Gardening Plant Problems Plant Diseases

How to Treat and Prevent Black Spot on Roses

This common disease can damage your plant without early treatment

Black Spot on Rose Leaves

The Spruce / Marie Iannotti

Black spot is a fungal disease (Diplocarpon rosae) that affects roses. The fungus develops black spots on the leaves, eventually causing them to turn yellow and drop off. Besides looking unsightly, black spot can seriously weaken the rose plant. Black spot thrives during cool, moist weather. Read on for information about treatments for black spot on roses.

treatment and prevention for black spots on roses

 Illustration: The Spruce / Melissa Ling

What Are the Symptoms of Black Spot?

  • Black spot will look like somewhat circular black spots on leaves. It usually occurs on the upper sides of leaves but can also develop on the undersides.
  • The outer margins of the black circles are ragged or feathery, usually surrounded by a ring of yellow.
  • Spots typically begin on the lower leaves and move upward. They can appear as early as when the leaves first unfurl. These spots can enlarge and eventually merge.

What Does Black Spot Do?

Affected leaves often fall off the plants; if left unchecked, the entire plant can defoliate. The loss of leaves reduces the plant's ability to photosynthesize food, weakening the bush and causing a decline in rose production.

The fungus can also infect young canes, causing dark purple or black blisters on the canes, and even the flowers may show some red spotting. Infected plants will set fewer flower buds; without leaves, they become stressed and susceptible to more problems.

black spot on roses
The Spruce / Christopher Lee Foto

What Causes Black Spot on Roses?

The fungal spores that cause black spots to germinate in the springtime are dispersed by splashing water from rain and watering, as well as wind that transports spores. Removing and destroying infected parts is essential; otherwise, your roses will get more black spots.

If you experience an extremely hot summer in July and August, the high temperatures may limit the development of future spores.

Life Cycle of Black Spot Disease

While there is no cure for infected leaves, black spot can be prevented. Existing spores overwinter on infected fallen leaves and stems, waiting for favorable conditions. The spores germinate in spring and must be continuously wet for seven hours before germination occurs. The spores develop fruiting bodies, called acervuli, in the black lesions. These produce spores that splash onto new tissue, spreading the disease.

Give the Plant Ideal Growing Conditions

True for avoiding any plant disease, a healthy, vigorous plant is less susceptible to problems. Follow these care guidelines:

Proper Light

Roses prefer a sunny location with well-draining soil and regular, weekly watering. Plant roses where they receive morning sun, which helps dry moisture from the leaves. Full, all-day sun is best.

Good Air Flow

Provide good air circulation around and through your rose plants. Do not plant your roses too close to other plants. If the plant gets too dense and air cannot get through, prune to open the spaces between canes. By providing good air circulation and ensuring canes don't cross, black spot will have a harder time spreading.

Proper Watering

Avoid getting the leaves wet while watering. There is not much you can do about rain, but avoid overhead sprinklers and focus water directly on the plant's roots.

Pruning

Cut back roses with black spot. The disease starts spreading within 10 days of the first symptoms. Spores spread by water. Spores can remain on leaves and stems and reinfect whenever conditions are favorable.

Remove any infected leaves and always clean thoroughly each fall. Remove and dispose of any remaining leaves when you do your dormant rose pruning in late winter or early spring. Prune out any canes showing signs of infection. Prune 6 to 8 inches below the infection and only prune in dry weather.

Disinfect your pruners with a 10 percent bleach solution or alcohol between cuts. Dispose of infected leaves and canes—do not compost them, as the spores can reinfect plants. Make sure to clean up fallen leaves and dispose of them properly.

person pruning diseased growth from a rose bush
The Spruce / Christopher Lee Foto 

Mulch

Apply a thick layer of mulch around the plant's base. Mulch prevents soil from splashing up on the plant, and if the spores are present in the soil, it will help stop black spot from spreading on the roses. Ensure the mulch doesn't contain rotting wood since artillery fungus can develop in a moist environment.

Topical Sprays for Treatment and Prevention

You can use commercial and homemade DIY solutions to prevent the spread of black spots. The treatment may seem time-consuming; it is a pesky problem that can only be slowed down as nothing can kill black spot on roses.

After treating the plant, you must spray it weekly, starting in early spring and after a heavy rain, to prevent black spots from reoccurring. Spray the entire plant, including the top and bottom of the leaves and the stems. Consider using a dormant spray over winter to smother overwintering spores.

  • Bordeaux mix: This fungicide contains copper sulfate and hydrated lime. It can be used as a powder or mixed with water and sprayed. Bordeaux mix also repels some insect pests but can burn plant leaves. It is generally used as a preventive step in the spring before plants leaf out.
  • Insecticidal soaps with added fungicide: You can use an organic fungicide, often sulfur, added to regular insecticidal soap. The soap coats the leaves and helps the fungicide adhere to the plant.
  • Neem oil: Neem is an organic fungicide and pesticide derived from the seeds of the neem tree. It gets inside the plant's system, so you do not need to worry about coating everything or reapplying after rain. However, it can burn plant leaves in the hot sun. You should not apply neem oil within two weeks of using a sulfur product.
  • Sulfur: Sulfur prevents fungus diseases. It is also used to control several insect pests. Sulfur comes as a finely ground powder. If you prefer to spray it on, look for one that is labeled as wettable so that it will mix with water.
spraying baking soda mixture onto roses
The Spruce / Ulyana Verbytska

Warning

Sulfur can be mildly toxic to humans and other animals. When you spray it, wear protective clothing. It can also corrode metal, so use a plastic sprayer. In hot weather, it can burn a plant's leaves.

Home Remedies for Black Spot on Roses

Organic remedies may work for some gardeners. Experimenting is encouraged if you keep the habit of frequently spraying roses to prevent black spots.

  • Baking soda spray: Dissolve 1 teaspoon of baking soda in 1 quart of warm water. Add up to 1 teaspoon of liquid soap. Spray leaves thoroughly. This mixture works as a preventive and offers some protection from powdery mildew.
  • Vinegar: Is vinegar good for black spot on roses? This vinegar-based recipe may be effective and safe for all rose problems, including black spot. Mix a tablespoon of white distilled vinegar with one cup of water, 1 and 1/2 tablespoons of baking soda, 1 tablespoon of dish soap, and 1 tablespoon of vegetable oil. Add that mixture to a gallon of water, spray it on the rose foliage, and reapply it every week to 10 days, especially after a rainstorm.
  • Milk: Another remedy is a spray mix of one part milk to two parts water applied weekly to control black spot. This can't kill the spores, but it may slow down the spread so you can get a handle on the problem.
  • Hydrogen peroxide: A mix of 1 tablespoon of hydrogen peroxide (3% concentration) and 1 cup of water may also work well on black spot.

Which Roses Are Most Resistant to Black Spot?

Roses most resistant to black spot include:

  • Hybrid floribundas
  • Shrubs
  • Rugosas
  • Canadian Explorer series roses: 'John Cabot' and 'William Baffin'
  • Climbing roses
  • Cultivars: 'Fortyniner,' 'Coronado,' 'Carefree Beauty,' 'Simplicity,' 'Bonica,' and 'Grand Opera' 

Roses least resistant to black spot include:

  • Hybrid tea roses
  • Grandifloras
  • Miniature roses
  • Yellow and copper-colored roses
The Spruce uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Rose Black Spot. Penn State Extension.

  2. Black Spot Of Roses - How Do You Treat Black Spot On Roses. Texas A&M Agrilife Extension Service.

  3. Black Spot. University of Illinois Extension.

  4. Black Spot of Rose. Missouri Botanical Garden.

  5. What Should Neem Be Used For On Plants? University of New Hampshire Cooperative Extension.

  6. Powdery Mildew of Roses: Symptoms, Causes and Environmental Factors. Texas A&M AgriLife Extension Service.

  7. Safe Rose Spray Recipe That Really Works. Horticulture Magazine.

  8. The Myth of Milk and Roses. Puyallup Research and Extension Center, Washington State University.

  9. Black spot of rose. Missouri Botanical Garden.