Utah Plant Disease Control No. 2
Revised March 1998
Major Groups of Chemicals for Plant Disease Control
Plant diseases caused by parasitic microorganisms such as fungi, bacteria, mycoplasma, viruses, and nematodes may sometimes be controlled through the use of chemicals. Chemicals that kill or retard fungi are fungicides, those that control bacteria and mycoplasma are bactericides, and those controlling nematodes are nematicides. Virus diseases cannot be controlled with chemicals. Since most plant diseases are caused by fungi, the majority of the chemicals listed her are fungicides. Fortunately, most of the fungicides and bactericides have low mammalian toxicity and do not present serious health hazards.
Most chemicals used to control plant diseases are "protectants" and must be applied before infection to protect the plant from invasion by a pathogen. A few chemicals are termed "eradicants" since they can eliminate an established infection. Some newer fungicides are systemics, meaning that they are absorbed by the foliage or roots and move within the plant to the site of infection. Systemic chemicals may be protectants, eradicants, or both.
The chemicals listed are grouped according to the active chemical component or chemical base. Only a few representative chemicals are included for each group. The names used are generally the common chemical names, not the commercial or trade names. Compounds accompanied by an asterisk (*) are no longer available for use in the United States.
| INORGANIC FUNGICIDES | |
| Sulfur Fungicides |
Sulfur, in many forms, is the oldest effective fungicide known and is still very effective for some diseases. It is available as a sulfur dust for control of powdery mildew; a wettable powder for control of foliar fruit diseases; and lime sulfur which is frequently used as an eradicant. Sulfur can cause damage to some plants and cannot be used when temperatures exceed 80-90 F. |
| elemental sulfur | |
| wettable sulfur | |
| flowable sulfur | |
| lime sulfur | |
| Copper Fungicides |
This group includes inorganic copper compounds which are practically insoluble in water. The copper ion provides the fungicidal as well as the phytotoxic properties of these compounds. The insolubility of these compounds allows for release of only low levels of copper, adequate for fungicidal activity but not enough to affect the plant. Because of their insolubility, they are not easily washed off by rain. They are relatively safe to use because of their low toxicity to animals and humans. With the exception of Bordeaux mixture and copper sulfate, they are often called fixed coppers. Some of the fungicides are also used to control bacterial diseases and as algaecides in waterways and ponds. |
| Bordeaux mixture | |
| copper sulfate | |
| copper oxychloride | |
| cupric oxide | |
| basic copper sulfate | |
| cupric carbonate | |
| copper hydroxide |
|
ORGANIC FUNGICIDES |
|
| Carbamates | This group of fungicides has been the most important, most versatile, and most widely used of the fungicides. Most contain a metal ion attached to an organic molecule derived from dithiocarbamic acid. They are chiefly used as foliar protectants, although thiram is a seed treatment. |
| ferbam* | |
| maneb | |
| zineb* | |
| mancozeb | |
| thiram | |
| ziram | |
| Dicarboximides | Captan, folpet, and captafol are extremely useful, wide-spectrum fungicides with low toxicity to plants and animals. They have been used primarily as foliage dusts and sprays on fruits, vegetables, and ornamentals. However, because they are probably carcinogens, these older dicarboximides are gradually being withdrawn. The newer dicarboximides--iprodione and vinclozolin--are loosely related to captan, folpet, and captafol but do not have as broad an action spectrum and are much more prone to the development of resistance by target fungi. However, they are quite useful against certain fungi, especially those which cause brown rot in stone fruit and white mold in vegetables. |
| captan | |
| folpet* | |
| captafol* | |
| iprodione | |
| vinclozolin |
| Substituted Aromatics | This is a rather arbitrary classification assigned to the benzene-derived fungicides which exhibit cross-resistance with the dicarboximide fungicides. Most are used as seed and soil treatments while others are used as foliage-protectant fungicides. Pentachlorophenol is used as a wood preservative as well as an herbicide. |
| hexachlorobenzene | |
| pentachlorobenzene | |
| chloroneb* | |
| pentachlorophenol | |
| ethazole (etridiazole) |
| Organic Coppers | These are generally used as foliar protectants. They are usually less toxic to plants than the inorganic coppers. Some of these organic copper fungicides are also used for control of bacterial diseases such as fire blight. |
| copper resinate | |
| copper oleate* | |
| copper oxinate | |
| copper linoleate |
|
ANTIBIOTICS |
|
| streptomycin | Antibiotics are organic compounds produced by microorganisms which inhibit or kill other microorganisms. Penicillin is an antibiotic commonly used for treating human diseases caused by bacteria. Antibiotics are also used in agriculture for control of bacterial and mycoplasma diseases.
Streptomycin is used as a dust or spray to control fire blight and soft rots of vegetables. Terramycin is used as a therapeutic injection to control mycoplasma diseases (e.g., western X of cherry and pear decline). Both are relatively non-toxic to mammals. |
| terramycin | |
|
SYSTEMIC FUNGICIDES |
|
| Benzimidazoles | These are effective against a broad spectrum of plant diseases including powdery mildew, Botrytis and Fusarium. They have both protective and eradicative properties. Their use may be limited, however, because resistance has been noted in several species of fungi. Benomyl (Benlate) has been withdrawn for home garden, landscape, and commercial greenhouse use. |
| benomyl | |
| thiabendazole (TBZ) | |
| thiophanate | |
| Oxathiins | These are very effective seed treatments for control of smuts, rusts, and other Basidiomycetes on cereal crops. |
| carboxin | |
| oxycarboxin |
| Sterol Inhibitors | Compounds in this large group inhibit sterol synthesis in sensitive fungi, especially rusts and mildews. They possess varied chemical structures but are all active at fairly low rates and with low mammalian toxicity. Some have eradicative activity against some fungi. |
| triadimefon | |
| dodemorph acetate | |
| propiconazole | |
| fenarimol | |
|
myclobutanil |
| Strobilurins | This is a new group of fungicides with broad spectrum activity against fungi, but is not registered on many crops due to its recent introduction onto the market. Strobilurins are locally systemic (mesosystemic) with translaminar activity. Fungicides in this class affect the electron transport chain in fungi mitochondria, causing energy production necessary for fungal metabolism to cease. |
| Trifloxystrobin | |
| Azoxystobin | |
| kresoxim-methyl |
| FUMIGANTS | |
| chloropicrin | These chemicals are unrelated, but the compounds are similar in that they are highly volatile with fumigant action. Most are biocides, e.g., they kill all soil-borne microbes, nematodes, and weeds. They are also very toxic to mammals. None of these are available for home use. |
| methyl bromide | |
| ethylene bromide | |
Sherman V. Thomson/Extension Plant Pathologist
Scott C. Ockey/Plant Disease Diagnostician
Listing of commercial products implies no endorsement by the authors or the Utah State Cooperative Extension Service. Criticism of products not listed is neither implied nor intended. Persons using such products are responsible for their use according to the current label directions of the manufacturer. Pesticide labels are legal documents, and it is a violation of federal and state laws to use a pesticide inconsistent with its labeling. The pesticide applicator is legally responsible for its proper use. Always read and follow the label.