Balanced nutrition and a couple of minerals can keep your garden disease free without weekly exposure to chemicals. Most diseases of plants will leave a healthy plant alone. It is the same with us, if we're healthy we don't get sick. Plants also have immune systems. This is where a balanced diet that contains the proper amount of copper, sulfur, potassium, magnesium and calcium will ensure that certain very commonplace and damaging fungi don't get a foothold in your garden.
Potassium is very important for resistance against powdery mildew and rust on roses.
Not in some crazy amount that is available to the plant in five seconds after application but instead long lasting natural sources from mineral deposits or from other natural source. When potassium is broken down in the soil by a healthy soil it will actually help to prevent the onset and spreading of powdery mildew and rust, which are tough problems for most chemical gardeners to control. High calcium levels along with an abundance of naturally available magnesium will cause your roses to produce thick healthy canes without problems with of slow root development in our heavy soils. Copper and sulfur are the two elements which I use as a spray fungicide if absolutely necessary. Other than dormant spraying minimal spraying should be necessary to prevent fungus and disease if the roses are fed naturally.