Published on Organic Gardening (http://www.organicgardening.com)
A thin layer of compost spread over the soil’s surface will fight plant diseases better than any chemical fungicide.
Links:
[1] http://www.organicgardening.com/compost-prevents-diseases-380
[2] http://www.organicgardening.com/learn-and-grow/common-plant-diseases-and-disorders