Botrytis fruit rot or gray mold of brambles is cause by the fungus Botrytis cinerea. Raspberries are very susceptible to Botrytis fruit rot which is one of the most common and serious diseases of raspberries. It is usually worse on red and yellow raspberries than on black raspberries. This disease is favored by cool (65o to 75o F), wet weather, and is especially bad when there is prolonged moisture just before or during harvest. Infection can happen during the blooming period or when fruit is nearly or fully ripe. Fruit can show this rot after it has been harvested, even when it looked healthy at harvest time.
Older foliage is also susceptible to infections from Botrytis, and left unchecked, may lead to cane infections. In the spring, cane infections have a bleached appearance.
Symptoms. Open flowers can become infected, especially if they have been damaged by frost. They become dark and shriveled. During humid or wet times, they are covered with a mass of fuzzy gray fungal growth. The fungus then grows into the fruit stems, and may cause them to turn black. If the weather is moist, the characteristic gray fuzzy fungal growth appears on the stems as well. When the fruit is almost ripe, it develops a watery rot on a few drupelets. These quickly turn tan, and, in moist weather, become covered with the fungal growth. This is most common near the stalk end of the fruit, but can appear anywhere. Often several fruits in the same cluster are affected. Infected berries left on the plants become “mummified,” or hard and dark, and are sources of innoculum for additional infections.
Prevention. Prune and thin canes to maintain good air circulation. Maintain narrow rows. Avoid excessive nitrogen fertilizer. Control weeds. Harvest fruit regularly. Do not allow overripe fruit to stay on the canes. After harvest, handle fruit gently, and keep it at 33o F. Never pack raspberries more than three fruit deep. There are some red cultivars that are somewhat resistant. Contact your local Cooperative Extension center for current recommendations for chemical control measures.
References:
- Bristow, P.R. 1991. Botrytis Fruit Rot and Blossom Blight. pp. 21-23 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.
- New England Small Fruit Pest Management Guide, 1996-1997. S. Schloemann, ed. University of Massachusetts Cooperative Extension System.
- 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.
By: Pamela S. Mercure, IPM Program Assistant, University of Connecticut
Updated by: Mary Concklin, IPM. 2012
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