The mildew that normally affects roses, is a form of powdery mildew. There is also a more serious - but rarer for of mildew (Downy Mildew) which this article is not concerned with. The white powdery mildew mould start off on the leaves and soon spreads to buds and other young rose shoots.
The affected foliage curls up and eventually falls off if not treated. Flower buds may not open properly, and if they do, will be severely affected. As distinct from Blackspot, Rose mildew is prevalent in dry hot conditions - in particular when the root area is dry and lacking moisture.
A light case of Powdery mildew in early summer.
It usually becomes visible in mid/late summer and autumn. In particular, hot autumns - with dry hot days followed by cold nights - will bring the powdery mildew disease to the forefront.
Poor air circulation is a well documented cause, and is particularly a problem with climbing roses against a wall, or bush roses within confined spaces.
The affected leaves and shoots showing any sign of mildew, should be cut off and burned. Combine this activity with a good all-round rose fertiliser feed to help establish new healthy growth. A good mulching of rotted organic matter will help conserve moisture at the root area.
There are several varieties that are very susceptible to rose Mildew - among them being Frensham and Iceberg climbing roses.
A preventative spraying routine can be started in early spring, though it is normally sufficient to start spraying at first sign of the mildew. Repeat applications of rose fungicide, or a combined spray will then be necessary - every two weeks. Read the label.
A good organic treatment for rose mildew, is with a mixture of Baking Powder and vegetable oil (The latter to help the baking powder to 'stick' to the rose leaves.
Prevention is best achieved by
In this case, the powdery mildew has all but taken over the rose bush and leaf drop will be inevitable. All that can be done at this stage, is to pick off the dead leaves and destroy by burning. Spray the remaining bush weekly - and the soil around it with Multirose or Systhane fungicide. Keep the rose well watered and ensure that the water soaks well into the root zone.
Far better to have 'prevented' this degree of rose mildew by following steps above.