Adding a 3 to 4 inch layer of composted manure, backyard compost, or organic mulch will ensure that these good guys have plenty of energy to keep the bad guys at bay. Many gardeners use a variety of chemical fungicides to compete with disease organisms in order to keep their gardens disease free. This is a very counter productive and environmentally insensitive method. If one is inclined to spray, it is the goal of this natural gardener to give you some alternatives to synthetic chemicals. It is widely distributed by retailers and can be found at most garden centers.
Copper sulfate is probably one of most widely used fungicides by farmers and gardeners alike.
It is effective at controlling a wide variety of disease organisms. It is easily found at all nurseries and garden centers and is a very powerful material. The oil extracted from the seed of the Neem tree of India is an effective control for many disease organisms, especially on roses. Neem is also used as an insecticide and is used in soaps and toothpastes to fight bacteria as well. I have a home brewed fungicide that has worked for many years in controlling a number of fungi on veggies and roses.