TW202504885A - Dialkali or alkaline-earth metal(ii) citrate as an eco-friendly and effective biocide, process and use thereof - Google Patents

Abstract

The invention relates to an advantageous metal citrate having the formula (i) (A,B)MC ₆H ₄O ₇with A being an alkaline cation chosen amongst NH ₄ ⁺and K ⁺, and B being an alkaline cation chosen amongst NH ₄ ⁺and K ⁺and Na ⁺; or (ii) AMC ₆H ₄O ₇with A being an alkaline-earth cation chosen amongst Ca ²⁺, Mg ²⁺, and with M being a metal having an oxidation state +2 and being chosen amongst Cu ²⁺, Zn ²⁺, Fe ²⁺and Mn ²⁺. 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

Dialkali metal-divalent metal citrate or alkaline earth metal-divalent metal citrate as environmentally friendly and effective biocide, method and use thereof

The present invention relates to the field of crop protection and relates to a compound which is particularly suitable as an effective and advantageous divalent metal-based biocide.

In particular, the present invention relates to a compound based on a divalent metal, which has a high solubility (especially in water) and the solution formed by the compound has a low ecotoxic impact. After the compound is applied to plants, plant products, seeds, tubers and/or fruits, it can form an insoluble or slightly soluble compound, thereby providing long-term good biocidal activity and reducing the risk of leaching in the soil. In addition, in addition to having biocidal activity, the compound of the present invention can also be used as a foliar fertilizer for plants. Finally, the compound of the present invention can reduce the amount of metals (especially copper metal) dispersed in the environment, optimize crop yields, and provide an environmentally friendly (i.e., with a low ecotoxic impact) solution.

The invention also relates to a composition comprising the compound, a propellant for preparing the compound, and a biocidal solution comprising the compound. The invention also relates to a method for applying the biocidal solution to plants, plant products, seeds, tubers and/or fruits. Finally, the invention also relates to the use of the compound as a biocide, for example in agriculture, turf, gardening, forestry and general disinfection fields.

Copper(II)-based biocides have long been known and have been used extensively in agriculture to protect and treat crops from various plant diseases, such as those caused by plant pathogenic fungi and/or bacteria.

Copper is known to have adverse ecotoxicological properties and therefore its application is widely restricted. Current EU regulations do limit the use of copper fungicides in organic farming to “a maximum of 28 kg of copper per hectare over a period of 7 years” (EU Commission, 2018).

Despite its ecotoxicity disadvantages, copper's use is still accepted and permitted due to its unique effects as a broad-spectrum fungicide and microbicide and its low resistance to resistance in plant pathogens. In the EU and some non-EU countries, copper remains the main remaining multi-site contact fungicide for downy mildew control, as some organic fungicides have been removed from the list of registered products, which has put pressure on increasing copper use rates that do not meet the recent restrictions on copper application per hectare and per year, especially for perennial crops such as grapes. Other systemic or translaminar single-site solutions have shown resistance issues, so these solutions need to be mixed with copper, which puts greater pressure on copper application rates. Finally, because copper (II)-based fungicides are currently the main solution available for bacterial control and cereal seed treatment, copper (II)-based fungicides must be retained.

One copper(II)-based fungicide that has long been in use and is still in use today is the well-known Bordeaux mixture, which is a suspension of copper sulphate (CuSO ₄ ) and lime. The ratio of copper sulphate to lime in Bordeaux mixture has varied over time, for example, as early as 1882, Bordeaux mixture was used to control septoria in grapes (at a rate of 37 kg per hectare). Other well-known copper(II)-based fungicides include alkaline copper oxychloride, copper hydroxide, copper carbonate and cuprous oxide. These known copper (II) compounds are insoluble in water at neutral pH. For example, the solubility of copper hydroxide in water is very low (about 0.5 mg/L at 20°C).

The biocidal activity of copper (II) based fungicides is measured by the free Cu ²⁺ available (biologically) in contact with the fungal structure and its tendency to release free Cu ²⁺ . Therefore, conventional insoluble copper (II) based fungicides usually need to be applied to plants in large amounts to effectively inhibit the growth of pathogenic fungi. At pH 7, the amount of soluble water-soluble Cu ²⁺ released is only about a few ppm, and even less at higher pH values, but this very small amount of available Cu ²⁺ is sufficient to ensure good antifungal activity.

Therefore, despite their biocidal efficacy, these known copper (II) based fungicides require relatively large application rates to achieve adequate effective Cu ²⁺ levels. This has a significant impact on cost-effectiveness and, in particular, results in increased soil residue contamination and ecotoxicity. In addition, the insolubility of these compounds in water necessitates their application in the form of suspensions, which are unstable due to sedimentation and result in poor uniformity of coverage/dispersion on the plants.

In addition, some known copper(II)-based fungicides may cause phytotoxic effects, especially on vulnerable species/plants.

In order to partially solve some of the above-mentioned shortcomings, the prior art also discloses the use of insoluble copper (II) compounds, such as copper hydroxide, copper carbonate or cuprous oxide, in the presence of a chelating agent to increase solubility and better control the biological effectiveness of Cu ²⁺ . In particular, U.S. Patent No. 6,562,757 discloses a plant protection composition, which is a mixture of copper hydroxide and a small amount of a chelating agent (e.g., calcium citrate or calcium malate), which, when placed in water, can partially dissolve the insoluble copper source (up to 43%), thereby increasing the effectiveness of Cu ²⁺ by gradual release, while controlling partial leaching. However, the amount of biologically effective Cu ²⁺ is still low, and the composition is still partially insoluble.

However, global health and environmental regulations are becoming increasingly stringent, requiring, for example, fewer chemical residues to be left on crops and in the soil and the use of less toxic and more environmentally friendly biocidal products. In particular, the future trend is to reduce the maximum dose allowed by EU regulations as much as possible to minimize accumulation in the soil and exposure of non-target organisms to copper.

In addition to copper (II), other transition metals (II) have also received attention for their potential as biocides and/or plant fertilizers/micronutrients, such as iron (II), zinc (II) and manganese (II). In particular, zinc (II) is a favorable alternative to copper (II) with biocidal activity (although generally lower than that of copper against certain diseases), but with less health and environmental impacts than copper.

Therefore, there is a need for a metal-based biocide that: (i) has high biocidal activity; (ii) is easy to apply, e.g. avoids sedimentation problems and has good dispersion; (iii) is environmentally friendly (i.e. has low ecotoxicity impact); and (iv) has a good balance between indirect properties such as leaching (high solubility) and persistence on plants (low solubility of the active ingredient).

In this context, a solid composition comprising an intimate mixture of copper (II) hydroxide and/or zinc (II) hydroxide and citric acid, wherein the molar ratio of metal to acid is 1 to 2, such as 1.5, 1.67 or 2, has recently been disclosed in European patent application PCT/EP2023/059715. The solid composition has the advantage of being soluble in water and is therefore suitable as a precursor for preparing a solution that can be easily applied to plants, from which, after evaporation/crystallization of the water, an irreversibly insoluble (or slightly soluble) compound can be formed on the plant, which has high biocidal activity and a good balance between indirect properties such as leaching and persistence (rain resistance). The resulting insoluble or slightly soluble compounds have the formula, for example, Cu ₂ (C ₆ H ₄ O ₇ ), Zn ₂ Cu(C ₆ H ₅ O ₇ ) ₂ and hydrates thereof. Thus, this recently disclosed copper/zinc(II)-based biocide combines the advantages of solubility (before/during application to plants) and insolubility (after application to plants). However, when the disclosed intimate mixture of copper(II) hydroxide/zinc(II) hydroxide and citric acid is dissolved in water at a certain molar ratio, the resulting biocidal solution has a low pH (e.g., about 4), which may cause phytotoxicity problems, especially for more delicate plants/species. In fact, even if the insoluble compounds formed by the applied biocidal solution after evaporation of water at a later stage will not harm plants, the biocidal solution may still be harmful to plants during the "drying stage" due to its low pH value.

The main purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art, especially to solve the shortcomings found in the above-mentioned recently disclosed copper-citrate system while retaining its advantages.

In particular, one of the objects of the present invention is to provide a compound which is particularly suitable for the preparation of metal-based biocidal solutions having a high biocidal activity, in particular requiring less divalent metal per unit treatment area than known copper (II)-based fungicides.

Another object of the present invention is to provide a compound which is particularly suitable for the preparation of metal-based biocidal solutions which exhibit no phytotoxicity or acceptably low phytotoxicity.

Furthermore, another object of the present invention is to provide a compound which is particularly suitable for preparing a metal-based biocidal solution and which has a low ecotoxicity impact.

Another object of the present invention is to provide a compound which is particularly suitable for the preparation of metal-based biocidal solutions which are easy to apply, for example avoid sedimentation problems, and remain stable and free of precipitation over a long period of time over the entire pH range (even in "hard water" or at highly alkaline pH values).

Another object of the present invention is to provide a compound which is particularly suitable for the preparation of metal-based biocidal solutions which can show a good balance between the indirect properties of leaching (high solubility) and high persistence on plants (low solubility of the active ingredient).

Another object of the present invention is to provide a compound which is particularly suitable for the preparation of a metal-based biocidal solution which, in addition to its biocidal activity, can also be used as a fertilizer.

Another object of the present invention is to provide a compound which is particularly suitable for the preparation of metal-based biocidal solutions and which is cost-effective.

Another object of the present invention is to provide a solution to the shortcomings of the prior art, which is simple and inexpensive to manufacture, and easy to manufacture and use.

The present invention relates to a metal citrate having the following chemical formula: •(A,B)MC ₆ H ₄ O ₇ , wherein “A” is an alkali metal cation selected from NH ₄ ⁺ and K ⁺ , and “B” is an alkali metal cation selected from NH ₄ ⁺ , K ⁺ and Na ⁺ ; or •AMC ₆ H ₄ O ₇ , wherein “A” is an alkali earth metal cation selected from Ca ²⁺ , Mg ²⁺ and a mixture thereof; In the above chemical formula, “M” is a metal with a +2 oxidation state selected from copper (Cu ²⁺ ), zinc (Zn ²⁺ ), iron (Fe ²⁺ ) and manganese (Mn ²⁺ ).

The present invention thus successfully finds solutions to the shortcomings of the prior art in a novel and progressive manner. The inventors of the present invention have indeed found that dibasic metal citrates or alkaline earth metal citrates having a specific chemical formula as described above are highly soluble in aqueous solutions and provide a highly stable biocidal solution. Surprisingly, the biocidal solution remains stable over a long period of time and over the entire pH range (even when using "hard water" or when the pH value is increased), i.e., does not produce any precipitation. In addition, this solution has a naturally neutral to alkaline pH value, thereby reducing phytotoxicity.

Furthermore, surprisingly, an irreversible insoluble or slightly soluble compound can be obtained from the above dialkali metal citrate or alkaline earth metal citrate solution after plant absorption/metabolism of alkaline metal cations or alkaline earth metal cations and evaporation of water. The compound exhibits high biocidal activity and achieves a good balance between leaching and persistence, and has low phytotoxicity and low ecotoxicity.

Finally, since the plants treated with/received by the metal citrate of the present invention can metabolize alkaline metal cations or alkaline earth metal cations in a beneficial way, the metal citrate of the present invention can also be advantageously used as a foliar fertilizer. This is particularly advantageous when alkaline metal cations such as potassium and ammonium are used.

In the present invention, the alkali metal cation or alkaline earth metal cation has the following three functions: (1) It can provide a highly soluble alkali metal or alkaline earth metal citrate compound, which forms a solution with a pH value of neutral to alkaline after dissolution, and does not produce precipitation when the solution is dissolved in "hard water" and/or when the pH value is increased (for example, pH>8.5); (2) Once the solution is applied to the plant, the alkali metal ions or alkaline earth metal ions are absorbed through the plant's metabolism, thereby forming an irreversible insoluble or slightly soluble metal-citrate complex (as described in PCT/EP2023/059715), which forms a protective and rain-resistant layer on the treated organs; (3) The metabolism of the alkali metal cations or alkaline earth metal cations by the plant will provide a fertilizer effect. In fact, these elements are commonly used to improve plant functions through primary metabolism, such as improving stem growth, water transport throughout the plant, flowering and fruiting.

This novel and progressive "alkali metal/alkaline earth metal-citrate pathway" is therefore able to address the drawbacks found in the aforementioned "copper/zinc-citrate pathway" (phytotoxicity due to low starting solution pH), while retaining its advantages and having an additional positive impact on plant health/growth through fertilizer effects.

In particular, when copper (II) is concerned, the inventive approach also allows reducing the copper content in the environment, since, for the same amount of copper metal, more active Cu²⁺ can be produced in aqueous solution compared to the known solid particle suspensions (e.g. copper hydroxide or Bordeaux liquid).

The present invention also relates to a composition comprising the above-mentioned dialkali metal citrate or alkaline earth metal citrate.

The present invention also relates to a biocidal solution, which comprises the above-mentioned dialkali metal citrate or alkaline earth metal citrate and water.

In addition, the present invention also relates to a method for preventing or inhibiting the growth of live pathogenic organisms on plants, plant products, seeds, tubers and/or fruits, which method comprises the step of applying the biocidal solution to the plants, plant products, seeds, tubers and/or fruits.

Finally, the present invention also relates to a use of the above-mentioned dibasic metal citrate or alkaline earth metal citrate, which is to use the above-mentioned dibasic metal citrate or alkaline earth metal citrate as a biocide in the following fields: Agriculture, including field crops, horticulture, arboriculture, viticulture, as a pre-harvest and/or post-harvest treatment; Lawns and gardens, including professional lawns; Forestry; Disinfection of fluids and surfaces.

Other features and advantages of the present invention will become more apparent through the following description of preferred embodiments.

Throughout this specification, when a range is expressed, unless otherwise explicitly stated, both endpoints of the range are included. In addition, all integers and sub-range values within a numerical range are explicitly included, just as if they were explicitly written out.

In the metal citrate of the present invention, for the sake of clarity, the citrate has an ionic state (or anionic charge) of -4, in other words, it is completely deprotonated (C ₆ H ₄ O ₇ ^4- )

According to the present invention, the "alkali metal" herein refers to alkali metals in a broad sense, including alkali metal ions and pseudo-alkali metal ions, especially NH ₄ ⁺ , K ⁺ and Na ⁺ . "Dialkali metal" conventionally means that there are two alkali metal cations in the chemical formula.

The metal citrate of the present invention may be a dibasic metal citrate with a chemical formula of (A,B)MC ₆ H ₄ O ₇ , wherein "A" is an alkali metal cation selected from NH ₄ ⁺ and K ⁺ , and "B" is an alkali metal cation selected from NH ₄ ⁺ , K ⁺ and Na ⁺ . Alternatively, the metal citrate of the present invention may be an alkali earth metal citrate with a chemical formula of AMC ₆ H ₄ O ₇ , wherein "A" is an alkali earth metal cation selected from Ca ²⁺ , Mg ²⁺ and a mixture thereof.

Preferably, the metal citrate of the present invention is a dibasic metal citrate with a chemical formula of (A,B)MC ₆ H ₄ O ₇ , that is, it contains at least one of potassium cations or ammonium cations, and can be one of K ₂ MC ₆ H ₄ O ₇ , KNH ₄ MC ₆ H ₄ O ₇ , (NH ₄ ) ₂ MC ₆ H ₄ O ₇ , KNaMC ₆ H ₄ O ₇ or NH ₄ NaMC ₆ H ₄ O ₇ .

More preferably, the chemical formula of the metal citrate of the present invention is (A, B) MC ₆ H ₄ O ₇ , wherein "A" is an alkali metal cation selected from NH ₄ ⁺ and K ⁺ , and "B" is an alkali metal cation selected from NH ₄ ⁺ and K ⁺ . These cations can provide a highly soluble alkali metal citrate, and after the plant metabolizes the NH ₄ ⁺ and/or K ⁺ ions, a slightly soluble or insoluble metal citrate can be formed, while providing a fertilizer effect, and thus is particularly beneficial.

In a more preferred embodiment, the chemical formula of the metal citrate is K ₂ MC ₆ H ₄ O ₇ . K ₂ MC ₆ H ₄ O ₇ can also be named as 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-1,2,3-tricarboxylate.

When the metal citrate of the present invention is an alkali earth metal citrate with the chemical formula AMC ₆ H ₄ O ₇ , and wherein "A" is an alkali earth metal cation selected from Ca ²⁺ , Mg ²⁺ and a mixture thereof, it means that it can be one of CaMC ₆ H ₄ O ₇ , MgMC ₆ H ₄ O ₇ or Ca _x Mg _y MC ₆ H ₄ O ₇ , wherein x＞0, y＞0, and x+y=1. For example, Ca ₂ MC ₆ H ₄ O ₇ can be named 1,2,3-propanetricarboxylic acid, 2-hydroxy-, metal(2+) calcium salt (1:1:2) (CAS index name) or (metal) calcium; 2-oxidopropane-1,2,3-tricarboxylate.

According to the present invention, "M" is a metal with a +2 oxidation state and is selected from Cu ²⁺ , Zn ²⁺ , Fe ²⁺ , Mn ²⁺ and mixtures thereof, that is, the metal M can be one of the above group, or a mixture of two, three or four of the metals. If more than one metal from the above group is selected, the ratio of each metal can vary over the entire range.

According to an advantageous embodiment, the metal M is chosen from Cu ²⁺ , Zn ²⁺ and mixtures thereof.

According to a preferred embodiment, the metal M is Cu ²⁺ . In this case, the chemical formula of the metal citrate of the present invention is (A,B)CuC ₆ H ₄ O ₇ or ACuC ₆ H ₄ O ₇ . In the present invention, as mentioned above, copper is advantageously used because it has long been proven to be highly effective against fungi or bacteria.

According to another preferred embodiment, the metal M is Zn ²⁺ . In this case, the chemical formula of the metal citrate of the present invention is (A,B)ZnC ₆ H ₄ O ₇ or AZnC ₆ H ₄ O ₇ . Zinc is an advantageous alternative because zinc also has biocidal activity (although its biocidal activity is generally lower than that of copper in certain diseases) and has less impact on health and the environment than copper.

According to another embodiment, the metal M is a mixture of Cu ²⁺ and Zn ²⁺ . In this case, the chemical formula of the metal citrate of the present invention is (A, B)(Cu, Zn)C ₆ H ₄ O ₇ or A(Cu, Zn)C ₆ H ₄ O _7. The co-presence of copper and zinc can synergistically enhance the biocidal activity because the total amount of metal (the total amount of copper and zinc) required to achieve the same biocidal activity/efficacy is less than the amount when one of the metals is used alone. In this embodiment, the ratio of copper to zinc (Cu/Zn) is preferably 0.5 to 2, and more preferably, the ratio of copper to zinc is 1. In this case, the chemical formula of the metal citrate of the present invention is (A,B)Cu _0.5 Zn _0.5 C ₆ H ₄ O ₇ or ACu _0.5 Zn _0.5 C ₆ H ₄ O ₇ .

Preferably, the metal citrate is amorphous. The metal citrate may be anhydrous or in the form of a hydrate.

In addition, preferably, the metal citrate of the present invention has a solubility in water of at least 500 g/L at 20°C, more preferably at least 1000 g/L at 20°C, and even more preferably at least 1500 g/L at 20°C. This is very advantageous because even at high concentrations, a solution can be obtained that is easy to handle (no precipitation problems) when applied to the target plants and can be evenly covered/spread on the target plants. In comparison, the solid mixture recently disclosed in European patent application PCT/EP2023/059715 (comprising copper (II) hydroxide and citric acid in a molar ratio of 1.5, 1.67 or 2) has a solubility of about 80 g/L.

The composition of the present invention preferably comprises greater than 80% by weight of the metal citrate of the present invention. More preferably, the composition comprises greater than 85% or even greater than 90% by weight of the metal citrate. In a very preferred embodiment, the composition consists essentially of the metal citrate, that is, the composition consists only of the metal citrate and a very small amount (e.g., less than 2% or 1% by weight) of possible impurities or other compounds.

The composition may also comprise a mixture of metal citrates of the formula (A,B)MC ₆ H ₄ O ₇ or AMC ₆ H ₄ O ₇ .

According to one embodiment, the composition may further comprise at least one additive selected from the following group: pH adjusters, film formers, anticaking agents, surfactants, wetting agents, antifoaming agents, anti-drifts, adhesives, thickeners, foaming agents, solidifying agents, other biocides, fertilizers, plant nutrients, soil nutrients and stabilizers. One example of a pH adjuster according to this embodiment and having advantages in the present _{invention is} an _alkali metal (potassium, ammonium and/or sodium) citrate or _{an alkali} earth metal citrate or a mixture thereof _{( especially K2C6H6O7} ; _{( NH4} ) _{2C6H6O7 ; Na2C6H6O7 ; CaC6H6O7} or _{MgC6H6O7 and hydrates} thereof) _.

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

According to another embodiment, the composition is in liquid form, for example, in the form of a concentrated aqueous solution. Since the metal citrate of the present invention has high solubility, it can be in liquid form.

The dibasic metal citrate of the present invention can be prepared by a variety of methods. For example, it can be prepared from divalent metal hydroxide M(OH) ₂ , potassium citrate and/or ammonium citrate and/or sodium citrate and optionally citric acid, and prepared in appropriate amounts according to the target dibasic metal citrate. Alternatively, it can also be prepared from divalent metal hydroxide M(OH) ₂ , citric acid and potassium bicarbonate and/or ammonium bicarbonate and/or sodium bicarbonate. In addition, for example, it can also be prepared from divalent metal hydroxide M(OH) ₂ , citric acid and potassium hydroxide and/or ammonium hydroxide and/or sodium hydroxide. In all cases, the metal (II) hydroxide M(OH) ₂ can be used in commercial solid form (which works very well when the metal is copper) or, better still, can be prepared in situ by hydrolysis of a metal sulfate or metal nitrate solution at high pH (which works very well for all metals M in the invention) to obtain a colloidal suspension and then to separate the metal hydroxide by centrifugation. Such a step results in a very active M(OH) ₂ colloid which can then be further reacted with alkaline citrate/citric acid ₍ especially in stoichiometric ratios) to obtain a long-term stable (no precipitation) transparent biocidal solution according to the invention. In the best method, the dibasic metal citrate of the present invention is prepared by: (i) hydrolyzing a metal sulfate or metal nitrate or metal chloride solution at a high pH (e.g., NaOH), (ii) centrifuging the obtained colloidal metal hydroxide, and (iii) dissolving the metal hydroxide in an alkaline citrate solution. Examples of potassium citrate include: K ₃ C ₆ H ₅ O ₇ , K ₂ HC ₆ H ₅ O ₇ , KH ₂ C ₆ H ₅ O ₇ and hydrates thereof, preferably dipotassium hydrogen citrate K ₂ HC ₆ H ₅ O ₇ . Examples of ammonium citrate include (NH ₄ ) ₃ C ₆ H ₅ O ₇ , (NH ₄ ) ₂ HC ₆ H ₅ O ₇ , NH ₄ H ₂ C ₆ H ₅ O ₇ , and hydrates thereof, preferably diammonium hydrogen citrate (NH ₄ ) ₂ HC ₆ H ₅ O ₇ . Examples of sodium citrate include Na ₃ C ₆ H ₅ O ₇ , Na ₂ HC ₆ H ₅ O ₇ , NaH ₂ C ₆ H ₅ O ₇ , and hydrates thereof, preferably disodium hydrogen citrate Na ₂ HC ₆ H ₅ O ₇ .

The alkali earth metal citrate of the present invention can be prepared by a variety of methods. For example, it can be prepared from metal hydroxide M(OH) ₂ , calcium citrate and/or magnesium citrate and optionally citric acid, and the appropriate amount can be selected according to the target alkali earth metal citrate. Alternatively, it can also be prepared from metal hydroxide M(OH) ₂ , citric acid and calcium carbonate and/or magnesium carbonate. In addition, it can also be prepared 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 can be used in commercial solid form or, better, can be prepared in situ by hydrolysis of a metal sulfate or nitrate solution at high pH to obtain a colloidal suspension, from which the metal hydroxide is then separated by centrifugation. Such a step results in very active M(OH) ₂ which is then (e.g. after separation) further reacted with alkaline earth metal citrate/citric acid (particularly in a _{stoichiometric} ratio) to obtain a long-term stable (no precipitation) transparent biocidal solution according to the invention. In the best method, the alkaline earth metal citrate of the present invention is prepared by: (i) hydrolyzing a metal sulfate or metal nitrate or metal chloride solution at a high pH (e.g., NaOH), (ii) centrifuging the obtained colloidal metal hydroxide, and (iii) dissolving the metal hydroxide in the alkaline earth metal citrate solution. Examples of suitable calcium citrates include: calcium hydrogen citrate CaHC ₆ H ₅ O ₇ and its hydrates. Examples of suitable magnesium citrates include: magnesium hydrogen citrate MgHC ₆ H ₅ O ₇ and its hydrates.

Due to its high solubility, the metal citrate of the present invention can be easily and quickly dissolved in water or water-based solvents to prepare the biocidal solution of the present invention. The use of the biocidal solution of the present invention can avoid the above-mentioned problems associated with the use of suspensions (such as sedimentation or the need for regular mixing, uneven plant coverage, etc.), and can achieve good and uniform coverage/dispersion on the target plants. Alternatively, the biocidal solution of the present invention can also be prepared by synthesizing the metal citrate in situ without the need to separate it into a solid form before re-dissolving it.

The biocidal solution may also contain additives, which may come from the composition and/or the solid mixture of the present invention and/or be added during the preparation of the solution. Examples of additives include: pH adjusters, film formers, anti-caking agents, surfactants, wetting agents, anti-foaming agents, anti-drifting agents, adhesives, thickeners, foaming agents, curing agents, other biocides, fertilizers and stabilizers.

The biocidal solution of the present invention has a neutral to alkaline pH value and is less phytotoxic (especially to more fragile plants) than the copper citrate solution described in European patent application PCT/EP2023/059715 (an acidic solution with a pH value close to 4).

Preferably, in the biocidal solution, the amount of the metal citrate and water of the present invention is such that the concentration of metal M in the biocidal solution is between 0.01 g/L and 5 g/L, more preferably, between 0.05 g/L and 3 g/L. Even more preferably, the amount of the composition and water is such that the concentration of metal M in the biocidal solution is between 0.1 g/L and 2 g/L.

Of course, the biocidal solution of the present invention can also be prepared from the composition of the present invention and water (by dissolving or diluting), and has the same embodiments as above, especially in terms of pH value and concentration.

According to the present invention, a method for preventing or inhibiting the growth of pathogenic organisms on plants, plant products, seeds, tubers and/or fruits comprises the step of applying the biocidal solution to the plants, plant products, seeds, tubers and/or fruits. Preferably, the application step is carried out by spraying, dusting, soaking, irrigation or coating.

In the embodiment where the metal M is copper, the amount of copper applied to the above-mentioned plants, plant products, seeds, tubers and/or fruits is less than 4000 g/ha (4000 grams/hectare, the registered maximum dosage for grapes) per season, preferably less than 3000 g/ha, more preferably less than 2000 g/ha, even less than 1000 g/ha or less than 500 g/ha. For the sake of clarity, the amount of copper in this embodiment is calculated based on the molar mass of copper element Cu.

When the biocidal solution of the present invention containing a metal citrate is applied to plants, plant products, seeds, tubers and/or fruits, water evaporation (due to ambient temperature, wind, etc.) and absorption/metabolism of alkali metal ions or alkaline earth metal ions by the plants will cause irreversible precipitation or crystallization of insoluble or slightly soluble metal citrate. This metal citrate can be in the form of an amorphous precipitate, a crystal form, or a mixed form thereof.

In particular, when the metal M is copper, the slightly soluble or insoluble metal citrate has the chemical formula Cu ₃ (C ₆ H ₅ O ₇ ) ₂ or Cu ₂ (C ₆ H ₄ O ₇ ), or a hydrate thereof (e.g. Cu ₂ (C ₆ H ₄ O ₇ ).H ₂ O), or a mixture thereof. In addition to copper citrate, other compounds may also crystallize or precipitate, such as "free" citric acid.

In particular, when the metal M is zinc, the slightly soluble or insoluble metal citrate _may have the chemical formula _Zn3 ( _C6H5O7 ) ₂ or _Zn2 ( _C6H4O7 ), or _a hydrate or _mixture thereof. In addition to zinc citrate, other compounds may also crystallize or precipitate, such as " _free " citric acid.

These sparingly soluble or insoluble metal citrates, in addition to their low solubility which increases their persistence on plants (through a protective and rain-resistant layer) while still having high biocidal activity, have low ecotoxicity. Thus, copper citrate is known to have no toxic effects on fish, birds, mammals, and bees (see "Pesticide Toxicity Profile: Copper-Based Pesticides", Fishel (2011), University of Florida Institute of Food and Agricultural Sciences, Florida Cooperative Extension Service, Office of Pesticide Information), and can be used as a plant protection agent at low concentrations as an environmentally acceptable agent (Georgopoulos et al., 2001). Furthermore, zinc citrate, especially Zn ₃ (C ₆ H ₅ O ₇ ) ₂ and its hydrates, increases its persistence due to its low solubility while maintaining excellent biocidal activity and is known to be "generally recognized as safe" as a food ingredient. In fact, in Europe, zinc citrate is included in the positive list of EU Regulation (EC) No. 1925/2006 on the nutritional fortification of foods. Zinc citrate is also included in the list of substances in Directive 2002/46/EC of the European Parliament and of the Council on vitamins and minerals that may be used in food supplements. In addition, zinc citrate is listed as a mineral salt in EU Regulation (EC) No. 609/2013 for infant and toddler foods, foods for special medical purposes and whole-day dietary replacement foods for weight management. Furthermore, in the United States, zinc citrate can be considered a substance that is classified as a dietary ingredient under Section 201(ff) of the Food, Drug, and Cosmetic Act. In oral care, zinc citrate products are classified as Class I active ingredients in terms of safety and Class III active ingredients in terms of efficacy. Since 2009, zinc citrate has fully complied with the "Generally Recognized as Safe" (self-affirmed GRAS) in the United States Food, Drug, and Cosmetic Act.

Advantageously, the solubility of the sparingly soluble or insoluble metal citrate is less than or equal to 1 g/L. More preferably, its solubility is less than or equal to 0.8 g/L. In addition, preferably, its solubility is greater than or equal to 0.1 g/L, more preferably greater than or equal to 0.2 g/L, or even 0.3 g/L. More preferably, its solubility is greater than or equal to 0.5 g/L. This property helps to achieve good bioavailability of divalent metal M and a balance between high leaching/high persistence.

In addition, since the irreversible precipitation/crystallization of the insoluble or poorly soluble metal citrate is caused by the metabolism/absorption of alkali metal ions or alkaline earth metal ions by the target plant, the present invention also has the advantage of bringing a beneficial fertilization effect to the target plant. In fact, potassium and nitrogen are elements commonly used to improve plant health, growth and function, such as improving stem growth, water transport throughout the plant, flowering and fruiting).

According to another aspect of the invention, the dibasic metal citrate or alkaline earth metal citrate is used as a biocide, in particular as a fungicide and/or bactericide, and is applied in the following fields: (i) agriculture, including field crops, horticulture, arboriculture, viticulture, as pre-harvest and/or post-harvest treatment; (ii) lawns and gardens, including professional turf; (iii) forestry; (iv) disinfection of fluids and surfaces.

Fungicides are known in the art as chemical or biological agents used to reduce, inhibit or eliminate fungi. Bactericides are known in the art as chemical or biological agents used to reduce, inhibit or eliminate bacteria.

For the sake of clarity, the disinfection of fluids and surfaces involved in the present invention includes multiple fields, such as medical, veterinary, household and industrial uses, but does not include any therapeutic uses. Fluids can be water, air, gas; and surfaces can be floors, work surfaces, toilets, medical equipment, prostheses, etc.

In particular, the alkaline metal citrate or alkaline earth metal citrate of the present invention is used as a biocide and is applied in the following fields: (i) agriculture, including field crops, horticulture, arboriculture, viticulture, as pre-harvest and/or post-harvest treatment; (ii) lawns and gardens, including professional lawns; (iii) forestry.

The metal citrates of the present invention can be used as biocides to treat various bacterial and fungal diseases on plants, plant products, seeds, tubers and/or fruits. In particular, the compositions of the present invention can be used as fungicides, for example, for the treatment of Plasmopara viticola , Phytophtora infestans and other fungal diseases of various pathological systems.

In addition (or in addition to being used as a biocide), the metal citrate of the present invention also has advantages in promoting plant growth and development, and can therefore be used as a fertilizer, for example as a foliar fertilizer or a plant nutrient. In fact, as mentioned above, when the alkali metal citrate of the present invention is applied to plants in the form of a solution, it will provide the plant with the metabolism of alkali metal ions (such as K ⁺ and/or NH ₄ ⁺ ) or alkaline earth metal (such as Ca ²⁺ and/or Mg ²⁺ ) ions. In addition, copper, zinc, iron and manganese are essential elements/trace nutrients required by plants. In particular, zinc is involved in the synthesis of growth hormones, so zinc is very important for root development and the emergence stage of crops. Copper can enhance photosynthesis and enzyme activity, and plays an important role in the formation of cell wall lignin. Iron is involved in many important compounds and physiological processes in plants (such as chlorophyll synthesis and enzyme function), so it is beneficial to plants. Manganese is an important trace nutrient required for plant growth/development, which can maintain metabolic processes in different parts of plant cells.

Finally, the metal citrates of the present invention may also be used to advantage in other fields outside of plant treatment. For example, the metal citrates of the present invention may have application value in food formulation (human or animal) or mineral extraction.

The following will further describe the embodiments of the present invention through examples and in combination with comparative examples that do not conform to the present invention. The following examples are for illustrative purposes only and are not intended to limit the scope of the present invention. [Examples]

(1) Preparation of dialkali metal M citrate and alkaline earth metal M citrate according to the present invention

According to the present invention, the preparation of dibasic metal citrate and alkaline earth metal citrate using copper (II) or zinc (II) as metal is carried out in three consecutive steps to obtain a stable and long-term clear concentrated solution, and then obtain the final product in solid form by evaporation. The specific method is as follows:

(a) Dissolve the dibasic metal hydrocitrate or alkaline earth metal hydrocitrate in water at a concentration of 0.5 to 1 mol per liter of water at room temperature in a flask using a magnetic stirrer. The amount/concentration of water required has no effect on the synthesis of the product. For calcium-based compounds, since calcium hydrocitrate is not currently available on the market, it is prepared in situ by an equimolar reaction of citric acid with calcium carbonate or calcium oxide. The resulting solution is stable for about 30 minutes and needs to be used quickly.

(b) Synthesis of highly active colloidal particles of M(II) hydroxide in aqueous solution by complete neutralization of 2 mol of an alkaline hydroxide selected from NaOH, KOH or LiOH with 1 mol of M(II) metal sulfate. The obtained colloid is separated by centrifugation and the sulfate or chloride residues are washed away.

(c) Freshly prepared M(II) hydroxide (from step (b)) is added to the dibasic metal hydrocitrate or alkaline earth metal hydrocitrate solution (from step (a)) to obtain a clear solution after a few minutes. This solution is stable for a long time and can therefore be used as a biocidal solution according to the present invention. Alternatively, the citrate can be isolated in solid form and subsequently redissolved for plant application.

(d) Drying the solution obtained in step (c) to obtain the dibasic metal citrate or alkaline earth metal citrate in solid form. Drying is carried out using a Rotavapor Büchi R 220 pro at a temperature range of 50°C to 90°C and a pressure starting at 150 mbar and decreasing to 1 mbar. Spray drying is also an effective alternative. The final product is a free-flowing powder that dissolves readily in water.

The following dibasic metal M (II) citrates or alkali earth metal M (II) citrates were prepared according to the above method: dibasic metal copper citrate 1: K ₂ CuC ₆ H ₄ O ₇ dibasic metal copper citrate 2: (NH ₄ ) ₂ CuC ₆ H ₄ O ₇ dibasic metal copper citrate 3: KNH ₄ CuC ₆ H ₄ O ₇ dibasic metal copper citrate 4: KNaCuC ₆ H ₄ O ₇ dibasic metal zinc citrate 1: K ₂ ZnC ₆ H ₄ O ₇ alkali earth metal zinc citrate 1: CaZnC ₆ H ₄ O ₇ Alkaline Earth Metal Copper Citrate 1: MgCuC ₆ H ₄ O ₇

The above dibasic metal M(II) citrates or alkaline earth metal M(II) citrates were characterized by: elemental analysis using X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma mass spectrometry (ICP); determination of citric acid content using the certified procedure of Agroscope STS0223; and evaluation of their amorphous characteristics using X-ray diffraction (XRD). All the prepared citrates were amorphous. In addition, the solubility of these citrates in water reached 1500 g/L. Their chemical formula was verified by complete analysis by XPS, citric acid content determination and ICP.

(2) Evaluation of the bioassay efficacy of dibasic copper citrate 1 against Plasmopara viticola on disc sections of grape leaves (laboratory test)

Methods: The protective activity of the dibasic copper citrate 1 (K ₂ CuC ₆ H ₄ O ₇ ) against grape spore fungus ( Plasmopara viticola ) was tested and compared with the fungicide Kocide ^® Opti as a reference. Kocide ^® Opti is a commercial fungicide with the active substance Cu(OH) ₂ , which was chosen as a reference due to its excellent efficacy against spore fungus.

Kocide ^® Opti was tested in a concentration range of 0.01 to 2 times the registered dose (equivalent to 0.1875 g/L of copper metal). The solution was applied by a Potter spray tower to a culture dish containing 10 leaf discs (variety Cabernet Sauvignon) placed on filter paper soaked in water. After application, the leaf discs were gently dried in a laminar flow cabinet. 24 hours after treatment, the back of the leaf discs was inoculated with a spore suspension (1.10 ⁵ spores per ml). The plates were then sealed and placed in a thermostatic incubator (22°C, high humidity using water-soaked filter paper, natural photoperiod). Disease incidence (percentage of leaf discs showing symptoms/sporulation) and severity (percentage of leaf disc surface showing symptoms/sporulation) were assessed on day 7 after inoculation.

Data on severity were processed by analysis of variance and mean comparison test (using XLSTAT software). Data were arcsine transformed before analysis. Different letters indicate statistically significant differences between treatments/concentrations. The half-maximal inhibitory concentration (IC50) that inhibited 50% of pathogen development was calculated using a four/five-parameter logistic regression module (XLSTAT software).

The formula for calculating efficacy is: ((the severity of the untreated control group - the severity of the fungicide) / the severity of the untreated control group) * 100 (the fungicide here can be Kocide ^® Opti/reference or dibasic copper citrate 1).

Results: In the water control, infection was sufficient, all leaf discs showed sporulation and the disease severity was 80.6%. As expected, the selected reference fungicide (Kocide ^® Opti) did not show sporulation. The results obtained are shown in Table 1 and illustrated in Figures 1 and 2.

[Table 1] form Relative concentration of copper Copper (g/L) Disc spore incidence (%) Severity (%) Standard error (severity) Anova+Tukey Kocide ^® Opti （Reference example） / 0.1875 0 0.0 0.0 Water control (“untreated”) 0 0 100 80.6 5.6 a Dibasic copper citrate 1 0.01 0.001875 100 54.0 6.2 a 0.05 0.009375 100 19.0 2.8 b 0.1 0.01875 50 2.5 0.8 c 0.25 0.046875 50 2.5 0.8 c 0.5 0.09375 50 2.5 0.8 c 0.75 0.140625 0 0.0 0.0 c 1 0.1875 0 0.0 0.0 c 2 0.375 0 0.0 0.0 c

Figure 1 shows in particular the observed severity (expressed as a percentage) versus the relative concentration of dibasic copper citrate 1, i.e. the ratio of the copper metal concentration in dibasic copper citrate 1 to the copper metal concentration corresponding to the registered dose of Kocide ^® Opti (0.1875 g/L Cu).

This biological test shows that the dibasic metal copper citrate 1 according to the present invention can completely inhibit the development of mycosis fungus at a copper metal concentration of 0.14 g/L (equivalent to 0.75 times the copper metal dosage of Kocide ^® Opti), and when the dosage is reduced to one-tenth of the reference dosage, that is, as low as 0.01875 g/L copper metal concentration, it still has an efficacy of 96%.

The severity data were processed by analysis of variance and mean comparison test (Tukey test: ^R2 = 0.828; Pr＞F: ＜0.0001). Data were arcsine transformed before analysis. Different letters (a, b, c) indicate significant statistical differences between treatments/concentrations. The modeled curves obtained to determine the theoretical dose for complete disease control showed _IC99 = 0.58 and _IC50 = 0.018. This is plotted in Figure 2. In addition, no phytotoxic symptoms were observed at all dibasic copper citrate 1 concentrations tested.

(3) Evaluation of the field efficacy of dibasic copper citrate 1 against grape syrup

Methods: The protective efficacy of the dibasic copper citrate 1 (K ₂ CuC ₆ H ₄ O ₇ ) against grape sap fungus ( Plasmopara viticola ) was tested. The efficacy trial was conducted in Switzerland (Nyon, 46° 23'54''N, 6° 13'53''E) on grapevines planted in 2000 with the Chasselas 800/3309 variety.

The experiment was set up as a completely randomized block design, with each of the twelve forms (different alternative fungicides) arranged in four replicate blocks, each with an area of 17.5 square meters, equivalent to 10 grape trees, as well as an untreated control group and an organic reference group (see Figure 3).

The vines were treated with dibasic copper citrate 1 at 300 g/ha (grams per hectare) copper equivalent, eight times throughout the growing season using a backpack sprayer (200 to 400 l/ha depending on vegetation growth). See Figure 3 and Table 2 for details of the application pattern.

[Table 2] Application times date Growth phase (BBCH) Application rate (l/ha) 1 J0 55 200 2 J0 57 250 3 J7 59 300 4 J14 65 350 5 J21 71 400 6 J28 71-73 400 7 J35 75 400 8 J42 77 400

Evaluation of the efficacy of dibasic copper citrate 1 against scurfycetoma: During the growing season, leaves and bunches were evaluated for disease four times and the incidence of scurfycetoma (percentage of organs with symptoms) and the severity of the disease (ratio of diseased area on leaves/bunches) were recorded. In each evaluation, 100 leaves and 50 bunches were randomly examined in each block. The incidence and severity of scurfycetoma were evaluated by observing 4 groups of 100 leaves and 4 groups of 50 bunches for each treatment on day 42 (BBCH stage 77). The incidence is the percentage of leaves/bunches with symptoms/spores. The severity is the percentage of the leaf/bunch surface with symptoms/spores. The efficacy is calculated by the following formula: (severity of the untreated control group - severity of the fungicide) / severity of the untreated control group * 100.

a. Evaluation of leaf fungus The results obtained for leaves are listed in Table 3 and plotted in Figure 4.

[Table 3] form Incidence rate (%) Standard Deviation Severity (%) Standard Deviation Efficacy (%) Untreated control group 50.12 12.23 8.92 4.80 Dibasic copper citrate 1 5.81 6.58 0.55 0.59 94

b. Evaluation of fruit bunch fungus The results obtained for the fruit bunches are listed in Table 4 and plotted in Figure 5.

[Table 4] form Incidence rate (%) Standard Deviation Severity (%) Standard Deviation Efficacy (%) Untreated control group 66.50 16.28 31.49 9.14 Dibasic copper citrate 1 5.96 6.31 1.65 1.95 95

(4) Evaluation of the bioassay efficacy of dibasic zinc citrate 1 against Plasmopara viticola on disc sections of grape leaves (laboratory test)

Methods: The protective capacity of dibasic zinc citrate 1 (K ₂ ZnC ₆ H ₄ O ₇ ) against grape syrup ( Plasmopara viticola ) was tested using the same method as dibasic copper citrate 1 (point 1).

Results: The results are listed in Table 5 and plotted in Figure 6.

[Table 5] Dibasic zinc citrate 1 Concentration (g/L) 0 1 5 10 15 20 Equivalent Zn (g/L) 0.00 0.18 0.90 1.80 2.70 3.60 Zn content (g/ha) 0 288 1440 2880 4320 5760 Severity (%) 73.1 18.0 0.0 0.0 0.0 0.0 Standard error (severity) 13.6 9.5 0.0 0.0 0.0 0.0 Efficacy (%) 75 100 100 100 100

Dibasic zinc citrate 1 can significantly reduce the severity of fungal disease at a product concentration of 1 g/L and can provide comprehensive disease control at higher concentrations.

(5) Evaluation of the bioassay efficacy of the alkaline earth metal zinc citrate against Plasmopara viticola on disc sections of grape leaves (laboratory test)

Methods: The protective capacity of the alkaline earth metal zinc citrate 1 (CaZnC ₆ H ₄ O ₇ ) against grape syrup ( Plasmopara viticola ) was tested using the same method as for the dibasic metal copper citrate 1 (point 1).

Results: The results are listed in Table 6 and plotted in Figure 7 (95% efficacy level is plotted for reference).

[Table 6] Dibasic zinc citrate 1 Concentration (g/L) 0 1 5 10 15 20 Equivalent Zn (g/L) 0.00 0.18 0.90 1.80 2.70 3.60 Zn content (g/ha) 0 288 1440 2880 4320 5760 Severity (%) 73.1 18.0 0.0 0.0 0.0 0.0 Standard error (severity) 13.6 9.5 0.0 0.0 0.0 0.0 Efficacy (%) 75 100 100 100 100

(6) Evaluation of the bioassay efficacy of the alkaline earth metal copper citrate 1 against Plasmopara viticola on disc sections of grape leaves (laboratory test)

Methods: The protective capacity of alkaline earth metal copper citrate 1 (MgCuC ₆ H ₄ O ₇ ) against grape syrup ( Plasmopara viticola ) was tested using the same method as for dibasic metal copper citrate 1 (point 1).

Results: The results are listed in Table 7 and plotted in Figure 8 (95% efficacy level is plotted for reference).

[Table 7] Alkaline earth metal copper citrate 1 Concentration (g/L) 0.000 0.096 0.240 0.481 0.962 Cu relative concentration 0 0.1 0.25 0.5 1 Equivalent Cu (g/L) 0 0.01875 0.046875 0.09375 0.1875 Cu content (g/ha) 0 30 75 150 300 Severity (%) 75.5 67.5 1.75 0.75 0 Standard error (severity) 2.1 3.6 0.5 0.4 0.0 Efficacy (%) 11 98 99 100

Application of the alkaline earth metal copper citrate 1 at a concentration of 0.24 g/l significantly reduced the severity of mycosis with an efficacy of over 95%, achieving the same level of protection as the reference agent Kocide ^® Opti (registered dosage).

[Figure 1] Results of the evaluation of the bioassay efficacy of dibasic copper citrate 1 against grape rosacea on disc sections of grape leaves (laboratory test). [Figure 2] Results of the evaluation of the bioassay efficacy of dibasic copper citrate 1 against grape rosacea on disc sections of grape leaves (laboratory test). [Figure 3] Experimental setup for the evaluation of the field efficacy of dibasic copper citrate 1 against grape rosacea. [Figure 4] Results of the evaluation of the field efficacy of dibasic copper citrate 1 against grape rosacea (leaf). [Figure 5] Evaluation results of the field efficacy of dibasic copper citrate 1 against grape oozyme (fruit bunches). [Figure 6] Evaluation results of the bioassay efficacy of dibasic zinc citrate 1 against grape oozyme on disc sections of grape leaves (laboratory test). [Figure 7] Evaluation results of the bioassay efficacy of alkaline earth metal zinc citrate 1 against grape oozyme on disc sections of grape leaves (laboratory test). [Figure 8] Evaluation results of the bioassay efficacy of alkaline earth metal copper citrate 1 against grape oozyme on disc sections of grape leaves (laboratory test).

Claims (15)

A metal citrate has a chemical formula of: (A,B)M(C ₆ H ₄ O ₇ ), wherein A is an alkali metal cation selected from NH ₄ ⁺ and K ⁺ , and B is an alkali metal cation selected from NH ₄ ⁺ , K ⁺ and Na ⁺ ; or AMC ₆ H ₄ O ₇ , wherein A is an alkaline earth metal cation selected from Ca ²⁺ , Mg ²⁺ and a mixture thereof; and in the above chemical formula, M is a metal with a +2 oxidation state and is selected from Cu ²⁺ , Zn ²⁺ , Fe ²⁺ , Mn ²⁺ and a mixture thereof. The metal citrate of claim 1, wherein the chemical formula of the metal citrate is (A,B)M(C ₆ H ₄ O ₇ ), A is an alkaline metal cation selected from NH ₄ ⁺ and K ⁺ , and B is an alkaline metal cation selected from NH ₄ ⁺ and K ⁺ . The metal citrate of claim 1 or 2, wherein M is selected from Cu ²⁺ , Zn ²⁺ and a mixture thereof. The metal citrate of claim 3, wherein M is Cu ²⁺ . The metal citrate of claim 4, wherein the chemical formula of the metal citrate is K ₂ CuC ₆ H ₄ O ₇ . A metal citrate according to any one of claims 1 to 5, wherein the solubility of the metal citrate in water at 20°C is at least 500 g/L, preferably at least 1000 g/L at 20°C. A composition comprising the metal citrate of any one of claims 1 to 6. The composition of claim 7 further comprises at least one additive selected from the group consisting of a pH adjuster, a film former, an anti-caking agent, a surfactant, a wetting agent, an anti-foaming agent, an anti-migration agent, an adhesive, a thickener, a foaming agent, a solidifying agent, other biocides, a fertilizer, a plant nutrient, a soil nutrient, and a stabilizer. The composition of claim 7 or 8, wherein the composition is in solid form, preferably in the form of powder, granules or tablets. A biocidal solution comprising the metal citrate of any one of claims 1 to 6 and water. A method for preventing or inhibiting the growth of live pathogenic organisms on plants, plant products, seeds, tubers and/or fruits, comprising the step of applying the biocidal solution of claim 10 to the plants, plant products, seeds, tubers and/or fruits. A method for preventing or inhibiting the growth of live pathogenic organisms on plants, plant products, seeds, tubers and/or fruits as claimed in claim 11, wherein the concentration of metal M in the biocidal solution is 0.1 g/L to 2 g/L. A method for preventing or inhibiting the growth of live pathogenic organisms on plants, plant products, seeds, tubers and/or fruits as claimed in claim 11 or 12, wherein the step of applying the biocidal solution as claimed in claim 10 to the plants, plant products, seeds, tubers and/or fruits is carried out by spraying, dusting, soaking, irrigation or coating. A use of a metal citrate as a biocide, comprising using a metal citrate as claimed in any one of claims 1 to 6, wherein the biocide is applied in the following fields: (i) agriculture, including field crops, horticulture, arboriculture, viticulture, as a pre-harvest and/or post-harvest treatment; (ii) lawns and gardens, including professional lawns; (iii) forestry; (iv) disinfection of fluids and surfaces. The use of metal citrate as a biocide as claimed in claim 14, wherein the biocide is a fungicide and/or a bactericide, preferably a fungicide.