This is the most common problem in gardens. It is a fungus encouraged by humid still conditions. The first sign is a white powder seen on the new growth of the plants and bud stems, some distortion of the leaves and flower heads may occur. This fungus can travel on the wind or from water splash. When killed the white powder will turn a grey colour.
Treatment
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.
Organic Rose care recommendation.
Eco Oil - for things that bite Eco Fungicide - for the diseases Charlie Carp - foliar feed (this will make your garden smell a bit fishy but it is great stuff)
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 have 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.
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.
