Peroxy acid treatment to control pathogenic organisms on growing plants

Abstract: The invention relates to a process of using peracid compositions, especially mixed peracid system, to treat filed, hydroponic or greenhouse growing plant tissue, seeds, fruits, growing media and containers. The peracid can lower the natural, plant pathogen and human pathogenic microbial load resulting in less waste to molding, spoilage, and destruction because of pathogenic poisons.

Description: Field of the Invention The invention relates to a method for growing a plant on a hydroponic substrate. Background of the Invention In the production of fruits and vegetables, plants can be grown in the field, in greenhouses, and hydroponically. Each location has its own growing medium, environment and growing conditions. Agricultural personnel work to maximize production by maximizing growing conditions while minimizing attack on seeds, seedlings, plants and fruit by living pests. Such pests include insects, rodents, bacteria, fungi, etc. Substantial attention has been given to antimicrobial compounds that attack bacteria and fungi on seeds, seedlings, growing plants and fruit in the production cycle on growing plants. The use of fungicides in agriculture is necessitated by the great losses caused by a wide variety of plant-pathogenic microorganisms. To be economic, the costs of controlling plant diseases by the application of bactericides and fungicides must be offset by potential gains of several fold. Large tonages of fungicides are required in the agriculture of apples, pears, bananas, cereals, cocoa, coffee, cotton, potatoes, tobacco, grapes, sprouts and other common fruits and vegetables including celery, leeks, onions, lettuce, spinach, brussel sprouts, potatoes, truffles, garlic, shallots, peppers, beans, tomatoes, almonds, pears, apples, peanuts and others. Fungicides are typically applied in water suspension with hydraulic sprayers or in the form of dust, granules or fumigants. Early fungicides included sulfur and polysulfides, heavy metals and others. Such harsh fungicides have been replaced by newer but still toxic materials such as quinones, organosulfur compounds, imidazolines and guanidines, trichloromethylthiocarboximides, chlorinated and nitrated benzenes, oxithines, benzimidazoles, pyrimidines, and others. These broad spectrum protectant materials effect enzyme and membrane systems of the target microorganism. Typically, the mode of action includes inhibition of fungal or bacterial energy production, interference with biosynthesis or disruption of cell membrane structure. The above fungicides have had some success; however, they are viewed as toxic materials and a substantial quantity of plant produce is wasted due to their deliterious effect. Accordingly, a substantial need exists to continue to develop antimicrobial materials that can protect growing plants including seeds, cuttings, seedlings, growing plants, plant parts, fruit, and other agricultural produce. Peroxy Acids Further, human and plant pathogenic bacteria and fungi can be a contamination problem in growing plants. We have found coli form, salmonella, and other bacteria common in the agricultural and greenhouse environment can contaminate growing plants and pose a threat to human health in consumption of fresh vegetables, fruit and produce. A substantial need exists for treatments that can reduce bacterial contamination. Peroxy acids are strong oxidizers and have the simple general structure given as formula (1), where R can be essentially any hydrocarbon group: Antimicrobial Treatments Peroxy-containing compositions are known for use in the production of microbicidal agents. One such composition is disclosed in Bowing et al., U.S. Pat. No. 4,051,059 containing peracetic acid, acetic acid or mixtures of peracetic and acetic acid, hydrogen peroxide, anionic surface active compounds such as sulfonates and sulfates, and water. Peracetic acid has been shown to be a good biocide, but only at fairly high concentrations (generally greater than 100 parts per million (ppm)). Similarly, peroxyfatty acids have also been shown to be biocidal, but only at high concentrations (greater than 200 ppm), such as in the composition disclosed in European Patent Application No. 233,731. GB 2187958 A and EU 0242990 A2 describe the use of either peracetic or per-propionic acid for controlling plant pathogens on flowers and fruit tissue. They are directed to edible field-grown plants and cereal crops. WO 94/06294 describes the use of a single peracid composition along with mixtures of aliphatic acids for vegetable disinfection. U.S. 5,168,655 relates to hydroponic treatment using peracids. The reference describes peracid treatments of hydroponic growing substrates (e.g., rock wool) prior to growth; i.e., the growth substrate is treated after a crop production cycle and prior to a subsequent crop-production cycle. In contrast, the present invention describes hydroponic treatment during the growth cycle. U.S. Patent No. 5,200,189 to Oakes et al. describes use of mixed peracid compositions to enhance microbial kill for hard surface sanitizing. Certain mixed peracids have now been found useful to enhance microbial kill on sensitive growing plant tissue or its harvested fruiting matter. U.S. Patent No. 2,512,640 to Greenspan et al. discloses the use of single peracid compositions to enhance microbial reduction on produce, reduce produce browning, and prevent spoilage. Greenspan does not disclose any mixed peracid synergies and applies the peracid only to harvested fruit. GB 2257630A describes the use of a single peracid which is activated by an activator (Fe, Cu, Br, I) for controlling microbial counts on hard surfaces, effluent waters and growing plant tissues. Again, this is a single peracid composition which fails to teach synergies between mixed peracids. DK 9300538 describes the use of peracetic acid, followed by a biological combat, for controlling pathogens in recirculating watering systems to plant crops. This reference does not describe any direct crop treatments. JP 07031210 teaches the use of 5 to 200 ppm peracetic and or perpropionic acids for treatment of seedling culture medium prior to planting; specifically for the control of slime, algae or fungi on the culture medium. The teaching is limited to the use of C 2 and C 3 acids and has no application to growing plant tissue. JP 07258005 A teaches the use of high levels (1000 ppm) of peracetic acid for controlling bacteria on rice. This application is intended only to effect disease control and not for hydroponic growth of the grain matter. DE 3003875 A describes the use of C 1 -C 4 peracids and hydrogen peroxide to control phytopathogenic pests on soil. This reference does not disclose any direct application to plants. Brief Description of the Invention We have found that a mixed peracid treatment composition can be used to protect growing plant tissue from the undesirable effects of microbial attack. The materials of the invention have been found to be excellent antimicrobial compounds but pose little toxic effects to agricultural workers or the ultimate consumer. The invention involves a method for growing at least one plant on a hydroponic substrate in a hydroponic liquid supply medium to produce usable fruit or vegetable products with reduced microbial contamination, the method comprising: a) establishing growing and living plant tissue in the hydroponic substrate; b) contacting the living plant tissue, the hydrophonic substrate and the hydroponic liquid with a dilute aqueous solution comprising an effective amount of a C 2 -C 12 percarboxylic acid; and c) harvesting an improved product. The dilute aqueous solution can be prepared from a concentrate composition, which concentrate composition can be diluted with a major proportion of water to form an antimicrobial sanitizing use solution having a pH in the range of about 2 to 8, with a C 2 -C 4 peroxycarboxylic acid concentration of at least 4 ppm, preferably about 10 to 75 ppm, and a C 8 -C 12 peroxyacid concentration of at least 1 ppm, preferably about 1 to 25 ppm. Other components may be added such as a hydrotrope coupling agent for solubilizing the peroxyfatty acid in the concentrate form and when the concentrate composition is diluted with water. The concentrate may contain 1 to 20 wt-% of a C 2 -C 4 peroxycarboxylic acid and about 0.1 to 20 wt-% of an aliphatic C 8 -C 12 peroxycarboxylic acid. An especially preferred embodiment of the composition includes a mixture of peroxyacetic acid and peroxyoctanoic acid. The composition may further contain about 1-15 wt % of a hydrotrope and about 5 wt-% of a chelating agent. In contrast to the prior art, we have discovered that at a low pH, (e.g. preferably less than 7) C 5+ peroxyacids such as peroxyfatty acids are very potent biocides at low levels when used in combination with a C 2 -C 4 peroxycarboxylic acid such as peroxyacetic acid, a synergistic effect is obtained, providing a much more potent biocide than can be obtained by using these components separately. This means that substantially lower concentrations of biocide can be used to obtain equal biocidal effects. As the term is used herein, a C 8 -C 12 peroxyacid (or peracid) is intended to mean the product of the oxidation of a C 8 -C 12 acid such as a fatty acid, or a mixture of acids, to form a peroxyacid having from about 5 to 12 carbon atoms per molecule. The C 8 -C 12 peroxyacids are preferably aliphatic (straight or branched). Peroxycarboxylic acid is intended to mean the product of oxidation of a C 2 -C 4 carboxylic acid, or a mixture thereof. This includes both straight and branched C 2 -C 4 carboxylic acids. The claimed invention includes a method of controlling fungi and microbial plant pathogens in growing plants. This treatment utilizes a combination of two different peroxy acids. This mixture comprises at least 4 parts per million (ppm) of a smaller C 2 -C 4 peroxy carboxylic acid and at least 1 ppm of a larger C 8 -C 12 peroxy carboxylic acid. An especially preferred embodiment of the composition includes a mixture of peroxyacetic acid (given as formula (2)) and peroctanoic acid (given here as formula (3)). The composition also may contain a hydrotrope for the purpose of increasing the aqueous solubility of various slightly soluble organic compounds. The preferred embodiment of the invention utilizes a hydrotrope chosen from the group of n-octanesulfonate, a xylene sulfonate, a naphthalene sulfonate, ethylhexyl sulfate, lauryl sulfate, an amine oxide, or a mixture thereof. The composition may also contain a chelating agent for the purpose of removing ions from solution. The preferred embodiment of the invention uses 1-hydroxyethylidene-1,1-diphosphonic acid. Finally, the invention is also useful for controlling fungi and microbial plant pathogens in growing plants on a hydroponic substrate. In this embodiment, the plant is contacted with a solution made by diluting in an aqueous liquid a concentrate containing the two peroxy acids. This mixture includes the smaller C 2 -C 4 peroxy carboxylic acid and the larger C 8 -C 12 aliphatic peroxy carboxylic acid. An especially preferred embodiment of the composition includes a mixture of peroxyacetic acid and peroctanoic acid. The composition may further contain a hydrotrope and a chelating agent. Further, the solution contains about 1-30 wt % of hydrogen peroxide (H 2 O 2 ). The preferred composition includes a mixture of acetic acid (formula (4)) and octanoic acid (formula (5)). Detailed Description of the Invention Peracids We have found surprisingly that peroxy acid compounds of the invention can be contacted directly with living plant tissue in a hydroponic system, in the form of a seed, a germinating seed, a cutting, a root steek, graft, tuber juvenile or adult plant and reduced microbial population without substantially affecting the health of the living tissue. The invention is also based upon the surprising discovery that when a C 8 -C 12 peroxyacid is combined with a C 2 -C 4 peroxycarboxylic acid, a synergistic effect is produced and greatly enhanced antimicrobial activity is exhibited when compared to the C 8 -C 12 peroxyacid or the C 2 -C 4 peroxycarboxylic acid alone. The present blend of a C 8 -C 12 peroxyacid and a C 2 -C 4 peroxycarboxylic acid can effectively kill microorganisms (e.g., a 5 log 10 reduction in 30 seconds) from a concentration level below 100 ppm and as low as 20 ppm of the peracid blend. A variety of C 8 -C 12 peroxyacids may be employed in the invention such as peroxyfatty acids, monoperoxy- or diperoxydicarboxylic acids, and peroxyaromatic acids. The C 8 -C 12 peroxyacids employed in the present invention may be structurally represented as: R 1 -CO 3 H, wherein R 1 is a hydrocarbon moiety having from about 7 to 11 carbon atoms. R 1 may have substituents in the chain, e.g., -OH, CO 2 H, or heteroatoms (e.g., -0-as in alkylether carboxylic acids), as long as the antimicrobial properties of the overall composition are not significantly affected. It should be recognized that "R 1 " substituents or heteroatoms may change the overall acidity (i.e., pKa) of the carboxylic acids herein described. Such modification is within the contemplation of the present invention provided the advantageous antimicrobial performance is maintained. Furthermore, R 1 may be linear, branched, cyclic or aromatic. Preferred hydrocarbon moieties (i.e. preferred R 1 's) include linear, saturated, hydrocarbon aliphatic moieties having from 7 to 11 carbon atoms (or 8 to 12 carbon atoms per molecule). Specific examples of suitable C 8 -C 12 carboxylic fatty acids which can be reacted with hydrogen peroxide to form peroxyfatty acids include such saturated fatty acids as caprylic (octanoic) (C 8 ), pelargonic (nonanoic) (C 9 ), capric (decanoic) (C 10 ), undecyclic (undecanoic) (C 11 ), lauric (dodecanoic) (C 12. These acids can be derived from both natural and synthetic sources. Natural sources include animal and vegetable fats or oils which should be fully hydrogenated. Synthetic acids can be produced by the oxidation of petroleum wax. Particularly preferred peroxyfatty acids for use in the composition of the invention are linear monoperoxy aliphatic fatty acids such as peroxyoctanoic acid, peroxydecanoic acid, or mixtures thereof. Other suitable peroxyacids are derived from the oxidation of dicarboxylic acids and aromatic acids. Suitable dicarboxylic acids include sebacic acid (C 10 ). An example of a suitable aromatic acid is benzoic acid. These acids can be reacted with hydrogen peroxide to form the peracid form suitable for use in the composition of the invention. Preferred peracids in this group include monoperoxy- or diperoxyadipic acid, monoperoxy- or diperoxysebacic acid, and peroxybenzoic acid. The above peroxyacids provide antibacterial activity against a wide variety of microorganisms, such as gram positive (e.g., Staphylococcus aureus ) and gram negative (e.g., Escherichia coli, salmonella, etc. ) microorganisms, yeast, molds, bacterial spores, etc. Preferred plant tissues are growing dicotyledon and growing monocotyledonis plants. When the above C 8 -C 12 peroxyacids are combined with a C 2 -C 4 peroxycarboxylic acid, greatly enhancd activity is shown compared to the C 2 -C 4 peroxycaroxylic acid, greatly enhanced activity is shown compared to the C 2 -C 4 peroxycarboxylic acid alone or the C 8 -C 12 peroxyacid alone. The C 2 -C 4 peroxycarboxylic acid component can be derived from a C 2 -C 4 carboxylic acid or dicarboxylic acid by reacting the acid, or the corresponding anyhdride or acid chloride, with hydrogen peroxide. Examples of suitable C 2 -C 4 carboxylic acids include acetic acid, propionic acid, glycolic acid, and succinic acid or their corresponding anhydrides or acid chlorides. Preferable C 2 -C 4 peroxycarboxylic acids for use in the composition of the invention include peroxyacetic acid, peroxypropionic acid, peroxyglycolic acid, peroxysuccinic acid, or mixtures thereof. The antimicrobial concentrate can comprise about 0.1 to 20 wt. %, preferably 0.1 to 5 wt. %, and most preferably 0.1 to 2 wt. % of a C 8 -C 12 peroxyacid, and 1 to 20 wt. %, preferably 1 to 15 wt. % and most preferably 4-15 wt. % of a C 2 -C 4 peroxycarboxylic acid. The concentrate composition preferably has a weight ratio of C 2 -C 4 peroxycarboxylic acid to C 8 -C 12 peroxyacid of about 15:1 to 1:1. The concentrate contains sufficient acid so that the end use solution has a pH of about 2 to 8, preferably about 3 to 7. Some acidity may come from an inert acidulant which may be optionally added (e.g., sulfuric or phosphoric acid). The peracid components used in the composition can be produced in a simple manner by mixing a hydrogen peroxide (H 2 O 2 ) solution, or by utilizing powdered peroxide generators such as percarbonates or perborates, with the desired amount of acid. With the higher molecular weight fatty acids, a hydrotrope coupler may be required to help solubilize the fatty acid. The H 2 O 2 solution also can be added to previously made peracids such as peracetic acid or various perfatty acids to produce the peracid composition of the invention. The concentrate can contain about 1 to 30 wt. %, preferably about 5 to 25 wt. % of hydrogen peroxide. The concentrate composition can further comprise a free C 8 -C 12 carboxylic acid, a free C 2 -C 4 carboxylic acid, or mixtures thereof. The free acids will preferably correspond to the starting materials used in the preparation of the peroxyacid components. The free C 8 -C 12 carboxylic acid is preferably linear and saturated, has 8 to 12 carbon atoms per molecule, and can also comprise a mixture of acids. The free C 8 -C 12 carboxylic acid and free C 2 -C 4 carboxylic acid can be present as a result of an equilibrium reaction with the hydrogen peroxide to form the peroxyacids. Other Components Various optional materials may be added to the composition to help solubilize the fatty acids, restrict or enhance the formation of foam, to control hard water, to stabilize the composition, or to further enhance the antimicrobial activity of the composition. The composition can contain a surfactant hydrotrope coupling agent or solubilizer that permits blending short chain perfatty acids in aqueous liquids. Functionally speaking, the suitable couplers which can be employed are non-toxic and retain the fatty acid and the perfatty acid in aqueous solution throughout the temperature range and concentration to which a concentrate or any use solution is exposed. Any hydrotrope coupler may be used provided it does not react with the other components of the composition or negatively affect the antimicrobial properties of the composition. Representative classes of hydrotropic coupling agents or solubilizers which can be employed include anionic surfactants such as alkyl sulfates and alkane sulfonates, linear alkyl benzene or naphthalene sulfonates, secondary alkane sulfonates, alkyl ether sulfates or sulfonates, alkyl phosphates or phosphonates, dialkyl sulfosuccinic acid esters, sugar esters (e.g., sorbitan esters), amine oxides (mono-, di-, or tri-alkyl) and C 8 -C 10 alkyl glucosides. Preferred coupling agents for use in the present invention include n-octanesulfonate, available as NAS 8D from Ecolab, n-octyl dimethylamine oxide, and the commonly available aromatic sulfonates such as the alkyl benzene sulfonates (e.g. xylene sulfonates) or naphthalene sulfonates. Some of the above hydrotropic coupling agents independently exhibit antimicrobial activity at low pH. This adds to the efficacy of the present invention, but is not the primary criterion used in selecting an appropriate coupling agent. Since it is the presence of perfatty acid in the protonated neutral state which provides biocidal activity, the coupling agent should be selected not for its independent antimicrobial activity but for its ability to provide effective interaction between the substantially insoluble perfatty acids described herein and the microorganisms which the present compositions control. The hydrotrope coupling agent can comprise about 0.1 to 30 wt. %, preferably about 1 to 15 wt. %, and most preferably about 2 to 15 wt. % of the concentrate composition. Compounds such as mono, di and trialkyl phosphate esters may be added to the composition to suppress foam. Such phosphate esters would generally be produced from aliphatic linear alcohols, there being from 8 to 12 carbon atoms in the aliphatic portions of the alkyl phosphate esters. Alkyl phosphate esters possess some antimicrobial activity in their own right under the conditions of the present invention. This antimicrobial activity also tends to add to the overall antimicrobial activity of the present compositions even though the phosphate esters may be added for other reasons. Furthermore, the addition of nonionic surfactants would tend to reduce foam formation herein. Such materials tend to enhance performance of the other components of the composition, particularly useful nonionic surfactant for use as a defoamer is nonylphenol having an average of 12 moles of ethylene oxide condensed thereon, it being encapped with a hydrophobic portion comprising an average of 30 moles of propylene oxide. Chelating agents can be added to the composition to enhance biological activity, cleaning performance and stability of the peroxyacids. For example, 1-hydroxyethylidene-1,1-diphosphonic acid commercially available from the Monsanto Company under the designation "DEQUEST" has been found to be effective. Chelating agents can be added to the present composition to control or sequester hardness ions such as calcium and magnesium. In this manner both detergency and sanitization capability can be enhanced. Other materials which are sufficiently stable at the low pH contemplated by the present composition may be added to the composition to impart desirable qualities depending upon the intended ultimate use. For example, phosphoric acid (H 3 PO 4 ) can be added to the composition of the invention. Additional compounds can be added to the concentrate (and thus ultimately to the use solution) to change its color or odor, to adjust its viscosity, to enhance its thermal (i.e., freeze-thaw) stability or to provide other qualities which tend to make it more marketable. The composition can be made by combining by simply mixing an effective amount of a C 8 -C 12 peroxyacid such as a peroxyfatty acid with some source of a C 2 -C 4 peroxycarboxylic acid such as peroxyacetic acid. This composition would be formulated with preformed perfatty acid and preformed peroxyacetic acid. A preferred composition of the invention can be made by mixing a C 2 -C 4 carboxylic acid, a C 8 -C 12 carboxylic acid, a coupler and a stabilizer and reacting this mixture with hydrogen peroxide. A stable equilibrium mixture is produced containing a C 2 -C 4 peroxycarboxylic acid and a C 8 -C 12 peroxyacid by allowing the mixture to stand for from one to seven days at 15°C. to 25°C. As with any aqueous reaction of hydrogen peroxide with a free carboxylic acid, this gives a true equilibrium mixture. In this case, the equilibrium mixture will contain hydrogen peroxide, a C 2 -C 4 peroxycarboxylic acid, a C 8 -C 12 carboxylic acid, a C 2 -C 4 peroxycarboxylic acid, a C 8 -C 12 peroxyacid, water, and various couplers and stabilizers. By using the above approach, the composition can be formulated by merely mixing readily available raw materials, e.g., acetic acid, hydrogen peroxide and fatty acid. By allowing solution time for equilibrium to be obtained, the product containing both of the active biocides is obtained. In varying the ratio of C 2 -C 4 carboxylic acid'to C 8 -C 12 carboxylic acid, it is easy to vary the ratio of C 2 -C 4 peroxycarboxylic acid to C 8 -C 12 peroxyacid. Method of Treatment The present invention contemplates a concentrate composition which is diluted to a use solution prior to its utilization as a microbicide. Primarily for reasons of economics, the concentrate would normally be marketed and the end user would dilute the concentrate with water to a use solution. A preferred antimicrobial concentrate composition comprises about 0.1 to 20 wt. %, preferably about 0.1 to 5 wt. %, of a C 8 -C 12 peroxyfatty acid, about 1 to 20 wt. % of a C 2 -C 4 peroxycarboxylic acid, about 1 to 15 wt. % of a hydrotrope coupling agent, and about 1 to 30 wt. % of hydrogen peroxide. Other acidulants may optionally be employed in the composition such as phosphoric acid. The level of active components in the concentrate composition is dependent upon the intended dilution factor and desired acidity in the use solution. The C 8 -C 12 peroxyacid component is generally obtained by reacting a C 8 -C 12 carboxylic acid with hydrogen peroxide in the presence of a C 2 -C 4 carboxylic acid. The resulting concentrate is diluted with water to provide the use solution. Generally, a dilution of 1 fluid oz. to 4 gallons (i.e. dilution of 1 to 500 by volume) of water can be obtained with 2% to 20% total peracids in the concentrate. The compositions of the invention can be applied to growing plant tissue in a variety of techniques. The aqueous solution can be sprayed, painted, daubed, fogged, flooded onto or into the plant, the plant hydroponic substrate, the agricultural earth. The material can be reapplied periodically as needed. Examples Initial testing The examples given herein describe the treatment of a snow mold fungus isolated from a mountain ash (Sorbus Americana) tree. Testing consisted of an untreated control versus treating the fungus with peroxy acetic acid (POAA) (C 2 ) and peroxyacetic/peroxyoctanoic (POAA/POOA) (C 2 /C 8 ) composition. This testing showed that the latter was very effective in killing the fungus. Thus, approximately 10 cm 2 of "snow mold" was removed from the branch section and split it into three parts; putting each into water. One section was untreated. A second was treated with 500 ppm peroxyacetic acid, and a third was treated using a mixed peracid system (C 2 /C 8 ). After two days: 1. The control was still thriving and very moist to the touch; with a large jelly-like volume of fungi. 2. The POAA sample treated was approximately 1/2 dead with what appears to be a dead outer crust over approximately 2/3 the sample and a dried completely dead patch over the rest. The 2/3 crusted area still had the soft jelly-like mass. 3. The C2/C8 penoxyacid blend treated Fungi appeared all dead and dried up. No mass of jelly left. Peroxy Acetic Acids Effect On Growing Plant Tissue The study was conducted on growing plant tissues using sprays done before 8:00 AM. Testing was conducted on usually disease free plants to investigate possible side effects such as burning of plant tissue. The data demonstrates both peracid compositions to be similar in effect to the growing plant tissue during application; with both being relatively inert on the tissue surfaces except for high surface area crops such as Asparagus leaves (no effect on stems). Peracid Formula Dosed Peracid (ppm) Plant type/treated area Observed effects 8 hrs after application POAA 100 American Basswood/ lower leaves No changes, no burning or tissue damage POAA/POOA 100 American Basswood/ lower leaves No changes, no burning or tissue damage POAA 100 American Basswood/ lower leaves (approx. 30') No changes, no burning or tissue damage POAA/POOA 100 American Basswood/ lower leaves (approx. 30') No changes, no burning or tissue damage POAA 100 State Fair Apple/whole tree (approx. 7') No changes, no burning or tissue damage POAA/POOA 100 State Fair Apple/whole tree (approx. 7') No changes, no burning or tissue damage POAA 100 Wild rose bush/whole (3') No changes, no burning or tissue damage POAA/POOA 100 Wild rose bush/whole (2') POAA 100 Asparagus/1/2 plant (approx. 4') Some yellowing found, apparent leaf burn on treated halves POAA/POOA 100 Asparagus/1/2 plant (approx. 4') Some yellowing found, apparent leaf burn on treated halves POAA 100 Pixwell Gooseberry/ 1/2 plant (approx. 3') No change POAA/POOA 100 Pixwell Gooseberry/ 1/2 plant (approx. 3') No change Continued Tests For Peracids On Plant Tissue Peracid Dosed ppm Plant/Area Comments 1 100 Basswood/lower branches No effects noted, no burn or bleaching 2 100 Basswood/lower branches No effects note, no burn or bleaching 1 100 Rose/whole No effects noted, no burn or bleaching 2 100 Rose/whole No effects noted, no burn or bleaching 1 100 1/2 asparagus plant Leaf yellowing and more bleaching - stopping application to avoid plant death 2 100 1/2 asparagus plant Leaf yellowing and more bleaching-stopping application to avoid plant 1 100 Beacon Apple/whole State Fair Apple/whole No effect, as above 2 100 State Fair Apple/whole NOTE: switched application order vs. last week No effect, as above 1 100 Gooseberry/half No effect, as above 2 100 Gooseberry/half No effect, as above 1 100 Pontiac Potato Plant/whole No effect, as above 2 100 Pontiac Potato Plant/whole No effect, as above 1 100 Beta Grapevine/1/2 vine No effect, as above 2 100 Beta Grapevine/1/2 vine No effect, as above Increased Dosage Tests: 1 300 Wild Plum/approx. 1/2 tree No effect, as above 2 300 Wild Plum/approx. 1/2 tree No effect, as above 1 300 Pontiac Potato/whole No effect, as above 2 300 Pontiac Potato/whole No effect, as above Peracid Dosed ppm Plant/Area Comments 1 300 Approx. 10' Wild Plum/whole No effect noticed, no burning or bleaching 2 300 Approx. 8' Wild Plum/whole No effect noticed, no burning or bleaching 1 300 Red Pontiac/whole Same as above - no effect 2 300 Red Pontiac/whole Same as above no effect 1 300 Gooseberry/1/2 Same as above - no effect 2 300 Gooseberry/1/2 Same as above no effect 1 300 Beebalm (menarda)/10 plants Slight leaf yellowing-killed snow mold on all plants-(approx. 16 with mold before treatment) 2 300 Beebalm (menarda)/10 plants Slight leaf yellowing-killed snow mold on all plants-(approx. 16 with mold before treatment) 1 300 Rose/whole No effects, as above 2 300 Rose/whole No effects. as above 1 300 Beacon Apple/whole No effects, as above 2 300 State Fair Apple. whole No effects, as above 1 300 American Basswood/ bottom No effects, as above 2 300 American Basswood/bottom No effects, as above 1 300 Hawthorne (approx. 7 1 )/whole No effects, as above 2 300 Hawthorne (approx. 8 1/2 1 )/whole No effects, as above 1 300 Betterboy Tomato/ whole No effects. as above 2 300 Betterboy Tomato/whole No effects, as above 1 300 Beta Grape/ 1/2 (10') vine No effects, as above 1 300 Beta Grape/ 1/2 (10') vine No effects, as above Working Examples Working Example 1: Minimum Inhibitory Concentration of Peracetic Acid vs. Mixed Peracid Composition against Botrytis cinera Plant Pathogen This example compares the effect of the prior art using peracetic acid (POAA) vs. the combination peracid formula of the present invention. The objective is to determine the minimum inhibitory concentrations against the Botrytis cinera ATCC 11542 plant pathogen organism. Botrytis cinera culture was prepared by inoculating the center of ten Sabouraud Dextrose Agar filled dishes and incubating at 26°C-30° for 15 days. Mycelial mats were removed by adding 10 mL of sterile water and using a sterile spatula to brush the microbial growth from agar surface. The suspension was transferred to tissue grinder and macerated with 10-25 mL of sterile water, then filtered through cheesecloth and stored in a glass bottle at 4°C until test time. Product dilutions were prepared in a Sabouraud Dextrose broth at levels of% POAA adjusted to deliver a part per million consternation of 30, 45, 60, 75, 150 and 300. Solutions were inoculated with 0.5 mL of the prepared culture suspensions and incubated at 26°C-30°C for 15 days to observe growth. One tube of Sabouraud Dextrose broth was used as a positive growth control for each culture, and 1 tube was used to observe sterility of broth. Table 1 compares the minimum inhibitory concentration (the lowest peracid efficacy level to impart no growth in the plant pathogen) of the mixed peracid compositions (line 1) and those of the single peracid (lines 2) for the reduction of common plant pathogens. The results demonstrate the 5-fold improved efficacy results of the mixed peracid compositions for the reduction of Botrytis cinera ATCC 11542 (cf., lines 1 and 2); i.e., the minimum inhibitory concentration for controlling Botrytis cinera is 60 ppm peracid with the current formulas, while 300 ppm peracid is required using the prior art. Minimum Inhibitory Concentration of Peracetic Acid vs. a Novel Mixed Peracid Composition against Botrytis cinera Plant Pathogen Minimum Inhibitory Concentration Run # Peracid Test Organism 30 (ppm) 45 (ppm) 60 (ppm) 75 (ppm) 150 (ppm) 300 (ppm) current art: Mixed Peracid Formula (POAA/POOA) t Botrytis cinera + + - - - - prior art: Prior Art (POAA) Botrytis cinera + + + + + - (-) = no growth, (+) = growth Working Example 2: Comparative Peracid Treatment of a Substrate vs. Alfalfa Sprouts For Microbial Control During Hydroponic Growing The objective of this example was to compare the use of a single peracid vs. mixed peracids for microbial reduction during hydroponic growth of alfalfa sprouts. Ongoing concern in the industry is the control of microbial populations; especially human and plant patogenics, but also nutrition-solution molds and fungi. The following test as conducted to determine potential microbial control during the hydroponic growing cycle. Table 2 compares the results of utilizing the continuous hydroponic treatment technique of the present invention in contrast to U.S. 5,168,655 which utilizes peracetic acid disinfection of hydroponic substrates; i.e., substantial (>5-log) microbial reductions can be found if the peracid treatment is ongoing vs. essentially no reduction if only the substrate is treated to hydroponic growth. Working Example 3: POAA and POAA-POOA Treatment of Alfalfa Sprouts with Variable Concentrations of Peracids The objective of this example was to evaluate microbial reduction using peracid misting during the daily hydroponic growth of alfalfa sprouts; against natural bacterial flora. Commercially, bean and alfalfa sprouts are grown by overhead misting of seed plates for 3-5 days. The sprouts are harvested and the seed waste disposed of. An ongoing concern in the industry is the control of microbial populations; especially human and plant pathogenics, but also nutrition-solution molds and fungi. The following test was conducted to determine potential microbial control during the hydroponic growing cycle. The alfalfa sprouts were soaked in various concentrations of equilibrium obtained peracetic (POAA) or peracetic-peroctanoic POAA-POOA solutions. One sample was soaked in water as a control. The following morning the alfalfa sprouts were placed into a sterile petri dish by evenly spreading the seeds on the bottom of the dish. The petri dishes were covered with cheese cloth for the growing procedure. During growing (days 1-4) the alfalfa seeds were treated twice daily at 8:00 AM and 4:45 PM by misting with 10 ml of the same concentration of peracid in which they were soaked. The water control was misted with water. Microbial samplings were taken at 8:00 AM each of the 4 treatment days. A 1:10, wt:wt, mixture of sprout:water was stomached and plated onto TGE Agar subculture media using a Pour Plate Technique with phosphate buffered dilutions of 10 -3 , 10 -5 , 10 -7 . After 48 hours at 35°C the micro results were determined and are shown in Table 3: The results of Table 3 demonstrate the ability to effect microbial populations during hydroponic growth of plant tissue using continuous peracid applications. In contrast to U.S. 5,168,655 which utilizes peracetic acid disinfection of hydroponic substrates prior to a crop production cycle, the microbial peracids of the present invention demonstrates the novel utility of using peracids to effect continuous microbial control during the entire hydroponic growth cycle, without loss to crop yield (see examples 4 and 5). The data also indicates the need to modify the dosing procedure to enhance the microbial reduction near the end of the hydroponic cycle. This hypothesis is tested in Example 3. Working Example 4: POAA and POAA-POOA Treatment of Alfalfa Sprouts with an Alternative Misting Procedure The objective of this example was to evaluate microbial reduction using a more continuous (hourly) peracid misting procedure during the daily hydroponic growth of alfalfa sprouts; against natural bacterial flora. This should allow for a lower dosage profile of peracids. Using the above microbial technique, the alfalfa sprouts were soaked in 80 ppm of POAA or POAA-POOA solutions. One sample was soaked in water as a control. The following morning the alfalfa sprouts were placed into a sterile petri dish by evenly spreading the seeds on the bottom of the dish. The petri dishes were covered with cheese cloth for the growing procedure. During growing (days 1-4) the alfalfa seeds were treated from 8:00 Am to 3:00 PM on an hourly basis by misting with 10 ml of the same concentration of peracid in which they were soaked. The water control was misted with water. Microbial samplings were taken at 4:00 PM each of the 4 treatment days. The results of Table 4 demonstrate the improved efficacy of: using a more continuous dosing system, and for using a mixed peracid system for microbial control during hydroponic growth of plant tissue. While peracetic acid can impart an initial (day 1-2) microbial reduction vs. the control (cf., experiment 1,2), it fails after the 2nd growing day. Conversely the mixed peracetic-peroctanoic acid (POAA-POOA) system yields continuous microbial control (> 20log) over the entire sprout growing time (experiment 3). For all the experiments the germination rate of the seed was greater than 95%. Working Example 5: POAA and POAA-POOA Continuous Misting Treatments of Alfalfa Sprouts The objective of this example was to evaluate microbial reduction using a continuous (hourly over 24-hours) peracid misting procedure during the daily hydroponic growth of alfalfa sprouts: against natural bacterial flora. Using the above microbial technique, the alfalfa sprouts were soaked in 80 ppm or POAA or POAA-POOA solutions. One sample was soaked in water as a control. The following morning the alfalfa sprouts were placed into a sterile petri dish by evenly spreading the seeds on the bottom of the dish. The petri dishes were covered with cheese cloth or the growing procedure. During growing (days 104) the alfalfa seeds were treated on an hourly basis (over the entire 24 hour day) by misting with 10 ml of the same concentration of peracid in which they were soaked. The water control was misted with water. Microbial samplings were taken at 4:00 PM each of the 4 treatment days. The results of Table 5 demonstrates the unexpected result that continuous 24 hour per day misting does not improve - over the previous examples 7-times per day peracid application - the final growing day microbial control efficacy for either peracid system during hydroponic production of plant tissue (cf.. Table 4, experiments 2.3 vs. Table 5 experiment 2,3). Additionally, the germination yield dropped off tremendously (< 50 %) in all the 24-hour per day studies as compared to the results of example 3. Peracetic Acid (POAA) and Peracetic-Peroctanoic (POAA-POOA) Treatments of Alfalfa Sprouts Using a Twenty Four Hour Per Day Misting Procedure Aerobic Plate Count Results 1 2 3 Day 4 results Sample Identification Microbial CFU/mL Log R Germination rate 1 Water Control 1.0 x 10 8 0 < 50 % 2 peracetic acid (POAA) 80 ppm 6.0 x 10 0.2 < 50 % 3 peracetic-peroctanoic acids (POAA-POOA) 80 ppm 3.5 x 10 6 1.9 < 40 % Working Example 6: POAA and POAA-POOA Daily Misting Germination Rates of Alfalfa Sprouts The objective of this example was to evaluate the germination rate for the various peracid applications during the hydroponic growing cycle of alfalfa sprouts. Using the above microbial technique, the alfalfa sprouts were soaked in 80 ppm of POAA or POAA-POOA solutions. One sample was soaked in water as a control. The following morning the alfalfa sprouts were placed into a sterile petri dish by evenly spreading the seeds on the bottom of the dish. The petri dishes were covered with cheese cloth for he growing procedure. During growing (days 1-4) the alfalfa seeds were treated using various application times as per examples 2-4 by misting with 10 ml of the same concentration of peracid in which they were soaked. The water control was misted with water. After 4 days the germination rate was visually determined. The results of Table 6 demonstrate: that proper selection of the application rate and peracid composition is necessary to impart both microbial reduction and hydroponic seed germination. Both upper and lower application limits are found. Peracetic Acid (POAA) and Peracetic-Peroctanoic (POAA-POOA) Treatments of Alfalfa Sprouts Using Variable Treatment rates Aerobic Plate Count Results 1 2 3 Peracid Treatment Rate Day 4 Microbial and Germination Results (Log Reduction and %) 2 treatments per day 7 treatments per day 24 treatments per day 1 POAA treated, Log Reduction 0 0 0.2 2 POAA-POOA treated. Log Reduction <0.1 2.2 1.9 3 POAA treated, % Germination >95% >95% < 50 % 4 POAA-POOA treated. % Germination >95% >95% < 80 % Working Example 7: Hydroponic POAA and POAA-POOA Treatments of Alfalfa Sprouts With a Pre-dosing Misting Procedure The objective of this example was to evaluate microbial reduction using a predosing of a peracid(s), followed by subsequent water-only mistings during the daily Hydroponic growth of alfalfa sprouts; against natural bacterial flora. Again, this allows for a lower overall dosage profile of peracids. Using the above microbial technique, the alfalfa sprouts were soaked in 80 ppm of POAA or POAA-POOA solutions for 16 hours. One sample was soaked in water as a control. The following morning the alfalfa sprouts were placed into a sterile petri dish by evenly spreading the seeds on the bottom of the dish. The petri dishes were covered with cheese cloth for the growing procedure. During growing (days 1-4) the alfalfa seeds were treated from 8:00 AM to 3:00 PM on an hourly basis by misting with water only (no peracids in these subsequent Hydroponic growth cycles). Likewise, the water control was misted with water. Microbial samplings were taken at 4:00 PM each of the 4 treatment days. The results of Table 7 demonstrate that the peracid systems impart a residual antimicrobial effect over the entire Hydroponic growing cycle. Surprisingly, the mixed peracid system yields a much improved efficacy verses the peracetic-alone formula; i.e., while peracetic acid can impart an initial (day 1) microbial reduction (> 1-log) vs. the control (cf., experiment 1,2), it fails after the 2nd growing day. Conversely the mixed peracetic-peroctanoic acid (POAA-POOA) system yields continuous microbial control (> 2-log) over the entire sprout growing time (experiment 3) even though the growing seeds were only inoculated in the peracid formula. For all the experiments the germination rate of the seed was greater than 95%.

Claims: A method for growing at least one plant on a hydroponic substrate in a hydroponic liquid supply medium to produce usable fruit or vegetable products with reduced microbial contamination, the method comprising: a) establishing growing and living plant tissue in the hydroponic substrate; b) contacting the living plant tissue, the hydrophonic substrate and the hydroponic liquid with a dilute aqueous solution comprising at least 4 parts per million of a C 2- C 4 percarboxylic acid and at least 1 part per million of an aliphatic C 8 - C 12 percarboxylic acid; and c) harvesting an improved product. The method of claim 1 wherein the percarboxylic acid comprises peracetic acid. The method of claim 1 or 2 wherein the aqueous solution comprises about 4 to 100 parts per million of a C 2 - C 4 percarboxylic acid and about 1 to about 100 parts per million of an aliphatic C8- C 12 percarboxylic acid. The method of claims 1-3 wherein the aqueous solution comprises a mixture of peroxyacetic acid and peroxyoctanoic acid. The process of claims 1-4 wherein the living tissue comprises a germinating seed. The method of claims 1-4 wherein the living tissue comprises a growing tuber. The method of claims 1-6 wherein the plant tissue comprises a growing dicotyledon. The method of claims 1-6 wherein the plant tissue comprises a growing monocotyledonis plant. The method of claims 1-4 wherein the living tissue comprises a plant cutting. The method of claims 1-4 wherein the plant tissue comprises rooting stock an a graft.

Inventors: ADKINS LEANNE J, CORDS BRUCE R, HANSON HEIDI M, HEI ROBERT D P, LOKKESMOE KEITH D, ADKINS, LEANNE J., CORDS, BRUCE R., HANSON, HEIDI M., HEI, ROBERT D.P., LOKKESMOE, KEITH D.
Applicants: ECOLAB INC, ECOLAB INC.
Application year: 1999
Main classification: A01N37
IPC codes: A01N37