Rose diseases

Black spot:  this is one of the most common rose diseases and hard to overcome. It's caused by a fungus that creates fuzzy edged black spots on the leaves, which can spread rapidly and cause the leaves to turn yellow. The condition is worse in damp weather, and it's best to try to get disease resistant roses wherever possible. , However, as with many living things, the fungus mutates and can  start to infect even the most resistant of roses in time, also resisting attempts at killing it off with fungicide sprays. 

The best defence is attack, so pick off the leaves as soon as you see any evidence of black spot, and be sure to destroy the leaves rather than compost them. Be sure to pick up any that drop to the ground and if you do need to spray, start early and follow the instructions to spray as often as required to keep the infection down as much as possible. 

Some black spot on roses will not kill them, but heavy infestations will weaken the plant, so keep it under control as much as possible. 

Powdery mildew:

Mildew thrives where the soil is dry, but the surrounding air is moist. It shows itself as powdery grey patches on leaves and the base of buds and young stems.  To prevent and control, water the soil well and mulch with organic matter. Prune the centre of the plant to ensure you have good air circulation and spray with a sulphur based spray to limit the spread. Clear up any fallen leaves and destroy them. 

 Rose rust:

You can identify rose rust by orange spores on the reverse of the leaf, and yellow / orange spots on the surface,  It tends to appear from midsummer onwards and causes the leaves to fall early, reducing the plant's vigour.  If found,  prune out early signs of rust, remove fallen leaves and if necessary spray with a fungicide that is recommended for rose rust.