GB2127690A - Novel pesticide granules - Google Patents

Abstract

A free flowing and water floatable granular form of a pesticide, e.g. a biological mosquito larvicide, comprises a solid wax cove or wax- coated cove less dense than water and a pesticide secured thereto by a matrix capable of releasing the pesticide in contact with water.

Description

SPECIFICATION Novel pesticide granules The present invention relates to granular forms of pesticides, e.g. biologicals, their preparation and their use.

Biological pesticides have been of increasing interest and attraction in recent years.

They are more or less highly sensitive to a wide variety of factors such as heat, light, chemicals and other influences encountered when existing outside of their native environment. Hence, stability (heat stability, light stability and shelf stability) is a basic concern and a major prerequisite of the biological pesticide.

Biological pesticides do consequently allow less flexibility in product forms compared to the synthetic chemicals for similar use.

Granular formulations of pesticides are of substantial interest for combatting pests.

Hitherto, granular formulations of unstable pesticides such as biologicals did not meet the necessary stability requirements. The US Patent Specification 3,420,933 discloses for example granular forms for the bacterial insecticide Bacillus sphaericus (a bacteria particularly toxic to mosquito larvae), which are at least 20% nonbuoyant in water and are prepared from conventional granule core materials such as vermiculite and clays. Granular formulations of biologicals prepared with such conventional core material suffer from a severe loss of potency within one week from their preparation.

The purpose of the invention is to provide a granular form suitable for use with stable as well as instable pesticides, particularly for instable pesticides especially for biological pesticides.

Another purpose of the invention is to provide a granular form that is appropriate for aquatic application (e.g. from the air) and that is capable of releasing the pesticide substantially on the surface of the water. The latter property has been found to be of particular interest when combatting mosquito larvae in water. The present invention provides a free flowing and water floatable granular form of pesticide wherein the granules comprise a) a solid wax core or solid wax coated core having a density less than water and which is inert to the pesticide and b) a pesticide secured to the wax core or wax coated core by a matrix which is inert to the pesticide and which is capable of releasing the pesticide when in contact with water.

The use of wax as a granule core or coating material not only enables the production of a floatable granule but provides the basis for a pesticide delivery system having potency stability and a number of other desired properties for a granular pesticide particularly for a granular pesticide useful in aquatic applications.

The term "floatable" is intended to indicate that the density of the granules of the invention should be less than water and that, even in contact with water, the granules should remain afloat during a time period sufficient to allow delivery of the pesticide at the water surface; suitably at least 95% of the granules of the invention should remain on the water surface 24 hours after application.

The term "wax" as used herein, is intended to embrace any hydrophobic substance satisfying the criteria of the invention (lighter than water, solid and inert to the pesticide). Suitable examples of such waxes are silicones and paraffin waxes, particularly the latter.

The term "solid" used in connection with wax core or wax coated core is intended to indicate that the wax core or wax coating should be solid at ambient temperature and have a melting point of more than 300and preferably at least 400C.

The preferred waxes have a melting point from 450C to 850C, more preferably 500C to 750C.

The wax employed should be inert in the sense of being non-deleterious to the pesticide to be incorporated into the granule. Particular attention should be given to said requirement where the pesticide involved is a biological pesticide.

Inertness can be routinely ascertained by simple trial and error if necessary. However, in general paraffinic substances are inert to biologicals and the paraffin waxes are preferred as the core material for the granules of the invention. Paraffin waxes having melting points in the more preferred range are readily available commercially in convenient finely divided ("prill") form, for example, Sun Wax 4412 (m.p. 600C) and Sun Wax Anticheck (m.p. 670C), both from Sun Petroleum Products Company, Wayne, Pennsylvania.

The wax core or wax coated core (hereinafter "core") may consist essentially of the solid wax material or may be a body comprising an inner base surrounded by the solid wax material to which the matrix will be secured. In the latter case it will only be required that the wax substantially completely coats the inner base and that such coating be of sufficient thickness such that the inner base will not adversely affect the pesticide and that,water will not penetrate the wax coating such as to cause the total granule to sink at least before its carried pesticide is substantially released on the surface of water.

A variety of finely divided or particulate materials may be employed as a base material to be coated by the wax (hereinafter "base material") to form the wax coated particulate core. Such base materials themselves desirably have a density less than that of water and may be of a mineral nature such as vermiculite or of an organic nature such as finely divided corn cobs, i.e. the material known as corn cob granules. In any case, any "core" which is a combination of a base material and the wax coating thereon desirably has a density less than water.

The principle advantage of employing a base material is a reduction in the cost of the particulate core. The amount of base material relative to wax in such wax coated cores may vary fairly widely and the base material may readily form the greater part of the core on either a weight or volume base.

It is accordingly generally preferred that such cores contain from 10% to 60% of wax and from 40% to 90% of base material by weight, more preferably from 1 5% to 35% by weight of wax and from 65% to 85% of base material subject to the requirement that the wax substantially coats the base material.

For example, a corn cob granule base material may be employed to form a wax coated core containing 7590% corn cob and 1025% wax on a weight basis. Particle size of particulate base material for forming such wax coated base particulate cores is preferably between 0.3 to 3.0 millimeters (mm), more preferably between 1 to 2 mm.

The wax coated cores may be prepared by conventional procedure for coating a liquified normally solid material on a particulate base. In general, it is preferred to first liquify the wax by heating it well above its melting point, e.g. at least 500C above its melting point, preferably 750C to 1 250C abov.e its melting point, and then distribute the melted wax onto the mass of particulate base material, e.g. by spraying, accompanied by mixing to insure a thorough and more or less even coating of the wax over the base material. Intense mixing is desirable and is continued until the temperature of the wax is well below its melting point, e.g. to virtually room temperature, in order to avoid undesired agglomeration of the resulting individual wax granules or cores.Heating of the mixture either by external means or by the application of an inert heated gas directly into the mass may be employed to ensure a thorough distribution of the wax prior to allowing the mass to cool to form the desired cores.

The particle size of the "core" is conveniently between 0.5 to 5 mm. When the core consists of wax such size is preferably between 0.5 and 3.0 mm, more preferably 1 to 2 mm. Wax coated cores have preferably a particle size between 1 to 4, more preferably between 2 to 3.5 mm.

As indicated, in the granules of the invention the pesticide is contained within a matrix which is in turn secured to the underlying "core".

The term "matrix" as used herein, is intended to embrace any system capable of securing the pesticide to the wax core; such matrix is conveniently essentially dry.

The term "essentially dry" as used in connection with the matrix intended to indicate that the properties of the matrix should allow a good flowability of the particle mass.

The matrix may be directly secured to the "core" or indirectly, via one or more discreet layers of a suitable inert coating.

Depending on the function of the matrix systems, it is hereinafter distinguished between "matrix coating material", which essentially acts to secure the pesticidedirectly or indirectly-to the core and "encapsulating matrix", which is essentially a protecting matrix, intended to indicate a complete embedding or surrounding of the pesticide in the matrix though a minor portion of the pesticide may be and usually is present or exposed at the matrix surface. It will be appreciated that the use of an encapsulating matrix is particularly indicated where it is required to preserve the stability of the pesticide.As, even in the simpler granules of the invention, the pesticide can be regarded as being encapsulated within its more immediate or adjacent matrix, the term "system matrix" or "matrix system" will be used hereinafter to indicate the essential and total matrix system having an overall encapsulating effect and comprising or consisting of an equally essential coating matrix.

The matrix material may be uniform (or homogeneous) or may consist of various matrix materials which may each surround the core (thus forming a multiple matrix (layer) and/or form a heterogeneous mixture of various matrix materials, involving e.g. a plurality of encapsulating matrixes within the matrix coating material. The action of water on the different matrixes may consequently be different and the different release systems may vary accordingly.

Each of such matrix material may be either water dispersible or water soluble or substantially nonwettable by water. The matrix material may substantially completely embed or only partially embed the pesticide or consist of various matrix materials of which some or one may substantially completely embed and the other(s) only partially embed the pesticide.

For example, water wettable e.g. dispersible encapsulated pesticide particles (such as biologicals) may be combined with a matrix coating which is substantially non-wettable by water (resp. water insoluble) to lead to the release of the toxicant by wetting of the water dispersible particle portion at the surface of the granule. Such action at the surface will generally expose other wettable particles or portions originally within the granule to the wetting and release action such that additional contained amounts of the pesticide can be released.

In general it will, however, be preferred particularly in the case of pesticide particles encapsulated in a water dispersible matrix, to use an essentially water wettable e.g. water soluble or dispersible matrix coating such that the entire matrix system is released from the case by the action of water.

The particular material to be employed as system matrix material will depend upon the particular pesticide to be developed and various factors of choice. Whereas a wide choice of matrix materials and coating vehicles will be available with pesticides other than biologicals, the selection of such materials is more critical where a biological pesticide is used as active ingredient. Typical materials suitable for use with biological pesticides are carbohydrates, proteinaceous materials from either animal or vegetable sources and selected materials from a synthetic source. Suitable carbohydrate materials include starches such as corn starch and various cellulosic materials such as ethylcellulose.

Suitable proteinaceous materials include by way of example casein, carrageenan, partially hydrolyzed vegetable seed proteins such as soybean protein and partially hydrolysed animal proteins. Representative synthetic materials include normally solid polyethyleneglycols and polyvinyl alcohol resins. The particular material suitable as a matrix and providing the more inert and stable medium for a particular pesticide will be usually known. Where not known, as in the case of new biological pesticide candidates, the approximate matrix material can be determined by routine experimentation. In general, the proteinaceous materials provide a stable medium for biological pesticide substances such as bacteria, viruses and fungi and may be generally employed.

As indicated at least the coating matrix of the matrix system must serve the function of securing the pesticide to the wax particulate core.

Accordingly, particularly in the embodiments in which the coating matrix is secured directly to the "core", the mechanism of securing is essentially one of surface bonding which is generally realized by the adhesive properties of materials employed in the coating matrix and such materials are further selected accordingly.

The term "adhesive" and the like as used herein will encompass the various properties by which adhesives may effect bonding including such properties and abilities as tackiness, penetration and the like, and, in addition, the benefits of cohesiveness as obtained particularly from film forming adhesives.

When employing coating matrix material producing water dispersible or other characteristically essentially non-film forming coatings, the property of tackiness becomes a more positive factor and consideration may be also given to maintaining tackiness of such coatings by allowing an appropraite residual moisture content and storing under conditions which will not rapidly depreciate residual moisture.

When employing film forming coating materials, the resulting film provides a particularly effective mechanism for bonding the coating matrix directly or indirectly to the "core" even though such film may be substantially interrupted by non-homogeneous particles contained therein.

The use of a film forming coating matrix is consequently a preferred embodiment of the invention. Suitable film forming coating materials are conveniently water soluble adhesive materials such as hydrolyzed animal proteins (a known constituent for envelope glue).

Where the pesticide is a biological pesticide, the system matrix material may be present in the biological manufacturing products a result of raw materials used in manufacture-, or may be selected from a separate source or both.

For example, bacteria and fungi useful as pesticides are usually produced commercially by fermentation in a nutrient medium comprising water, carbohydrates, proteins, and various compatible inorganic salts. The resulting product on a dry basis usually contains a major portion, typically at least 80% by weight, of carbohydrate and protein residues which are at least partially water dispersible and such products may be conveniently used as such as the system matrix material or as a component thereof in preparing the granules of the invention. Fermentation products in which the proteinaceous residue alone is at least 50% by weight of the product on a dry basis are common, and are preferred in the case of fermentation products either for use alone or in admixture with one or more other matrix materials to form a coating composition.

Such fermentation batch products may be employed as a coating after making any required adjustments to bring the water content thereof to the desired level, e.g. by evaporation under vacuum.

Alternatively, the drying of the fermentation batch product, e.g. by spray drying according to known procedures, produces a dry particulate mass in which the particles constitute an encapsulation of the biological pesticide in a matrix composed of the residue of the fermentation nutrient medium. (A suitable example of such particulate form is the technical powder form of a bacterial insecticide such as Bacillus thuringiensis Israeliensis). Such particulate mass may be mixed with water to form a tacky, paste-like composition which may be coated onto the "core" to form a granule in which the biological active material is secured in a coating matrix composed of the nutrient residue.

On the other hand, and in accordance with the more preferred embodiments of the invention, the dry powder, obtained for example by spray drying of the fermentation batch, is a particularly suitable form to be applied to the "core" particles while still wet from a first coating of matrix coating material.

The application of such preferred embodiment to biological pesticides not normally produced by fermentation, e.g. virus pesticides, may also be accomplished, e.g. with the aid of fine particles comprising a virus pesticide encapsulated in a water dispersible proteinaceous matrix.

The invention also provides a method of preparing the granules of the invention which comprises the steps i) applying to the "core" a liquid coating matrix composition optionally containing pesticide, and ii) adding pesticide in solid form substantially upon completion of step i) whereby step ii) is optional in the case where the coating matrix composition does contain pesticide.

The coating procedure may be effected according to coating techniques known per se using e.g.

a) known methods of coating liquid matrix material containing the pesticidal material onto essentially dry particles-which are either uncoated or which have a dried previous coating (hereinafter Variante A), b) known methods of coating dry pesticidal particulate material onto "core" particles wetted by a previous coating (Variente B), followed by such drying as necessary to obtain a free flowing mass.

The method of Variante A is conveniently effected by intimately admixing the pesticide or pesticidal material with the liquid matrix material, which mixture is then coated-directly or indirectly-onto the "core".

According to the method of Variante B), the pesticidal material in solid form e.g. in particulate or powder form is coated onto and/or absorbed to the "core" while wet from a previous matrix coating material.

The term "pesticidal material" as used herein indicates that said material may consist essentially of the pesticide or may be in composition form e.g. in wettable powder form or beencapsulated in a suitably inert material (or encapsulating matrix).

When liquid coating is employed the solvent of dispersing delivery vehicle is desirably water, though organic solvents may be employed. The matrix material employed in the method of variante A should preferably be essentially water dispersible or water soluble to allow the release of the pesticide when in contact with water.

In the more preferred embodiments of the invention fine dry particles encapsulating the pesticide in an encapsulating matrix, are coated onto and at least partially embedded into a nondried matrix coating which has been previously applied to the "core". In such a process the "core" material in desired particulate (e.g. in prill) form is mixed together, e.g. by tumbling in a suitable mixer, and the coating matrix material then sprayed, (suitably in the form of an aqueous solution) or otherwise applied the "core" mass followed by sufficient continued mixing to coat the coating matrix substantially over the entire surface of the individual "core" particles. Solution concentrations of the order to 20 to 50%, preferably 30 to 40%, on a weight to volume ratio are suitable for spray application in many cases.

The coating is desirably accomplished more or less at room temperature or otherwise below the melting point of the wax. The amount of coating matrix material on a dry basis may vary depending upon a number of factors including the material employed, thickness of the coating desired, capacity to coat and the like. In general, the amount of coating is very small relative to the weight of the "core" material and may also be relatively minor compared to the amount of pesticidal material (e.g. finely divided encapsulated biological pesticide) to be later added. For example, the coating matrix in the more preferred embodiments may represent from 0.5 to 5.0% by weight of the "core".

Mixing time to coat the coating matrix solution onto the "core" will vary but may be accomplished in a relatively short time of from 1 to 20 minutes, more typically 3 to 10 minutes.

When such coating is completed, the mixing or other tumbling of the liquid coated wax particulate mass is continued to avoid unnecessary agglomeration.

The addition of pesticide in dry from (in finely divided encapsulated or powder form) may be commenced immediately after coating is complete or after a modest delay depending upon the drying characteristics of the matrix coating and the desired amount of pick-up or degree of adsorption in the matrix coating. The addition of the pesticidal material is accomplished by controlled and/or intermittent introduction or distribution into the mass of tumbling coated "core" particles in order to obtain a more or less even coating of the pesticide particles on the coated "core" particles.

The addition time of the pesticidal material may be of the order of 1 to 20 minutes, more typically 2 to 10 minutes; the addition is preferably conducted at room temperature and desirably below the melting point of the wax core or wax coating material. The amount of the matrix material (dry weight) on or in which the pesticide is coated may be relatively minor compared to the amount of pesticidal material; it may for example represent from 3.0 to 25%, more typically 5.0 to 20% by weight of said pesticidal material.The particular amount of pesticidal material to be employed will i.a. depend on the capacity of the liquid matrix coating solution to take up the pesticidal material, the final desired characteristic of the product (such as potency) and practical consideration such as the time necessary to dry the product and the necessity to avoid undesired agglomeration of the particles in the fluid particulate mass.

When addition of the pesticidal material is completed, the resulting particulate mass is maintained in a state of agitation and subjected to drying in order to obtain a free flowable particulate product. Such drying may be suitably effected with a heated inert gas, such as heated air, which is introduced into the agitated mass.

Where a biological is used as pesticide it is usually necessary to control the temperature of the drying conditions or heated gas at modest levels. In general air temperature of from 380C (1000F) to 71 CC (1600F) may be satisfactorily employed, more suitably air temperatures of from 43 OC ( 1 1 OOF) to 600C (1400F). It is generally unnecessary to completely dry the mass and a satisfactory product may be obtained on a reduction of the mositure content to at most no more than 10%, preferably to no more than 8%.

Retention of some moisture may be desirable, as previously indicated.

Drying time will vary depending upon particular situations and may range from 1 5 minutes to 3 hours, e.g. 1 hour.

Drying may be facilitated or carried out at reduced temperature, e.g. about room temperature, by addition of a moisture absorbing material in substantial quantities, e.g. 50% to 150% by weight of the granular product mass.

Such material may then also serve as a diluent for the product. A suitable material for such purpose is (unwaxed) corn cob granule even though such material is unsuitable as a core material when unwaxed. Any agglomerates forming during drying may be broken up, e.g. by hand.

The particle size of the product may vary somewhat widely, for example, from 0.5 to 5 millimeters. When employing typical commercially available prill wax forms the particle size of the particles in the final product may vary typically from say 0.5 to 4 millimeters, more preferably from 1 to 2 millimeters. When employing wax coated base cores, the final products may vary typically from 1 to 5 millimeters in size, more typically from 2 to 4 millimeters.

The resulting product may then be mixed and coated with a small amount, e.g. 0.1 to 4.0% by weight of the granule, preferably 0.5 to 2%, of an anti-caking agent such as calcium stearate, various silicas such as High Sil, Aerosil and the like as desired.

In the preferred embodiment in which fine particles of an encapsulated biological are coated onto wax which is wetted with a matrix coating material the exact nature of the final product will vary depending upon various factors such as the amount of encapsulated material applied to the coating matrix material. The use of only modest amounts of a finely divided encapsulated biological can result in a more or less substantially complete embedding of the biological containing particles in the matrix coating. The application of the larger amounts of the biological up to the take-up capacity of the liquid matrix coating will result additionally in a significant portion of the biological containing particles being less than fully embedded and even in some case tacked as much to each other as to the coating matrix.The latter product will allow the time staggered release of a high or maximum dosage of highly loaded particles. When employing a film coating matrix material some of the encapsulated particles containing the biological may penetrate the matrix coating without substantially affecting the cohesive benefit of said film coating matrix. These systems, especially such employing water soluble matrix coatings, produce a particularly good granule in accordance with the invention. The invention enables the preparation of granules releasing at least 80% of the contained pesticide within up to 24 hours.

The more preferred granules of the invention, including particularly those with wettable matrix coatings, are readily capable of releasing at least 50% of the contained pesticide within 3 hours and 80% within 6 hours.

The present invention is particularly appropriate for biological substances having use as pesticides, e.g. bacteria, viruses and fungi, all of which classes may be adapted for use in accordance with the invention and its description herein. Bacterial insecticides, particularly of the Bacillus type, such as Bacillus thuringiensis (Berliner), and Bacillus sphaericus, represent a broad class of particular interest for use in the invention. Current commercial products utilizing Bacillus thuringiensis are represented by the varieties Kurstaki and Israelensis. The invention is of most immediate interest for use with said Israelensis (B.t.i) variety which is currently the clear biological of choice for combatting mosquito, black fly and related larvae pests in an aquatic environment.

The invention therefore also provides a method of combatting mosquito larvae (culicidae) and related pests in an aquatic environment which comprises applying to said locus an insecticidally effective amount of a granular form of the invention comprising a biological mosquito larvicide.

The amount to be applied will depend on various factors such as the mode of application, the development stage of the larvae, the habitat and the potency of the granules.

For aerial application larger quantities will be required than for ground application. Where first to third instar larvae are predominant lower application rates will be required than when late third to early fourth instar larvae are predominant in the insect population.

The potency of the granules will i.a. depend on the amount and potency of biological insecticide introduced in the granules; it can be determined by bioassay and may for example be expressed in AeDes Aegypti Units (AAU) per mg formulated product (a bioassay method accepted by the US Environmental Protection Agency). The amount to be applied will consequently be also dependent on the potency resp. AAU/mg of the granules. In general, satisfactory results however will be obtained with granules of the invention when applied at a rate of from 2 to 7 kg/ha, e.g. 2 to 3 kg/ha in floodwater, stagnant or standing ponds, ditches creeks, 3 to 5 kg/ha in lagoons, tidal waters, salt marches, catch basins and stormretention areas and 5 to 7 kg/ha in water polluted with sewage. Suitable granules have e.g. a potency of from 200 to 600 AAU/mg.

Granules having a potency of 200 to 300 AAU/mg e.g. of 260 AAU/mg allow a perfect distribution of the active ingredient. Granules having a potency of 300 to 600 AAU/mg, e.g. of 520 AAU/mg will therefore not necessarily allow a reduction of the application rate, though a better persistency may be achieved with such granules.

While the invention has been described with reference to applications in aquatic environments, it will be evident that it may be also readily applied in non-aquatic uses of pesticides where granular applications are desired.

It will be appreciated that the matrix securing the pesticide to the wax core need not encapsulate the pesticidal substance unless normally required to preserve its stability in one manner or another as a biological needs to be so protected. However, by employing matrix coating compositions in which the agent is intimately admixed an essential encapsulation of the pesticide will occur within the final granule in a system matrix secured the wax core, particularly when the pesticide is secured in conventional wettable powder form onto the wax particulate core. Where the wettable powder enclosing the agent is a water dispersible matrix, this is secured to the wax core in a more or less underlying coating matrix which is preferably water soluble.

It will be evident, however, that a far wide choice of matrix materials and coating vehicles will be available with agents other than biologicals since such other agents usually do not present the stability problems characteristic of biologicals, although the requirement of employing matrix materials and procedures which are non-deleterious to the agent remains.

Examples and related information In the following examples Mortality Assays are conducted by filling plastic dish pans measuring 12.5x27.5x32.5 cm with 8 liters of dechlorinated tap water to provide a depth of 10 cm and surface area of 0.093 m2. For each assay 25 larvae of Aedes Aegypt (2nd or 4th instar) are added to the pan. Brewer's yeast is also added to each pan at the rate of 25 mg. per liter of water to provide food for the larvae. The assay is then conducted by distributing on the water surface a predetermined amount (rate) of the granules to be investigated and determining the mortality of larvae as a percentage of all larvae originally present at a time from 1 8 to 24 hours after addition of the granules.

In the examples parts and percentages are by weight and temperatures are in C unless otherwise stated.

Example 1 To a coating mixer is added 95 parts of Sun Wax Antichek prilled parafiin wax (Sun Petroleum products Company, Wayne, Pennsylvania). The mixer is turned on and there is added to the tumbling mass 20 parts of a paste-like composition prepared by thoroughly mixing 15 parts of water with 5 parts of a technical powder form of Bacillus thuringiensis israelensis (B. ti.) that is at least partially wettable and has a potency of 2300 AAU/mg.The B.t.i. powder is prepared in the conventional manner for preparation of a technical B.t. powder by evacuating the contents of the fermentation vat (originally about 6% solids in aqueous medium) to about 1418% solids of which about 4060% are proteinaceous and 110% starch at a temperature of 400 and vacuum of 625-75 mmHg (Torr) (25-30 in/Hg) and spray drying the resulting mixture. The inlet temperature of the spray dryer is 1770 and the outlet temperature is 660. The mixing after addition of the B.ti. is continued for about 3 minutes in order to evenly coat the B. t. I. paste onto the wax.While mixing is continued, air heated to about 520 is introduced for a period of about 30 minutes and the resulting free flowing granular mass is recovered.

The granules are stored for 4 weeks at 400 and are then evaluated in the Mortality Assay where the particles float and give a mortality of 100% against the 4th instar larvae 24 hours after application at a rate of 3.36 kg/ha (3 pounds per acre).

Example 2 A wettable powder of B.t.i. prepared as in Example 1 in an amount of 5 parts is mixed with 10 parts of melted polyethyleneglycol obtained under the designation Polyglycol E4000 from the Dow Chemical Company. The mixing is continued from about 2 minutes at a temperature of 400.

The resulting mixture while still molten is added to an operating coating mixer containing 85 parts of Sun Wax Antichek prilled paraffin wax and mixing is continued for about 3 minutes. The resulting granules are then stored at 400 for two weeks and then evaluated in the Mortality Assay where a 100% mortality is observed against the 4th instar 24 hours after application at a rate of 3.36 kg/ha.

Example 3 To a Stockes tablet coating machine is charged 22.7 kg (50 pounds) of Sun Wax Antichek prilled paraffin wax. The rotor is turned on and then there is slowly added to the tumbling wax particles 550 ml of an aqueous colloid protein solution. The colloid protein solution is prepared by mixing 198 g of a partially hydrolyzed animal protein obtained under the designation Colloid No. 1-V from Swift Adhesives 8 Coatings with a sufficient water heated to a temperature of 600 to form a 36% by weight solids solution. The addition of the cooled protein solution takes about 3 minutes and mixing is continued after addition for about 3-5 minutes to evenly cost the protein solution on the wax granules.There is then slowly added onto the tumbling protein coated wax granules 3000 g of B. ti. wettable powder prepared as indicated in Example 1. The addition takes place over about 10 minutes and mixing is continued after addition for about 5 minutes to more or less evenly distribute the B.ti.

wettable powder onto the protein coated wax particles. While further continuing the mixing, the resulting particles mass is treated for about 3045 minutes with dry air heated to a temperature of 500 in order to reduce the moisture content to below about 8%. Any lumps in the resulting mass are loosened by hand and the mass then screened to remove any remaining lumps. The resulting product consists of brownish granules with no excess powder formation and is free flowing and the individual particles thereof float on water. The final formation is 87.2 percent wax, 12.0 percent B.t.i. wettable powder and 0.8 percent colloid protein and has a specific gravity of 1.881/keg.

Said final granular mass has a potency of 520 AAU/mg and after 4 weeks storage at 400 produces a 100% mortality of the 4th instar 24 hours after application at a rate of 3.36 kg/ha in the Mortality Assay. Addition of High Sil silica (1.0% of resulting product) improves the storability of the granules by avoiding agglomeration of the granules.

Example 4 To a ribbon blender (Day Model 758) operating at 280 r.p.m. and containing 80 parts (about 45 kg) of No. 2 corn cob granules ) 1.5-3 mm) there is added portion-wise 20 parts of paraffin wax (some way as Example 1) which was added in about 4-6 portions from containers whose contents were distributed evenly over the corn cob granule mass. Mixing is continued for about 4 minutes after addition of all of the melted wax during which time the melted wax was more or less evenly coated over the individual corn cob granules and solidified to form a dried wax coating. A charge of 88 parts of the resulting wax coated corn cob granule cores was placed in a similar ribbon blender and mixer together while distributing evenly thereover 4.5 parts of the colloid protein solution used in Example 1.

Mixing is continued for about 5 minutes after such addition in order to evenly distribute the colloid protein solution over the wax surface of cores. While mixing is continued 10 parts of B.t.i.

wettable powder prepared as in Example 3 is evenly distributed over the resulting mass and then mixing is continued for an additional 3-5 minutes to insure an even coating of the powder onto the protein coated wax cores. There is then added 100 parts of No. 2 corn cob granules (unwaxed) and 0.4 part of hydrophobic silica obtained as Aerosil R972 followed by continued mixing for 5 minutes to obtain a uniform mixture.

The addition of the unwaxed corn cob granules facilitates drying of the mass and serves as a diluent in the product. The resulting mass is screened through a No. 6 mesh screen (0.33 cm) to obtain the final granular product. These granules produce a 100% Mortality of the 4th instar after 24 hours in the Mortality Assay when applied at a rate of 0.9 kg per/acre and after storage for 3 weeks at 40C provide mortality against the 4th instar in the Mortality Assay of 85% and 100% when applied at the 2.24 and 4.48 kg/ha rates respectively. When applied to water by overhead free-fall application about 98% of the coated granules remain afloat on the water surface 24 hours after application.

Granular spray and foliage penetration characteristics of the granules are judged to be excellent, as are the free fall characteristics of the granules.

It will be evident that the products of the foregoing examples and others prepared in accord with the invention to contain a mosquito larvicide provide a particularly useful and improved granule for combatting mosquito larvae in an aquatic environment containing the same by overhead application, i.e. above the water and any vegetation e.g. reeds, growing therein.

Claims (10)

Claims

1. A free flowing and water floatable granular form of a pesticide wherein the granules comprise a) a solid wax core or solid wax coated core having a density less than water and which is inert to the pesticide and b) a pesticide secured to the wax core or wax coated core by a matrix which is inert to the pesticide and which is capable of releasing the pesticide when in contact with water.

2. A granular pesticide according to Claim 1, in which the wax is a paraffin wax having a melting point of at least 400C.

3. A granular pesticide according to Claim 2, in which the material of the wax coated core is corn cob granule.

4. A granular pesticide according to any one of Claims 1 to 3, in which the pesticide is a biological pesticide.

5. A granular pesticide according to Claim 4, in which the biological pesticide is a biological mosquito larvicide.

6. A granular pesticide according to Claim 5, in which the pesticide is Bacillus thuringiensis var.

Israelensis.

7. A granular pesticide according to any of Claims 1 to 6, in which the matrix material is from 0.5 to 5% by weight of the "core" and from 5.0 to 25% of the pesticidal material.

8. A method of combatting mosquito larvae and related pests in aquatic environment which comprises applying to said locus an insecticidally effective amount of a granular pesticide according to Claim 5.

9. A method of Claim 8, in which the mode of application is an overhead application.

10. A process of preparing granules according to Claim 1 to 8, which comprises i) applying to the core a liquid coating matrix composition optionally containing pesticide, and ii) adding pesticide in solid form substantially upon completion of step i) whereby step ii) is optional in the case where the coating matrix composition does contain pesticidal.