Black spot is a fungus which is airborne and usually found in warm humid conditions. It can be caused by either the climate or by over crowding a rose. Some roses are also more susceptible to disease.
The first sign is black spots on the leaves which goes on to develop yellowing in the area around the spot. If left alone it can spread quite quickly and eventually defoliate the plant. When the fungus has been killed, the leaves will not loose their marking and will eventually drop off.
Remove as many of the affected leaves and buds as possible without denuding the plant.
Spray roses during the growing season with preferred chemical. Never in the heat of the day. Rose sprays used during the growing season will only hold the problem in place. The new growth should become clean.
Note: Always use caution when spraying chemicals and read the instructions on the back of the packaging.
Put all three of these in the recommended dosages (on bottle) into one spray bottle. Religiously spray both under and over leaves till they drip.
This will need to be repeated once a week as it is organic, not systemic.
When winter pruning has been done and all waste removed, spray with Lime sulphur on the plant and ground around. This will clean the area of fungal problems giving you a fresh start in the new growing season.
Prevention is better than a cure
If you are living where roses are known to have this problem, make sure there is good air circulation around your rose and prune to take away dense foliage from the heart of the bush.
Start your chosen spray routine before you see the problem on the leaves.
Make sure your roses are well watered and fed regularly. A happy rose is a healthy rose.
Choose varieties that are strong growers and either newer varieties or those recommended by the rose society in your area.
Important: signs and symptoms will vary significantly between varieties, even within similar categories. The information provided here is a basic summery of the most common affects and will not always be applicable to all rose varieties.