Good watering, feeding, pruning and air circulation help to keep roses healthy and disease free.  

 There are two basic methods of spraying roses throughout the growing season. 

1) Preventative spraying- spray regulary (every two weeks or so) to prevent disease from taking hold.

We stock a very good product Combat-

Combat 3 in 1 for Roses is a unique worlds first Insecticide, Fungicide & Fertiliser all in one.

2) Targetted Spraying - Spray your roses when they are attacked by a particular pest or disease. This way you can spray the most effective spray for the disease your rose has.

e.g-

Aphids- spray confidor

Mites- spray with Mavrik or mite killer.

Black Spot- Neem oil, copper spray.

Powdery mildew- fungus fighter, yates Zaleton.

Rust- Copper Oxichloride. 

The old addage, prevention is better than cure applies here though, so be prepared to spray 2 or 3 times to erradicate stubborn diseases.