Question: Why do all the leaves drop off my rose bushes, early in the summer? BH, New York
Answer: Black spot, a fungus disease, is probably the worst enemy of roses. Black spots appear on the leaf, spread in size, and the leaf finally drops. Defoliated plants lose their vigor and, though they send out new leaves, they produce fewer and inferior blooms, and are less likely to survive a hard winter. High temperature and high humidity are ideal conditions for the spread of black spot. In warm weather whenever a leaf is moist for six hours or more without, protection it may be infected. It is controlled through the use of either dusts or sprays which are designed to kill the spores before they infect the leaves. All purpose rose dust containing sulfur, or liquid sprays containing wettable sulfur applied regularly should control black spot. The leaf cannot be cured after it is infected. The fungicide must be on the leaf in advance of the fungus spores. Keeping the fungicide on the plant is the secret of adequate protection. Captan is a good fungicide to use in controlling black spot, if used regularly.
