Blackspot is probably the most off-putting aspect of rose growing, however there are a few simple steps that will prevent it.
Choose blackspot resistant varieties, there are lots of them and we are happy to recommend them – but please note they are resistant not immune. If your neighbour has blackspot-infected roses, so will you, only at a later date!
Keep your roses well fed with a proper rose fertilizer at least twice a season, but if you’re on poor sandy or chalky soil feed monthly, from March to August.
Try to avoid watering in the evening, water in the morning, trying to keep the leaves dry or, better, invest in a watering system that uses a seep hose. Evening watering encourages the growth of fungal infections as the leaves will remain damp overnight.
Prune to the heights mentioned in How to Grow.
If you use a fungicide or insecticide, make sure that you use different ones as blackspot builds up resistance to such products in a similar way to bugs and antibiotics. Suitable products include Provado Ultimate Bug, Greenfly & Blackfly Killer and Rose Clear Ultra. Alternatively, Greenacres Horticultural Supplies make a product called Wettable Sulphur and this is very effective in treating blackspot. However, it will take a year for you to see results.
We have had success with Uncle Tom’s Rose Tonic which we use on the nursery. Spraying regularly helps the plant fend off nasties!
Finally, it’s important not to get stressed out by blackspot as nothing in nature is perfect.