ENCAPSULATED PESTICIDAL COMPOSITION AND A METHOD FOR MAKING IT

Abstract: A method of encapsulating a pesticide for the purpose of reducing the phytotoxicity to plants while essentially maintaining pesticidal activity. The products is produced by drying a mixture of pesticide on a particulate carrier suspended in a polymer latex.

Description: A PESTICIDAL COMPOSITION AND A METHOD FOR ITS PREPARATION This invention relates to a method of encapsulating a pesticide for the purpose of reducing the phyto- toxicity to plants while essentially maintaining pesticidal activity. The invention also relates to an encapsulated pesticidal composition useful in such method, produced by drying a mixture of pesticide on a particulate carrier suspended in a polymer latex. Various methods for encapsulating are known. The following references disclose conventional methods: U.S.P. 2,800,457, Green et al., July 23, 1957, teaches a method of making oil-containing capsules by emulsifying oil in an aqueous-sol using two hydrophilic colloidal materials having opposite electric charges, cooling the mixture and recovering the gelled product. U.S.P. 2,800,458, Green, July 23, 1967,discloses a saltcoacervation method for encapsulating oi using gellable hydrophilic colloidal material. U.S.P. 3,015,128, Somerville, January 2, 1962, deals with a centrifugal encapsulating apparatus for covering filler material such as kerosene with a medium such as a mixture of polyvinyl alcohol and sodium alginate in 2 water/glycero solvent. U.s.P. 3,016,308, Macaulay, January 9, 1962,teaches rupturable capsules containing a liquid using ether a non-ionizable water-soluble or an hydrophobic water-insoluble film former. U.S.P. 3,423,489, Arens et al., January 21, 1969, deals with an encapsulating process for liquid materials using two separate streams, one for the encapsulating material and the other for the liquid filler. U.S.P. 3,4290,827, Ruus, Febfruary 25, 1969, discloses a process for encapsulating substances such as liquids or dispersions in a shell based on condensation polymers using two separate polymer reactants, such polymer being formed at the interface of the substance within the reaction medium. Many chemicals useful for the control of pests such as insects, acarids, fungi, etc. may cause phytotoxicity to the leaves of plants or trees sensitive to such chemicals when applied at pesticidally effective concentrations. The results are loss of green leaf surface or partial defoliation of the plant as well as reduction of yield and possible loss ot plants. It is important to maintain pesticidal activity of such chemicals while reducing the phytotoxicity of the active material to the plants. It has been found that the phytotoxic effects of such chemicals can be greatly reduced or completely eliminated when the pesticide is applied to z particu- late carrier material and the resulting carrier-pesticide combination is subsequently encapsulatea with a polymer material. Concentrations of pesticide cn carrier water ials may typlcally be from 5 to Bo percent, preferably 20 to 65 percent by weight, largely depending on the ability of the carrier to absorb the chemical. Typical carrier material is a finely divided powder such as diatomaceous earth, in which category is included equivalent materials derived from diatomaceous earth, having a small particle size (e.g. surface area of 5 to 200 m 2/g, preferably 10 to 95 m 2/g). The pesticide may be a liquid or solid but is preferably liquid. The pesticide may be an acariclde (e.g., a sulfite acaricide), insecticide, fungicide, etc. The pesticide-on-carrier particles are ordinarily dispersed in water using a mixture of dispersing and wetting agents such zs sodium ligncsulecnate and ncr- ionic surfactants for producing an aqueous dispersion or pesticide on the carrier. Other surfactants which can be used are polymerized salts of alkyl naphthalene sulfonic acid and the sodium sulfosuccinates. Latex is then added to the water-surfactant (pesticide-carrier) slurry with agitation sufficient to disperse the carrier and pesticide particles throughout the latex. If nec essay, such latexes may be further stabilized by the addition of suitable stabilizers such as polyvinyl alcohol or hydroxyethyl cellulose. The latex particle size may typically vary from 0.1 to 25 microns, preferably 0.5 to 8 microns, in diameter. Some thickening of the slurry occurs when the latex is combined with the pesticide-on-carrier water slurry. Usually, water is added to the slurs reducing the final solids to about 30 , which results in a slurry viscosity of from 25 to 250 centipoise. A dry powdery product is obtained b drying the latex-carrier pesticide suspension, typically by passing the suspension through a spray dryer, for example at a temperature of from 120 to 2200 C. The choice of spray drying equipment is not critical although spray dryers where the suspension is introduced from the top into the hot air stream are frequently more desirable. When a mixture of relatively large and small particle size latexes is used, a more uniform polymer coating of the carrier/pesticide may be achieved. Additional -surfactants may be added to the particles for better wetting and dispersion when the product is used in a spray solution to be applied to a crop. A typical process for making the product may-be summarized as follows: 1. Mix carrier and liquid or solid pesticide at about room temperature to 100 C maximum. 2. Add carrier/pesticide particles to water containing dispersing and/or wetting agents while agitating. 3. Add latex rcontaining polyvinyl acetate polymer or other suitable polymer) to suspension achieved by step (2) with agitation. 4. Pass product of step (3) through spray dryer. Optionally, a portion of the dispersing/wetting agents may be added to the product achieved by step (1). Additional surfactant can be mixed with the product of step (4) to assure good dispersion of the product when used in a spray application. Example 1 Preparation of Encapsulated Acaricide. (A) 2-[4-(1,1-dimethylethyl)phenoxy]cyclohexyl 2-propynyl sulfite (a liquid, also known as propargite) at about 500C is sprayed onto diatomaceous earth (sur- face arwea 95 mê/g) in a ribbon blender. Surfactants indicated in the recipe below are then added while agi- tating and the mixture is hammer milled. Eight separate: preparations are prepared and combined. The following recipe (wherein parts are expressed by weight) is used: Propargite, 84.6% active 286 parts Diatomaceous earth 240 parts Highly purified sodium 2 parts lignosulfonate Octyiphenoxy polyethox- 2 parts yethanol absorbed on mag nesium carbonate Polymerized sodium salts 2 parts of alkyl naphthalene sulfonic acid The product (A) contains 46.7% of active acari- cide. (B). The above mixture is further modified using the recipes below (wherein amounts are expressed in grams): Sample Number 1 2 3 Acaricide on diatomaceous 404.9 404.9 404.9 earth (A) Highly purified sodium lignosulfonate 9.0 3.5 Octyl phenoxy polyethox- 3.0 1.2 1.5 yethanol absorbed on mag- nesium carbonate Polymerized sodium salts 3.0 1.2 1.5 of alkyl naphthalene sulfonic acid Dioctyl ester of sodium - 1.2 sulfosuccinic acid Polyvinyl acetate latex 131.0 175.0 - 87.0 (PVAC) 55% solids Water 110.0 1100.C 1100.0 PVAC, weight percent 10.9 1O.2 10.4 Acaricide 36.7 Sodium N-methyl-N-palmitoyl taurate 1.5 Propylene glycol 2.0 Sodium alkyl naphthalenesulfonate 1.0 Salts of lignosulfonic acid Diatomaceous earth (surface area 95 m2/g) . 7.1 Diatomaceous earth (surface area 10-20 m 2/g) 13.0 Attapulgus clay 34.7 Under agtation, the surfactants are added to the water until dissolved. The acaricide on dato- maceous earth is then added as rapidly as the slurry permits. The polymer latex is added with stirring. The slurry is spray-dried at 110 nil per minute at an input temperature of 2200 C. After drying, sample 1 contains 37.7% active ingredient, sample 2 contains 35.0 , while sample 3 contains 39.3% acaricide. Sample 4, which is a control sample that is outside the invention, included for purposes of comparison only, is prepared by spraylng the acaricide into a mixture of the fillers and then adding surfactants. Hammer milling is used to make the product uniform. The resulting product contains 31% active acaricide. Acaricidal Test (C) The ability of these formulations to kill two-spotted spider mites is determined using the following procedure: Cowpea (Vigna sinensis Germaine's Blackeye #5) are planted, 3 seeds per pot. When grown to first trifoliate stage, each pot is thinned to the best two plants. These are sprayed with a JGA 502 Devilbiss (trademark) spray gun for 20 seconds each pot. Spray solutions are made using added tion of water to bring solutions to concentration indicated in Table I. 1, 8, 14 and 28 days after spraying, twospotted spider mites are applied to each: leaf inside a "Tanglefoot" (trademark) circle on the top of each leaf. The number of live mites remaining seven days after application is counted. The percent control is calculated using the following equation: % control = number of live minutes/in untreated check 100 x number of live mites/sample@ number of live mites in untreated check number of live mites in untreated check The results are summarized in Table I. Table Rate % Control Composition ppm 1day 8day 14 day 28day 1 500 - 96 87 86 100 81 47 71 20 18 40 26 20 50 - 2 500 - 100 96 80 100 83 77 59 50 20 19 69 40 29 . 5 0 - 3 500 - 100 100 100 100 85 85 75 .67 20 60 70 56 5 7 - - 4 500 - 100 10C 100 100 100 89 98 56 20 86 50 37 33 5 60 - The results in Table I show that samples 1, 2 and 3 are as effective in controlling two-spotted spider mites as the untreated control 4 over a 28 day period. Herbicidal Test (D) The effect of these treatments on te phytotoxicity of acaricide to cowpeas is tested as in (C) except mites are not applied. Higher concentrations of acaricide are used to exaggerate possible phytotoxic effects. The samples are rated 7 days after spraying. The degree of damage produced is determined, and the results shown in Table II are obtained. Table IT Damage Damage Sample No. Primary Leaves Trifoliate Leaves ppm: 8000 2000 500 8000 2000 500 1 15 5 1 Mod. Trace S1gbt 2 15 2 0 Mod.Slight Trace 3 10 3 0 Mod.Slight Trace 4 (Control) 95 20 0 Sev.Mod/Sev.Slight The results in Table II show that the encapsulating material substantially reduces phytotoxic damage to leaves by the acaricide. 95% damages means essentlally all of the green leaf surface has been destroyed. (E) Potted Tioga strawberries are sprayed with a spray containing one pound active propargite per acre in 32 gallons of water. One half pint of adjuvant surfactant per 100 gallons cf water is included in each treatment. Ten replicate pots are used for each treatment. Five days after treatment the plants are rated for phytotoxicity. On a 1 to 10 scale (1 = least damage), the results whown in Table III are obtained: Table III Samle No. ean phytotoxicity damage 1 5.0 2 5.5 3 6.0 4 (Control) 9.0 The data in Table III shown considerable improvement in damage reduction to strawberries when the encapsulated samples 1, 2 and 3 are used compared with the non-encapsulated control 4. Example 2 Preparation of Encapsulated Acaricide Production scale equipment is used for sample preparation applying various amounts of encapsulating polymer. The acaricide-on-carrier is prepared by spraying hot (about 500 C) acaricide into diatomaceous earth in a Littleford-Lodige (trademark) mixer. The following recipe is used: (A) Propargite, 86.5± 18.5 pounds Diatomaceous earth 16.0 Highly purified sodium 0.2 lignosulfonate Dioctyl ester of sod- 0.2 ium sulfosuccinic acid After all of the propargite has been sprayed into the diatomaceous earth, the surfactants are added. An assay of 47 percent of acaricide is deten-ined. (B) In the same manner as in Example 1(B), 2 slurry is prepared containing the pesticide-on- carrier mixture. Encapsulation is carried out using polyvinyl acetate latex (552 solids) and sufficient water to provlde the specified percentage of active acarlcide, according to the following recipes: : Sample 5 6 7 8 9 Propargite on DE (see A) , 22.5 21.25 20.0 17.5 13.75 pounds Polyvinyl acetate-dry, 2.5 3.75 5.0 7.5 11.75 pounds Highly purified sodium lignosulfonate, grams 35.0 95.0 78.0 125.0 104.00 Dioctyl ester of sodium 9.0 - - - sulfosuccinic acid, grams polyethoxy Octyl phenoxy/ethanol - 32.0 23.0 40.0 34.0 absorbed on magnesium carbonate, grams Polymerized - 32.0 23.0 40.0 34.0 salts of alkyl naphthalene sulfonic acid, grams Polymer wt.- 10.0 15.0 20.0 30.0 45.0 Active acaricide wt.- 44.3 42.5 40.0 33.6 27.5 Acaricial Test (C) Acaricidal tests are conducted using using the procedure outlined in Example 1 (C) except for the one-day test. The control of the spider mites is calculated as before. Tests results are shown in Table IV. Table IV .% Control 8 Day 28 Day Sample No. 500ppm 100ppm 20ppm 500ppm 100ppm 20ppm 5 100 100 72 100 87 45 6 100 100 81 100 80 25 7 100 100 91 93 58 7 8 100 98 86. 95 70 18 9 100 100 79 100 27 5 4(Con- 100 98 77 100 55 45 trol) The results in Table IV clearly Indicate tbat the en- capsulated products are essentially as effective in killing spider mites as the untreated control material (Sample 4). Herbicidal Test (D) The phytotoxic effects of these preparation to cowpeas is shown in Table V. The acaricide is applied as in Example 1 (D). The amount of damage by the acaricide is rated 7 days after application. Table V primary Leaves Trifoliates %Damage Damage Sample 8000ppm 2000ppm 500ppm 8000ppm 2000ppm 500ppm 5 60 15 .3 Sev. Slight Trace 6 15 3 1 Mod.Sev. " 0 7 0 1 0 Nod. Trace 0 8 5 0 0 Mod.Sl. " 0 9 0 0 0 Trace 0 0 4(Con- 95 45 15 Sev. Sev.Mod. Slight trol) Considerable phytotoxicity to primary leaves (i.e. bronzing and almost complete destruction of the green leaf surface) is evident at 500 ppm to 8000 ppm of the untreated control 4. Damage to the trifoliates (which are just emerging when the sprays are applied) represent curling, twisting and stunting of the leaf growth. These results show that as the polymer weight percentage is increased the phytotoxic effect of the pesticide is considerabi reduced. Example 3 The samples prepared in Example 2 are evaluated on 3-year old Bartlett pear trees The entire leaf surface is treated, and each solution is applied to runoff at the two applications rates used. Phytotoxicity readings are taken 14 days after spraying, with the results shown in Table VI. Table VI Phytotoxicitt Application rate-pp.,. Sample No. 300 600 5 Trace-Sl. Trace-Sl. 6 Trace Trace 7 0 Trace 8 ' 0 0 9 0 Trace 4(Control) Moderate- Moderate-Severe Slight Moderate defoliation defollation Bartlett pears are very sensitive to this acaricide. Defoliation may occur even at a low rate normally used to control spider mites. Reduction in phytotoxicity is found even at the lowest polymer weight percentage. Samples 7, 8 and 9 having higher polymer weighs percentage exhibit essentially no damage, whereas non-treated controls 4 cause moderate to severe damage. Example 4 This example demonstrates the effects of using a blend of large and small particle size polyvinyl acetate latexes. (A) Preparation of Encapsulated Acaricide The acaricide on diatomaceous earth (DE) used in Example 2(A) is used. The slurry preparation technique is the same as in 2 (B). The following preparations are made. Sample 10 11 12 13 1 15 Propargite on DE, lbs. 21.25 19.0 22.5 12.7 17.5 25:2 Polyvinyl acetate 3.75 -1.705 2.5 1.3 7.5 9.8 Latex A, lbs. Polyvinyl acetate - 1.705 - 1.3 - 9.6 Latex B, lbs. Highly purified 23.0 150.0 35.0 65.0 125.0 160.C sodium lignosulfonate, g polythoxy Octyl phenoxy/ethanol - 50.0 - 23.00 40.0 53.0 absorbed on mg carbonate, g Polymerized sodium - 50.0 - 23.0 40.0 53.C salts of alkyl naphthalene sulfonic acids, g Diocty ester of sodium 6.0 - 9.0 - - sulfosuccinic acid a g Acaricide,% weight 41.6 38.5 44.3 33.5 41.6 34. Polyvinyl acetate latex A (55% solids) has a particle size of 2-8 microns and latex B (55% solids) has a particle size of 0.5 - 1.5 microns. (B) Phytotoxicity to cantelopes is demonstrated using the method of Example 1 (D). The results obtained at a rate of 1 pound of active acaricide per acre are shown in Table VII. Table VII Phytotoxicity to Cantelopes Sample Latex Mean Damage 10 A 4.13 11 A & B 3.93 12 A 5.2C 13 A & B 5.00 14 A 2.73 15 A & B 1.117 4 (Control) 8.60 The results in Table VII show reduce phytotoxicity resulting when a mixture of large and small particle size latexes are used rather than a single particle size latex.

Claims: CLAIMS: 1. A method for encapsulating a pesticide characterised in that the method comprises the following steps: (a) absorbing said pesticide on a solid particulate carrier; (b) dispersing the product of step (a) in water; (c) adding a latex to the dispersion of step (b); and (d) drying the suspension obtained from step (c). 2. A method according to claim 1 characterised in that the said pesticide is a liquid pesticide, and the said drying is spray drying. 3. A method according to claim 1 or claim 2 characterised in that said carrier is diatomaceous earth and said latex is polyvinyl acetate latex. 4. A method according to any of the preceding claims characterised in that the dispersion obtained by step (b) contains dispersing and/or wetting agent. 5. A method according to any of the preceding claims characterised in that step (c) is carried out while agitating the dispersion. 6. A method according to any of the preceding claims characterised in that said pesticide is an acaricide. 7. A method according to claim 6 characterised in that said acaricide is a sulfite acaricide. 8. A method according to claim 7 characterised in that said sulfite is 2-/4-(1,1-dimethylethyl) phenoxy/cyclohexyl 2-propynyl sulfite. 9. An encapsulated pesticidal composition characterised in that it comprises a solid carrier having absorbed thereon a liquid pesticide, the pesticide-on-carrier material being covered by a solid polymer. 10. A composition according to claim 9 characterised in that said polymer is polyvinyl acetate. 11. A composition according to claim 9 or claim 10 characterised in that said carrier is diatomaceous earth.

Inventors: REYNOLDS, JAMES ADELBERT
Applicants: UNIROYAL, INC.
Application year: 1980
Main classification: A01N25
IPC codes: A01N25, A01N41