Fungicides with copper

The hydrogen peroxide is normally destroyed by catalase and peroxidases, but some may be transformed to OH-, the hydroxyl radical, which is extremely reactive and modifies all biomolecules in its vicinity. Membrane lipids are destroyed. The mode of action of copper salts and paraquat is in many ways the same, although their target organisms are quite different. 

It may be of interest to know that the most efficient peroxidase contains selenium and is the reason why selenium is a necessary trace element. The most efficient superoxide dismutase in eukariotic cells contains copper. Copper is thus an important element for protection against free radicals but is also responsible for their formation. Copper ions form very stable SH compounds and would have been toxic without being superoxide generators. 

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In the European Union (EU) replacement of copper-based fungicides with other methods of disease control is a priority in organic farming policy (Anonymous, 2002). They were due to be prohibited by law for use in organic farming in the EU from March 2002 but the ban was delayed because of the increased risk of crop diseases and associated economic losses for organic producers in the medium to long term, until effective alternative... 

Crop protection with copper-based fungicides in organic production systems... 

Table 18.1 Examples of crop diseases treated with copper-based fungicides (based on Gianessi and Puffer, 1992 and British Crop Protection Council, 2004)... 

Batusic, M., Gangl, H., and Tiefenbrunner, W. (1999). The influence of inorganic fungicides with the agents copper hydroxide and sulphur on fermentation and population dynamics of the yeasts Sacchromyces cerevisiae Hansen and Sacchromyces bayanus in must. Pflan-... 

Copper Naphthenate. When naphthenic acids are neutralized with alkali, they react with a number of metal salts to form naphthen-ates. Because of its fungicidal properties, copper is normally the metal used. The naphthenic acids 2 are structurally variable (3). The... 

Stems with sunken lesions. Cause Anthracnose. Sunken lesions with pink blisters appear on stems. Plants may die. Cultural controls such as regular fall cleanup and thinning stems to improve air circulation are effective. Treat severe problems with copper fungicide sprays. 

How to Use You can purchase pyrethrin products alone or combined with fungicides, like copper or sulfur. To apply pyrethrin safely and effectively, wear protective clothing and follow label directions for mixing, spraying, or dusting. Two applications may be necessary for complete control. 

The fungicidal properties of dithiocarbamates, like thiram, are probably associated with their ability to chelate with essential trace metals such as copper and zinc. Additionally, the 1 1 metal chelates are themselves fungicidal with the ability to penetrate lipid barriers in the fungal cell, and are probably the ultimate toxicants in these fungicides.3 Alkyl esters of dithiocarbamic acids are readily prepared by treatment of sodium dithiocarbamate (4) with the appropriate alkyl halide (Scheme 20). 

This is important, because more authors have recently reported the development of resistance to copper compounds (Reddy and Apparao, 1970). When systematically sprayed with copper-containing fungicides, Gloeosporium ampelophagum, which causes anthranose in vine, developed over the course of time a 5 to 8-fold copper tolerance. Resistance has also been demonstrated in vitro by these authors. 

Copper(II) oxychloride came into use at the beginning of the century, and due to its very easy handling, economical preparation and relatively low price, is today the most widely used copper-containing fungicide. This compound, 3Cu(OH)2 CuClj HjO, is a green or bluish-green powder insoluble in water, and is prepared by the oxidation of copper(I) chloride solutions with air. It is generally used as a wettable powder, sometimes as pasty or liquid preparations. It is compatible with almost all pesticides. In some modern formulations it has been combined with copper strearate or oil (Toman et al., 1967 Screenivasan, 1968). 

Powell (1946) and Mason (1948) found that the 2 1 complex of 8-hydroxyquinoline with copper, oxine-copper, has a stronger fungicidal action than 8-hydroxyquinoline. Albert et al. (1953) attributed this to the fact that the organic part of the compound makes copper lipoid-soluble and thus accelerates its penetration into the cell. Inside the cell the 2 1 complex dissociates into a 1 1 complex and free 8-hydroxyquinoline. The active toxic agent is the ionised 1 1 complex of nonlipoid properties, which reacts with the enzymes in the fungus and blocks their function. This theory is also supported by the research work of McNew and Gershon (1969). 

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