Rose plants -- particularly hybrid teas -- can suffer from botrytis blight, caused by the fungus Botrytis cinerea, a disease that potentially damages rose buds and flowers. Although fungicides are available treat this disease, the causal fungus can develop resistance to a fungicide after multiple applications. Use adequate sanitary and care practices to eliminate the need for potentially harmful chemicals.
Identifying Botrytis Blight
Proper identification of botrytis blight allows you to rule out other pest and disease problems and determine the best course of treatment. Roses infected by Botrytis develop dark splotches on the canes and suffer twig dieback. Buds may fail to open and flower petals are spotted. Decaying tissue is often covered by a gray fuzz. Botrytis blight is most typically a problem when weather is cool and foggy or there is otherwise high humidity or excess moisture around the rose.
Excellent hygiene is key to preventing botrytis blight or limiting its spread. Remove fallen flowers and leaves from the area promptly. Replace any organic mulch around the rose annually and discard or destroy the old mulch. If the plants you used as ground cover under the rose harbor decaying material, they may warrant removal. Dispose of any infected tissue by burning it or burying it under at least a foot of soil.
Pruning and Deadheading
Deadhead or prune off dying or infected flowers as soon as the flower begins to wilt or you recognize damage. Prune off any infected portions of stems, making cuts several inches below diseased tissue. Prune out crowded or damaged stems annually to improve circulation. When pruning your roses, disinfect your pruning tools with an alcohol or bleach solution between cuts.
Proper cultural care is the key to avoiding serious problems with blight. Water your roses adequately and apply a suitable fertilizer to fortify the rose's ability to resist and withstand disease. High humidity and moisture favor the development of botrytis blight. Overhead irrigation or other types of watering practices that wet the leaves encourage spore germination and the spread of disease. Make sure to allow adequate space between your rose plants; overcrowding them impairs air circulation.
- HDRA: Organic Management Practices for Roses
- University of California Statewide Integrated Pest Management Program: Roses: Diseases and Abiotic Disorders
- University of California Statewide Integrated Pest Management Program: Rose
- University of Illinois Extension: Botrytis Blight or Gray Mold of Ornamental Plants
- Cornell University Cooperative Extension of Schenectady County: Botrytis Blight
- Colorado State University Cooperative Extension: Common Rose Diseases
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