How to Manage Pests

Pests in Gardens and Landscapes

Black spot—Diplocarpon rosae

Black spot causes black spots to develop on the upper surface of leaves and succulent stems. The spots have feathery or fiberlike margins and no powdery growth on the undersides of leaves. Small black fruiting bodies are often present in spots on upper sides of leaves. Yellow areas develop around the spots. Leaves may drop.

Solutions

The black spot fungus requires free water to reproduce and grow, so leaves should never be allowed to remain wet for more than 7 hours. (When hosing off aphids, do so in the morning so leaves have a chance to dry by midday.) Provide good air circulation around bushes. Remove fallen leaves and other infected material and prune out infected stems during the dormant season. Black spot is usually not a problem during California's dry summers unless overhead sprinklers are used, but the disease can be serious where rainy summers prevail or in cooler areas. Miniature roses are more susceptible than other types, although a few varieties are reliably resistant to all strains of black spot. A combination of bicarbonate of soda plus horticultural oil can be used to manage black spot (as well as powdery mildew). Use about 4 teaspoons of baking soda per gallon of water with a 1% solution of narrow-range oil. Avoid getting on open blossoms. Neem oil can also be effective. Preventive sprays of fungicides such as triforine or chlorothalonil may also be effective.

See the pest note for more information on treating diseases and disorders common to roses.

Spots on upper surface
Spots on upper surfaces of rose leaves

Yellow areas develop
Yellow areas develop around spots


Statewide IPM Program, Agriculture and Natural Resources, University of California
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