WSU Whatcom County Extension

Integrated Pest Management for Raspberries

Spur Blight

(Didymella applanata)

Insects and Invertebrates

 

Spur Blight

 

Symptoms

Symptoms first appear on primocanes in late spring or early summer. Purple to brown lesions appear just below the leaf or bud, usually on the lower portion of the stem. These lesions expand, sometimes covering the area between two leaves. In late summer or early fall, bark in the affected area splits lengthwise and small black specks, fungal fruiting bodies (pycnidia), appear in the lesions. They are followed shortly by many slightly larger, black, erupting spots, another form of fungal fruiting body (perithecia). Leaflets sometimes become infected and develop brown V-shaped lesions. Infected leaves become chlorotic and drop prematurely when the disease is severe, leaving only petioles without leaf blades attached to the cane. If the disease spreads along the canes, young canes will turn brown up to 20 inches from the ground. Infected areas turn gray in winter.

 

Life History

Spur blight is caused by the fungus Didymella applanata. It survives the winter in lesions on diseased canes. Spores are released the following spring and summer, during wet and rainy periods, and carried by splashing rain and wind to nearby primocanes. Spores germinate in the presence of water and produce new infections where the fungus will again over winter. The fungus can infect leaves, petioles, and canes.

 

Monitoring

Scout 3-5 sites per field, (depending on field size) and evaluate 10-20 hills, spaced 3-5 hills apart on both sides of the aisle way. In early spring, scout for infected tissue appearing around buds as cracked, gray areas containing tiny black pimples. In late spring begin checking floricanes and primocane foliage for brown wedge-shaped lesions, characteristic of spur blight. During harvest, examine primocanes for lesions, which appear as dark brown areas around buds on the cane. Petioles may be left attached to the cane. Record percent infected hills.

 

Spur Blight                  Spur Blight Cane

 

Thresholds and Management

A starting threshold is recommended if 10% of hills were shown to be infected after harvest the previous season.

The disease is initially managed by a delayed dormant lime-sulfur application, followed by 2 to 3 early summer (mid May to early June) fungicide applications. Fungicides with a short PHI are available for use during harvest where symptoms are seen.

Promote air circulation and proper drying of plant tissue through pruning and trellising to open plant canopy. Maintain a narrow row by burning back early first year primocanes and controlling weeds. Minimize or adjust irrigation to prevent plants from being wet for extended periods of time. Avoid excessive use of nitrogen fertilizer since it promotes excessive growth of very susceptible succulent plant tissue. Manage weeds within and between rows to improve air circulation. Wild brambles serve as a reservoir for the disease and should be removed from field borders. After harvest, remove and destroy all old fruited floricanes and any primocanes that are infected.

 

Resources

Cornel University, Department of Horticulture: Managing Raspberry Cane Diseases
http://www.fruit.cornell.edu/berry/ipm/ipmpdfs/Raspberry%20cane%20disease%20mgmt.pdf

Ohio State University Extension: Spur Blight of Raspberries
http://ohioline.osu.edu/hyg-fact/3000/pdf/HYG_3008_08.pdf

Oregon State University Extension, Plant Disease Control: Raspberry – Spur Blight
http://plant-disease.ippc.orst.edu/ShowDisease.aspx?RecordID=955

University of Illinois Extension, Integrated Pest Management: Spur Blight and Cane Blight of Raspberries
http://ipm.illinois.edu/fruits/diseases/spur_blight/index.html

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