The present invention discloses methods for prevention and prophylactic treatment of plant diseases by application of glyphosate to a plant in need of treatment. In certain embodiments, soybean plants in need of treatment at vegetative and reproductive growth stages prior to or subsequent to infection, may be treated with glyphosate in order to prevent infection or suppress disease development, symptomatology, and yield loss. Application of a fungicide (e.g. a strobilurin fungicide such as pyraclostrobin or picoxystrobin) together with glyphosate, is also contemplated. Soybean diseases that may be treated in this manner include Soybean Sudden Death, Brown Stem Rot, Stem Canker, and Charcoal Rot, among others.