Synthetic or biosynthetic compounds used to control fungal diseases in animals and plants. A fungistat prevents the spread of a fungus, whereas a fungicide kills the fungus. Seeds and seedlings are protected against fungi in the soil by treating the seeds and the soil with fungicides. Seed-treating materials must be safe for seeds and must resist degradation by soil and soil microorganisms. Some soil fungicides are safe to use on living plants. Others are injurious to seeds and living plants. These compounds are useful because they are volatile. Used before planting, they have a chance to kill soil fungi and then escape from the soil. Formic acid, acetic acid, and propionic acid up through pelargonic acid and capric acid (the C1 -C10 volatile fatty acids) possess significant fungicidal activity. Many of them are present in natural foodstuffs that are resistant to fungal attack. Use of the volatile fatty acids and their salts in bread to prevent ropy mold is widespread. A. I. Virtanen was awarded the Nobel prize in 1945 for his discovery and development of these lower volatile fatty acids to prevent fungal growth and so preserve the nutritious quality of cattle fodders. Since these volatile fatty acids stop fungal growth, they prevent mycotoxin generation and lessen the risk of cancer from exposure to mycotoxins. Two types of fungicides are used to control plant diseases: (1) Surface protectants remain on the plant surface and exert their toxic action on fungi before they have penetrated into plant tissue. (2) Systemic fungicides move into plant tissue and exert their toxic action on fungi which have already penetrated internally. These fungicides can also provide surface protection by acting on fungi before they have penetrated the plant. Most agricultural fungicides are systemic compounds that act at a single target site in fungal cells, such as cell membranes, microtubules, or ribosomes. There have been very few instances of fungal resistance to surface protectant fungicides which is attributed to their action at multiple sites within fungal cells. However, most systemic fungicides that act at a single site have generated serious problems with fungal resistance. A single gene mutation in a fungus can lead to loss of effectiveness of all fungicides in a particular mode-of-action group. Experience has shown that frequent, uninterrupted use of a fungicide increases the risk for development of a resistant strain of the target organism. That risk can be reduced by alternating use of fungicides with different modes of action or by using them in mixtures. Fungi | 
