There is no need for harmful fungicides that can cause severe physical problems, can have a negative affect on outdoor pets and bees, as well as wipe out entire earthworm populations from a single spraying. Balanced nutrition and a couple of minerals can keep your garden disease free without weekly exposure to chemicals. Most plant diseases will leave a healthy plant alone. Plants also have immune systems. This is where a balanced diet, containing 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.
You want to provide potassium from long-lasting natural sources, such as mineral deposits. When potassium is broken down in the 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 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.