WO2001033961A1

WO2001033961A1 - Method for preserving crops

Info

Publication number: WO2001033961A1
Application number: PCT/US2000/031012
Authority: WO
Inventors: Gary Allen Secor; James P. Ringo
Original assignee: Raytec Corporation; North Dakota State University
Priority date: 1999-11-09
Filing date: 2000-11-09
Publication date: 2001-05-17
Also published as: AU1483901A

Abstract

The present invention is a method for preserving crops such as fruits and vegetables during storage, shipping, and processing by applying dry compositions that are capable of generating chlorine dioxide when activated by moisture diretlty onto the surface of the crop. The moisture on the surface of the crop or ambient moisture in the atmosphere initiates a chemical reaction that produces chlorine dioxide. The chlorine dioxide preserves the crops by acting as an antimicrobial agent to combat microorganisms that cause crop disease. Applying the dry formulation directly to the surface of the crop increases the efficiency of the dry formulation for preventing disease caused by microorganisms when compared to prior methods that used the dry formulations to produce fumigation gases to combat the microorganisms.

Description

METHOD FOR PRESERVING CROPS

BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to methods for preserving crops such as fruits and vegetables and particularly to methods for preserving crops during storage, shipping, and processing by applying dry compositions that are capable of generating chlorine dioxide when activated by moisture directly onto the surface of the crop.

Description of the Prior Art

Losses due to mycoses and bacterioses of stored crops are estimated to be in the billions of dollars per year. The use of chemical, biological, and other methods to protect stored crops from damage by fungal and bacterial organisms and prevent these losses has been somewhat successful. For example, U.S. Patent No. 4,593,040, issued to Adam, et al. on June 3, 1986, discloses using benzyl phenol derivatives and carbendazin to protect horticultural crops from decay caused by microorganisms during storage. U.S. Patent No. 5,334,619, issued to Vaughn, et al. on August 2, 1994, discloses using 2-nonanone as an antifungal agent against decay organisms of berries and other small fruit. U.S. Patent No. 4,975,277, issued to Janisiewicz, et al. on

December 4, 1990, discloses using isolates of Pseudomonas cepacia and the antifungal compound pyrrolnitrin to control post-harvest decay of apples. U.S. Patent No. 5,215,747, issued to Hairston, et al. on June 1, 1993, discloses using Bacillus subtilis endospores and chemical fungicides to protect crops against phytopathogenic fungi.

One particular method that has proved useful to prevent losses due to mycoses and bacterioses is the fumigation of stored crops with chlorine dioxide gas. Chlorine dioxide is known to have bactericidal, viricidal, algicidal, and fungicidal properties and is known to be an excellent disinfectant and oxidizer with bleaching and deodorizing properties. Chlorine dioxide is used principally as a primary disinfectant for surface waters to reduce the formation of trihalomethane compounds as disinfection byproducts and for odor and taste problems. Chlorine dioxide is an effective biocide at concentrations as low as 0.1 ppm and over a wide pH range. Chlorine dioxide is thought to penetrate cell walls and cell membranes and react with vital amino acids in the cytoplasm of the cell to kill the organism. The by-products of this reaction are chloride or chlorite, compounds shown by toxicological studies to pose no significant adverse risk to human health in drinking water applications. Chlorine dioxide, however, is not stable during storage and typically must be generated on-site using conventional chlorine dioxide generators. Further, concerns for safety have caused the U.S. Department of Transportation to prohibit the transport of chlorine dioxide except in very small quantities as a frozen hydrate. Examples of methods to generate chlorine dioxide on site include: U.S. Patent No. 5,895,638, issued to Tenney on April 20, 1999, discloses a process of producing chlorine dioxide by the reduction of chlorate ions with hydrogen peroxide. U.S. Patent No. 5,851,374, issued to Cowley et al. on December 22, 1998, discloses a method for producing chlorine dioxide by reacting chlorate ions with a persulfate in an aqueous acid reaction medium containing sulfuric acid. U.S. Patent No. 5,707,546, issued to Pitochelli on January 13, 1998, discloses a method of preparing and storing a stable solution of chlorine dioxide in a non-aqueous, water-immiscible liquid. U.S. Patent No. 4,731,193, issued to Mason et al. on March 15, 1988, discloses an aqueous solution capable of forming a foam that contains chlorine dioxide. Generating chlorine dioxide on-site for the treatment of stored crops is cumbersome and difficult because of the need to handle the generator and the chemicals associated with the generation process. This difficulty is aggravated by the need to repeat the process periodically to ensure effective treatment.

To avoid the difficulty of having to generate chlorine dioxide on-site, dry formulations of chlorine dioxide that are activated by moisture were developed. These dry formulations generally contain the chemicals (e.g., sodium chlorite and an acid) necessary to generate chlorine dioxide impregnated in an inert carrier or a carrier that facilitates the reaction. Typically, ambient moisture from the atmosphere is adsorbed by the dry formulation to form conditions that facilitate the reaction of the chemicals and the release of chlorine dioxide into the atmosphere surrounding the dry formulation. This chlorine dioxide gas diffuses throughout the atmosphere and fumigates the surroundings. Dry formulations have an added advantage in that they can be formulated to control the rate of release of chlorine dioxide. U.S. Patent No. 4,689,169, issued to Mason et al. on August 25, 1987, discloses a dry composition for the controlled production of gaseous chlorine dioxide that comprises a dry and inert diluent, a metal chlorite selected from the group consisting of alkali metal chlorites and alkaline earth metal chlorites, and a dry agent capable of reacting with a metal chlorite in the dry state to produce chlorine dioxide selected from the group consisting of dry oxidizing agents and dry acids. U.S. Patent No. 5,705,092, issued to Wellinghoff et al. on January 6, 1998, discloses a multilayered composite for providing sustained release of chlorine dioxide that includes a hydrophobic layer containing an acid releasing agent, and a hydrophilic layer containing chlorite anions. U.S. Patent No. 5,885,543, issued to Klatte on March 23, 1999, discloses a method for producing chlorine dioxide using calcium chloride impregnated zeolite or aqueous calcium chloride with sodium chlorite.

Typically, these dry formulations are impregnated into the walls of containers that store the harvested crops, are inserted in large granular form into the containers, or are contained in packages that are placed into the containers. When ambient moisture comes into contact with the dry formulation, the chemicals that generate chlorine dioxide react and produce the gas. The chlorine dioxide gas diffuses out of the container wall or package and serves as a fumigant that kills microorganisms and preserves the stored crops from decay caused by the microorganisms. This method has proven effective but has some disadvantages. For example, the method depends exclusively on activation by ambient moisture from the atmosphere and relies on the ability of the chlorine dioxide gas to diffuse out of its package and throughout the container in an efficient manner. Also, large amounts of the dry composition are often required to ensure that sufficient chlorine dioxide gas is generated and that fumigation occurs effectively. Thus, dry compositions must be added in excess to ensure that the microorganism population is reduced sufficiently to prevent loss due to disease. There is, therefore, a need for better and more efficient methods for using these dry formulations to preserve crops during storage, shipping, and processing.

BRIEF SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a method for preserving crops, particularly during storage, shipping, and processing.

It is another object of the present invention to provide a method for more efficiently using dry compositions that generate chlorine dioxide gas to preserve crops, particularly during storage, shipping, and processing.

These and other objects are achieved by applying dry compositions that are capable of generating chlorine dioxide (ClO₂) when activated by moisture directly onto the surface of the crop. The dry compositions interact with moisture and generate chlorine dioxide when and where it is needed to combat disease causing microorganisms. Applying the dry formulation directly to the surface of the crop increases the efficiency of the dry formulation for preventing damage caused by microorganisms such as fungi and bacteria when compared to prior methods that used the dry formulations to produce fumigation gases to combat the microorganisms.

The present invention is, therefore, capable of achieving the objects of the invention and attaining the benefits and advantages described as well as those which are inherent therein. Other and further objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon reading the detailed description of the invention.

DETAILED DESCRIPTION OF THE INVENTION The term "microorganism" as used herein means fungi, bacteria, algae, mycoplasmids, protozoa, viruses, and other organisms that cause crop disease and whose growth can be prevented, inhibited, or destroyed by chlorine dioxide.

The term "fungus" or "fungi" as used herein means a wide variety of nucleated, sporebearing organisms which are devoid of chlorophyll. Examples of fungi include yeasts, mildews, molds, rusts, and mushrooms.

The term "bacteria" or "bacterium" as used herein means any prokaryotic organism that does not have a distinct nucleus.

The terms "fungicide" and "bactericide" as used herein mean the ability of a substance to prevent, inhibit, or destroy the growth of fungi and bacteria, respectively. The terms include chlorine dioxide (ClO₂) and sodium chlorite solutions as used herein.

The term "antimicrobial" as used herein means the ability of a substance to prevent, inhibit, or destroy the growth of microorganisms. The terms include chlorine dioxide (ClO₂) and sodium chlorite solutions as used herein.

The term "crop" as used herein is defined to include the seed for the crop. The term "crop disease preventing amount" as used herein means an amount sufficient to prevent, inhibit, mitigate, palliate, ameliorate, stabilize, reverse, slow, or delay the progression of crop disease caused by microorganisms, particularly fungal and bacterial crop disease. A crop disease preventing amount can be administered in one or more applications, doses, or administrations. The term "preserving" as used herein means actions taken to minimize or prevent disease before it occurs and also actions taken to minimize the damage caused by disease after it occurs. The present invention provides a method for preserving crops during storage, shipping, or processing by applying one or more dry compositions that are capable of generating chlorine dioxide when activated by moisture directly onto the surface of the crop. Surprisingly, it has been found that applying the dry formulation directly to the surface of the crop increases the efficiency of the dry formulation for preventing damage caused by microorganisms such as fungi and bacteria when compared to prior methods that used the dry formulations to produce fumigation gases to combat the microorganisms. Although not bound by theory, it is believed that contact between the dry formulation and the surface of the crop has at least five distinct advantages over the fumigation methods previously used. First, when compared to the use ambient moisture alone, the combination of ambient moisture and moisture from the surface of the crop generates the chlorine dioxide gas more quickly, more efficiently, and in higher concentrations in areas where crop damage is likely to occur. This occurs because areas where there is sufficient surface moisture to activate the reaction are the moist areas where microorganisms are likely to thrive and cause crop damage. Second, applying the dry composition to the surface of the crop ensures that the vast majority of the microorganisms on the crop will come into contact with the chlorine dioxide gas. Previous fumigation methods generated the gas from packages containing the dry composition and relied upon diffusion to ensure that all crop surfaces with microorganisms were exposed to the gas. Often, the gas did not contact all surfaces because of some relatively "air tight" areas produced by the way the crop packed during storage or by dirt or other contaminants that effectively prevented the gas from diffusing to all the surface areas where microorganisms were likely to cause crop damage. By applying the dry compositions directly onto the surface of the crop, the present method increases the probability that all surfaces with microorganisms will be exposed to chlorine dioxide gas. Third, the dry composition on the surface of the crop is activated only in sub-areas of the storage container where moisture occurs and crop damage is likely. By generating the chlorine dioxide in these sub-areas of the storage container where moisture is present and not generating chlorine dioxide in sub-areas of the storage container that are exposed to very little moisture, much less dry composition is required to preserve the crop. It is, therefore, not necessary to use the relatively large amount of dry composition required to ensure that the entire storage container is fumigated, even in areas where there is very little moisture and microorganisms are not likely to grow and cause crop damage. Fourth, a pseudo timed release effect is obtained by generating the chlorine dioxide in sub-areas only when moisture is present. Since different sub-areas may become moist at different times during storage, the dry composition in a particular sub-area will only be consumed and chlorine dioxide generated when it is needed. For example, the area near the surface of a storage pile or the area near the door of a storage bin may become moist shortly after the crop is placed in storage while the area in the interior of a storage pile or the area at the back or bottom of a storage bin may not become moist at all or may become moist several days or weeks after storage. Since the dry compositions only produce chlorine dioxide when exposed to moisture, the chlorine dioxide will be available in different areas at different times when it is needed. Fifth, applying dry compositions containing sodium chlorite directly onto the crop surface produces sodium chlorite solutions on the crop surface when the dry composition interacts with moisture. In these surface solutions, the sodium chlorite that has not reacted to produce chlorine dioxide gas serves as an antimicrobial agent that helps to prevent disease and preserve the stored crop. In fumigation methods, in contrast, the sodium chlorite is located in the package and cannot interact with the disease causing microorganisms.

The dry compositions useful in the present invention can be any dry composition that can be formulated and applied directly onto the surface of a crop and that is capable of generating chlorine dioxide when exposed to moisture. Numerous such compositions are known in the art and others will likely be developed. Compositions known to be useful in the method of the present invention include, but are not limited to, those disclosed in U.S. Patent Nos. 5,885,543 issued to Klatte on March 23, 1999; 5,853,689 issued to Klatte on December 29, 1998; 5,777,850 issued to Jakob et al. on July 7, 1998; 5,707,739 issued to Wellinghoff et al. on January 13, 1998; 5,730,948 issued to Klatte et al. on March 24, 1998; 5,567,405 issued to Klatte et al. on October 2, 1996; 5,314,852 issued to Klatte on May 24, 1994; 5,278,112 issued to Klatte on January 11, 1994; 4,689,169 issued to Mason et al. on August 25, 1987; 4,547,381 issued to Mason et al. on October 15, 1985; 4,104,190 issued to Hartshorn on August 1, 1978; 3,591,515 issued to Clement on July 6, 1971, all incorporated herein by reference. Such dry compositions usually involve the reaction of sodium chlorite (NaClO₂) or sodium chlorate (NaClO₃) with acid or by other known reactions to produce chlorine dioxide. In a preferred embodiment, the dry compositions comprise sodium chlorite and at least one organic acid impregnated into an inert carrier or mixtures of inert carriers. The organic acid can be any organic acid capable of reacting with sodium chlorite when the two compounds are exposed to moisture. Preferably, the organic acid is selected from the group consisting of citric acid, lactic acid, tartaric acid, maleic acid, malic acid, glutaric acid, adipic acid, acetic acid, and formic acid. In another embodiment, the dry compositions comprise sodium chlorite and at least one mineral acid impregnated into an inert carrier or mixtures of inert carriers. The mineral acid can be any mineral acid capable of reacting with sodium chlorite when the two compounds are exposed to moisture. Preferably, the mineral acid is selected from the group consisting of sulfuric, hydrochloric, and phosphoric acid. The inert carrier(s) can be any carrier chemically compatible with the sodium chlorite and the organic or mineral acid but is preferably selected from the group consisting of zeolite, kaolin, mica, bentonite sepiolite, diatomaceous earth, and synthetic silica. Generally, the composition comprises from about 1 to about 75 percent by weight sodium chlorite, from about 1 to about 20 percent by weight organic or mineral acid, and from about 5 to about 98 percent by weight of inert carrier(s). Preferably, the dry composition comprises from about 5 to about 40 percent sodium chlorite, from about 1 to about 20 percent organic or mineral acid, and from about 40 to about 94 percent by weight of inert carrier(s). In a preferred embodiment, the dry composition comprises sodium chlorite and citric acid impregnated into zeolite in the above weight percentages.

The dry compositions may contain additional components such as adhesives, thickeners, penetrating agents, stabilizers, surfactants, binders, organic solids, inorganic solids, catalysts, and the like as required to produce a composition suitable for a particular application, particularly those additional components that could enhance the ability of the dry composition to adhere to the surface of the crop or to facilitate the release of chlorine dioxide.

Catalysts can be added to the dry compositions of the present invention to increase the release rate of chlorine dioxide when the composition interacts with moisture. U.S. Patent No. 5,008,096, issued to James P. Ringo on April 16, 1991, incorporated herein by reference, discloses a method for enhancing generation of chlorine dioxide from an aqueous medium containing a chlorine dioxide precursor which comprises contacting the aqueous medium with a catalytic amount of a catalyst selected from the group consisting of a transition metal, a transition metal oxide and mixtures thereof.

The dry compositions are prepared for application to the crop surface by grinding the dry composition alone or with any additional components into finely divided particles that can be conveniently applied to the crop and that will adhere to the surface of the crop. Preferably, the dry composition alone or with any additional components is ground to a powder having a particle size of from about 0.01 to about 10 millimeters, preferably from about 0.03 to about 1 millimeter, in diameter and applied directly to the surface of the crop. Dry compositions can also be prepared by creating a solution containing chlorine dioxide precursors and spraying the solution onto inert carriers and any other components that will comprise the composition. When only small amounts of moisture are sprayed onto the composition, the composition absorbs the moisture and produces a dry composition that can be used without further processing. If it is determined that spraying the solution onto the inert carrier and other components has introduced excess moisture into the composition, the composition can be dried before use, preferably by heating the composition to remove the moisture.

The compositions are applied to the surface of the crop using any convenient method such as spraying, dusting, scattering, coating, pouring, or simple mixing with the crop during processing, transferring, or otherwise handling the crop. The best method is chosen in accordance with the intended objectives and the prevailing circumstances.

In a preferred embodiment, the dry compositions are formulated as dusts, i.e., free-flowing admixtures of the dry composition with finely divided solids which act as dispersants and carriers, and dusted onto the crops as they are transported along a conveyor belt to storage. Generally, these dusts are prepared by grinding the dry composition with finely divide solid substances such as talc, natural clays such as kaolin, flours, bentonite, pyropyllite, diatomaceous earth, and other organic and inorganic solids. The rate of application for the dry formulations will vary depending upon the composition, the conditions in which the dry composition will be used, the type of crop being treated, and other similar factors. Application rates should be sufficient to elicit the desired effect of microbial control while not producing adverse phytotoxic effects on the treated crops. Generally, the composition is applied to the crop in amounts of from about 0.1 grams to about 10 grams per kilogram of crop, preferably from about 0.25 grams to about 2.5 grams per kilogram of crop.

In one embodiment, the crops are placed in storage after the dry compositions have been applied to the crops. Moisture on the surface of the crop, ambient moisture in the atmosphere, or a combination of ambient moisture and surface moisture initiates a chemical reaction involving the compounds in the dry composition that generates chlorine dioxide. The generated chlorine dioxide preserves the crops during storage by acting as an antimicrobial agent to combat microorganisms that cause crop disease. Very little chlorine dioxide will be produced in storage conditions with low humidity atmospheres containing crops with minimal amounts of surface moisture, i.e., storage conditions where microorganisms are not likely to grow and very little chlorine dioxide is needed to preserve the crop. If ambient or surface moisture increases and causes conditions where microorganisms are likely to grow and damage the crop, the moisture will initiate the reaction and generate chlorine dioxide that will destroy the microorganism and preserve the crop. Importantly, the chlorine dioxide will be generated only in sub-areas of the storage container where the moisture is present. For example, if a small hole occurred in the side of the container and moisture entered through the hole, chlorine dioxide would only be generated in the area surrounding the hole where moisture increased and provided favorable conditions for microorganism growth and crop damage. Similarly, if particular pieces or units of a crop had high surface moisture due to contamination or natural conditions, chlorine dioxide would only be generated in the area surrounding the unwanted moisture that provides conditions for microorganism growth and crop damage. Surprisingly, it has been discovered that applying the dry composition directly onto the surface of the crop increases its efficacy at least two fold and often three or more fold. It is believed that this increased efficacy results because the dry composition is located on the surface of the crop and therefore located where moisture is present and crop damage is likely to occur. By generating the chlorine dioxide in sub-areas where moisture is present, as opposed to generating chlorine dioxide in large amounts to fumigate the entire storage area, much less of a dry composition is required to accomplish the same result as fumigation. Similarly, if the same amount of dry composition is used in the present method as is used for fumigation, the present method will be much more effective in preserving crops because the chlorine dioxide will be present in higher concentrations in areas where it is needed and therefore used much more efficiently.

In another aspect, the present invention provides a method for preserving crops during storage, shipping, or processing by applying a dry composition containing sodium chlorite as the chemical that generates chlorine dioxide directly onto the surface of the crop. When the dry composition containing sodium chlorite interacts with moisture, a solution of sodium chlorite and the other components of the composition, e.g., the acid, is formed on the surface. While most of the sodium chlorite is eventually consumed to produce chlorine dioxide, some of the sodium chlorite remains in solution for extended periods. During the time that sodium chlorite remains in solution and before it reacts to produce chlorine dioxide, the sodium chlorite serves as an antimicrobial agent that prevents crop disease caused by microorganisms and preserves the crops during storage. Crops that may be treated according to the method of the present invention include, but are not limited to, cereals such as wheat, barley, rye, oats, rice, sorghum and related crops; beets; soft fruits such as apples, pears, plums, peaches, almonds, cherries, strawberries, raspberries and blackberries; legumes such as beans, lentils, peas, and soybeans; cucumbers; melons; citrus fruits such as oranges, lemons, grapefruits, and mandarins; vegetables such as spinach, lettuce, asparagus, cabbages, carrots, onions, tomatoes, potatoes, and paprika; and the seed of such crops.

The method of the invention is effective at preventing crop disease caused by most microorganisms, particularly fungi and bacteria. The method is effective against fungi including, but not limited to, the Oomycetes, Ascomycetes and Fungi imperfecti classes which include Cladosporium cucumerinum, Phytophthora infestans, Botrytis cinerea, Pseudoperonospora cubensis, Sphaerotheca fuliginea, and Erysiphe graminis. As generally known in the art, fungicides have a wide spectrum of activity. Therefore, if a fungicide is effective against one member of a class it is usually effective against other members of the same class. Furthermore, if fungi from the same class cause disease on different crops the same fungicide will be effective against the disease in the different crops because fungicides are disease-specific rather than crop specific. (Fungicides in Plant Disease Control by Y. L. Nene and P. N. Thapliyal, International Science Publishers, New York, N.Y., USA, 1993). The method according to the present invention is useful for controlling such diseases as cucumber downy mildew caused by Pseudoperonospora cubensis, tomato late blight caused by Phytophthora infestans, grape downy mildew caused by Plasmopara viticola, and potato late blight caused by Phytophthora infestans. The method also controls other common fungi that have a particular impact on potatoes by causing disease, including Fusarium species, Helminthosporium solani, Alternaria solani, and Rhizoctonia solani.

The method is effective against bacteria including, but not limited to, those in the Pseudomonas, Erwinia, Agrobacterium, Xanthomonas, and Clavibacter species. Pseudomonas and Xanthomonas species, in particular, affect a large number of different crops. For example, Pseudomonas syringae pathovar tomato causes bacterial speck of tomato and Pseudomonas solanacearum causes bacterial infections in potatoes. Potatoes and many other crops, such as celery, head lettuce, carrot, radish, tomato, and cabbage are susceptible to bacterial soft rots caused by these microorganisms. Erwinia carotovora, ubiquitous in soil and surface water, is a soft rot bacterium that softens and rots storage tissues of many crops. The bacterium typically enters crop tissue through injuries caused by harvesting, processing, insects, and the like. The bacterium invades the injury site and rapidly multiply and macerate the tissue. Erwinia carotovora subsp. carotovora and Streptomyces scabies have a substantial impact on the potato industry. In a preferred embodiment, the dry compositions useful in the method of the present invention are applied directly to the surface of harvested potatoes during the process used to place the potatoes into storage. The dry compositions thus applied preserve the potatoes and prevent disease caused by microorganisms, particularly potato late blight caused by Phytophthora infestans. Generally, potatoes are harvested in the potato field by any conventional means and transported by truck from the field to storage shed sites. The harvested potatoes are removed from the truck and transported by a mechanical conveyor to a grading and sorting table where culling is performed based on size and quality. The potatoes are then conveyed to a dirt eliminator which removes gross soil, rock, and detritus. A mechanical conveyor then moves the potatoes to a piler for placement of the potatoes into large piles within the storage shed.

According to the present invention, the potatoes are dusted with the dry composition while being conveyed to the piler or while being placed into piles using any of many commercially available devices for the application of dust or powders to crops, e.g., pesticide dusting applicators. The preferred dry composition for treating potatoes is about 90 percent zeolite, 5 percent sodium chlorite, and 5 percent citric acid by weight. The dry composition is applied at the rate of about 1 pound of dry composition per ton of treated potatoes (0.5 grams composition per kilogram of potatoes).

While the preferred embodiments involve applying the dry compositions of the present invention to the crop during storage, shipping, and processing, the compositions can be applied to the crop in any situation where it would be beneficial to use chlorine dioxide to preserve a crop, e.g., in the field before harvest to preserve the crop. According to the present invention, a method is provided for preserving crop seed during planting by applying one or more dry compositions that are capable of generating chlorine dioxide when activated by moisture directly onto the surface of the crop seed immediately prior to planting. Applying the dry compositions of the present invention to crop seed inhibits or prevents disease caused by microorganisms during the planting process and during the period after the seed is planted. "Immediately prior to planting" refers to the period from when the seed is removed from storage and the process for preparing the seed for planting begins to the time that the seed is planted. "During planting" refers to the period from immediately prior to planting to a time after the seed is planted in the soil when disease caused by microorganisms is likely to occur. Generally, the dry compositions are applied to the crop seed on the day of planting or within the 24 hour period preceding planting.

The rate of application for the dry formulations to the crop seed will vary depending upon the composition, the conditions in which the dry composition will be used, the type of crop seed being treated, and other similar factors. Application rates should be sufficient to elicit the desired antimicrobial control while not causing adverse phytotoxic effects or adversely effecting sprouting or germination. Generally, the composition is applied to the crop seed in amounts of from about 0.1 grams to about 50 grams per kilogram of crop seed, preferably from about 1 gram to about 30 grams per kilogram of crop seed. The amount of dry composition used is typically greater than the amount used to preserve crops during storage, shipping, and processing because microorganisms are known to be present in the soil and because of the vulnerability of the crop seed to disease during planting, e.g., the seeds are cut or bruised during processing. In a preferred embodiment, seed potatoes are cut into sections for planting and the dry compositions are applied to the potato sections. The dry compositions interact with the moisture from the potato and generate chlorine dioxide that protects the freshly cut potato seed from disease caused by microorganisms that may be present in the environment where the seed potato is prepared and handled during the planting process. The potato sections are then placed into the ground and covered with soil. The dry compositions interact with the moisture in the potato section and the moisture from the soil and generate chlorine dioxide that protects the planted potato seed from disease caused by microorganisms that may be present in the soil. Essentially, the chlorine dioxide acts as an antimicrobial agent that preserves the potato seed after it has been prepared for planting and after planting by inhibiting or preventing disease caused by microorganisms.

In order to further illustrate the methods and compositions of the present invention, the following examples are given. Example 1

Equipment and Methods

Efficacy trials were conducted under controlled laboratory conditions using specially designed chambers to simulate storage conditions for commercial potatoes.

These chambers were made of white PVC pipe measuring 15 inches in diameter by 24 inches in length. Each end of the chamber was covered with removable plywood to which 1/4 inch rubber matting had been glued to seal the chamber. The wooden ends were secured in place by bolts and wing nuts. A vaporizer was attached to each chamber through a hole in the lower portion of the PVC pipe, which was used to maintain high humidity. A small vent hole was drilled near the top of the chamber. Generally, potato tubers were inoculated and placed into the chambers, the chambers were sealed, and the humidity maintained at high levels for 48 hours. The tubers were then removed and incubated for an additional time to allow disease to develop.

Experimental Procedure

A dry composition containing 5% by weight sodium chlorite and 95% by weight of a citric acid activator and impregnated zeolite composition was tested for the determination of efficacy in the control of Phytophthora infestans, the etiological agent of late blight disease in stored potatoes. A 200 ppm aqueous solution of chlorine dioxide was tested as a control. Russet Norkotah potatoes were washed, bruised, and inoculated with 5 milliliters of an aqueous suspension of P. infestans strain US8 at 20,000 cfu/ml. A set of forty tubers weighing a total of about 15 pounds were used for each test. Inoculated potatoes were placed into the simulated storage chambers either untreated (control) or treated with chlorine dioxide. Chlorine dioxide was applied to the treated samples in one of two formulations. One set of treated samples was dusted with about 8.0 grams of dry composition per 15 pounds (-6800 grams) of potatoes prior to placement into the storage units. Another set of treated tubers were sprayed at a rate of 6.0 milliliters per minute with a 200 ppm aqueous chlorine dioxide solution. (Purogene®, Bio-Cide International, Inc.) using a commercial vaporizer after placement into storage.

Tests were conducted with samples at time intervals of 0, 6, 12, and 24 hours between inoculation and treatment with chlorine dioxide. Potatoes were treated with the chlorine dioxide for forty-eight hours, removed from storage, and transferred to humid plastic storage boxes and incubated for 14 days at 18° C. At the end of 14 days, the tubers were evaluated for percent infection with late blight. The results are shown in Table 1.

Table 1

Referring to Table 1, the results show the superiority of dry chlorine dioxide compositions for preserving crops during storage. The average percentage of untreated potatoes that developed P. infestans infection was about 63%. The average percentage of infection for aqueous solution based chlorine dioxide treated potatoes was about 45%. Incidence of infection in the dry composition chlorine dioxide treated samples was only about 14%. Thus, the incidence of late blight infection for the dry composition treated potatoes was less than one-fourth that of the untreated control and less than one-third that of the aqueous solution chlorine dioxide treated samples. While specific embodiments of the present invention have been shown and described in detail to illustrate the utilization of the inventive principles, it is to be understood that such showing and description have been offered only by way of example and not by way of limitation. Protection by a patent for this invention in all its aspects as the same are set forth in the appended claims is sought to the broadest extent that the prior art allows.

Claims

What is claimed is:

1. A method for preserving a crop comprising applying a crop disease preventing amount of a dry composition that is capable of generating chlorine dioxide when activated by moisture directly onto the surface of the crop.

2. The method of claim 1 wherein the dry composition comprises sodium chlorite, one or more inert carriers, and an acid selected from the group consisting of organic acids and mineral acids.

3. The method of claim 2 wherein the dry composition comprises from about 1 to about 75 percent by weight sodium chlorite, from about 1 to about 20 percent by weight an acid selected from the group consisting of organic acids and mineral acids, and from about 5 to about 98 percent by weight of inert carriers.

4. The method of claim 2 wherein the organic acid is selected from the group consisting of citric acid, lactic acid, tartaric acid, maleic acid, malic acid, glutaric acid, adipic acid, acetic acid, and formic acid.

5. The method of claim 2 wherein the organic acid is citric acid.

6. The method of claim 2 wherein the mineral acid is selected from the group consisting of sulfuric acid, hydrochloric acid, and phosphoric acid.

7. The method of claim 2 wherein the mineral acid is phosphoric acid.

8. The method of claim 2 wherein the inert carrier is selected from the group consisting of zeolite, kaolin, mica, bentonite sepiolite, diatomaceous earth, and synthetic silica.

9. The method of claim 2 wherein the inert carrier is zeolite.

10. The method of claim 1 wherein the dry composition is applied to the crop in an amount of from about 0.1 grams to about 10 grams per kilogram of crop.

11. The method of claim 1 wherein the crop is selected from the group consisting of wheat, barley, rye, oats, rice, sorghum, beets, apples, pears, plums, peaches, almonds, cherries, strawberries, raspberries, blackberries, beans, lentils, peas, soybeans, cucumbers, melons, oranges, lemons, grapefruits, mandarins, spinach, lettuce, asparagus, cabbages, carrots, onions, tomatoes, potatoes, and paprika.

12. The method of claim 1 wherein the crop is potatoes.

13. The method of claim 1 wherein the crop disease is caused by microorganisms.

14. The method of claim 1 wherein the composition further comprises a catalytic amount of a catalyst selected from the group consisting of transition metals, transition metal oxides, and mixtures thereof.

15. A method for preserving potatoes during storage, shipping, and processing comprising applying a crop disease preventing amount of a dry composition that is capable of generating chlorine dioxide when activated by moisture directly onto the surface of the potatoes.

16. The method of claim 15 wherein the dry composition comprises from about 1 to about 75 percent by weight sodium chlorite, from about 1 to about 20 percent by weight an acid selected from the group consisting of organic acids and mineral acids, and from about 5 to about 98 percent by weight of inert carriers.

17. The method of claim 15 wherein the dry composition is applied to the potatoes in an amount of from about 0.1 grams to about 10 grams per kilogram of potatoes.

18. The method of claim 15 wherein the composition further comprises a catalytic amount of a catalyst selected from the group consisting of transition metals, transition metal oxides, and mixtures thereof.

19. A method for preserving crop seed during planting comprising applying a crop disease preventing amount of a dry composition that is capable of generating chlorine dioxide when activated by moisture directly onto the surface of the crop seed immediately prior to planting.

20. The method of claim 19 wherein the dry composition comprises from about 1 to about 75 percent by weight sodium chlorite, from about 1 to about 20 percent by weight an acid selected from the group consisting of organic acids and mineral acids, and from about 5 to about 98 percent by weight of inert carriers.

21. The method of claim 19 wherein the dry composition is applied to the crop seed in an amount of from about 0.1 grams to about 50 grams per kilogram of crop seed.

22. The method of claim 19 wherein the crop seed is a potato seed.

23. The method of claim 19 wherein the composition further comprises a catalytic amount of a catalyst selected from the group consisting of transition metals, transition metal oxides, and mixtures thereof.