AN OIL-IN-WATER PREPARATION FOR USE AS A PESTICIDAL COMPOSITION, AND A METHOD FOR COMBATING PESTS THEREWITH

Abstract: An oil-in-water preparation for use as a pesticidal composition contains from about 1 to about 60 % by weight of a pesticidal organophosphorus compound, dispersed in the aqueous phase at a maximum droplet or particle size of below about 20 mu m and at an average droplet or particle size of from about 1 to about 10 mu m, from about 2 to about 20 % by weight of a polyvinyl alcohol having a molecular weight of from about 3,000 to about 100,000 and having from about 10 to about 30 % of its hydroxy groups esterified as the acetate ester, or from about 2 to about 20 % by weight of a polyalkylene glycol ether, the balance being substantially water. The above preparation is, without use of a thickener and an organic solvent, a stable emulsion concentrate which upon dilution with water provides a pesticidal composition suitable for combating pests.

Description: An oil-in-water preparation for use as a pesticidal composition, and a method for combating pests there¬ with. This invention relates to an oil-in-water pre¬ paration for use as a pesticidal composition, contain¬ ing, as essential ingredients, an organophosphorus com¬ pound as an active compound dispersed in the aqueous phase at a maximum droplet or particle size of below about 20 μm and at an average droplet or particle size of from about 1 μm to about 10 μm, and a polyvinyl alcohol " or a polyalkylene glycol ether. The invention also relates to a pesticidal composition and a method for combating pests therewith. The preparation of the invention is a concentrate which must be diluted with water to be put into a ready-for-use form. Because the active compound is usually a thick oily compound at normal ambient temperature or a low melting solid, it is desirable as a matter of convenience and practicali¬ ty to formulate the compound into a more easily handled form like the said concentrate. Aqueous suspensions of solid pesticide particles having a size of from 5 to 10 μm and containing poly- vinyl alcohol, ethylene or propylene glycol, and as an essential ingredient, a thickener such a methyl cellu¬ lose, are disclosed in US-Patent No. 3,399,991. The suspension of solid particles is achieved only in a mixture containing a thickening agent. US-Patent No. 4,283,415 discloses an oil-in-wa¬ ter pesticidal emulsion having emulsified liquid drop¬ lets or particles of from 1 to 200 um in size and con¬ taining polyvinyl alcohol or gum arabic, and a thicke¬ ner. Suspension stability is achieved only in a viscous mixture containing a thickener. While in the latter US-Patent it is a question of a pyrethroid as the active compound, US-Patent No. 4,303,640 discloses a similar insecticidal oil-in-water emulsion in which the active compound is an organophos- phorus compound. However, also in that case the addi¬ tion of a thickener has been found necessary in order to achieve suspension stability. Another type of pesticidal emulsifiable concen¬ trates with an organophosphorus compound as an active ingredient contains as its major ingredient a large amount of an organic solvent, or they may contain both a thickener and an organic solvent. However, due to the organic solvent such formulations have various draw¬ backs including phytotoxicity to plants, eye and skin irritation to humans and animals, flammability, and the like. Moreover, they are sensitive to extremes in water temperature and water hardness. It would be desirable if pesticidal emulsifi¬ able concentrates could be provided which contain neither a thickener nor an organic solvent, and yet have the necessary stability. Such an emulsifiable concentrate has been provided by the oil-in-water preparation of the invention, which is characterized by containing from about 1 to about 60% by weight of the organophosphorus compound, from about 2 to about 20% by weight of a polyvinyl alcohol having a molecular weight of from about 3,000 to about 100,000 and having from about 10 to about 30% of its hydroxy groups esterified as the acetate ester, or from about 2 to about 20% by weight of a polyalkylene glycol ether, the balance being substantially water. By the way, EP Patent Application No. 0111580 Al discloses a somewhat similar pesticidal oil-in-wa¬ ter emulsion containing from 2 to 20% by weight of a polyvinyl alcohol. However, the active ingredient therein is solely a synthetic pyrethroid which belongs to a different class of pesticides than the above- mentioned organophosphorus compounds, and since the possibilities of formulating a pesticid to special flowable formulations are highly dependent on the chemical nature of the active substance, it is not obvious that formulation prescriptions for pyrethroids can be used for a quite different chemical class as the organophosphorus compounds. Furthermore, according to EP 0111580 Al the active ingredient should have an average particle size less than 1 μm. This means that the formulation appears as a so-called solubilized emulsion or micro-emulsion which has quite different characteristics to those of normal emulsions. For example, a solubilized emulsion appear as a clear transparent liquid which is thermo- dynamically highly stable and therefore does not require a thickener. On this background it is surprising that organo¬ phosphorus compounds having an average droplet or par- tide size of from about 1 μm to about 10 μm can be made up to a stable emulsion without using a thickener. In preparing a solubilized emulsion of organo¬ phosphorus compounds, use is required of quite a con¬ siderable amount of emulsifier or a considerable amount of homogenizing power, or a combination thereof. The oil-in-water preparation of the present invention exhibits a pesticidal activity equivalent to or exceeding that of conventional emulsifiable concen¬ trates. Moreover, it is freeze-thaw stable and 40°C storage stable and show good water dispersibility. Furthermore, it is less irritating to skin and eyes, non-flammable and shows no solvent phytotoxicity. The elimination of the thickener not only saves in cost by material and processing step, but it provides a more readily dispersible formulation. As organophosphorus compound in the oil-in-water preparation of the invention there can be used, for example, malathion, fenitrothion, ethion, ethyl para- thion or methyl parathion. Malathion is (0,0-Dimethyl-S-(l, 2-di-(ethoxycarbonyl)- ethyl)-phosphorodithioate) hereafter called malathion Fenitrothion is (0,0-Dimethyl-0-(3-methyl-4-nitrophe- nyl)-phosphorothioate) hereafter called fenitrothion Ethion is (0,0,0' ,0'-Tetraethyl-S,S'-methylene bis-(phosphorodithioate) ) hereafter called ethion Ethyl parathion is (0,0-Diethyl-0-(4-nitrophenyl)- phosphorothioate) hereafter called ethyl parathion Methyl parathion is (0,0-Dimethyl-0-(4-nitrophenyl)- phosphorothioate) hereafter called methyl parathion In the oil-in-water preparation of this inven¬ tion, the active ingredient must usually be dispersed as liquid droplets or particles having an average size of less than 10 μm. Minimum growth in particle size during a prolonged storage is critical. Therefore, an effective, stable emulsion is critical to the prepara¬ tion of this invention. As mentioned above, the oil-in-water preparation of this invention can contain from about 2 to about 20% by weight of a polyvinyl alcohol, and it preferably contains from about 4 to about 6.5% by weight thereof. A suitable polyvinyl alcohol having a molecular weight and a degree of esteri ication within the ranges stated above is MOWIO 5-88 (HOECHST) which has an average molecular weight of about 35,000 and is 86.7-88.7 mole percent hydrolyzed, i.e. it has from 11.3 to 13.3 mole percent of its hydroxy groups esterified as the acetate ester. Instead of the polyvinyl alcohol the preparation of this invention can contain, as mentioned above, from about 2 to about 20% by weight of a polyalkylene glycol ether, and it preferably contains from about 2 to about 8% by weight thereof. The polyalkylene glycol ether can be, e.g., Atlas G 5000. When the preparation of this invention contains a polyvinyl alcohol, it can be prepared by dispersing the liquid droplets or the particles of the active ingredient by mechanical means. The dispersing of the liquid droplets or the particles of the active ingre- dient can be done in a commercial stirrer such as a Silverson, a Warring Blender or a Rannier homogenizer, usually at high speed and power. When the preparation of this invention contains a polyalkylene glycol ether, the dispersing can be done by premixing the active ingredient and the poly¬ alkylene glycol ether while heating to about 50°C and then adding this premix to the water phase while stir¬ ring. In the stirrer, the active ingredient is dis- persed in the aqueous phase as liquid droplets or par¬ ticles. Stirring while heating is continued for about 2 to 20 minutes, i.e. until the average droplet or particle size is less than 10 μ and all individual particles are less than 20 μm and preferably less than 10 μm in diameter. The resulting formulation is freeze- thaw stable and 40°C storage stable and show good dispersibility. The preparation of the present invention is, as mentioned above, a concentrate of the pesticidally active component. Before normal use, this concentrate is diluted with water to a concentration usually cor¬ responding to from 0.01 to 1.0% by weight of the active ingredient. Therefore, the ability of the preparation to disperse easily in water is critical. in accordance with the above, the invention also relates to a pesticidal composition, which is characterized by comprising the preparation of the invention diluted with sufficient water to provide a concentration of from about 0.01 to about 1.0% by weight of the active ingredient. However, according to circumstances the said concentration may be greater than 1.0% by weight. The organophosphorus compounds used are highly active pesticides, particularly against insects, mites and ticks. In the use of the composition of the present invention for combating insects, mites and ticks, the composition is applied to the respective locus in a pesticidally effective amount. Thus, the invention also relates to a method for combating pests, which method is characterized by applying to the pests or to a locus infested there¬ with or liable to be infested therewith, a pesticidal composition according to the invention in a pesticidal¬ ly effective amount. The term "freeze-thaw stable" as used herein with reference to oil-in-water emulsions is defined to mean that the respective emulsion has passed the Freeze-Thaw Cycle Test. This test is as follows: Freeze-Thaw Cycle Test 1) A 30 to 50 ml sample of emulsion is placed in a 100 ml screwtop glass bottle and capped. 2) The bottle is placed in a freezing compartment for 16 hours at -15°C. It is then heated to 40°C for 8 hours. 3) Repeat Step 2 six more times (to give a total of 7 cycles) . 4) Examine the emulsion. The sample must show no visual signs of oiling (separation of the oil component) or solidification. The sample should move and flow as freely with minimal hand stir- ring as it did before the test. Unless all of these requirements are satisfied, the emulsion is not freeze-thaw stable. The term "40°C storage stable" as used herein with reference to oil-in-water emulsions is defined to mean that the respective emulsion has passed the 40°C Storage Test. This test is as follows: 40°C Storage Test 1) A 40 to 90 g sample of the emulsion is stored at 40°C in a capped glass bottle or other sealed container. 2) The droplet or particle size of this sample is checked at the end of a 14 day period. a) In this procedure, the sample is shaken and one drop (from a pipette) is added to 5 ml of deionized water and shaken until homoge- neous . b) Two drops of this dispersed sample are placed on a microscope slide and covered with a cover glass. c) Examine slide with a microscope using an oil-immersion lens under 1000X magnification, d) If not more than 10% of the droplets or particles are observed having diameters greater than 40 μm, the test is passed. The invention is further illustrated by the following Examples wherein the temperatures are in degrees centigrade (°C). EXAMPLE 1 To an aqueous phase consisting of 5 g of PVA (Mowiol 5-88) and 45 g of deionized water was added 50.0 g of malathion. A concentrated emulsion was made by stirring the mixture in a commercial mixer (Silver- son) at maximum rpm for about 2 minutes. The resulting emulsion was freeze-thaw stable and 40°C storage stable and showed good water disper- sibility. EXAMPLE 2 To an aqueous phase consisting of 5 g of PVA (Mowiol 5-88) and 45 g of deionized water was added 50.0 g of fenitrothion. A concentrated emulsion was made by stirring the mixture in a commercial mixer (Silverson) at maximum rpm for about 2 minutes. The resulting emulsion was freeze-thaw stable and 40°C storage stable and showed good water disper- sibility. EXAMPLE 3 To an aqueous phase consisting of 6 g of PVA (Mowiol 5-88) and 54 g of deionized water was added 40.0 g of methyl parathion (crystallized) which was dissolved by heating to 50°C. A concentrated emulsion was made by stirring the mixture in a commercial mixer (Silverson) at maximum rpm for about 2 minutes and by heating to 50°C. After cooling at room temperature, the resulting emulsion was freeze-thaw stable and 40°C storage stable and showed good water dispersibility. EXAMPLE 4 60 g of ethyl parathion was mixed with 6.0 g of Atlas G 5000 at 50°C . 34 g of deionized water was heated separately to 50°C . The oil phase was added to the aqueous phase and a concentrated emulsion was made by stirring the mixture in a commercial mixer (Silver¬ son) at maximum rpm for about 2 minutes. The resulting emulsion was freeze-thaw stable and 40°C storage stable and showed good water disper- sibility. EXAMPLE 5 60 g of ethion was mixed with 6.0 g of Atlas G 5000 at 50°C. 34 g of deionized water was heated se¬ parately to 50°C. The oil phase was added to the aqueous phase and a concentrated emulsion was made by stirring the mixture in a commercial mixer (Silverson) at maximum rpm for about 2 minutes. The resulting emulsion was freeze-thaw stable and 40°C storage stable and showed good water disper- sibility. EXAMPLE 6 50 g of methyl parathion was mixed with 6.0 g of Atlas G 5000 at 50°C 44 g of deionized water was heated separately to 50°C. The oil phase was added to the aqueous phase and a concentrated emulsion was made by stirring the mixture in a commercial mixer (Silver¬ son) at maximum rpm for about 2 minutes. The resulting emulsion was freeze-thaw stable and 40°C storage stable and showed good water disper- sibility. EXAMPLE 7 50 g of malathion was mixed with 6.0 g of Atlas G 5000 at 50°C. 44 g of deionized water was heated se- parately to 50°C. The oil phase was added to the aqueous phase and a concentrated emulsion was made by stirring the mixture in a commercial mixer (Silverson) at maximum rpm for about 2 minutes. The resulting emulsion was freeze-thaw stable and 40°C storage stable and showed good water disper- sibility.

Claims: PATENT CLAIMS 1. An oil-in-water preparation for .use as a pesticidal composition, containing, as - essential ingredients, an organophosphorus compound as an active compound dispersed in the aqueous phase at a maximum droplet or particle size of below about 20 μm and at an average droplet or particle size of from about 1 μm to about 10 μm, and a polyvinyl alcohol or a polyalky¬ lene glycol ether, characterized by containing from about 1 to about 60% by weight of the organophosphorus compound, from about 2 to about 20% by weight of a polyvinyl alcohol having a molecular weight of from about 3,000 to about 100,000 and having from about 10 to about 30% of its hydroxy groups esterified as the acetate ester, or from about 2 to about 20% by weight of a polyalkylene glycol ether, the balance being substantially water. 2. A preparation according to claim 1, charact¬ erized in that the organophosphorus compound is select¬ ed from malathion, fenitrothion, ethion, ethyl para- thion and methyl parathion. 3. A preparation according to claim 1 or 2, characterized by containing from about 4 to about 6.5% by weight of said polyvinyl alcohol . 4. A preparation according to claim 1 or 2, characterized by containing from about 2 to about 8% by weight of said polyalkylene glycol ether. 5. A preparation according to claim 1, 2 or 4, characterized in that ATLAS G 5000 is used as poly¬ alkylene glycol ether. 6. A pesticidal composition, characterized by comprising the preparation according to any one of claims 1 to 5 diluted with sufficient water to provide a concentration of from about 0.01 to about 1.0% by weight of the active ingredient. 7. A method for combating pests, characterized by applying to the pests or to a locus infested there¬ with or liable to be infested therewith, a pesticidal composition according to claim 6 in a pesticidally effective amount.

Inventors: MOELLER JENS CHRISTIAN, NIELSEN VITA, OLSEN MOGENS RINE, VENNEBERG LEIF, MOELLER, JENS, CHRISTIAN, NIELSEN, VITA, OLSEN, MOGENS, RINE, VENNEBERG, LEIF
Applicants: CHEMINOVA AS, A/S CHEMINOVA
Application year: 1988
Main classification: A01N25
IPC codes: A01N25