Plant diseases fungicides

Sulfur and its compounds are among the oldest and most widely used pesticides. Elemental sulfur is especially effective as a dust for the control of mites attacking citms, cotton, and field crops and as a protectant against chiggers, Trombicula spp., attacking humans. Sulfur also is a valuable fungicidal diluent for other dust insecticides and is used in wettable form as a spray mixture. Time sulfur has been a standard dormant spray for the control of the San Jose Quadraspidiotuspemiciosus and for other scales and various plant diseases. Time sulfur is a water-soluble mixture of calcium pentasulfide,... 

The fungicides are among the chemicals of wide use as plant diseases control agents in intensive agriculture. At the same time these pesticides could have toxic effects, when accumulated in man and animals. Because of general society concern about fungicides use, they should be monitored in waters, soils and crops. 

By far the greatest emphasis in the research and application of microbial antibiotics has been concerned with animal and human health. Despite the extent of the problems relating to plant disease, the practical use of antimicrobial antibiotics in plant agriculture has been limited to a few crops and compounds Only streptomycin and actidione (XI) at present enjoy commercial importance. This may be due in part to the wider applicability of the less expensive synthetic fungicides and in part to the difficulty of arousing much public sympathy for a sick plant. 

Alkylenebis(dithiocarbamates) compounds, known also as ethylenebisdithiocarba-mates (EBDCs), are nonsystemic, low-toxicity pesticides with strong and broad fungicide activity on plant diseases. Developed by Rohm and Haas and E. I. du Pont de Nemours, they are used to protect vegetables and fruit crops. 

Copper compounds are used in agriculture to treat mildew and other plant diseases in the food industry as preservatives, additives, or coloring agents in preservatives of wood, leather, and fabrics in coin manufacture and in water treatment (ATSDR1990 Roncero et al. 1992). The use of copper-containing pesticides is traditional along the Mediterranean Coast, especially the use of Bordeaux mixture, a copper sulfate-based fungicide that has been widely used for more than a century to... 

This comprehensive definition makes it elear that a wide number of substances may be eonsidered to be pestieides, and that the eommonality among all pestieides is their ability to provide eontrol over pests. A variety of classifications for pesticides have been developed that are specific for the type of pest controlled. Insecticides, for example, are pesticides that control insects, while herbicides control weeds and fungicides control plant diseases (molds). In addition to these major classifications of pesticides, there are many other classifications. These include nematicides (for nematode control), acaracides (mite control), rodenticides (rodent control), molluscicide (snail and slug control), algacides (algal control), bacteriocides (bacterial control), and defoliants (leaf control). 

Molds and other plant diseases are controlled by fungicides, which act to affect the growth or metabolism of fungal pests. Many different fungicides exist, including sulfur, aryl- and alkyl-mercurial compounds, Aw-dithiocarbamates, and chlorinated phenols. 

Fermentation products have played a rather minor role in the control of plant diseases. Table VI gives a classification of agents used on plants. These are divided into pesticides and growth modulators. The pesticides are classified as bactericides, fungicides, insecticides, miticides, nematicides and herbicides. There are fermentation products in each of these categories, and these are listed in Table VII. 

Sulfur-Based Pesticides. Sulfur (elemental) has been used as an effective acaricide, fungicide, and insecticide. For ease of use, a number of special formulations are available, ranging from sulfur dusts (up to 95% sulfur) a wettable powder (30 to 90%) and paste-like solutions in which the sulfur is ground to a fine colloidal form. Such formulations may contain up to 50% sulfur. Target plant diseases of sulfur when used as a fungicide include apple scab, brown rot. downy and powdery mildew, and peach scab. Against insects, sulfur is effective for mite, scale, and tJirip. Most formulations are not injurious to honeybees. 

The agricultural use of pesticides such as insecticides, herbicides, and fungicides has clearly reduced crop losses due to insects, weeds, and plant diseases in the US and throughout the world. The benefits from agricultural pesticides include improved crop yields, greater availability of fruits, vegetables, and grains, and lower consumer costs (Ecobichon, 1996). 

The much wider disease control spectrum of the benzimidazole fungicides (eg. benomyl, BCM, thiabendazole) - permitted far wider usage. In the beginning, these were suitable for control of numerous plant diseases, but a new phenomenon soon emerged - resistance Due to the specific mode of action of these fungicides, resistance could appear quite rapidly. The conventional fungicides previously used had a broad biocidal activity and resistance had never been experienced. 

Azolyl-0,N-acetals. Significant progress was achieved in the control of plant diseases with the discovery of the highly active class of so-called "triazolyl-0,N-acetal" fungicides at the beginning of the nineteen seventies. These compounds are 0,N-acetals of 2-ketoalde-hydes or 2-hydroxyaldehydes in which the triazole residue forms a part of the 0,N-acetal function. 

In spite of the common mode of action, many other factors are significant for the successful use of individual azole compounds either for control of plant diseases or in the treatment of mycoses. Apart from the nature of the infection, the infection pressure, climatic conditions, the uptake of the fungicide by the plant, its transport and distribution within the plant, and plant compatibility are all important criteria in the complex interaction between pathogen, plant and fungicide. In medicine, high activity, good tolerance and optimal pharmacokinetic properties are prerequisites for therapeutic utility. 

Cohen, Y. Samoucha, Y. (1984) Cross-Resistance to Four Systemic Fungicides in Metalaxyl-Resistant Strains of Phytopthora infes-tans and Pseudoperonospora cubensis. Plant Disease 68, 137-139. 

Benomyl was hailed as the solution to many plant diseases. However, resistance has occurred in Cercospora, Erysiphe, Botrytis, Sclero-tinia, Venturia, and other fungal genera. Fortunately, resistance to triadimefon has not yet appeared in wheat pathogens in areas of the world where the fungicide has been in widespread use for at least ten years. This is a hopeful sign. Triadimenol is closely related to tridimefon but has not yet been used extensively and one can only speculate regarding future resistance problems. 

Siegel, M. R. 1981. Sterol-inhibiting fungicides Effects on sterol biosynthesis and sites of action. Plant Disease 65 986-989. 

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