Causes, Prevention and Cures
Although it looks unsightly, Black Spot on Roses can easily be prevented if you take few basic precautions. Good watering and planting methods are number one.
Cleanliness in the garden by cleaning up and removing any clippings is second. And of course you can look for ‘Black Spot Resistant’ roses if you happen to live in humid areas where the problem is most pronounced.
What is Black Spot
‘Black spot’ is a fungal disease that causes purple or black spots on the foliage of roses, (picture right) the foliage then to turn yellow and drops off. So thats the severe case, in milder cases only some foliage will be affected, and this will depend on the climate, and the type of rose, some roses are more resistant to black spot than others.
What causes Black Spot ?
Its a fungus (Diplocarpon rosae) that thrives it wet humid conditions but can also affect roses in cooler areas.
How do we prevent Black Spot ?
Good air circulation, watering techniques, remove all diseased foliage and wood. Use appropriate techniques listed below.
- Avoid watering the foliage
- Water roses in the morning so that they have a chance to dry before nighttime.
- Remove all infected foliage from the ground and plant.
- Prune away diseased stems.
- All diseased foliage and wood should be burnt or disposed of.
- Always used sterilised secateurs.
- Mulch around plants helps prevent splash from watering so mold spores are less likely to splash onto the foliage.
- Water with a watering wand which has a slower and softer flow, again preventing splash back from the soil.
Treatments and Cures For Black Spot on Roses
Lots of fungicides are available, in spray form. Some larger rose growers spray with lime sulphate in winter and then use Triforine (a systemic fungus control) in spring, lots of other sprays are available and all do a similar job, however we suggest using a different treatment or spray each year and the fungus is very adaptable and will become resistant to an extent.
Organic methods to treat black spot. Two recipes will work well.
Bicarb soda water, detergent, seaweed solution.
For a 5 litre spray bottle use
- 2 tsp of bicarb soda
- 1/4 tsp detergent or liquid horticultural soap
- 1/2 tsp seaweed solution/seaweed feriliser
Mix with the 5 litres of water and spray both beneath and on top of the leaves.
Milk and Water
This is an old remedy.
- 1 part milk
- 2 parts water
Again spray both beneath and on top of the leaves.
What about Black Spot resistant roses ?
Yes they do exist and to a certain extent are a great alternative, especially in warmer climates, however the fungus, as mentioned does tend to adapt, so be aware? Knockout roses are regarded as being one of the best types of resistant roses.
Can you prevent Black Spot?
The best prevention is to provide roses a sunny position, do not plant to close together to improve air flow and remove any diseased material and dispose of it.