Symptoms. The symptoms can vary widely depending on the host. In general, symptoms on leaves appear as watersoaked spots which become gray to brown as they enlarge to cover most of the leaf and cause it to wither. Spots often start at a point of injury. These spots may develop concentric rings of light and dark tissue, giving them a somewhat target-like appearance. On flowers, watersoaked to brown flecks which may enlarge rapidly to become large tan to brown areas, appear on the petals. This can quickly spread to nearby petals as well. The fungus may grow down the flower stalk , causing it to collapse. Buds may rot. The fungus may also infect stems, causing a tan to brown canker to develop on the stem, or they may die back from pruning wounds. Cankers can weaken the stem. They may cause the plant to wilt, perhaps die, and to fall over. On some plants, the crown can become rotted. Cuttings can rot from the base. On all infected plant parts, in high humidity the fungus will produce characteristic spores . All affected areas become covered with a fuzzy gray fungal growth. Under magnification, the millions of spores are seen to be formed in clusters that resemble bunches of grapes. When a plant that is covered in the spores is tapped, a cloud of gray "smoke" (spores) is often seen. This fungus also causes damping-off of seedlings.

Gray mold spores (botrytis) on seedling. E. Marrotte photo

Gray mold spores on geranium. D. Kerbow photo.

Prevention.

• Sanitation alone is often not sufficient to control Botrytis in the greenhouse, but it is a very good place to start. Clean the greenhouse thoroughly between crops. All debris, including prunings and dead leaves, should be removed from the greenhouse immediately.
• Infection of plants usually begins at wounds. Plants should be handled carefully to avoid wounds. Plants should not be pinched or pruned more often than necessary. Avoid allowing leaves to come into contact with potting medium. Remove spent flowers as soon as possible.
• Prevent chilling injury.
• Keeping foliage dry is extremely important to control this disease.
• Ventilate the greenhouse to decrease relative humidity and prevent dew from falling on plants at night.
• Avoid watering late in the day and at other times than do not promote fast leaf drying.
• Avoid overhead watering and overwatering.
• Space plants adequately on the bench, and use open-mesh benches to improve airflow.
• Keep the relative humidity in the canopy below 93%.
• For bedding plant production, time seeding and transplanting to avoid holding plants longer than necessary.
• Major genetic resistance has not been identified, although cultivars of the same plant species differ in their resistance to this fungus.
• See current recommendations for chemical control measures.

By Pamela S. Mercure, IPM Program Assistant, University of Connecticut, 1998.

References.

Chase, A.R. 1995. Compendium of Ornamental Foliage Plant Diseases. APS Press, St. Paul, MN.

Daughtery, M.L., R.L. Wick, and J.L. Peterson. 1995. Compendium of Flowering Potted Plant Diseases. APS Press, St. Paul, MN.

Trolinger, J.C. and D.L. Strider. 1985. Botrytis Diseases in Diseases of Floral Crops, Volume 1. D.L. Strider, ed. Praeger, New York. Chapter 2

This information was developed for conditions in the Northeast. Use in other geographical areas may be inappropriate.

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