The present invention relates to the plant-protection field and has more particularly as subject the antifungal treatment of crops, as well as cupric compositions which can be used in this treatment.
Cultivated plants are subject to many diseases due in particular to phytopathogenic fungi, the most well known of which is Plasmopara viticola, which is responsible for grape downy mildew.
The means for combating these parasites involve various types of compositions which may be classified in two main categories:
cupric compositions, the active principle of which is the copper ion Cu2+;
synthetic organic products, the activity of which is not directly related to the presence of Cu2+ copper ions.
The role of the Cu2+ copper ions as means for protecting against diseases caused by phytopathogenic fungi has been known for a long time. Thus, for example, copper sulphate is known to be a very good fungicide but it is highly phytotoxic, due to its acidity and to its high solubility in water, where all the copper is found in the form of aqueous cupric ions (Cu2+(aq)).
In order to overcome this problem of phytotoxicity, the use of copper sulphate alone has been replaced by that which makes use of its neutralized form, it being possible for this neutralization to be carried out with an alkaline agent, such as, for example, calcium hydroxide or sodium hydroxide.
One of these neutralized forms, which has been used for a very long time and is still being used, is the result of an aqueous mixture of copper sulphate and lime, a mixture which is better known under the name of Bordeaux mixture.
Other conventional-type cupric compositions which are also used in this field are, for example, copper oxychloride, copper hydroxide, copper carbonate and cuprous oxide.
These conventional cupric fungicides are generally formulated in the form of aqueous suspension or soluble concentrates, dispersible granules or wettable powders.
They are generally used in the proportion of 3000 g of copper metal equivalent per 200 liters of water and per hectare, by spraying over the plants to be protected (foliage, stem, fruits).
Cupric fungicides, such as Bordeaux mixture, copper oxychloride, copper hydroxide, copper carbonate and cuprous oxide, are complexes which are very slightly soluble in water at neutral pH. The amount of soluble aqueous copper (Cu2+(aq)) released by these is of the order of a few ppm (1 to 10 mg/l) at pH 7, but this very small amount of Cu2+(aq) copper is sufficient to ensure the antifungal activity with respect to phytopathogenic fungi such as Plasmopara viticola. 
However, despite their fungicidal effectiveness, conventional cupric fungicides exhibit three major disadvantages:
the non-control of the amount of Cu2+(aq) active principle released after application,
the disappearance of a portion or of all of the antifungal activity of Cu2+(aq) by formation of complexes with some biological molecules (in particular thiols) present at the surface of the leaf,
partial coverage of the plant, the extent of which varies according to the fineness of the product.
Despite good neutralization of the cupric compound and of its formulation, the amount of aqueous copper released can vary substantially and can cause phytotoxicity. This is because the amount of Cu2+(aq) copper released from the solid composition deposited on the leaves during spraying changes in a way which cannot be predicted as a function of the variation in the various factors of the environment in the region of the solid. These factors are, for example, ambient humidity, dissolved carbon dioxide gas, the temperature and the presence of certain plant and/or microorganic exudates, such as acetic acid. The amount of Cu2+(aq) can thus change, for example, from a few ppm to more than 100 ppm, resulting in a risk of phytotoxicity. Although Bordeaux mixture is the cupric compound which is the least sensitive to these variations, the equilibrium between optimum fungicidal effect and phytotoxicity, a function of the amount of Cu2+(aq) selectively released into the microenvironment, nevertheless remains uncontrollable with conventional cupric compounds.
Their second disadvantage lies in the complexing of Cu2+(aq) by certain plant and/or microorganic exudates which render non-bioavailable, and therefore inactive against the pathogenic agent, a portion of the active material (Cu2+(aq)) resulting from the cupric compound. Some molecules belonging to the group of the thiols can thus remove a portion of the active material (Cu2+(aq)) by precipitation. Some of the effectiveness of the conventional cupric compound is thus lost.
Finally, the cupric particles constituting the reservoir of Cu2+(aq) ion are partially lost by mechanical entrainment (leaching) when it rains, despite an appropriate adherent-type formulation and/or the use of a Bordeaux mixture as cupric compound, the latter being recognized as the most adherent to foliage in comparison with other conventional cupric compounds. This phenomenon increases in importance as the acidity of the environment increases.
The result of these disadvantages is that, on the one hand, the quality of the fungicidal protection provided by the cupric compounds varies with environmental factors and that, on the other hand, the total amount of copper sprayed per hectare is greater than the minimum amount of copper needed in bioavailable form. This necessitates the use of a minimum dose of 3000 g/ha of copper metal to ensure good fungicidal protection.
The aim of the invention is thus to overcome these disadvantages and to provide cupric plant-protection compositions which correspond better to the requirements of maximum effectiveness with lower doses of copper per hectare (in comparison with the use of conventional cupric products), while not exhibiting the risk of phytotoxicity or while reducing it.
It is known, from Patent Application WO 91/13552, that the presence of certain copper chelates, such as copper citrate or copper malate, makes it possible to increase the fungicidal protection. However, these copper chelates exhibit the disadvantage of being very soluble and thus completely leachable, which does not make possible lasting protection against the pathogenic agent.
It has now been found that sparingly soluble calcium, zinc or manganese chelates, in combination with a conventional cupric fungicide constituting a source of Cu2+ ions, make it possible to obtain in situ (on the plant) the gradual release of the corresponding copper chelate.
The main subject of the invention is therefore a process for the plant-protection treatment of plants, characterized in that it consists in combining a copper source, in non-chelated form, and a sparingly soluble calcium and/or zinc and/or manganese chelate in order to obtain, in situ, the gradual release of a soluble copper chelate.
Another subject of the invention is a plant-protection composition comprising a copper source, in non-chelated form, and at least one chelate of an xcex1-hydroxycarboxylic, diphosphonic, polyphosphonic or xcex1-hydroxyphosphonic acid and of calcium and/or of zinc and/or of manganese.
In the process and the plant-protection composition according to the invention, the copper source, in non-chelated form, is advantageously chosen from conventional cupric compounds, such as, for example, Bordeaux mixture, copper hydroxide, copper oxychloride, copper carbonate, cuprous oxide and copper hydroxide sulphates (brochantite, posnjakite, antlerite).
According to a preferred embodiment of the present invention, use is made, as copper source, of a Bordeaux mixture in accordance with Patent FR 2,739,256, the contents of which are incorporated here by way of reference. In the Bordeaux mixture in accordance with the abovementioned patent, virtually all the copper is in the brochantite state and, in the dry state, it does not comprise more than 20% by weight of bassanite. Such a Bordeaux mixture can be obtained by reacting an aqueous copper sulphate solution and an aqueous lime suspension in a Ca(OH)2/CuSO4 molar ratio of between 0.60 and 0.75 (preferably between 0.65 and 0.70 approximately) at a temperature ranging from ambient temperature to 90xc2x0 C. (preferably between approximately 40 and 70xc2x0 C.) and for a time sufficient to convert virtually all the copper complexes to brochantite. The reaction product exists in the form of a more or less concentrated aqueous suspension which does not comprise bassanite and which, optionally after concentrating in the form of a paste (for example by centrifuging), can be used directly in the manufacture of fungicidal formulations of SC type (liquid suspension concentrates) or of WG type (water-dispersible granules). In the manufacture of wettable powders of the WP type, the paste obtained after concentrating is dried under conditions such that the content of bassanite in the dry product does not exceed 20%; this content can be easily monitored by analysis of the copper assay of the dry product, which must not exceed 27.3% by weight.
The expression xe2x80x9ccalcium and/or zinc and/or manganese chelatexe2x80x9d is understood here to mean any compound or mixture of compounds exhibiting the element or elements calcium and/or zinc and/or manganese chelated by at least one xcex1-hydroxycarboxylic, diphosphonic, polyphosphonic or xcex1-hydroxyphosphonic acid, with or without neutralization of the acid functional groups by an alkaline agent.
Mention may be made, as examples of xcex1-hydroxycarboxylic acids, of citric, glycolic, tartronic, gluconic, lactic, malic, tartaric and saccharic acids, it being possible for the final five to be in the L or D or DL form.
Mention may be made, as examples of phosphonic or xcex1-hydroxyphosphonic acids, of nitrilotris(methylenephosphonic), ethylenediaminetetrakis (methylenephosphonic), hexamethylenediaminetetrakis(methylenephosphonic), diethylenetriaminepentakis(methylenephosphonic) and 1-hydroxyethane-1,1diphosphonic acids.
In the context of the present invention, the solubility in water of the calcium and/or zinc and/or manganese chelate to be used can range from 0.001 to 50 g/l at ambient temperature. The choice will advantageously be made of a chelate with a solubility of between 0.01 and 5 g/l.
The amount of calcium and/or zinc and/or manganese chelate in the composition according to the invention must be sufficient to gradually chelate and dissolve at least a portion of the Cu2+ ions present in the copper source.
Use will generally be made, in the compositions according to the invention, of a chelate/copper molar ratio of between 0.005 and 10, preferably of between 0.01 and 5 and, more preferentially, of between 0.05 and 1.
The compositions according to the invention can be presented in the form of suspensions, of wettable powders, of dustable powders or of dispersible granules. Generally, the presence of a calcium, zinc or manganese chelate in the plant-protection compositions does not in any way prevent the latter from being able to be formulated using adjuvants commonly used by the person skilled in the art (surface-active agents, antifoaming agents, inert fillers, and the like) and from also being able to comprise conventional organic fungicides.
It has been possible to demonstrate the notable effectiveness of the compositions according to the invention in a wide pH range (2.5 to 12), in particular in neutral or alkaline medium, where the copper is not in the Cu2+(aq) form but is bonded to the chelate in question while remaining soluble. It is, however, recommended to adjust the pH of the compositions so that, after dilution and during application, the pH is between 5.0 and 9.0 and more particularly between 6.0 and 9.0, so as to avoid, during application, phytotoxicity or a depressive effect on the plant due to an excessively acidic or excessively alkaline pH. Moreover, the joint use of certain plant-protection active materials, such as, for example, cymoxanil, which is unstable in alkaline medium, requires the pH of the composition to be adjusted.
In any event, the adjustment of the pH, if it is required, can be carried out using any conventional alkaline agent and in particular sodium hydroxide, potassium hydroxide, aqueous ammonia or lime.
The calcium and/or zinc and/or manganese chelates to be used according to the invention can be prepared according to general methods known to the person skilled in the art. An appropriate method consists, for example, in neutralizing the acid functional group(s) of the precursor xcex1-hydroxycarboxylic, diphosphonic, polyphosphonic or xcex1-hydroxyphosphonic acid or acids with one or more basic compound(s) of the abovementioned metals. Thus, for example, calcium citrate is obtained from citric acid and calcium hydroxide, which are used in solution in water in stoichiometric ratios appropriate for achieving neutrality of the suspension.
The use dose of the compositions according to the invention can vary within wide limits. It can range from 30 to 3000 g of copper per hectare but it is preferably between 300 and 3000 g of copper per hectare and, more particularly, between 500 and 2500 g.