

Thresholds and Management

Thresholds are dependent on variety and history of infection.  Consider treatment if 1-3% of plants are infected.

Prune out flagged branches before next spring. Pruning when symptoms are obvious ensures that diseased branches are removed. Avoid wounding and limit overhead irrigation. Encourage plants to harden off in winter to avoid frost damage. Plant resistant cultivars. Fungicides applied during bloom may offer some protection. Consult the fungicide label.

 

Resources

Michigan State University, Michigan Blueberry Facts, Phomopsis
http://www.blueberries.msu.edu/phomopsis.htm

Michigan State University Extension, Blueberry Phomopsis in Michigan Factsheet
http://web1.msue.msu.edu/vanburen/bbphomop.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