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IPM Scouting in Woody Landscape Plants

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Black spot
IPM scouting in woody landscape plants > black spot
Cause: Diplocarpon rosae (fungus)

Host: Roses

Symptoms: This fungal disease gets its common name from the symptoms produced on the leaves. Infected leaves drop off. Defoliation is worse in hot, humid weather. Leaf petioles, twigs, and canes may also be infected.

How it’s spread: Splashing rain spreads the spores.

Management: At least seven hours of continuous leaf wetness with temperatures above 68°F are needed for spore germination. Use trickle irrigation or water early in the day to allow roses to dry quickly. Plant the roses in sunny locations with good air circulation. Rake up and destroy infected leaves; prune out infected canes before new growth starts in spring. Choose resistant cultivars where possible. Roses vary widely in their susceptibility to black spot; many hybrid teas, particularly yellow and orange roses, are particularly susceptible to black spot. Although black spot isn’t fatal, the disease can defoliate and weaken susceptible cultivars. Several fungicides are labeled for control.
Black spot
Symptoms of black spot begin on the lower leaves and progress upward; the fungus overwinters on infected leaves and canes.
Resistance: Roses reported resistant to black spot include: Rosa wichuriana, R. roxburgii and some of the R. rugosa hybrids. Consult a current reference for a more complete listing of resistant cultivars and hybrids. Suggested reference for more detailed information on managing roses: Healthy Roses: Environmentally Friendly Ways to Manage Pests and Disorders in Your Garden and Landscape. Flint, M. L., and J. F. Karlik. 2000. Oakland: University of California ANR Publication 21589.
Black spot Leaf symptoms, showing irregular black spots with fringed margins. Yellow halos develop as the disease symptoms progress.

Additional information

This information was developed from A Pocket IPM Scouting Guide for Woody Landscape Plants by Diane Brown-Rytlewski. Purchase this in a pocket-sized guide for reference in the orchard from MSU Extension (publication E-2839).
The MSU IPM Program maintains this site as an access point to pest management information at MSU. The IPM Program is administered within the Department of Entomology, fueled by research from the Michigan Agricultural Experiment Station, delivered to citizens through MSU Extension, and proud to be a part of Project GREEEN.
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Updated 10/11/07