Cankers are usually at the base of the plant, but can be a few feet aboveground. Stem cankers begin in the fall as small, watersoaked spots,. By December they have turned red. In the spring, they grow to reddish-brown spots up to 4" in length. This canker is usually centered around a leaf scar and often has a target pattern. As the canker grows, the center turns gray and dies, while the edges remain red. Tiny black dots, the fungal spore-producing structures, can be seen in the center of the older cankers.

Prevention. Prune out and destroy stems with cankers as these are the source of the spores. Improve air circulation in the bushes by controlling weeds and pruning bushes. Some resistance is available to this disease. See current recommendations for chemical control measures.

Phomopsis Twig Blight is another canker disease, caused by Phomopsis vaccinii. This is currently the most prevalent twig canker of blueberries in New England. It is favored by wet weather and temperatures of 70^o to 80^o F. This disease is most severe in seasons following winters with mild spells interspersed with cold weather. Periods of hot, dry weather during the growing season may predispose plants to this disease.

Symptoms. Symptoms first appear on small twigs and then spread to larger branches. Small branches, usually about 2" to 6" long, may wilt suddenly and die. Leaves turn reddish and remain attached to the stem. Cankers begin as elongated brownish areas on 1-year-old stems, and can become up to 4" long. They can be at ground level up to several feet above the ground. On older stems, the cankers become grayish and flattened and grow up to 8" long. Side branches that become encompassed by the canker will wilt in hot weather. The cankers become covered with tiny black dots, which are the fungal spore producing structures. The cankers are similar to the Fusicoccum cankers, but do not have the target-like appearance.

Prevention. The spores enter the plant through wounds, including wounds from frost or winter injury, so it is important to avoid wounding the plants. Avoid planting in sites that are prone to spring frosts. Do not fertilize late in the season; it delays dormancy, which may lead to winter damage. Before bud break in the spring, prune out and destroy diseased and weak stems and cut them all the way to the ground to make sure all diseased wood is removed. Water during dry spells. Some cultivars are more resistant than others to this disease. See current recommendations for chemical control measures.

Coryneum Canker is a fungal disease caused by Coryneum microstictum. This disease appears only in Southeastern New England. It usually occurs in conjunction with other canker diseases and the cankers are similar to those found in other canker diseases. They often occur on wounded wood, either from sunscald or mechanical injury. Cold stress can predispose bushes to this disease. Prevention measures recommended for Fusicoccum or Godronia Canker and Phomopsis Twig Blight are useful in preventing this disease as well.

By Pamela S. Mercure, IPM Program Assistant, University of Connecticut

References:
Bristow, P.; R. Byther; R. Ingram and D. Ramsdell. 1992. Nematode and disease management. Chapter 9 in Highbush Blueberry Production Guide. M.P. Pritts and J. F. Hancock, eds. Notheast Regional Agricultural Engineering Service.

New England Small Fruit Pest Management Guide, 1996-1997. S. Schloemann, ed. University of Massachusetts Cooperative Extension System.

Ramsdell, D.C. 1995. Phomopsis Canker. pp. 14-15 in Compendium of Blueberry and Cranberry Diseases. F.L. Caruso and D.C. Ramsdell, eds. APS Press, St. Paul, MN.

Ramsdell, D.C. 1995. Fusicoccum Canker (Godronia Canker). p. 15 in Compendium of Blueberry and Cranberry Diseases. F.L. Caruso and D.C. Ramsdell, eds. APS Press, St. Paul, MN.

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