Black spot on roses is a common disease which infects our prized and cherished roses. Diplocarpon rosae is a type of fungus which develops black spots on the leaves of roses. The leaves turn yellow and drop off weakening the plant and infecting nearby rose bushes.
How to identify black spot
The first sign of black spot on plants are circular black spots on the leaves with feathered edges. As the fungus spreads, the leaf begins to yellow and fall off. The markings can be found either on the upper or underside of the plants leaves. The fungus can also infect young canes and spread through the whole plant.
The spores are carried on the wind from other infected plants and settle on the leaves and in the soil. The fungus can overwinter in the soil and on leaves and stems waiting for the perfect conditions to grow.
How to keep your rose healthy
Black spot thrives in damp, humid conditions. Under the right conditions, it spreads up through the rose and if left untreated will defoliate the whole plant.
- Try to keep the plant dry by watering at the base of the rose avoiding water splashing on the leaves.
- Keep plants pruned to create good air circulation which will help to maintain dry leaves.
- Plant roses well apart from other plants to allow good air flow between plants.
- Keep the rose beds free of fallen foliage to maintain healthy soil conditions and remove the chance of further infection.
- Deadhead the roses and remove any infected foliage. Try not to remove too much because the plant needs enough foliage to feed and survive.
- Either burn the infected leaves or discard in a rubbish bag.
- Do not put infected foliage into a compost bin because this will infect your healthy compost.
- Cover the roses bed with mulch or a good quality organic compost. This will feed the plant with nutrients and protect the soil of further infection.
- Spray the plant with an organic fungicide or make a homemade solution of bicarbonate of soda (baking soda) a drop of eco-friendly dish soap and water.
- Spray the stems, upper and underside of the leaves thoroughly. Re-apply the spray weekly and especially after rain.
Keep roses happy and healthy with ideal growing conditions
With a little TLC your rose bush will spring back to life, healthy and happy. Practice good plant maintenance, removing any further infected foliage. Water the base of the plant in the morning to allow any water on the leaves to dry out throughout the day. Continue to spray the plant throughout the growing season. In the autumn when most of the plants in the flower beds have died back, lightly dig over the soil removing fallen debris. Apply an organic mulch to protect the plant through the winter months and prevent the spread of dormant spores.