FUNGICIDES

Fungicides are a class of pesticides that are marketed specifically for the purpose of killing or inhibiting the growth of fungus. Fungus are defined under the Federal Insecticide, Fungicide, and Rodenticide Act as "any non-chlorophyllbearing thallophyte (that is, any non-chlorophyllbearing plant of a lower order than mosses and

Table 1

liverworts), as, for example, rust, smut, mildew, mold, yeast, and bacteria, except those on or in living man or other animals and those on or in processed food, beverages, or pharmaceuticals." Although the United States statutory definition excludes fungi that would grow on food, beverages, and pharmaceuticals, biologically these are fungi. Thus, in the United States, products designed to kill fungi are regulated by the U.S. Environmental Protection Agency as pesticides and/or by the Food and Drug Administration under food and drug law (a chemical may fall under the purview of both agencies).

The benefits of fungicide use have been many. In agriculture, fungicides control pests that may rob water and nutrients from crop plants or may cause food spoilage as the products are brought to market. Fungicides may also prevent the growth of fungi that produce toxins, such as aflatoxins. Fungicides also have important industrial applications and are important in preserving the purity and safety of certain pharmaceutical agents.

In 1997 there were an estimated $0.8 billion in sales of fungicides in the United States, about 7 percent of the total pesticide market. In 1997, worldwide, 5.7 billion pounds of pesticides were used, of which 0.5 billion were fungicides. Of the1.2 billion pounds of conventional pesticides used in the United States in 1997, a total of 81 million pounds of fungicides were used; 79 percent of the use was in agriculture. Generally, the United States has experienced a downward trend in total fungicide use since 1970.

There are numerous classes of fungicides, with different modes of action as well as different potentials for adverse effect on health and the environment (see Table 1). Most fungicides can cause acute toxicity, and some cause chronic toxicity as well. Hexachlorobenzene, now banned or severely restricted in most parts of the world, has been associated with human poisoning from contaminated seed grain and poisoning of infants from misuse in laundry solutions. Metam sodium and other thiocarbanates are skin irritants that can cause reactive airway disease at low doses and severe toxicity and even death at high doses. The ethylene bis dithiocarbamates (EBCDs) are suspected human carcinogens and are tightly regulated in the United States.

Organic mercurials have caused severe acute and chronic toxicity. Worldwide, there have been a number of incidents of treated seed grain fed to people, with disastrous consequences in terms of acute poisoning and damage to fetuses. Phenyl mercuric acetate is no longer used as a paint preservative in the United States because it off-gases elemental mercury into the air, with the potential for causing toxicity to young children. Organotin compounds also have serious human toxicity and are very toxic to the environment; their use is banned or severely restricted in most of the world. Likewise, due to human toxicity concerns, cadmium is no longer used as a fungicide in the United States.

Lynn R. Goldman

(see also: Mercury; Pesticides; Toxic Substances Control Act; Toxicology )

Bibliography

Reigart, J. R., and Roberts, J. R. (1999). Recognition and Management of Pesticide Poisoning, 5th edition. Washington, DC: U.S. Environmental Protection Agency.

Sine, C., ed. (1998). Farm Chemicals Handbook. Willoughby, OH: Meister.

Fungicide

A fungus is a tiny plant-like organism that obtains its nourishment from dead or living organic matter. Some examples of fungi include mushrooms, toadstools, smuts, molds, rusts, and mildew.

Fungi have long been recognized as a serious threat to natural plants and human crops. They attack food both while it is growing and also after it has been harvested and placed into storage. One of the great agricultural disasters of the second half of the twentieth century was caused by a fungus. In 1970, the fungus that causes southern corn-leaf blight swept through the southern and midwestern United States and destroyed about 15% of the nation's corn crop. Potato blight, wheat rust, wheat smut, and grape mildew are other important disasters caused by fungi.

Chestnut blight is another example of the devastation that can be caused by fungi. Until 1900, chestnut trees were common in many parts of the United States. In 1904, however, chestnut trees from Asia were imported and planted in parts of New York. The imported trees carried with them a fungus that attacked and killed the native chestnut trees. Over a period of five decades, the native trees were all but totally eliminated from the eastern part of the country.

It is hardly surprising that humans began looking for fungicides—substances that will kill or control the growth of fungi—early on in history. The first of these fungicides was a naturally occurring substance, sulfur. One of the most effective of all fungicides, Bordeaux mixture was invented in 1885. Bordeaux mixture is a combination of two inorganic compounds, copper sulfate and lime.

With the growth of the chemical industry during the twentieth century, a number of synthetic fungicides have been invented; these include ferbam, ziram, captan, naban, dithiocarbonate, quinone, and 8-hydroxyquinoline.

For a period of time, compounds of mercury and cadmium were very popular as fungicides. Until quite recently, for example, the compound methylmercury was widely used by farmers in the United States who used it to protect growing plants and to treat stored grains.

During the 1970s, however, evidence began to accumulate about a number of adverse effects of mercury- and cadmium-based fungicides. The most serious effects were observed among birds and small animals who were exposed to sprays and dusting or who ate treated grain. A few dramatic incidents of methylmercury poisoning among humans, however, were also recorded. The best known of these was the 1953 disaster at Minamata Bay, Japan.

At first, scientists were mystified by an epidemic that spread through the Minamata Bay area between 1953 and 1961. Some unknown factor caused serious nervous disorders among residents of the region. Some sufferers lost the ability to walk, others developed mental disorders, and still others were permanently disabled. Eventually researchers traced the cause of these problems to methylmercury in fish eaten by residents of the area. For the first time, the terrible effects of the compound had been confirmed.

As a result of the problems with mercury and cadmium compounds, scientists have tried to develop less toxic substitutes for the more dangerous fungicides. Dinocap, binapacryl, and benomyl are three examples of such compounds.

Another approach has been to use integrated pest management and to develop plants that are resistant to fungi. The latter approach was used with great success during the corn blight disaster of 1970. Researchers worked quickly to develop strains of corn that were resistant to the corn-leaf blight fungus and by 1971 had provided farmers with seeds of the new strain.

See also Minamata disease

[David E. Newton ]

RESOURCES

BOOKS

Chemistry and the Food System. A Study by the Committee on Chemistry and Public Affairs. Washington, DC: American Chemical Society, 1980. Fletcher, W. W. The Pest War. New York: Wiley, 1974.

Selinger, B. Chemistry in the Marketplace. 4th ed. Sydney: Harcourt Brace Jovanovich, 1989.

Fungicide

Fungicides are chemicals that inhibit the growth of fungi. A fungus is a tiny plantlike organism that obtains its nourishment from dead or living organic matter. Some examples of fungi include mushrooms, toadstools, smuts, molds, rusts and mildew.

Fungi have long been recognized as a serious threat to plants and crops. They attack food while it is growing and after it has been harvested and is placed in storage. One of the great agricultural disasters of the second half of the twentieth century was caused by a fungus. In 1970, the fungus that causes southwest corn-leaf blight swept through the southern and Midwestern United States and destroyed about 15% of the nation’s corn crop. Potato blight, wheat rust, wheat smut, and grape mildew are other important diseases caused by fungi. Fungi can attack agricultural crops, garden plants, wood and wood products (dry rot in particular is a major problem), and many other items of use to humans.

Fungicides usually kill the fungus that is causing the damage. Sulfur, sulfur-containing compounds, organic salts of iron, and heavy metals are all used as fungicides. Other fungicide types include carba-mates or thiocarbamates such as benomyl and ziram, thiozoles such as etridiazole, triazines such as anilazine, and substituted organics such as chlorothalonil. Many non-drug fungicides have low mammalian tolerance for toxicity, and have been shown to cause cancer or reproductive toxicity in experimental animal studies.

Fungicides operate in different ways depending upon the species that they are designed to combat. Many are poisons and their application must be undertaken carefully or over-application may kill other plants in the area. Some fungicides disrupt some of the metabolic pathways of fungi by inhibiting energy production or biosynthesis, and others disrupt the fungal cell wall, which is made of chitin, as opposed to the cellulose of plant cell walls. Chitin is a structural polysaccharide and is composed of chains of N-acetyl-D-glucosamine units. Fungal pathogens come from two main groups of fungi, the ascomycetes (rusts and smuts) and the basidiomycetes (the higher fungi—mushrooms, toadstools, and bracket fungi).

Human fungal infections, such as athlete’s foot, can be treated by fungicides normally referred to as antifungal agents or antimycotics. Compounds such as fluconazole, clotrimazole, and nystatin are used to treat human fungal infections.

The first known fungicide was a naturally occurring substance, sulfur. One of the most effective of all fungicides, Bordeaux mixture, was invented in 1885. Bordeaux mixture is a combination of two inorganic compounds, copper sulfate and lime.

With the growth of the chemical industry during the twentieth century, a number of synthetic fungicides have been developed: these include ferbam, ziram, naban, dithiocarbonate, quinone, and 8-hydroxyquinoline. For a period of time, compounds of mercury and cadmium were very popular as fungicides. Until quite recently, for example, the compound methylmercury was widely used by farmers in the United States to protect growing plants and treat stored grains. During the 1970s, however, evidence began to accumulated about a number of adverse effects of mercury- and cadmium-based fungicides.

As a result of the problems with mercury and cadmium compounds, scientists have tried to develop less toxic substitutes for the more dangerous fungicides. Dinocap, binapacryl, and benomyl are three examples of such compounds.

Another approach has been to use integrated pest management and to develop plants that are resistant to fungi. The latter approach was used with great success during the corn blight disaster in 1970. Researchers worked quickly to develop strains of corn that were resistant to the corn-leaf blight fungus and by 1971 had provided farmers with seeds of the new strain.

Fungicide

A fungus is a tiny plant-like organism that obtains its nourishment from dead or living organic matter . Some examples of fungi include mushrooms , toadstools, smuts, molds, rusts and mildew .

Fungi have long been recognized as a serious threat to plants and crops . They attack food both while it is growing and after it has been harvested and placed in storage. One of the great agricultural disasters of the second half of the twentieth century was caused by a fungus. In 1970, the fungus that causes southwest corn-leaf blight swept through the southern and Midwestern United States and destroyed about 15% of the nation's corn crop. Potato blight, wheat rust, wheat smut, and grape mildew are other important diseases caused by fungi.

Chestnut blight is another example of the devastation that can be caused by fungi. Until 1900, chestnut trees were common in many parts of the United States. In 1904, however, chestnut trees from Asia were imported and planted in parts of New York. The imported trees carried with them a fungus that attacked and killed the native chestnut trees. Over a period of five decades, the native trees were all but totally eliminated from the eastern part of the country.

It is hardly surprising that humans began looking for fungicides (substances that will kill or control the growth of fungi) early in history. The first of these fungicides was a naturally occurring substance, sulfur . One of the most effective of all fungicides, Bordeaux mixture, was invented in 1885. Bordeaux mixture is a combination of two inorganic compounds, copper sulfate and lime.

With the growth of the chemical industry during the twentieth century, a number of synthetic fungicides have been developed: these include ferbam, ziram, naban, dithiocarbonate, quinone, and 8-hydroxyquinoline. For a period of time, compounds of mercury and cadmium were very popular as fungicides. Until quite recently, for example, the compound methylmercury was widely used by farmers in the United States to protect growing plants and treat stored grains. During the 1970s, however, evidence began to accumulated about a number of adverse effects of mercury- and cadmium-based fungicides. The most serious effects were observed among birds and small animals who were exposed to sprays and dusting or who ate treated grain. A few dramatic incidents of methylmercury poisoning among humans, however, were also recorded. The best known of these was the 1953 disaster at Minamata Bay, Japan. At first, scientists were mystified by an epidemic that spread through the Minamata Bay area between 1953 and 1961. Some unknown factor caused serious nervous disorders among residents of the region. Some sufferers lost the ability to walk, others developed mental disorders, and still others were permanently disabled. Eventually researchers traced the cause of these problems to methylmercury in fish eaten by residents in the area.

As a result of the problems with mercury and cadmium compounds, scientists have tried to develop less toxic substitutes for the more dangerous fungicides. Dinocap, binapacryl, and benomyl are three examples of such compounds.

Another approach has been to use integrated pest management and to develop plants that are resistant to fungi. The latter approach was used with great success during the corn blight disaster in 1970. Researchers worked quickly to develop strains of corn that were resistant to the corn-leaf blight fungus and by 1971 had provided farmers with seeds of the new strain.

See also Agrochemicals; Herbicides; Pesticides.

Fungicides

Fungicides are chemicals that inhibit the growth of fungi . Fungi can attack agricultural crops, garden plants, wood and wood products (dry rot in particular is a major problem), and many other items of use to humans. Fungicides usually kill the fungus that is causing the damage. Sulfur, sulfur-containing compounds, organic salts of iron, and heavy metals are all used as fungicides. Other fungicide types include carbamates or thiocarbamates such as benomyl and ziram, thiozoles such as etridiazole, triazines such as anilazine, and substituted organics such as chlorothalonil. Many non-drug fungicides have low mammalian tolerance for toxicity, and have been shown to cause cancer or reproductive toxicity in experimental animal studies.

Fungicides operate in different ways depending upon the species that they are designed to combat. Many are poisons and their application must be undertaken carefully or over-application may kill other plants in the area. Some fungicides disrupt some of the metabolic pathways of fungi by inhibiting energy production or biosynthesis, and others disrupt the fungal cell wall, which is made of chitin , as opposed to the cellulose of plant cell walls. Chitin is a structural polysaccharide and is composed of chains of N-acetyl-D-glucosamine units. Fungal pathogens come from two main groups of fungi, the ascomycetes (rusts and smuts) and the basidiomycetes (the higher fungi—mushrooms, toadstools, and bracket fungi).

Human fungal infections, such as athlete's foot, can be treated by fungicides normally referred to as antifungal agents or antimycotics. Compounds such as fluconazole, clotrimazole, and nystatin are used to treat human fungal infections.

See also Candidiasis; Mycology