Gardening Technique Unit Screen//v.1

Fungicides are chemicals that kill or inhibit the growth and development of fungi found on or in plants or in the soil. Most fungicides, called protectants, work by protecting healthy plant parts from infection. They form a chemical barrier between the fungus and the plant tissues, killing the spores and fungal strands before they can enter the plant. Protective fungicides cannot cure fungal infections that are already established on or in plant tissues. A few fungicides, called eradicants, can kill fungi growing on and sometimes in infected plant parts.

Most fungicides are nonsystemic; they do not penetrate the leaves, stems, and roots, but protect only the surface of the plant. Protective, nonsystemic fungicides must be applied so that the plant is thoroughly and evenly covered. Areas that are missed and new growth that is not treated are susceptible to infection. The activity of fungicides diminishes as they are washed off by rain or irrigation water, or broken down by ultraviolet light from the sun. A spreader-sticker helps a fungicide spread over and stick to leaf, stem, and fruit surfaces, and resist degradation. A few fungicides are systemic. They are absorbed into the plant roots, leaves, or stems, and are transferred throughout part or all of the plant, providing protection against invading fungi. Some fungicides (broad-spectrum) control many types of fungi, while others (narrow-spectrum) control only a few types of fungi. Fungi may develop resistance to fungicides, especially narrow-spectrum fungicides that are used exclusively.

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