Copper fungicidal action

According to the investigations of Fattinger (1950), the fungicidal action of copper is enhanced by cadmium, cobalt, nickel and zinc compounds in Alternaria tenuis and Trichothecium roseum cultures. Zinc sulfate (ZnSO 7HjO) was tried in place of copper sulfate its effect however was inferior to that of the copper compound. Nevertheless, it is still used against rosette disease a physiological disease caused by zinc deficiency. 

McCallan and Wilcoxon (1936) were the first to report that fungal spores can solubilise copper. In the bathing medium of Neurospora sitophilus spores they detected malic acid and certain amine acids which were able to dissolve copper even from dry deposits of Bordeaux mixture. In this case, complex compounds of the copper(II) ions are formed and, as shown already by the investigations of Bodnar and Terenyi (1930), the fungicidal action of copper(II) complexes proved to be superior to that of copper(II) ions. Horsfall et al. (1937) made similar observations. This phenomenon can be explained by the much higher lipoid solubility of copper(II) complexes (Horsfall, 1957 Durkee, 1958) which allows them to penetrate the cell more easily. They dissociate in the cell, and copper(II) ions are liberated. Thus, complex-forming compounds seem to aid the transport of the... 

The composition and action of basic copper(lI) carbonate depend on its mode of preparation. This salt of composition, Cu(OH)2 CuCOj, is known in mineralogy as malachite. It is a green substance, practically insoluble in water. It dissolves in ammonium hydroxide, and was previously used for the treatment of vine against downy mildew (Gastine, 1889). Later, it was used for treating seeds, either alone or in combination with other (arsenic) compounds. It has found wide use, particularly in the USA. The blue compound of composition 2CuCOj Cu(OH)j, known by the name azurite, has a poorer fungicidal action. 

The initial toxicity of a freshly prepared aqueous dazomet solution is low, but after 24 hours, when a substantial quantity of the N-methyldithiocarbamate ester has been converted into methylisothiocyanate, its fungicidal activity increases considerably. A similarly strong fungicidal action develops on the addition of copper ions to the freshly prepared solution, which indicates that the ester bond has been ruptered and the active copper complex of N-methyldithiocarbamate has formed. 

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). 

Most fungicides developed for plant disease control before 1965 are multisite biochemical inhibitors that lack the chemical properties and biological specificity required for internal therapeutic action in higher plants. This group of plant protectants include such compounds as the Inorganic copper fungicides, captan, chlorothalonil, dithiocarbamates and chlorinated quinones. 

Organic tin compounds are contact fungicides. Their range of action is similar to that of copper compounds, but they are considerably more potent. However, their use for plant protection is limited by their phytotoxicity to more sensitive plants, and by their strong and lasting toxic action on warm-blooded organisms. Recent research has been concerned mainly with the reduction of both of these harmful effects. 

The range of action of carboxamides can be extended also to fungus species less sensitive to them by combination with protective fungicides, which also produce a partial synergistic effect in the combined seed-dressings. Copper oxine, chloroneb, mancozeb and other fungicides are used in combination with carboxamides (Richard and Vallier, 1969 Ranney, 1972 Baicu and Nagler, 1974). 

Inclusion of an effective fungicide in poly(ester-urethanes) prevents their degradation by microbiological action. Effective agents of this type include copper-8-quinolinolate and A -(trichloromethylthio) phthalimide (Tungitrol 11 —Nuodex). Poly(ether-urethanes) resist microbiological degradation. 

Derivatives of thiocarbamic acid are a family of very important fungicides used in many plant-care products. Manganese salts (maneb), zinc salts (zineb), sodium and iron salts have no action on aluminium, whatever their degree of dilution. On the other hand, copper salts of dithiocarbamic acid may attack aluminium. 

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