WSU Whatcom County Extension

Integrated Pest Management for Blackberries

Purple Blotch

(Septocyta ruborum)

Diseases

 

Purple Blotch

 

Symptoms

All blackberries and hybrid berries are affected by this disease. The causal organism is a fungus similar to Septoria rubi, which causes leaf and cane spot. Dark green irregularly shaped lesions form on canes late in the growing season. In winter and spring, the lesions turn purple with a red margin. Small black fruiting structures (pycnidia) are found in the center of mature lesions on floricanes, which only infect primocanes. Affected areas are ½ to 2 inches long and develop into cankers, which girdle the cane.

 

Life History

The fungus that causes purple blotch survives on infected canes. Spores are released and spread to primocanes from April to mid August. Spores are dispersed by splashing water or rain. Most spores are released when temperatures are near 70º F. Symptoms do not develop unless a chilling requirement is met.

 

Monitoring

Monitor in the spring before primocanes emerge and when lesions have turned purple and are easy to find. Scout 3-5 sites per field (depending on field size) and evaluate 10-20 hills, spaced 3-5 hills apart at each site. Record severity on a scale of 0-3 for each site scouted.

 

Purple Blotch

 

Thresholds and Management

No threshold or tolerance level available.

Fungicide applications will not remove the disease once it has developed, but will prevent infection from spreading on young primocanes. For every-year (EY) producers, sprays usually occur after harvest, in October (before every rains begin), and at bud break in early March.

Use an alternate-year fruiting program, where canes are trained up as they grow. If canes are allowed to lie on the ground, the disease can be just as severe as in fields where berries are harvested annually. Control weeds to reduce humidity and to increase spray coverage. Remove old fruiting canes after harvest. Trellis canes in August through early September or wait until late winter (February or March). Canes trained after early September may be more susceptible to winter injury.

 

Resources

Oregon State University Extension, Plant Disease Control: Blackberry Purple Blotch
http://plant-disease.ippc.orst.edu/ShowDisease.aspx?RecordID=168

University of California, IPM Online: Purple Blotch, Septocyta ruborum
http://www.ipm.ucdavis.edu/PMG/GARDEN/FRUIT/DISEASE/purpleblotch.html

USDA IPM Centers, Crop Profile for Blackberry in Oregon: General Production Information
http://www.ipmcenters.org/cropprofiles/docs/ORblackberries.pdf

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WSU Whatcom County Extension 1000 N. Forest St., Suite 201, Bellingham, WA 98225 (360) 778-5800 whatcom@wsu.edu