BLACKSPOT on Roses
The following article is based upon information furnished by the Department of Plant Pathology of Ohio State University. The authors quoted are Jim Chatfield and Stephen Nameth. In this year, where Blackspot appears to be a problem, we want our members and readers of The Rosarian to receive the best possible data on Blackspot. The climatic conditions in Northern California this past year have greatly altered our rose culture programs.|
Blackspot is the most important of infectious rose diseases. It occcurs only in roses, and is widely spread among many rose species and cultivars. Symptoms first appear as irregular black splotches with fringed margins, mostly on the upper side of the leaf. Slight yellowing occurs and surrounds the affected area. In due time defoliation will result. The fungus can overwinter on fallen leaves and stem tissue, reinfesting the following year. The spores can germinate and reinfect in one day!
Control Hints: Keep foliage as dry as possible. Avoid planting your roses near surrounding vegetation (even near by weeds). If summer rains occur there is a good possibility of reinfestation. Good sanitation in your rose beds is of primary importance. Disease resistance can be found in some cultivars. These roses are listed on page nine of this publication.
Control Measures: If you do not have a spray program, you may be in for trouble. We recommend the following fungicides: Funginex gives good control if used on a regular basis. Any of the copper based spray work well. Systhane provides excellent control of Blackspot. Daconil and any of the products containing Daconil, like Sentinel, should keep your garden free of any severe infestations. The addition of Cloud Cover can help prevent an infestation. Best of all, make a point of checkng your roses on a regular basis. Once blackspot takes hold, it is difficult to maintain control.
"The San Francisco Rosarian," July 1998.
Additional information may be found in our book:
"Growing Roses in the San Francisco Bay Area
and Other Maritime-Influenced Climates."