Rose Diseases - Fungal
canes to rub against each other. Remove one or the other during annual pruning. When pruning canes, prune close to the node ("budeye"). Failing to do this permits the cane to die back, rot and create a condition favorable to Canker spores. If infestations are severe, remove the offending shrub.
Botrytis — Many rosarians don't even recognize this fungal disease. It attacks blooms and canes of established plants, and the bare roots of improperly stored or shipped plants. It appears as a gray-brown fuzzy mold. Buds may fail to open or open only partially. A gray-black lesion usually appears on one side, extending from the bottom of the bud down the bloom stem. On partially opened blooms, petal edges may appear brown and soft, an appearance similar to larval thrips damage or "balling."
Botrytis fungal spores favor continued wet weather and darkened conditions. Watch mail-ordered, bare-root roses carefully. If fungicides are selected, those commonly used for Blackspot will suffice for control. However, smart cultural practices will do much towards control. Plant roses where they will receive early morning sun, thus drying blooms and buds of dew. When symptoms first appear, remove blooms and bloom stems as soon as possible to reduce spore proliferation.
Anthracnose — This fungal disease overwinters in the lesions of older rose canes. As wet conditions occur in spring and early fall, spores attack nearby canes and leaves. Symptoms appear as round, quarter-inch (six-mm), dark black, brown or purple spots on leaves. As these spots mature, they turn tan or light gray in color with dark red around the margin. The leaf tissue within these rings may separate from the underside of the leaf, leaving a tissue paper effect. Symptoms on stems and canes are raised brown or purple spots.
Control is best achieved by removing the entire shrub if infestation is severe. Otherwise, infected canes should be pruned away in early spring before leaves appear.
Next time, we'll answer the question, "When is a rose disease not a disease?"
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