WO2001058265A2

WO2001058265A2 - Method for controlling parasites present in soils

Info

Publication number: WO2001058265A2
Application number: PCT/EP2001/000943
Authority: WO
Inventors: Giovanni Ardizzone; Mario Belluati; Lucio Filippini
Original assignee: Caffaro S.P.A.
Priority date: 2000-02-10
Filing date: 2001-01-29
Publication date: 2001-08-16
Also published as: ITMI20000212A0; ITMI20000212A1; AU4235601A; IT1317823B1; WO2001058265A3

Abstract

A method for controlling parasites present in soils, which includes the on-site preparation of chlorine dioxide and the direct distribution on the soil of the prepared chlorine dioxide, so that the product distributed on the soil contains an amount of chlorine ions, bonded so as to form chlorine dioxide, which is higher than 20 % with respect to all the chlorine ions that are present. The method achieves high activity and reduced environmental impact.

Description

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METHOD FOR CONTROLLING PARASITES PRESENT IN SOILS

TECHNICAL FIELD The present invention relates to a method for controlling microorganisms, insects and nematodes which can cause significant damage to crops of economic interest

BACKGROUND ART Agricultural soils are often infested by a variety of phytopathogenic microorganisms, insects and nematodes which can cause severe economic damage to crops and are unlikely to be successfully controllable after sowing or bedding the plants It is therefore customary to treat the soil prior to sowing or bedding with a biocidal product Methyl bromide, a gaseous halogenated compound, is particularly used

Methyl bromide, by penetrating in the soil due to its high specific density, is in fact able to eliminate the presence of the above-cited soil parasites even at a depth of approximately 10-15 cm below ground level

This agronomic activity, however, is associated with considerable environmental problems, since methyl bromide is one of the gases responsible for the thinning of the ozone layer Accordingly, it has been decided to gradually restrict the amounts allowed for use, with the aim of excluding any agronomic and industrial use by the year 2005

Currently, methyl bromide is applied with methods which are able to significantly reduce its dispersion into the atmosphere and therefore also reduce the amount actually introduced in the environment For example, an appropriately provided network of cannulas which dispense the gas under plastic films impermeable to the gas is used

Moreover, methyl bromide is in any case a compound which constitutes a high risk for its users, since it is a toxic gas and a potential cancer-causing agent

Compounds such as alkyl isocyanates, particularly methyl isocyanate, or alkyl isothiocyanates, particularly methyl isothiocyanates, are currently used as possible replacements of methyl bromide and are applied to the soil as such or, more conveniently, as precursor compounds capable of converting into the above- cited isocyanates during or after their application to the soil These compounds, while not being a risk for the ozone layer, are in any case less effective than methyl bromide and are still highly toxic for the user s The use of stabilized chlorine dioxide for controlling parasites in soils is known from Japanese patent applications 10036209, 9278614, 9071502, 8283112, 8133916, 7179315, 1125310 Stabilized chlorine dioxide is formed by acidified sodium chlorite which is partially converted into chlorine dioxide. However, this conversion is partial, in order to achieve the intended effect it is lo necessary to use an excess of the product Moreover, the chlorite tends to separate into chloride, which sahfies the soil and damages it, and into chlorate, which is such a persistent herbicide that it also damages the crops

DISCLOSURE OF THE INVENTION The aim of the present invention is to overcome the above drawbacks with ID a method for controlling parasites present in soils which includes the on-site preparation of chlorine dioxide and the direct distribution to the soil of the prepared chlorine dioxide

WAYS OF CARRYING OUT THE INVENTION The expression "on-site preparation" designates, according to the present 20 invention, preparation directly at the site where the ground to be treated is located

Accordingly, the Applicant has found surprisingly that the use of a product in which the amount of chlorine ions bonded to form chlorine dioxide is more than 20% of all present chlorine ions, when applied appropriately to the soil before 25 sowing or bedding, is able to control microorganisms, weeds, insects and nematodes which damage crops of economic interest, showing distinctly higher activities than stabilized chlorine dioxide, with smaller secondary effects and with less raw material, with a low environmental impact and a low risk for the user

The Applicant has also surprisingly found that the method according to the 30 invention is often responsible for an unexpected lush growth of the plants accompanied by a brilliant green coloring of leaf systems.

The method according to the invention has a particularly high activity against microorganisms, insects and nematodes which damage crops of economic interest, such as horticultural and ornamental crops. It has an excellent plant-treating activity when applied to the soil prior to sowing or bedding.

Preferably, the amount of chlorine ions bonded to form chlorine dioxide is more than 50%, more preferably 70%, with respect to all the chlorine ions that are present.

The chlorine dioxide can be applied as it is or diluted in aqueous solutions, wherein the chlorine dioxide content can vary between 0.025% and 2.5%.

Preferably, the chlorine dioxide concentration can vary between 0.05% and 1.5%.

A solution in which the chlorine dioxide content varies between 0.1% and 1 % is even more preferred.

The use of chlorine dioxide with a lead time which can vary between 2 and 20 days, preferably between 5 and 10 days, is particularly convenient.

Examples of preventable diseases, cited in order to better illustrate the present invention and without any limiting intent, are: -- Phvtophthora capsici on peppers - Rhizoctonia solani on various horticultural plants - Sclerotinia spp. on various horticultural plants.

The chlorine dioxide can be obtained by reduction of the chlorate (CI0₃ ^') (as described, for example, in Canadian patents 825,084, 826,577, 543,589, E85- 9566784, E90-956783, 1 ,079,931 , 652,250) or by oxidation of the chlorite (CI0₂ ), D. Gates, The chlorine dioxide book, Water disinfection series, AWWA, 1998; W. Massechelin, Chlorine dioxide - Chemistry and Environmental impact of oxychlohne compounds - Ann Arbor, 1979. In this second case, which is preferable when one wishes to obtain solutions having a higher degree of purity, the process for generating chlorine dioxide in solution can be performed with chlorine (Cl₂) (gaseous chlorine or in a solution as hypochlorous acid HCIO) or with hydrochloric acid according to the following reaction: -

5 NaCIO + 4 HCI -> 4 CI0₂ + 5 NaCI + 2 H₂0 In this case, the ge neration of chlorine dioxide in appropriately provided devices known as generators occurs starting from solutions of chlorite and hydrochloric acid at two different levels of concentration The choice of the concentration of the reagents to be used is a function of the required hourly productivity for generators with a productivity below 600 g ClO^h, diluted reagents are normally used, concentrated reagents are used instead for higher capacities

The expression "concentrated reagents" is used to designate solutions of 25% sodium chlorite and 33% hydrochloric acid, while the expression "diluted reagents" is used to designate solutions of 7 5% sodium chlorite and 9% hydrochloric acid In practice, the concentrations of the reagents in the generation chamber of the generator are the same in both cases since when concentrated reagents are used the generator is provided with a device for diluting them The chlorine dioxide is generated in a reaction chamber designed to withstand a pressure of 4 bar which has a volume which ensures a minimum retention time of 10 minutes. Depending on the type of generator, the reagents (and any dilution water) are propelled or drawn into the reaction chamber

A theoretical 100% conversion, based on the stoichiometry of the reaction, occurs when one obtains 1 g of CI0₂ from 1 676 g of NaCI0₂ The "theoretical" weight ratio R=HCI/NaCI0₂ would be equal to 0 32, but in practice, in order to obtain quantitative conversions, it varies between 0 85 and 1.25, accordingly, for example, 1 g of HCI (instead of 0 32 g) is reacted with 1 g of NaCI0₂

By working in an excess of hydrochloric acid it is therefore possible to facilitate the conversion of the chlorite to dioxide, minimizing the parasite reactions, and obtain an efficiency (η) of the generator calculated as follows η = 100 x produced CI0₂ / theoretical CI0₂ (where "produced CI0₂" is the actual concentration in g/L determined analytically and "theoretical CI0₂" is indeed the theoretical amount of chlorine dioxide expected on the basis of the amount of chlorite), which is ≥ 95% - 5 -

Thus, for example, a generator capable of generating up to 1000 g CI0₂/h, fed with a 24.9% sodium chlorite solution and a 32.8% hydrochloric acid solution together with the appropriate dilution water, generates 650 g/h of chlorine dioxide, consuming 4420 g/h of hydrochloric acid (an excess equal to 230%) and 4570 g/h of chlorite at a flow-rate of 63.5 mL/min together with 17 g/h of chlorine with a degree of purity of the produced dioxide higher than 95% and an efficiency of the process, with respect to the chlorite supply, which is also higher than 95%.

For convenient agronomic use of these oxidizing compounds, it is also important that their contents in chloride ions and chlorate ions be minimal, since high concentrations of the above-cited chloride and chlorate ions can lead to negative effects on the growth of the crops.

Accordingly, preference is given to the use of chlorine dioxide obtained by means of an electrochemical generation method in which sodium chlorite (NaCI0₂) is fed to the anode section, producing a chlorine dioxide solution, while in the cathode section, fed with water and separated from the anode section by a membrane, the reaction products are constituted by soda and hydrogen gas. The dissolved chlorine dioxide is then conveyed through a selective membrane which only allows the gases (vapor and chlorine dioxide) to pass, thus obtaining an extremely pure solution of the intended product which is free from chlorides and chlorates, as disclosed, for example, in Canadian patent 2182127, 1997.

In this manner, the chlorine dioxide used for the control of microorganisms, weeds, insects and nematodes which damage crops of economic interest is free from chloride ions and chlorate ions.

More particularly, the reaction involved in this case is the following: NaCI0₂ + H₂0 + energy --> CI0₂ + NaOH + ¹/₂H₂

Oxidation of the chlorite (CI0₂ --> CI0₂ + e^") occurs at the anode (large- surface electrode), and production of hydrogen (H⁺ + e^" --> ¹/2H₂) and formation of NaOH (soda) occur at the cathode by combination of the OH ion with the Na⁺ ion, which migrates to the cathode from the anode through the membrane, made of nafion or similar material, that separates the anode section and the cathode section. The chlorine dioxide dissolved as gas in the electrolytic liquid together with the vapor, after passing through selective membranes which are permeable only to gases, is redissolved in water. The solution, depleted of CI0₂, is returned to the cell by means a pump after enrichment with 25% sodium chlorite up to the intended concentration and control of pH in a range between 4.5 and 6.

The sodium chlorite solution fed to the anode is diluted and, in the steady state, is at a concentration of 0.1 M; a voltage of 1.33 V is applied to the cell and the circulating current varies between 2 and 3 KA/m². The hourly production capacity is a function of the type of cell and of the surface of the electrodes. Thus, for example, in this configuration an electrochemical chlorine dioxide generator with a generation capacity up to 1.2 kg/h is capable of producing 100 g/h of CI0₂ by means of a solution which contains 1382 mg of CIO^L and 7 mg of CI^L with a purity of more than 98%.

The chlorine dioxide prepared on site can be applied to the soil directly in gaseous form (by covering the soil with sheets) or as an aqueous solution.

The example listed hereafter is given merely as an illustration and does not intend to limit the aim and objects of the present invention in any way. EXAMPLE 1

A sample of soil was brought to the temperature of 20°C with thermostat control and divided into identical 100-gram fractions which were placed in jars of inert material provided with a hermetic plug and insertable in a structure which can rotate in order to allow continuous mixing of the content. The resulting samples were treated with different concentrations of chlorine dioxide, using methyl bromide (BM) as a comparison product. The liquid products were introduced in the soil by means of pipettes calibrated starting from solutions having a known titer; the solid products were introduced by weighing, and the gaseous ones were introduced by means of a suitable precision apparatus provided with a flowmeter capable of metering known volumes of gas in a time- controlled manner. 01/58265

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The soil being considered (density 850 g/L), which had a pH of 8.1 at the concentration of 10 g/L, has a dry content of 85% once dispersed in water and a microbiological contamination as listed in Table 1.

Table 1 : Biological contamination of examined soil

The treatments performed are listed in Table 2.

Table 2: treatments performed

The chlorine dioxide solution was prepared by reaction of chlorite and hydrochloric acid; the chlorine dioxide gas was generated electrochemically. Six hours after the treatment and again 10 days after the treatment, soil samples were taken in order to check the extent of the reduction in biological contamination.

The results can be expressed as follows: Table 3: Total aerobic coun (CFϋ/a)

Table 4: Total coliforms (CFU/100 α)

Table 5: Fecal coliforms (CFU/100 q)

Table 6: Fecal streptococci (CFU/100 q)

Table 7: Fungi (CFU/o)

The results show that the chlorine dioxide, regardless of the preparation method, is capable of drastically reducing the microbiological contamination of the soil to levels which are equal and/or better than the more established treatments in the agronomic field with methyl bromide.

Moreover, in practice, the amount of chlorine ions bonded to form chlorine dioxide can also be higher than 90%, increasing the effectiveness of the method.

Claims

CLAIMS 1 . A method for controlling parasites present in soils, comprising the on-site preparation of chlorine dioxide and the direct distribution on the soil of the prepared chlorine dioxide.

2. The method according to claim 1 , wherein the product distributed on the soil contains an amount of chlorine ions, bonded to form chlorine dioxide, of more than 20% with respect to all the chlorine ions that are present.

3. The method according to claim 2, wherein said amount is higher than 50%, preferably higher than 70%.

4. The method according to at least one of the preceding claims, wherein said chlorine dioxide is prepared starting from sodium chlorite by reaction with a substance chosen among gaseous chloride, hypochlorous acid and hydrochloric acid.

5. The method according to claim 4, wherein said chlorine dioxide is prepared according to the following reaction:

5 NaCI0₂ + 4 HCI --> 4 CI0₂ + 5 NaCI + 2 H₂0 preferably performed with an excess of hydrochloric acid.

6. The method according to at least one of the preceding claims, wherein said chlorine dioxide is prepared by electrochemical generation.

7. The method according to claim 6, wherein sodium chlorite is supplied to the anode section, producing a chlorine dioxide solution with a pH which is preferably between 4.5 and 6.

8. The method according to claim 6 or 7, wherein a chlorine dioxide solution is conveyed through a selective membrane which allows only gases to pass.

9. Every new characteristic or new combination of characteristics.