Mildew

There are two forms of mildew ‘powdery’ and ‘downy’.

Downy mildew is more likely to occur on roses grown under glass and is far less common than powdery mildew. Extreme differences between day and night time temperatures can be contributory, as can poor ventilation. Unlike Powdery Mildew, Downy mildew is more brown or blue in shade and will attack the mature leaves first. Use a proprietary fungicide to prevent it spreading and remove any affected leaves. Mildew is difficult to control organically, the only advice to offer is that a well-tended rose will be less susceptible than a neglected one and that if it does appear ensure that the affected leaves are removed and destroyed.

Powdery mildew is the most prevalent in the garden and is most likely to occur in situations that are dry and airless. A grey to white coloured powder will appear initially on young leaves and succulent shoots, causing them to become distorted and therefore stalling the growing process. If it is not checked it will then spread onto older leaves and stems and eventually onto flower buds where it will prevent them from opening and thus causing them to fall. Because it is not often seen until after the first flush of flowers, when the summer heat is more intense, a degree of prevention can be assumed with a regular spraying regime earlier on. Once in place it is difficult to cure although fungicides will prevent it from spreading. It is best to cut it away and destroy it.