Fungicides are chemicals that can limit and control to some degree, the attack on plants from spores, and moulds. While there are several available for use on flowers and decorative plants, there are very few that are licensed to be used by Amateurs for use on food. There are none that can be described as being truly organic, but the organic organisations allow under duress, Bordeaux mixture, which is based on copper.
Bordeaux mixture can help to control Blight on potatoes, and tomatoes. It is used for the control of Canker on apples and pears.
“Fruit and Vegetable Disease Control” (Dithane no longer available). This is a very useful chemical for the control of Blight on potatoes and tomatoes. To be effective, it is best applied by spraying the plants just before the blight is expected to strike, and every two weeks while blight is active.