Read in detail about black spot on roses, and learn how to identify, treat, and prevent healthy, beautiful blooms.
Black Spot on Roses are a common issue that can ruin the beauty and weaken the plants. This fungal problem causes dark circles on the foliage. By opting for proper care and treatment, you can prevent this problem. Read about the reasons and solutions below.
Black Spot on Roses
This fungal disease (Diplocarpon rosae) impacts roses. It emerges as a black spot on the foliage, which causes it to become yellow and fall off. Apart from looking unattractive, it badly weakens the rose plant. Black spots occur in cool, moist weather, whereas intense summer controls the disease.
What does Black Spot Do?
They appear like slightly circular black spots on the foliage. Black spots emerge on the upper sides and also on the undersides of the foliage. The exterior edges of the black circles are scruffy or feathered and encircled by a yellow ring.
Spots start to develop on the lower leaves and move upward. They emerge when the leaves unfurl first, enlarge, and blend. Diseased foliage drops off the plants, and if untreated, the whole plant becomes leafless. Black spots also affect young canes, resulting in black or dark black blisters. Blooms may display some red spots. A contaminated plant will produce fewer flower buds without foliage, making the plant vulnerable to more issues.
How Black Spot Spreads?
The spores spread through the wind but germinate in moisture, and humid and wet conditions over a long time can cause black spots.
Roses that are Vulnerable to Black Spot
All rose varieties can be affected by black spots, but some are much more prone than others. According to the University of Nebraska-Lincoln Extension, floribundas, climbing roses, and shrub roses are the most disease-resistant, whereas hybrid tea roses, miniature roses, and grandifloras are the least resistant.
Generally, rose plants with many leaves or ground-touching foliage are more susceptible to fungus than rose plants with a ventilated open canopy.
How To Solve Black Spot Problem
You can bring back affected leaves, but black spots can be prevented. Existing spores hibernate on diseased dropped foliage and stems. They germinate during spring and spread through water splashed on the plant during watering. Before infection takes place, spores remain constantly wet for 7 hours. Spores form fruiting bodies, known as acervuli, in the black wounds.
Provide the Rose Plant with Favorable Growing Conditions
A healthy, strong plant is less sensitive to issues. Roses favor a sunny area, well-draining soil, and normal weekly watering. The full sun location helps dry moisture from the foliage.
1. Appropriate Watering
Water the plants carefully and do not let them touch the foliage; you can not do anything for rain, but prevent overhead watering and aim only to hydrate the roots.
2. Right Air Flow
Avoid planting roses near other plants, give the proper air circulation, and prune so space stays open between canes. With good air circulation, it will become challenging for black spots to spread and infect the rose plant.
3. Mulching
Spread a thick layer of mulch near your rose plant; it stops soil from splattering on the plant. If spores exist in the soil, it will hinder the dissemination of the fungus. Avoid using mulch that has rotting wood, as artillery fungus can emerge in a moist atmosphere.
4. Pruning
Cut back affected foliage and dispose of it while pruning dormant roses during late winter or early spring. Spores stay on the leaf and stem and spread again in wet surroundings through water. Remove any canes with symptoms of infection. Snip off 6-8 inches below the infection in dry weather. Before pruning, sterilize the pruning shears with 10 percent alcohol or bleach between the cuts. Discard diseased foliage and canes and avoid putting them in compost as they can spread infection again.
5. Insecticidal Soap with Fungicide
Use organic fungicide added with sulfur to regular insecticidal soap; it layers the foliage and helps the fungicide to stick to the plant.
6. Baking Soda Spray
Take 1 quart of water, add one teaspoon of baking soda and one teaspoon of liquid soap, and mix thoroughly. Fill the solution in a spray bottle; it’s a preventive measure that protects rose plants from powdery mildew.
7. Bordeaux mix
This fungicide has copper sulfate and hydrated lime. You can use it in powder form or blend it with water and spray it on the infected area. It repels pests but can burn the foliage.
8. Sulfur
It prevents fungal infections, you can get it in both powder or in spray forms. Though sulfur is slightly toxic to humans and animals. Use plastic sprayers, wear gloves, and avoid using them in hot weather.
9. Neem Oil
It penetrates the plant, so you are not required to re-apply it after rain. Though it can burn the foliage in hot weather. Avoid using neem oil within two weeks of applying the product, which has sulfur.
10. Grow Resistant Varieties
While looking for black spot-resistant cultivars, also check for powdery mildew and rust fungus. You can go for Rugosas, a new ground cover, and shrub, or the Canadian Explorer rose series, such as, ‘William Baffin’, ‘John Cabot,’ and ‘Oso Easy landscape roses.’
11. Milk
Mix one part milk with two parts water, and fill this solution in a clean spray bottle. Apply it weekly to control the black spot. This will not kill the spores but might slow the infestation.