PESTICIDAL FORMULATIONS

Abstract: A microencapsulated pesticide formulation comprises non-encapsulated pesticide as well as encapsulated pesti­ cide. The two pesticides may be the same or different, and typically a formulation of 25% permethrin has 20% per­ methrin inside the capsules and 5% outside.

Description: This invention relates to pesticidal formulations. It is known to encapsulate pesticidal compounds in small "microcapsules" of material, to provide a dry flowable formulation and/or to obtain a formulation having a longer effective life. The latter effect is obtained because the microcapsules protect the pesticide from degradation, but themselves slowly degrade, or are broken by applied pressure, to release the pesticide over a period. Alternatively, the pesticide may slowly diffuse through the walls of the microcapsules. In some prior art processes, the microcapsules are not separated from the reaction mixture and small amounts of non-encapsulated pesticides may therefore be present in the product. Similarly, small amounts of unencapsulated pesticide may arise due to leakage as described above. In the context of compositions which do not have a pyrethroid both inside and outside the microcapsules, there have been proposals to deliberately have a certain level of non-encapsulated pesticide - see, for example, EP-A-8 207 (du Pont; encapsulated methomyl with inter alia non-encapsulated permethrin at a ratio of 1:10 to 10:10) and EP-A-17 409 (Monsanto). It has now been found to be advantageous to provide a formulation comprising microcapsules containing a pyrethroid and non-encapsulated pyrethroid. Accordingly, one aspect of the present invention provides a pesticidal formulation for application to a surface over which crawling insect or acarine pests will crawl, the formulation comprising a microencapsulated pyrethroid and a non-microencapsulated pyrethroid wherein, in relation to the total amount of pyrethroid in the formulation, the proportion which is non-encapsulated is at least 5%. The terms "microencapsulated" or "microcapsule" are used in this specification to refer to capsules having a diameter of less than 4 mm, particularly less than 2 mm. Commonly, however, microcapsules have an average diameter of between 1 micron and 100 microns. The microencapsulated pyrethroid may be the same as or different from the non-encapsulated pyrethroid. More than one pyrethroid may be encapsulated, and more than one pyrethroid may be non-microencapsulated. The encapsulated pyrethroid(s) may be in one or more than one type of microcapsule. In relation to the total amount of pyrethroid in the formulation, the proportion which is non-encapsulated is preferably at least 10%. 15 to 30%, particularly 25%, is preferred. Upper limits of 50%, especially 40% and more especially 30%, are particularly preferred, in conjunction with any of the said lower limits. The microcapsules may be formed by any known means, for example by the so-called "Pennwalt" method described in UK Patent Specification No. 1 091 141, the entire contents of which are incorporated herein by reference. The non-encapsulated material may be a wettable powder, an emulsifiable concentrate, a micro-emulsion, a dust or any other suitable form. Any known pyrethroid may be used in the formulation, for example permethrin, deltamethrin, cyhalothrin or cypermethrin. The total proportion of pyrethroid in the formulation will depend upon the pyrethroid(s) in question and the use to which the formulation is being put, but is generally between 0.001 and 90%, typically between 0.01 and 90%, preferably (in the case of permethrin) 10 to 50%, conveniently 20-40%. In the case of other pesticides, these amounts may be varied to suit the potency of the pesticide. For example, deltamethrin or cypermethrin might be used at 1 to 10%, conveniently 2 to 4%. Other excipients known in the art may also be used, for example diluents, carriers, dyes, lubricants, stabilisers, surfactants and, in particular, synergists such as piperonyl butoxide. Formulations in accordance with the invention may be used against insect and acarine pests and are particularly suitable for coating surfaces such as wood, concrete, brickwood, paint, plaster or metal in order to provide a long-lasting residual action or for use in bait formulations. Surfaces in buildings may be treated to combat crawling insects such as cockroaches or ants, or flying insects, such as houseflies or mosquitoes, when they walk on the treated surface. The inclusion of non-encapsulated pesticide provides an immediate dose of such pesticide even before the encapsulated pesticide becomes available, and it has been found that careful control of specific insect populations can be more easily achieved. For example, a large initial dose of pesticide can be used to control, flush out or activate all or almost all of the active adult population of, say, a population of cockroaches, with a continued lower dose from the encapsulated material being provided thereafter to control immigration of adults and emergence of nymphs. A knock-down agent may be used as the non-encapsulated pyrethroid, with a kill agent inside the microcapsules. It has also been found that the presence of the pesticide outside the microcapsule stabilises the pesticide inside the capsule, and the capsule itself, particularly when the pesticides are the same, thus prolonging the active life of the encapsulated material. Formulations in accordance with the invention may take the form of dry granular matter or aqueous suspensions. Alternatively, a water-soluble wall material way be used in a non-aqueous solvent. The formulations may be packaged in any convenient way, for example in drums or sachets, and would normally be diluted before use. Conveniently, the (optionally diluted) formulation is sprayed onto the surface to be treated, to the point of "run off", by means of compression sprayers, hydraulic sprayers, mist blowers or the like. The following non-limiting examples illustrate specific embodiments of the invention. Example 1 An oil-in-water encapsulation with a polyurea-polyamide skin represents production of a copolymer (strengthened by cross-linking) by interfacial polycondensation. Charges were prepared as follows: In flask: 200 ml 0.5% aqueous "Elvanol 50-42" solution In 1st funnel: 100 ml xylene 15 ml toluene 2,4-diisocyanate 2 ml trimesoyl trichloride (for cross-linking) 120 g permethrin plus 50 ml "Solvesso 200" In 2nd funnel: 10 g ethylenediamine 5 g diethylenetriamine 10 g sodium carbonate, monohydrate 80 ml distilled water ["Elvanol" (RTM) is a protective colloid comprising polyvinyl alcohol available from DuPont, Wilmington, Delaware; "Solvesso 200" is a blend of aromatic hydrocarbons available from Exxon.] During the addition from the first funnel, which was rapidly effected, the mixture was strongly agitated to form visible droplets, the agitation being slowed down following completion of the first addition. Slow agitation was continued during the second, similarly rapid, addition. Contents were stirred for one hour and then filtered. Capsules of xylene were obtained, containing permethrin. The microcapsules were mixed with permethrin and "Etocas" 29" surfactant (a castor oil derivative available from Croda Chemicals, Goole, UK) in water to give a 25% permethrin dilutable aqueous suspension having 20% permethrin inside the microcapsules and 5% outside. Example 2 The procedure of Example 1 was followed, except that the trimesoyl trichloride was omitted and toluene 2,6-diisocyanate was used 20/80 with the toluene 2,4-diisocyanate to give a total of 15 ml as before. A polyurea wall is thereby formed. To form an emulsifiable concentrate outside the capsules, a blend of 5% permethrin, 2-5% nonylphenol ethylene oxide condensates 2-5% calcium dodecyl benzene sulphonate and about 5% of "Solvesso 200" was made, the percentages relating to the total formulation when the e.c. is added to the microcapsule preparation Biological Test The formulation of Example 1 was diluted with water 160X and sprayed onto male Blattella germanica . The time for knockdown of 50% of the insects (KT₅₀) was 6.6 minutes, and all of the insects were dead after day 1.

Claims: A pesticidal formulation for application to a surface over which crawling insect or acarine pests will crawl, the formulation comprising a microencapsulated pyrethroid and a non-microencapsulated pyrethroid wherein, in relation to the total amount of pyrethroid in the formulation, the proportion which is non-encapsulated is at least 5%. A formulation according to Claim 1 wherein the pyrethroid inside the microcapsules is the same as the pyrethroid outside the microcapsules. A formulation according to Claims 1 or 2 wherein, in relation to the total amount of pyrethroid in the formulation, the proportion which is non-encapsulated is at least 10%. A formulation according to Claim 3 wherein, in relation to the total amount of pyrethroid in the formulation, the proportion which is non-encapsulated is 15-25%. A formulation according to any one of the preceding claims wherein the microcapsules are of polyurea and/or polyamide. A formulation according to any one of the preceding claims wherein the pyrethroid is in each case permethrin. A formulation according to any one of the preceding claims wherein the formulation has a total amount of pyrethroid equivalent to 20-40% permethrin. A method of controlling insect or acarine pests by applying a formulation according to any one of the preceding claims to a surface over which the pests will crawl. A process for preparing a formulation according to any one of Claims 1 to 7 by microencapsulating a pyrethroid and mixing the preparation so formed with a further pyrethroid, or a further amount of the same pyrethroid, in conjunction with one or more suitable diluents, solvents or carriers.

Inventors: CHADWICK, PETER ROBIN, JEFFRIES, DAVID ALAN
Applicants: THE WELLCOME FOUNDATION LIMITED
Application year: 1987
Main classification: A01N25
IPC codes: A01N25