Anthracnose is a common and destructive disease caused by the fungus Gloeosporium venetum. It was first reported in America in 1882. Blackberries, black raspberries, and purple raspberries can become severely infected with this fungus; with severe infections, red raspberries can cause high yield loss. Although young, actively growing plant parts are more prone to infection, plants can become infected anytime during the season.
Symptoms. The first symptom of this disease is usually reddish-purple round to oval spots on the first-year canes in the late spring. The spots grow and become sunken, and the centers become tan to gray with purple edges. The spots may grow together, making large irregular patches, or even completely encircling the canes. This may weaken the canes and cause them to break or the bark to split. Canes that are infected their first year may not survive the winter. If they do, they produce fewer leaves in the spring, and these leaves are weak and pale. The fruiting stems may also become infected, and may die.
First-year canes may also become infected later in the season. When this happens, shallow gray areas appear which may have tiny reddish dots in them.
Fruit growing on diseased canes may develop brown, scabby areas, as the individual drupelets become sunken and light tan in color. The fruit has a bitter taste, and is not marketable.
On the leaves, tiny purple spots may appear. These develop white centers that may fall out. These spots remain small.
Spur blight is caused by the fungus Didymella applanata. It affects red, black, and purple raspberries. Blackberries appear to be highly resistant. Spots appear on new canes in mid-to late summer.
Symptoms. Spots on leaves of first-year canes begin at the edges and grow inwards, following the veins. The spot is V-shaped, and brown with yellow edges. The entire leaf is usually pale. Leaves usually fall off. The fungus grows through the leaf, and into the cane.
Chestnut brown-to purple spots are formed on the canes, usually around a leaf joint. The spots may grow together, although they usually stop before the next leaf joint is reached. On the second-year canes, the spots fade to gray, and tiny black dots appear in them. Infected canes are weakened. Fewer fruiting spurs are formed and those are usually weakened. If the disease remains confined to the lower portions of the plant, little yield loss occurs.
Cane blight is another fungal disease of brambles, caused by Leptosphaeria coniothyrium. It was first described in New York in 1902. It is potentially serious on all the cane fruits, but is most common on black raspberries. It also infects roses and other woody plants. It only infects canes that were damaged in their first year. The disease can result in winter injury, failure of the buds to open, and wilting and death of the canes.
Symptoms. Symptoms do not appear until the late fall. Symptoms are not usually centered around a leaf joint, but around an injury. If the bark of first-year canes is scraped away from an injured area, a brown stripe can be seen. Usually, however, the first noticeable symptom is large brown-to purple (or dark red-to purple on blackberry) spots or streaks on the second-year canes. These may appear on the length of the whole cane, or on one side of it. The buds or fruiting spurs that are in the streaked area may wilt, be weakened, or die. If the spot completely encircles the cane, it may wilt, or be killed and fall over easily.
Prevention of cane diseases. Plant disease-free nursery stock. Cut off “handles” of new tip-layered cutting plants at ground level and destroy them. Prune out diseased canes and old fruiting canes each year after harvest, and destroy them. This must be done before new canes emerge in the spring. For cane blight prevention, any pruning, topping, or tipping should be done when dry weather is predicted for at least three days to allow cuts to heal. It is also important to prevent damage to the canes by machinery or other means.
Air circulation is important to keep the stand dry and prevent infection. Thin canes to improve air circulation. Maintain narrow rows. Control weeds. Certain trellising systems, such as the V-trellis, allow better air circulation, and will help prevent this disease. Avoid overhead irrigation if these diseases have been a problem. Avoid excessive fertilizer, especially nitrogen. Resistance is available to all of these diseases. See current recommendations for chemical control measures.
By Pamela S. Mercure, IPM Program Assistant, University of Connecticut, 1998.
Updated by: Mary Concklin, UConn IPM. 2012
New England Small Fruit Pest Management Guide, 1996-1997. S. Schloemann, ed. University of Massachusetts Cooperative Extension System.
Travis, J.W. and J. Rytter. Anthracnose. 1991. pp. 3-5 in Compendium of Raspberry and Blackberry Diseases and Insects. M.A. Ellis, R.H. Converse, R.N. Williams, and B. Williamson, eds. APS Press, St. Paul, MN.
Wilcox, W. 1989. Disease Scouting and Management. Chapter 8 in Bramble Production Guide. NRAES-35. M. Pritts and D. Handley, eds. Cooperative Extension, Ithaca, NY.
Williamson, B. 1991. Spur Blight. pp. 7-9 in Compendium of Raspberry and Blackberry Diseases and Insects. M.A. Ellis, R.H. Converse, R.N. Williams, and B. Williamson, eds. APS Press, St. Paul, MN.
Williamson, B. Cane Blight. 1991. pp. 5-7 in Compendium of Raspberry and Blackberry Diseases and Insects. M.A. Ellis, R.H. Converse, R.N. Williams, and B. Williamson, eds. APS Press, St. Paul, MN.
This information was developed for conditions in the Northeast. Use in other geographical areas may be inappropriate.
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