- Botrytis is a fungal blight that prefers cool, humid weather, and primarily affects the buds and flowers. The buds of an infected rose may fail to open and develop fuzzy, gray spore mats. Those flowers that do open are usually covered in dark spots: dark pink or red on pale roses and red to dark brown or black on darker flowers. The blooms eventually wilt and turn black or brown. Prevent this disease by maintaining good air circulation around plants and choosing blight-resistant varieties. Control already-infected roses using fungicide application.
- These tiny insects feed on all parts of the plant, but do the most cosmetic damage to flower petals. The bugs themselves look like tiny brown slivers, and may not be obvious until they move. Thrips suck sap and juices from the rose, leaving behind dying tissue and dark scars. Thrips are difficult to control with insecticides, since they hide deep within the flower. Reduce populations by removing and destroying spent blooms as soon as they lose their looks. Clean up garden litter around roses tor reduce the chance of overwintering.
- Also called curculios, these long-nosed insects create holes in rose buds and flowers, which can look like dark spots. The adults lay their eggs in the buds, and larval weevils eat the petals and other flower parts. Many buds won't open at all, but those which do often appear tattered and spotted. Control these pests by hand-picking or applying insecticide.
- This fungal condition usually produces dark brown to black spots on the leaves, surrounded by yellow rings. Black spot can also affect the flowers. This fungus reproduces enthusiastically in wet weather, especially in plants with poor air circulation. It breeds and overwinters in fallen leaves and other rose detritus. Reduce the risk of this condition by removing all infested material and destroying it immediately. Many roses varieties are resistant to this condition. When cultural methods aren't enough to control black spot, use fungicides, neem oil or sulfur.
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