Rose Black Spot
Gary W. Moorman, Professor of Plant Pathology
A common disease of roses called black spot is caused by the fungus Diplocarpon rosae . This fungus readily attacks young expanding leaves and young canes. Fungal spores which were formed on infected fallen leaves or on canes are splashed to the new lower leaves of roses in the spring by rain or sprinkler irrigation. The spores must remain wet for several hours in order for the spore to germinate and invade the leaf. If temperatures are warm following infection, symptoms may become visible in 3 days. New spores can form in as few as 10 days after infection. Thus under some conditions the fungus can infect a plant, begin producing new spores, and spread to other leaves within two weeks.
Leaves - dark spots up to 1/2 inch in diameter have "feathery" edges when some rose cultivars are infected. Spots are smaller with more distinct edges in other cultivars. These spots may have a yellow halo surrounding them. Infected leaves yellow and fall.
Canes - small purplish spots form on the current years growth.
Because the fungus spore must have free water on the leaf or cane in order to germinate and penetrate, take steps to insure that plant surfaces dry quickly or are not wetted.
- Avoid dense plantings.
- Maintain good weed control so that air circulation around the plants is good.
- Avoid wetting the plants when irrigating.
- If plants are misted or sprinkler irrigated, only do so when the plant surfaces will dry quickly.
Because the fungus survives from year to year in infected material,
- rake and destroy fallen leaves.
- prune out canes that have symptoms of black spot disease.
When feasible, plant resistant cultivars. David Thompson, Bebe Lune, Coronado, Ernest H. Morse, Fortyniner, Grand Opera, Lucy Cromphorn, Sphinx, Tiara, Carefree Beauty, and Simplicity are considered resistant. Teas, hybrid teas, hybrid pertetuals, Pernetianas, Austrian briers, and polyanthas are usually very susceptible while rugosa hybrids, moss roses, and wichuraianas are more resistant. The American Rose Society recommends the following varieties as resistant: Bride's Dream, Canadian, White Star, Cary Grant, Dainty Bess, Duet, Electron, Elina, Elizabeth Taylor, Helmut Schmidt, Keepsake, Lady, Lady Rose, Lady X, Las Vegas, Mikado, Nantucket, Olympiad, Otto Miller, Pascale, Polarstern, Precious Platinum, Princess of Manaco, Pristine, Sheer Bliss, Sunbright, Tansinnroh, and Uncle Joe.
Apply a fungicide with a spreader-sticker added so that young tissues are protected. In the spring as daily temperatures reach the high 50F range, begin applying a fungicide every 2 weeks. As the leaves emerge, make fungicide applications each week. Cease spraying when day temperatures average in the 80F range or when weather is dry. Resume spraying in the autumn when temperatures moderate and rainfall or dew regularly occur.
Active Ingredients and Trade Names of the Chemicals
|FRAC Group No.||Risk Level||Class||Active ingredient||REI Restricted Entry Interval||Trade names (EPA Reg. No.)|
|1||3||Benzimidazole||thiophanate methyl||12||3336 (1001-69), OHP 6672 (51036-329-59807), Fungo Flo (51036-329-59807) Systec 1998 (48234-12)|
|Triazole||propiconazole||24||Banner MAXX (100-741), Propiconazole (51036-403), Spectator (62719-346-10404), Kestrel (66222-41-81943)|
|12||Echo (60063-7), PathGuard (60063-7-499), Concorde (72167-24-1812), Pegasus (72167-24-1812)|
|Copper, fixed||copper hydroxide||48||Kocide (352-656)|
|Dithiocarbamate||mancozeb||24||Dithane (707-180), FORE (707-87), Pentathlon (1818-251)|
|manganese + zinc||24||Protect T/O (1001-65)|
|NC||1||neem oil||4||Trilogy (70051-2), Triact (70051-2-59807)|
|1 + M||thiophanate methyl + chlorothalonil||Spectro 90(1001-72), ConSyst (48234-7)|
|1 + M||thiophanate methyl + mancozeb||Zyban (58185-31)|
Notice: The user of this information assumes all risks for personal injury or property damage.
Warning! Pesticides are poisonous. Read and follow all directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams or ponds.
Issued in furtherance of Cooperative Extension work, Acts of Congress, May 8 and June 30, 1914, in cooperation with the U. S. Department of Penn State College of Agricultural Sciences research and extension programs are funded in part by Pennsylvania counties, the Commonwealth of Pennsylvania, and the U.S. Department of Agriculture.
Visit Penn State Extension on the web at extension.psu.edu.
Where trade names appear, no discrimination is intended, and no endorsement by Penn State Cooperative Extension is implied.
This publication is available in alternative media on request.
The Pennsylvania State University is committed to the policy that all persons shall have equal access to programs, facilities, admission, and employment without regard to personal characteristics not related to ability, performance, or qualifications as determined by University policy or by state or federal authorities. It is the policy of the University to maintain an academic and work environment free of discrimination, including harassment. The Pennsylvania State University prohibits discrimination and harassment against any person because of age, ancestry, color, disability or handicap, national origin, race, religious creed, sex, sexual orientation, gender identity, or veteran status. Discrimination or harassment against faculty, staff, or students will not be tolerated at The Pennsylvania State University. Direct all inquiries regarding the nondiscrimination policy to the Affirmative Action Director, The Pennsylvania State University, 328 Boucke Building, University Park, PA 16802-5901; Tel 814-865-4700/V, 814-863-1150/TTY.