Fungicides are chemicals used to cure diseases in gardens, lawns, crops and even carpets. Companies will use fungicides to protect seeds during shipment and storage. There are many different chemicals used in fungicides, and each one treats a different disease. The many potential dangers associated with fungicides depend on the chemical and its misuse. Every fungicide package contains several warnings and steps for safe use. Fungicides are dangerous for humans, nature and animals if used improperly.

Toxicity: Humans
Wearing long sleeve shirts, shoes with socks, gloves, a covering over the mouth and safety glasses are all safety requirements when applying fungicide. Many of the chemicals have adverse effects that harm the skin, lungs and eyes. Fungicide chemicals such as metam-sodium, ziram and ferbam are known to cause contact dermatitis, chronic skin disease, visual disturbances, pulmonary edema and other effects. Some may be fatal. All fungicides are poisonous when ingested.The chemical captafol may effect people with Asthma, and drinking alcohol after being exposed to thiram may also cause adverse reactions.

Toxicity: Nature
Many fungicides, such as chlorothalonil, are toxic to animals. According to the University of South Florida, chlorothalonil is dangerous for tadpoles, oysters and fish. Rain, or irrigation, may cause the fungicide applied to plants to run off into nearby water or contaminate groundwater. Not only does that harm the animals in the water, but it also contaminates the water which other animals may drink. Strong winds may blow the chemicals away from the diseased crop and toward other non-diseased areas. Labels state not to spray fungicides in winds greater than 10 miles per hour. Grains treated with fungicides should not be fed to livestock, as it may poison them.

Resistance
Over time, a fungus may become resistant to the chemicals in fungicides. The fungus evolves, creating a mutant gene, and becomes immune to the fungicide. There are a couple of reasons for the resistance. Many fungicides attack only one part of the fungus, called single site mode of action, and so the fungus only needs to change one thing to become immune. Fungicides with single site mode of action are used because they are less dangerous on the environment. Heavy doses of the same fungicide on the same fungus may also cause resistance. Most fungi that become resistant to one fungicide will become resistant to others. It is called cross-resistance.

Alternatives
When planting, use plants or vegetables that are resistant to disease. Many different plants have resistance to different diseases, reducing the need for fungicide application. If a fungicide is necessary, there are safer organic fungicides available. These fungicides are safer for the environment, but may still cause problems if used improperly. Some organic fungicides include copper, sulfur, natural oils and baking soda. Misuse of copper and sulfur may burn plants. Some organic fungicides are harmful if ingested. Always read labels before using any fungicide.

From：www.ehow.com