fungicide, type of pesticide that is effective against fungal diseases in vineyards. The first of the modern fungicides used for any crop was the bordeaux mixture used on grapevines against downy mildew in 1885. Fungicides are applied by spraying at times which are deemed effective to prevent fungal development or control existing disease. Fungicides are thus classified as protectants or eradicants, depending on the timing of application. Protectant fungicides are applied before the fungus infects the vines and they prevent infection by inhibiting fungal development on the plant surface.