Dialkali or alkaline-earth metal(II) citrate as an eco-friendly and effective biocide, process and use thereof

Abstract

The invention relates to an advantageous metal citrate having the formula (i) (A,B)MC6H4O7 with A being an alkaline cation chosen amongst NH4+ and K+, and B being an alkaline cation chosen amongst NH4+ and K+ and Na+; or (ii) AMC6H4O7 with A being an alkaline-earth cation chosen amongst Ca2+, Mg2+, and with M being a metal having an oxidation state +2 and being chosen amongst Cu2+, Zn2+, Fe2+ and Mn2+ It concerns also a biocidal solution, a process of application of said solution on plants, and the use of said metal citrate as a biocide.

Description

[0001] DIALKALI OR ALKALINE-EARTH METALflR CITRATE AS AN ECO-FRIENDLY AND EFFECTIVE BIOCIDE, PROCESS AND USE THEREOF

[0002] Technical Field

[0003] The present invention is in the domain of crop protection. It relates to a compound particularly useful as an effective and advantageous metal(ll)-based biocide.

[0004] In particular, the present invention relates to a metal(ll)-based compound that is highly soluble (esp. in water), that gives solutions which are of lower ecotoxicity footprint, and that is able to form an insoluble or slightly soluble compound once applied on plants, plant products, seeds, tubers and / or fruits, thereby providing a remarkably good biocidal activity over time and reducing the risk of lixiviation in the soil. Moreover, the compound of the invention may act also as a foliar fertilizer for plants, in addition to its biocidal activity. Finally, the compound of the invention allows reaching a reduction of metal amounts (esp. copper) spread in the environment and the optimization of yields in agriculture as well as provides a solution that is globally eco-friendly (i.e., with a lower ecotoxicological footprint) .

[0005] The present invention also relates to a composition comprising said compound, to a precursor to prepare said compound and to a biocidal solution comprising said compound. It also relates to a process of application of said biocidal solution on plants, plant products, seeds, tubers and / or fruits. Finally, it also relates to the use of said compound as a biocide, for example in agriculture, lawn and garden, forestry, and in the field of disinfection in general.

[0006] Prior art

[0007] Copper(ll)-based biocides has been known for a long time and are largely used in agriculture, for protecting and treating crops against a wide range of plant diseases, like phytopathogenic fungi and / or bacteria.

[0008] Copper is known to show an unfavorable ecotoxicological profile. Its use is therefore broadly regulated, in terms of amounts applied on sites. Current EU regulations indeed limit the use of copper fungicides in organic agriculture to maximum 28 kg of copper per hectare over a period of 7 years (European Commission, 2018) .

[0009] Despite its drawbacks in terms of ecotoxicity, the use of copper is still accepted and authorized due to its unique effectiveness as a wide-spectrum fungicide and bactericide, and exemption from the risk of resistance developing in phythopathogens populations. Copper will also be a key remaining contact multisite fungicide for downy mildew control in EU and some other non-EU countries since some organic fungicides have been removed from the registered products list. This puts pressure on more applications of copper not compatible with recent restrictions rates per ha and per year, notably on perennial crops such as grapes. Other systemic or translaminar single-site solutions show already documented resistance issues and must be used in mixture with copper. This situation will again put more pressure on copper volumes. Finally, copper(ll)-based fungicides have to be preserved since they represent the main solution available for bacteria control as well as seed treatments for cereals.

[0010] One copper(ll)-based fungicide that has been used for a very long time and is still used, is the well-known « Bordeaux mixture », a suspension of copper sulphate and lime in a ratio that has changed with time. It was used for example, as early as 1882, to control the downy mildew on grapes (37kg / ha at that time) . Other copper(ll)-based fungicides are also known like, for example, copper oxychloride, copper hydroxide, copper carbonate and cuprous oxide. These conventional copper(ll) compounds are insoluble in water at neutral pH. For example, copper hydroxide has a very low solubility in water (in the order of 0.5 mg / L at 20°C).

[0011] Biocidal activity of the copper(ll) -based fungicides is measured by the free Cu2+(bio) available for contact with fungal structures, and it propensity to the release of free Cu2+. Therefore, the insoluble conventional copper(ll)-based fungicides are normally applied on plants in large amounts to effectively inhibit the development of pathogenic fungi. The amount of soluble aqueous copper Cu2+released is of the order of a few ppm at pH 7, even less at higher pH, but this very small amount of available Cu2+is sufficient to ensure a good antifungal activity.

[0012] Hence, despite their biocidal effectiveness, conventional copper(ll)- based fungicides need relatively high amounts to be applied to reach appropriate level of available Cu2+. This impacts greatly cost effectiveness, and above all, contributes to high soil residue contamination and ecotoxicity. Moreover, their insolubility in water forces to use them in the form of a suspension in water, with issues of instability of suspension due to settlement and lower or less homogeneous coverage / spreading on plants.

[0013] Next to that, some known copper(ll)-based fungicides can cause phytotoxic effects, especially for fragile cultivars / plants. In view of solving partially some of the above drawbacks, it is also described in the art to use insoluble copper(ll) compounds, like copper hydroxide, copper carbonate or cuprous oxide, in the presence of chelating agents, in order to increase solubility and to better control Cu2+bioavailability. In particular, patent US6562757 describes a plant-protection composition which is an admixture of copper(ll) hydroxide and low amounts of a chelating agent (e.g. calcium citrate or calcium malate) that, when put in water, allows to dissolve partially the insoluble copper source (potentially maximum 43%), thereby increasing the Cu2+availability through gradual release while controlling leaching partially. Nevertheless, the amount of bioavailable Cu2+is still low and the composition is still partially insoluble.

[0014] Though, global health and environmental regulations are becoming more and more stringent, for example requiring less chemical residue on crops and in the soil, and using less toxic and more eco-friendly biocidal products. In particular, the will is to decrease the maximum dosage allowed by the EU regulations as much as possible in the future in order to minimize the accumulation in soil and the exposure to copper for nontargeted organisms.

[0015] Furthermore, next to copper(ll), other transition metal(ll) are also of interest as a biocide and / or as a plant fertilizer / micronutrient, like for example iron ( II) , zinc(ll) and manganese(ll) . In particular, zinc(ll) is an advantageous alternative to copper(ll) as it has a biocidal activity (even if generally lower than copper for some diseases) but its effect on health and environment is less detrimental than copper.

[0016] Therefore, a need exists for a metal-based biocide (i) having a high biocidal activity, (ii) being easily applied, e.g. avoiding issues of settlement and allowing good spreading, (iii) being eco-friendly (i.e., with a lower ecotoxicological footprint) and (iii) showing a good equilibrium between indirect properties of leaching (high solubility) and high persistence (low solubility of the active ingredient) on plants.

[0017] In that context, it has been described recently in European patent application PCT / EP2023 / 059715 (not yet published) a solid composition comprising an intimate mixture of copper(ll) and / or zinc(ll) hydroxide and citric acid, with the molar ratio metal / acid from 1 to 2, for example at 1.5 or 1.67 or 2. This solid composition is advantageous because it is soluble in water and, therefore, suitable as a precursor to prepare a solution that can be easily applied on plants, and (ii) from said solution, it is obtained, upon water evaporation / crystallization, an irreversibly insoluble (or slightly soluble) compound on plants that shows a high biocidal activity and a good equilibrium between indirect properties of leaching and persistence (rain fastness properties). The obtained insoluble or slightly soluble compounds are, for example, of the formula CU2(C6H4OZ) and ZnzCu^HsOz and their hydrates This recently described copper / zinc(ll)-based biocide therefore combines advantages of, on the one hand, solubility (before / during application on plants) and, on the other hand, insolubility (after application, once on plants) . Nevertheless, it appears that the biocidal solution obtained when dissolving in water said described intimate mixture of copper / zinc(ll) hydroxide and citric acid in specific molar ratio has a low pH (e.g. in the order of 4), which therefore brings potentially issues regarding phytotoxicity, especially for more fragile plants / cultivars. Indeed, even if the insoluble compound formed upon water evaporation at a later stage will not damage plants, the "drying phase" of the applied biocidal solution could be harmful to plants due to the low pH of the solution.

[0018] Objectives of the invention

[0019] The present invention has notably the objective of overcoming the cited drawbacks of the prior art and, in particular, to solve the drawback identified for the copper-citrate system recently described while keeping its advantages.

[0020] In particular, an objective of the invention is to provide a compound that is particularly suitable for the preparation of metal-based biocidal solution showing a high biocidal activity, in particular requiring less metal(ll) per treated surface than conventional copper(ll)-based fungicides.

[0021] Another objective of the invention is to provide a compound that is particularly suitable for the preparation of metal-based biocidal solution, showing the absence of phytotoxicity or an acceptable reduced level of phytotoxicity.

[0022] Still another objective of the invention is to provide a compound that is particularly suitable for the preparation of metal-based biocidal solution which has a low ecotoxicological footprint.

[0023] Still another objective of the invention is to provide a compound that is particularly suitable for the preparation of metal-based biocidal solution that is easily applied, e.g. avoiding issues of settlement, and that remains stable with no precipitation over time and in the whole range of pH (thus even in "hard water" or at very basic pH) .

[0024] Still another objective of the invention is to provide a compound that is particularly suitable for the preparation of metal-based biocidal solution that shows a good equilibrium between indirect properties of leaching (high solubility) and high persistence (low solubility of the active ingredient) on plants. Still another objective of the invention is to provide a compound that is particularly suitable for the preparation of metal-based biocidal solution that also acts as a fertilizer, in addition to its biocidal activity.

[0025] Still another objective of the invention is to provide a compound that is particularly suitable for the preparation of metal-based biocidal solution, that is cost- effective.

[0026] Another objective of the invention is to provide a solution to the disadvantages of the prior art that is simple and cheap to manufacture and use.

[0027] Description of the invention

[0028] The invention relates to a metal citrate having the formula :

[0029] - (A.BjMCdFhOz with A being an alkali cation chosen amongst NH4+and K+, and B being an alkali cation chosen amongst NH4+and K+and Na+; or

[0030] - AMC6H4O7 with A being an alkaline-earth cation chosen amongst Ca2+, Mg2+and mixtures thereof, and with M being a metal having an oxidation state +2 and being chosen amongst copper (Cu2+), zinc (Zn2+), iron (Fe2+) and manganese (Mn2+).

[0031] Hence, the invention lies on a novel and inventive approach since it enables to find a solution for the disadvantages of prior art. The inventors have indeed found that such dialkali or alkaline-earth metal citrates with this specific formula is highly soluble in aqueous medium and provides a biocidal solution with a high stability. It was surprisingly discovered that such a solution remains indeed stable, i.e. does not give any precipitation, over time and in the whole range of pH (thus even if "hard water" is used or if pH is increased). Moreover, this solution has naturally a neutral to basic pH, then it has a lowered phytotoxicity.

[0032] Next, it was surprisingly found that, from said solution of dialkali or alkaline- earth metal citrate, one can obtain, upon alkali or alkaline-earth cations absorption / metabolization by plants and water evaporation, an irreversibly insoluble or slightly soluble compound that shows a high biocidal activity and a good equilibrium between leaching and persistence as well as a low phytotoxicity and a low ecotoxicological footprint.

[0033] Finally, advantageously, the metal citrate of the invention acts also as a foliar fertilizer, due to the beneficial alkali or alkaline-earth cations metabolization by the treated / receiving plants. This is particularly advantageous with alkaline cations like potassium and ammonium.

[0034] In the invention, the role of alkali or alkaline-earth cations is therefore triple:

[0035] (1 ) it allows to provide an alkali or alkaline-earth metal citrate compound that is highly soluble, gives a neutral to basic-pH solution once dissolved, with no precipitation when the product is dissolved in "hard water" and / or if pH is increased, e.g. up to a pH > 8.5;

[0036] (2) once the solution is applied on plants, alkali or alkaline-earth ions will be absorbed by plants through their metabolism and this will then allow the formation of an irreversibly insoluble or slightly soluble metal- citrate complex (like in PCT / EP2023 / 059715) which will form a protective and rainfast layer on the treated organs; and

[0037] (3) the metabolization of alkali or alkaline-earth cations by plants will provide fertilization. Indeed, these are elements commonly used to improve plant functions like stem growth, movement of water throughout the plant, flowering and fruiting, through the primary metabolism.

[0038] This new and inventive "alkali / alkaline-earth metal-citrate route" therefore allows to solve the drawbacks identified for the previously described "copper / zinc-citrate route" (phyto toxicity due to low pH of the starting solution), while keeping its advantages and with an additional positive effect on plant health / growth through fertilization.

[0039] In particular, esp. when considering copper(ll), the route of the invention allows also to reduce the amounts of copper in the environment as there are more active Cu2+in an aqueous solution than in well-known suspensions of solid particles (e.g. copper hydroxide or Bordeaux mixture) for the same amount of copper metal.

[0040] The invention relates also to a composition comprising said dialkali or alkaline-earth metal citrate.

[0041] The invention relates also to a biocidal solution comprising said dialkali or alkaline-earth metal citrate and water.

[0042] Moreover, the invention also relates to a process of preventing or inhibiting the growth of living pathogenic organisms on plants, plant products, seeds, tubers and / or fruits, comprising the step of applying said biocidal solution on plants, plant products, seeds, tubers and / or fruits. Finally, the invention relates to the use of said dialkali or alkaline-earth metal citrate, as a biocide in: agriculture, including field crops, horticulture, arboriculture, viticulture, as preharvest and / or postharvest treatment; lawn and garden including professional turf; forestry; disinfection of fluids and surfaces.

[0043] Other features and advantages of the invention will be made clearer from reading the following description of preferred embodiments.

[0044] Throughout the present text, when a range is indicated, the extremities are included, except if explicitly described in another way. In addition, all the integral and subdomain values in the numerical range are expressly included as if explicitly written.

[0045] In the metal citrate of the invention, for the sake of clarity, the citrate has an ionization state (or anionic charge) at -4 or, in other words, it is completely deprotonated (CdFUO?4-) .

[0046] According to the invention, by "alkali", it is intended herein alkali in a broad sense, including alkali and pseudo-alkali ions, especially NH4+and K+and Na+. "Dialkali" means conventionally that there are two alkali cations in the formula.

[0047] The metal citrate of the invention may be a dialkali metal citrate with the formula (A.BJMCdF Oz, with A being an alkali cation chosen amongst NH4+and K+, and B being an alkali cation chosen amongst NH4+and K+and Na+. Alternatively, it may be an alkaline-earth metal citrate of the formula AMC6H4O7 with A being an akaline-earth cation chosen amongst Ca2+and Mg2+and mixture thereof.

[0048] Preferably, the metal citrate of the invention is a dialkali metal citrate with the formula (A,B)MC6H4O?. This means that at least one of potassium and ammonium cations is present and that it may be one of K2MC6H4O7, KNH4MC6H4O7, (NF ^MCdF Oz, KNaMC6H4O7and NFUNaMCilWz.

[0049] Very preferably, the metal citrate of the invention has the formula (A,B)MC6H4O7 with A being an alkali cation chosen from NH4+or K+and B being an alkali cation chosen from NH4+or K+. Those cations are of particular interest as they are able to provide a very soluble alkali metal citrate that will bring a slightly soluble or insoluble metal citrate upon NH4+and / or K+ions metabolization by plants, while providing fertilizing effect. In a very preferred embodiment, the metal citrate has the formula K2MC6H4O7. This K2MC6H4O7 may also be named dipotassium metal citrate or 1 ,2,3- propanetricarboxylic acid, 2-hydroxy-, metal(2+) potassium salt (1 :1 :2) (CAS Index Name) or metal;dipotassium;2-oxidopropane-l ,2,3-tricarboxylate.

[0050] When the metal citrate of the invention is an alkaline-earth metal citrate with the formula AMC6H4O7 with A being an akaline-earth cation chosen amongst Ca2+, Mg2+and mixtures thereof, this means that it may be one of CaMC6H4C>7, MgMC6H4C>7 or CaxMgyMC6H4C>7 with x > 0, y > 0 and x + y = 1. For example, the Ca2MC6H4C>7 may be named 1 ,2,3-propanetricarboxylic acid, 2-hydroxy-, metal(2+) calcium salt (1 :1 :2) (CAS Index Name) or metal; calcium; 2-oxidopropane-l ,2,3-tricarboxylate.

[0051] According to the invention, M is a metal having an oxidation state +2 and being chosen amongst Cu2+, Zn2+, Fe2+and Mn2+and mixture thereof. This means that the metal M could be one of the list or a mixture of two or three or four metals from the list. In case of more than one metal is chosen from the list, the ratio between each metal present could vary in the whole range.

[0052] According to an advantageous embodiment, metal M is chosen amongst Cu2+and Zn2+and mixture thereof.

[0053] According to a preferred embodiment, metal M is Cu2+. In such a case, the metal citrate of the invention has the formula (A,B)CuC6H4O7 or ACUC6H4O7. Copper is advantageous in the invention as, as already explained, it has since a long time demonstrated its high effectiveness against fungi or bacteria.

[0054] According to still another preferred embodiment, metal M is Zn2+. In such a case, the metal citrate of the invention has the formula (A,B)ZnC6H4O7 or AZnC6H4O7. Zinc is an advantageous alternative as it is also known to have a biocidal activity (even if generally lower than copper for some diseases) and its effect on health and environment is less detrimental than copper.

[0055] According to another embodiment, metal M is a mixture of Cu2+and Zn2+. In such a case, the metal citrate of the invention has the formula (A,B) (Cu,Zn)C6H4O7 or A(Cu,Zn)C6H4O7. The presence of a copper and zinc together allows to increase synergistically biocidal activity, as less metal amounts (total amount copper + zinc) are needed to achieve the same biocidal activity / efficacity than when using one of these metals individually. In this embodiment, the ratio between copper and zinc, Cu / Zn is preferably from 0.5 to 2. Very preferably, the ratio Cu / Zn is equal to 1 . In such a case, the metal citrate of the invention has the formula (A,B)Cuo,s Zno.sCdFUCy or ACuo.s Zno.sCdFUCy. Preferably, said metal citrate is amorphous. Said metal citrate may be anhydrous or in a hydrated form.

[0056] Preferably also, the metal citrate of the invention has a water solubility of at least 500 g / L at 20°C, and more preferably at least 1000 g / L at 20°C or even at least 1500 g / L at 20°C. This is very advantageous as one can obtain a solution, even at high concentrations, that allows to be easily applied on targeted plants (without settlement issues) and that covers / spreads homogeneously on targeted plants. As a comparison, the solid mixtures described recently in European patent application PCT / EP2023 / 059715, comprising copper(ll) hydroxide and citric acid at molar ratio 1.5 or 1.67 or 2, show solubility of the order of 80 g / L.

[0057] The composition of the invention preferably comprises more than 80% in weight of the metal citrate of the invention. More preferably, the composition comprises more than 85% in weight or even more than 90% in weight of said metal citrate. In a very preferred embodiment, the composition consists essentially in said metal citrate. This means that the composition consists only in said metal citrate with possibly impurities or other compound(s) in very low amounts (e.g. less than 2 or 1 wt%).

[0058] The composition may also comprise a mixture of metal citrates having the formula (A.BJMCdEhO? or the formula AMC6H4O7.

[0059] According to an embodiment, the composition may comprise further at least one additive selected from the group of pH regulating agents, film-forming agents, anti-caking agents, surfactants, wetting agents, anti-foaming agents, anti-drifts, sticking agents, thickeners, foaming agents, solidifying agents, other biocides, fertilizers, plant nutrients, soil nutrients and stabilizers. One example of pH regulating agent according to this embodiment and advantageous in the invention is an alkali (potassium, ammonium and / or sodium) or an alkaline-earth citrate salt or a mixture thereof (esp. K2C6H6O7; ( N H4) 2C6H6O7; NO2C6H6O7; CaC6H6O7 or MgC6H6O7 and their hydrates).

[0060] According to an embodiment, the composition is in a solid form, preferably in the form of a powder, granules or tablets. If it is in the form of a powder, it is preferably in the form of a free-flowing powder.

[0061] According to an embodiment, the composition is in a liquid form, for example in the form of a concentrated aqueous solution. This is possible due to the high solubility of the metal citrate of the invention.

[0062] The dialkali metal citrate of the invention may be prepared by various methods. For example, it may be prepared starting from metal(ll) hydroxide M(OH)2, potassium citrate and / or ammonium citrate and / or sodium citrate, and optionally citric acid, in appropriate amounts depending on the targeted dialkali metal citrate. Alternatively, it may also be prepared starting from metal(ll) hydroxide M(OH)2, citric acid and potassium bicarbonate and / or ammonium bicarbonate and / or sodium bicarbonate. For example also, it may be prepared starting from metal(ll) hydroxide M(OH)2, citric acid and potassium hydroxide and / or ammonium hydroxide and / or sodium hydroxide. In all cases, the metal(ll) hydroxide M(OH)2 may be used in a commercial solid form (this works very well when metal is copper) or, alternatively and more preferably, it may be prepared in situ by hydrolysis at high pH of a solution of a metal sulfate or nitrate (this works very well for all metals M according to the invention) which gives a colloidal suspension which is then centrifugated to isolate the metal hydroxide. Such a step gives a M(OH)2 colloids that is very reactive and may then react further (e.g. after separation) with alkali citrate / citric acid, esp. in stoichiometric amounts, to give a clear stable (no precipitation) over time biocidal solution according to the invention. In a most preferred way, the dialkali metal citrate of the invention is prepared by (i) hydrolysis at high pH (e.g. NaOH) of a solution of a metal sulfate or nitrate or chloride, (ii) centrifugation of the obtained colloidal metal hydroxide and (iii) dissolution of said metal hydroxide in a solution of alkali citrate. Examples of potassium citrates are K3C6H5O7 or K2HC6H5O7 or KH2C6H5O7 and their hydrates, preferred one being dipotassium hydrogen citrate K2HC6H5O7. Examples of ammonium citrates are (NH^sCdHsCy or ( N H4) 2HC6H5O7 or NH4H2C6H5O7 and their hydrates, preferred one being diammonium hydrogen citrate (NH^HCdHdCy. Examples of sodium citrates are NasCdHsCy or NO2HC6HSO7 or NaH2C6HsC>7 and their hydrates, preferred one being disodium hydrogen citrate Na2HC6HsC>7.

[0063] The alkaline-earth metal citrate of the invention may be prepared by various methods. For example, it may be prepared starting from metal hydroxide M(OH)2, calcium citrate and / or magnesium citrate, and optionally citric acid, in appropriate amounts depending on the targeted alkaline-earth metal citrate. Alternatively, it may also be prepared starting from metal hydroxide M(OH)2, citric acid and calcium carbonate and / or magnesium carbonate. For example also, it may also be prepared starting from metal M hydroxide M(OH)2, citric acid and calcium hydroxide and / or magnesium hydroxide. In all cases, the metal hydroxide M(OH)2 may be used in a commercial solid form or, alternatively and more preferably, it may be prepared in situ by hydrolysis at high pH of a solution of a metal sulfate or nitrate which gives a colloidal suspension which is then centrifugated to isolate the metal hydroxide. Such a step gives a M(OH)2 that is very reactive and then react further (e.g. after separation) with alkaline- earth citrate / citric acid, esp. in stoichiometric amounts, to give a clear and stable (no precipitation) over time biocidal solution according to the invention. In a most preferred way, the alkaline-earth metal citrate of the invention is prepared by (i) hydrolysis at high pH (e.g. NaOH) of a solution of a metal sulfate or nitrate or chloride, (ii) centrifugation of the obtained colloidal metal hydroxide and (iii) dissolution of said metal hydroxide in a solution of alkaline-earth citrate. Appropriate examples of calcium citrates are calcium hydrogen citrate CaHCdHsO? and its hydrates. Appropriate examples of magnesium citrates are magnesium hydrogen citrate MgHCdHsO? and its hydrates.

[0064] Due to its high solubility, the metal citrate of the invention may be easily and quickly dissolved in water or in a water-based solvent, in order to give a biocidal solution according to the invention. With the biocidal solution of the invention, one avoids issues exposed above (settlement or needs for regular mixing, poor coverage of plants, etc.) related to use of suspensions and one can obtain a good and homogeneous coverage / spreading on targeted plants. Alternatively, the biocidal solution of the invention may be prepared by in situ synthesis of the metal citrate without isolating it in a solid form before its redissolution.

[0065] The biocidal solution may also comprise additive(s), that come(s) either from said composition and / or from the solid mixture of the invention and / or added during the preparation of said solution. Examples of additives are pH regulating agents, filmforming agents, anti-caking agents, surfactants, wetting agents, anti-foaming agents, anti-drifts, sticking agents, thickeners, foaming agents, solidifying agents, other biocides, fertilizers and stabilizers.

[0066] The biocidal solution of the invention has advantageously a neutral to basic pH which renders it of lower phytotoxicity (esp. for fragile plants) compared to the copper-citrate solution described in European patent application PCT / EP2023 / 059715 (with an acidic pH near 4) .

[0067] Preferably, in the biocidal solution, the amounts of the metal citrate of the invention and water are such that the biocidal solution has a concentration in metal M between 0.01 g / L and 5 g / L and, preferably, between 0.05 g / L and 3 g / L. More preferably, the amounts of the composition and water are such that the biocidal solution has a concentration in metal M between 0.1 g / L and 2 g / L.

[0068] The biocidal solution of the invention may of course also be prepared from the composition of the invention and water (by dissolution or by dilution), and with the same above embodiments, notably in terms of pH and concentrations. According to the invention, the process of preventing or inhibiting the growth of living pathogenic organisms on plants, plant products, seeds, tubers and / or fruits, comprises the step of applying said biocidal solution on plants, plant products, seeds, tubers and / or fruits. Preferably, said step of applying is carried out by spraying or pulverizing or dipping or drench or coating.

[0069] According to the embodiment, where the metal M is copper, the amount of copper applied on said plants, plant products, seeds, tubers and / or fruits is below 4000 g / ha by season (registered maximal dosage for grapes), preferably below 3000 g / ha, more preferably, below 2000 g / ha, or even below 1000 g / ha or below 500 g / ha. For the sake of clarity, the amount of copper according to this embodiment is determined / computed based on the molar mass of the copper element, Cu.

[0070] When the biocidal solution of the invention comprising a metal citrate is applied on plants, plant products, seeds, tubers and / or fruits, water evaporation (through ambient temperature, wind, etc.) and alkali or alkaline-earth ions absorption / metabolization by plants occur which leads to the precipitation or crystallization of an irreversibly insoluble or slightly soluble metal citrate. This metal citrate is in the form of an amorphous precipitate or in a crystalline form or in the form of a mixture thereof.

[0071] In particular, in the embodiment where the metal M is copper, said slightly soluble or insoluble metal citrate has the formula Cu3(C6HsOz)2 or Cu2(C6H4Oz), or one of their hydrates (for example, Cu2(C6H4Oz) .H2O), or a mixture thereof. Together with copper citrate(s), other compounds may also crystallize / precipitate, like for example, "free" citric acid.

[0072] In particular also, in the embodiment where the metal M is zinc, said slightly soluble or insoluble metal citrate has the formula Zn3(C6HsOz)2 or ZmtCdFUOz), or one of their hydrates or a mixture thereof. Together with zinc citrate(s), other compounds may also crystallize / precipitate, like for example, "free" citric acid.

[0073] Next to their low solubility increasing their persistence on plants (through a protective and rainfast layer) while still having a high biocidal activity, such slightly soluble or insoluble metal citrates show a low ecotoxicological footprint. Hence, copper citrates are known to cause no toxic effects on fish, birds, mammals and bees (see notably, "Pesticide Toxicity Profile: Copper-based Pesticides" from Fishel (201 1 ), Pesticide Information Office, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida) and can be used for plant protection at lower concentrations as an environmentally acceptable agent (Georgopoulos et al., 2001 ) . Moreover, zinc citrates, in particular of the formula ZnsfCdHsO?^ and its hydrates, are advantageous as, next to their low solubility increasing their persistence while keeping a very good biocidal activity, they are known as food ingredients "generally recognized as safe". Indeed, in Europe, zinc citrates are on the positive list of Regulation (EC) No. 1925 / 2006 on food fortification. They are also listed in Directive 2002 / 46 / EC of the European Parliament and the Council relating to food supplements as vitamins and mineral substances which may be used in the manufacture of food supplements. Furthermore, it is listed as mineral salt in the EU Regulation (EC) No. 609 / 2013 on food intended for infants and young children, food for special medical purposes, and total diet replacement for weight control. Next, in the US, zinc citrates can be considered as substances classified as dietary ingredients according to FDC Act., § 201 (ff). In oral care, zinc citrate products are classified as Class I active ingredient with respect to safety and a Class III active ingredient with respect to efficacy. Since 2009, zinc citrates are "generally recognized as safe" (self-affirmed GRAS) in full compliance with the US Food, Drug, and Cosmetic Act.

[0074] Advantageously, the solubility of said slightly soluble or insoluble metal citrate is below or equal to 1 g / L. Preferably, it is below or equal to 0.8 g / L. Preferably also, it is higher than or equal to 0.1 g / L or better, higher than or equal to 0.2 g / l, or even 0.3 g / L. More preferably, it is higher than or equal to 0.5 g / L. This is advantageous to reach a good M(ll) bioavailability and an equilibrium between high leaching / high persistence properties.

[0075] Moreover, because the irreversible precipitation / crystallization of the insoluble or slightly soluble metal citrate is induced by metabolization / absorption of alkali or alkaline-earth ions by targeted plants, the invention is also advantageous as this brings beneficial fertilizing effect for those plants. Indeed, potassium and nitrogen are elements commonly used to improve plant health, growth and functions like stem growth, movement of water throughout the plant, flowering and fruiting.

[0076] According to another aspect of the invention, the dialkali or alkaline-earth metal citrate is used as a biocide, especially as a fungicide and / or as a bactericide, in the following field: i) agriculture, including field crops, horticulture, arboriculture, viticulture, as preharvest and / or postharvest treatment; ii) lawn and garden including professional turf; iii) forestry; iv) disinfection of fluids and surfaces.

[0077] Fungicides are known in the art as either chemical or biological agents used to mitigate, inhibit or destroy fungi. Bactericides are known in the art as either chemical or biological agents used to mitigate, inhibit or destroy bacteria.

[0078] For the sake of clarity, the disinfection of fluids and surfaces according to the invention are concerned by numerous domains like medical, veterinary, domestic and industrial uses, excluding any therapeutic uses. Fluids may be water, air, gas; and surfaces may be floors, work surfaces, toilets, medical devices, prothesis.

[0079] In particular, the alkali or alkaline-earth metal citrate according to the invention is used as a biocide in: i) agriculture, including field crops, horticulture, arboriculture; viticulture, as preharvest and / or postharvest treatment; ii) lawn and garden including professional turf; iii) forestry.

[0080] The metal citrate of the invention is advantageously used as a biocide for treating various bacterial and fungal diseases, on various plants, products of plants, seeds, tubers and / or fruits. In particular, the composition of the invention is advantageously used as a fungicide, e.g. for treating fungal diseases such as, but not limited to, grapevine downy mildew (P / asmopara viticola), potatoes mildew (Phytophtora infestans) and numerous other pathosystems.

[0081] Next or in addition to its use as a biocide, the metal citrate of the invention may also be advantageous for promoting growth and development of plants and may therefore be used as a fertilizer, e.g. as a foliar fertilizer, or as a plant nutrient. Indeed, as already explained above, the alkali metal citrate of the invention, when applied on plants as a solution, will provide a metabolization of alkali (K+and / or NH4+) or alkaline-earth (Ca2+and / or Mg2+) ions by plants. Moreover, copper, zinc, iron and manganese are essential elements / micronutrients for plants. In particular, zinc is important for root development and at crop emergence due to its role in growth hormone synthesis. Copper improves photosynthesis and enzyme activity and also plays an important role in the formation of lignin in cell walls. Iron is beneficial for plants as it is involved in many important compounds and physiological processes in plants (chlorophyll synthesis, enzyme functions). Manganese is an important micronutrient for plant growth / development and sustains metabolism within different plant cell compartments.

[0082] Finally, the metal citrate of the invention can also be used advantageously in other domains than that of plant treatment. For example, it may be useful in food formulations (human or animal) or in mineral extraction.

[0083] Embodiments of the invention will now be further described by way of examples, together with a comparative example not in accordance with the invention. The following examples are provided for illustrative purposes, and are not intended to limit the scope of this invention.

[0084] Examples

[0085] 1 ) Preparation of dialkali and alkaline-earth M citrates according to the invention

[0086] The preparation of the dialkali and alkaline-earth metal citrates according to the invention, with metal being copper(ll) or zinc(ll), was performed in three consecutive steps in order to obtain a concentrated solution (stable and clear over time) , followed by evaporation to obtain the final product in a solid (form.

[0087] The detailed method used was as follows:

[0088] (a) Dissolution in water of the dialkali or alkaline-earth hydrogen citrate, in a flask with a magnetic stirrer, with a concentration of 0.5 to 1 mole per liter of water at room temperature. The concentration / amount of water required has no impact on the synthesis of the product.

[0089] For calcium-based compounds, as calcium hydrogen citrate does not exist commercially to date, it was prepared in situ by equimolar reaction of citric acid with calcium carbonate or oxide. The obtained solution is only stable over time for around 30 minutes and was therefore used quickly.

[0090] (b) Synthesis of highly reactive colloidal particles of M(ll) hydroxide, in aqueous solution, with complete neutralization of two moles of an alkali hydroxide chosen from NaOH, KOH or LiOH with one mole of a sulfate of said metal M(ll). The so- obtained colloid was isolated by centrifugation and washed from sulfate or chloride residues.

[0091] (c) Addiition of the freshly produced M(ll) hydroxide (from step (b)) into the solution of the dialkali or alkaline-earth hydrogen citrate (from step (a)) until a clear solution is obtained, after a few minutes. This solution, os it is stable over time, may be used as such as a biocidal solution according to the invention. Alternatively, the citrate may be isolated in a solid form, and put later in solution for plant application.

[0092] (d) Drying the solution obtained at step (c) to obtain the dialkali or alkaline-earth metal citrate in a solid form. Drying was done with a Rotavapor Buchi R 220 pro in a temperature range of 50°C to 90°C and a pressure starting from 150 mbar down to 1 mbar at the end of the process. A spray-drying was also an effective alternative.

[0093] The final product is in the form of a free-flowing powder, easily soluble in water.

[0094] The following alkali or alkaline-earth metal M(ll) citrates were prepared according to the above-described method:

[0095] - Dialkali copper citrate 1 : K2CUC6H4O7

[0096] - Dialkali copper citrate 2: (NH^CuCdFUO?

[0097] - Dialkali copper citrate 3: KNH4CUC6H4O7

[0098] - Dialkali copper citrate 4: KNaCuC6H4C>7

[0099] - Dialkali zinc citrate 1 : K2ZnC6H4C>7

[0100] - Alkaline-earth zinc citrate 1 : CaZnC6H4C>7

[0101] - Alkaline-earth copper citrate 1 : MgCuC6H4C>7

[0102] They were characterized with:

[0103] X-ray photoelectron spectroscopy (XPS) and inductively Coupled Plasma (ICP) for elemental analysis; the accredited procedure Agroscope STS0223 for dosing citrate; and XRD to evaluate its amorphous character.

[0104] All the obtained citrates were amorphous. Moreover, they all showed a solubility in water up to 1500 g / L. Their formula were validated by complete analysis through XPS, citrate dosing and ICP.

[0105] 2) Bioassay efficacy assessement of dialkali copper citrate 1 against downy mildew fP / asmopara viticola} on grapevine leaf discs (lab tests)

[0106] - Methodology:

[0107] The dialkali copper citrate 1 (K2CUC6H4O7) was tested as preventive protection towards grapevine downy mildew (Plasmopara viticola), in comparison of Kocide® Opti as reference fungicide. Kocide Opti is a commercial fungicide whose active substance is CU(OH)2 and it was chosen as a reference for its excellent effectiveness against downy mildew.

[0108] Concentrations ranging from 0.01 to 2-fold the registered dosage of Kocide® Opti (namely 0.1875 g / L in equivalent of copper metal), were tested. Solutions were applied by means of a Potter spray tower on Petri dishes containing 10 leaf disks (cv Cabernet Sauvignon) on water-soaked filter papers. After application, the leaf discs are gently dried under a laminar flow hood. Inoculation is carried out 24 hours after treatment, using a suspension of sporangia (1 ,10ssporangia. ml-') on the abaxial side of the leaf disks. The boxes are sealed and placed in an incubator (22°C constant, high hygrometry ensured by the water-soaked filter papers, natural photoperiod) . The incidence (percentage of foliar disc showing symptoms / sporulation) and the severity (percentage of foliar disk surface showing symptoms / sporulation) were assessed 7 days post-inoculation.

[0109] The severity data were submitted to a variance analysis associated with comparative mean test (XLSTAT software). Data were converted by arcsine transformation prior to analysis. A different letter indicates a significant statistical difference between the treatment / concentration. The inhibitory concentration of 50% of the pathogen development (ICso) was calculated, using the Four Five-parameter logistic regression module (XLSTAT software).

[0110] Efficacity is computed using the formula: ((untreated control severity - fungicide severity) / untreated control severity)*! 00 (herein fungicide is either Kocide Opti / reference or the alkali copper citrate 1 ) .

[0111] - Results:

[0112] Infection rate is satisfactory in the water control with all discs sporulating and a severity disease of 80.6%. The selected fungicide of reference (Kocide® Opti) presents no sporulation, as expected.

[0113] The results obtained are given in Table 1 and illustrated in Figures 1 and 2.

[0114] Table T

[0115] Figure 1 shows in particular the observed severity (in %) versus the relative concentration of the alkali copper citrate 1 , namely the ratio between the concentration in copper metal of the dialkali copper citrate 1 and the concentration in copper metal corresponding to the registered dose of Kocide Opti (0.1875 g / l Cu).

[0116] The present bioassay shows a total inhibition of downy mildew development at 0.14 g / l copper metal for the dialkali copper citrate 1 according to the invention (0.75 fold the registered dose of Kocide Opti in copper metal equivalent) and an efficacy of 96% up to a dose reduced by a factor of 10 compared to the reference, i.e. as low as 0.01875 g / l copper metal.

[0117] The severity data were submitted to a variance analysis associated with comparative mean test (Tukey test: R2= 0.828; Pr>F : <0.0001 ). Data were converted by arcsine transformation prior to analysis. A different letter (a,b,c) indicates a significant statistical difference between the treatment / concentration. The obtained modelled curves to determine the theoretical dosage allowing a total control of the disease gives IC99 = 0.58 and IC50 = 0.018. This is illustrated at Figure 2.

[0118] Moreover, no symptoms of phytotoxicity were observed at any of the concentrations tested for the alkali copper citrate 1 .

[0119] 3) Field scale efficacy assessement of dialkali copper citrate 1 against downy mildew on grapevine

[0120] - Methodology:

[0121] Dialkali copper citrate 1 (K2CUC6H4O7) was tested as preventive protection towards grapevine downy mildew (Plasmopara viticola).

[0122] The efficacy trials were carried out in Switzerland (Nyon, 46° 23' 54' ' N, 6° 13' 53' ' E) on a plot planted in 2000 with the cultivar Chasselas 800 / 3309. The experimental setup was organized in a complete randomized block design. Twelve modalities (different alternative fungicides) were arranged in four replicates of 17.5 square meters equal to 10 vines, including untreated control and organic reference (Figure 3) .

[0123] Alkali copper citrate 1 was applied eight times vine plants over the season by backpack sprayer (200 to 400 l / ha dependent on vegetation growth) at a rate of 300g / ha equivalent copper metal (see Figure 3 and Table 2 for details regarding the application mode).

[0124] Table 2

[0125] - Efficacy assessment of dialkali copper citrate 1 against downy mildew:

[0126] During the growing season, disease assessments on leaves and bunches were carried out four times by recording disease incidence (proportion of organs with symptoms) and disease severity (proportion of diseased leaf / bunch area) of downy mildew. For each assessment, 100 leaves and 50 bunches per block were randomly assessed. The evaluation of the incidence and severity of downy mildew disease was performed at J42 (BBCH 77) by observation of 4 x 100 leaves and 4 x 50 bunches per modality. Incidence is the percentage of leaves / bunches showing symptoms / sporulation. Severity is the percentage of leaves / bunches surface showing symptoms / sporulation. Efficacity is computed using the formula: (untreated control severity - fungicide severity) / untreated control severity)*! 00. a. Evaluation of downy mildew disease on leaves

[0127] The results obtained for leaves are given in Table 3 and illustrated in Figure 4.

[0128] Table 3 b. Evaluation of downy mildew disease on bunches

[0129] The results obtained for bunches are given in Table 4 and illustrated in Figure 5

[0130] Table 4

[0131] 4) Bioassav efficacy assessement of dialkali zinc citrate 1 against downy mildew (Plasmopara viticola) on grapevine leaf discs (lab tests)

[0132] - Methodology:

[0133] The dialkali zinc citrate 1 (fcZnCdFUO?) was tested as preventive protection towards grapevine downy mildew (Plasmopara viticola), using the same method as for the dialkali copper citrate 1 (point 1 )).

[0134] - Results:

[0135] The results obtained are given in Table 5 and illustrated in Figure 6.

[0136] Table 5

[0137] Dialkali zinc citrate 1 shows a significant reduction in the severity of downy mildew as early as 1 g / l of the product and provides total disease control at higher concentrations.

[0138] 5) Bioassav efficacy assessement of alkaline-earth zinc citrate 1 against downy mildew (Plasmopara viticola) on grapevine leaf discs (lab tests)

[0139] - Methodology:

[0140] The alkaline-earth zinc citrate 1 (CaZnCdFUOz) was tested as preventive protection towards grapevine downy mildew (Plasmopara viticola), using the same method as for the dialkali copper citrate 1 (point 1 )).

[0141] - Results: The results obtained are given in Table 6 and illustrated in Figure 7 (showing the 95

[0142] % efficacy level for illustration).

[0143] Table 6

[0144] 6) Bioassay efficacy assessement of alkaline-earth copper citrate 1 against downy mildew IPIasmooara viticola) on grapevine leaf discs (lab tests)

[0145] - Methodology:

[0146] The alkaline-earth copper citrate 1 (MgCuCdFUO?) was tested as preventive protection towards grapevine downy mildew (Plasmopara viticola), using the same method as for the dialkali copper citrate 1 (point 1 )).

[0147] - Results:

[0148] The results obtained are given in Table 7 and illustrated in Figure 8 (showing the severity level at 95 % efficacy for illustration).

[0149] Table 7

[0150] Application of the alkaline-earth copper citrate 1 drastically reduces the severity of downy mildew at 0.24 g / l with an efficacy superior to 95%, in the same level of protection than the reference Kocide Opti (registered dosage) .

Claims

CLAIMS1 . Metal citrate having the formula :- (A,B) M(C6H4OZ), with A being an alkali cation chosen amongst NH4+and K+, and B being an alkaline cation chosen amongst NH4+and K+and Na+; or- AMC6H4O7 with A being an akaline-earth cation chosen amongst Ca2+and Mg2+and mixture thereof, and with M being a metal having an oxidation state +2 and being chosen amongst Cu2+, Zn2+, Fe2+and Mn2+and mixture thereof.

2. Metal citrate according to claim 1 , characterized in that it has the formula (A,B)M(C6H4O / ), with A being an alkali cation chosen amongst NH4+and K+and B being an alkali cation chosen amongst NH4+and K+.

3. Metal citrate according to claim 1 or 2, characterized in that metal M is chosen amongst Cu2+and Zn2+and mixture thereof.

4. Metal citrate according to preceding claim, characterized in that metal M is Cu2+.

5. Metal citrate according to preceding claim, characterized in that it has the formula K2CUC6H4O7.

6. Metal citrate according to one of the preceding claims, characterized in that it has a water solubility of at least 500 g / L at 20°C, preferably at least 1000 g / L at 20°C.

7. Composition, characterized in that it comprises a metal citrate according to claims 1-6.

8. Composition according to preceding claim, characterized in that it comprises further at least one additive selected from the group of pH regulating agents, film-forming agents, anti-caking agents, surfactants, wetting agents, anti-foaming agents, anti-drifts, sticking agents, thickeners, foaming agents, solidifying agents, other biocides, fertilizers, plant nutrients, soil nutrients and stabilizers.

9. Composition according to claims 7-8, characterized in that it is in a solid form, preferably in the form of a powder, granules or tablets.

10. Biocidal solution, comprising a metal citrate according to claims 1 -6 and water.11 . Process of preventing or inhibiting the growth of living pathogenic organisms on plants, plant products, seeds, tubers and / or fruits, characterized in that it comprises the step of applying a biocidal solution according to claim 11 on plants, plant products, seeds, tubers and / or fruits.

12. Process according to preceding claim, characterized in that said biocidal solution has a concentration in metal M between 0.1 g / L and 2 g / L.

13. Process according to any of claims 11-12, characterized in that said step of applying is carried out by spraying or pulverizing or dipping or drench or coating.

14. Use of a metal citrate according to claims 1-6, as a biocide in: i) agriculture, including field crops, horticulture, arboriculture, viticulture, as preharvest and / or postharvest treatment; ii) lawn and garden including professional turf; iii) forestry; iv) disinfection of fluids and surfaces.

15. Use according to the preceding claim, as a fungicide and / or as a bactericide, preferably as a fungicide.

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