{"id":4551,"date":"2011-01-28T12:19:02","date_gmt":"2011-01-28T17:19:02","guid":{"rendered":"http:\/\/extension.umaine.edu\/ipm\/"},"modified":"2021-08-31T15:49:52","modified_gmt":"2021-08-31T19:49:52","slug":"5097e","status":"publish","type":"page","link":"https:\/\/extension.umaine.edu\/ipm\/ipddl\/publications\/5097e\/","title":{"rendered":"Black Spot of Rose"},"content":{"rendered":"

\n \n \"Print\n <\/a>\n <\/div><\/h3>\n

Pest Management Fact Sheet #5097<\/h3>\n

Authors: Dr. Alicyn Smart, Dr. Bruce Watt, and Abigayl Novak<\/em><\/p>\n

For information about UMaine Extension programs and resources, visit extension.umaine.edu<\/a>.
\nFind more of our publications and books at extension.umaine.edu\/publications\/<\/a>.<\/strong>
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Other Name:<\/strong> Leaf blotch, Leaf spot, Blotch, Rose actinonema, Rose leaf asteroma, and Star sooty mold
\n<\/em>Pathogen:<\/strong>\u00a0Diplocarpon rosae<\/em> (sexual stage) and Marssonina rosae<\/em> (asexual stage)<\/h4>\n

Introduction<\/h3>\n

Black spot of rose is one of the most common and important diseases of roses throughout the world. In a natural environment, this disease is prevalent and becomes a major issue, frequently causing epidemics. It is caused by the fungus\u00a0Diplocarpon rosae<\/em> and will progressively weaken the plant so that fewer and fewer blooms form if the disease is left unchecked. Plants weakened by this disease are increasingly subject to winter injury.<\/p>\n

As is true with most fungi, this fungus requires free water for infection to occur. The spores require at least 7 hours of wetness before they can germinate. Fruiting structures of the pathogen called acervuli form within two weeks of the initial infection. These structures release spores which are blown, splashed or otherwise carried to new tissue initiating new infections. A temperature of 65\u00b0F is ideal for spore germination and the disease develops most rapidly at about 75\u00b0F. Temperatures of and above 85\u00b0F inhibit the spread of the disease. The fungus survives the winter in fallen leaves and at infection sites on the canes. Spores will not survive in the soil, and individual spores will not survive longer than a month.<\/p>\n

Host Plants<\/h3>\n
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  • Rosa <\/em>species<\/li>\n<\/ul>\n

    Symptoms<\/h3>\n

    As the name implies, infected leaves develop black spots, especially on the upper leaf surface. The circular or irregularly shaped spots can be up to 1\/2 inch in diameter and typically have fringed borders. As the disease progresses, the leaf margin begins to yellow, and then the entire leaf (Figure 1). The plant will then start to drop these leaves. Close inspection of the spots will reveal the presence of the acervuli (Figure 2), which produce two-celled spores (conidia) (Figure 3). The fungus may also infect the canes where lesions appear purple at first then progress to black.<\/p>\n\n\t\t