Fosphite: Fosphite is a reduced-risk fungicide for use on potato. Fosphite's active ingredient is phosphorus acid, which is toxic to tovarious fungi like phytophthora, pythium and downey mildew. When used in accordance with the label, Fosphite can offer superior protection against these diseases while remaining safe to applicators and the environment.
Benefits also include: excellent control of pink rot and late blight, the low application rate translates into lower cost, it's registered as a "Reduced Risk Pesticide" by the EPA, it's environmentally safe, kills fungi and is non-phytotoxic. It also works as a foliar and soil applied fungicide.
Additional benefits include the ability of phosphate ions to help promote proactive immune systems in potato plants. Fosphite kills the disease on contact and helps boost the plants natural defenses against further infection. Do not use Fosphite in conjunction with copper products.