AU7015898A - Controlled release pesticidal compositions - Google Patents

Description

WO 98/48623 PCT/AU98/00299 1 CONTROLLED RELEASE PESTICIDAL COMPOSITIONS FIELD AND BACKGROUND OF THE INVENTION This invention relates to pesticidal controlled release compositions. More 5 particularly it relates to such compositions containing a pesticidal active ingredient and which are in the form of granules or pellets and intended for soil application. Controlled release (CR) formulations that include pesticidal active ingredients are well known. They are commonly used for agricultural applications but may also be used for non agricultural applications. These CR formulations typically allow the 10 continuous release of the active ingredient over a period of time to enable efficacious levels of pesticide to be available against the target species over a period of time. However, some CR formulations allow the release of the active ingredient at a non uniform rate and in some cases there may be periods of time when no active is released as well as periods of time where large amounts of active 15 ingredient are released. In this specification all such formulations are regarded as CR formulations. The pesticidal active ingredients include insecticides, fungicides, herbicides and growth regulators. They may also include microorganisms as the active ingredient. CR formulations for soil application are known and typically consist of a 20 pesticide, synthetic polymer, fillers and control release agents and are in the form of pellets or granules. The formulations may alternatively comprise naturally occurring polymers rather than synthetic polymers and in some cases the polymers may be replaced with other organic or inorganic materials. These formulations are very effective in most soils. However they may suffer from a number of deficiencies 25 when applied in difficult or aggressive soils such as those with pH above 6.0 or those containing high levels of microbes. Difficult or aggressive soils are soils which can result in less than efficacious levels of the pesticide being maintained in the soil over the desired time period. In such soils, conventional CR formulations typically either fail to maintain efficacious amounts of pesticide in the soil and/or the duration 30 of the release period is significantly diminished. These formulations are thus generally not able to maintain the required persistence of active ingredient in the difficult or aggressive soil. In Australian sugar cane growing regions normal soil pH is < 6.0. However, in certain regions and in others as a result of agricultural practices such as liming, soil pH may be in excess of 6.0 and up to 8 or more and WO 98/48623 PCT/AU98/00299 2 the use of conventional CR formulations can lead to unsatisfactory results. This is particularly evident with chlorpyrifos formulations used against canegrubs. It is believed that in normal soils CR granules or pellets continually replenish the pesticidal active ingredient in the soil zone immediately surrounding the granule 5 as the released active ingredient dissipates. An effective concentration of pesticide active ingredient is required to be maintained to control the target pest. In difficult or aggressive soils the degradation mechanism in the soil can influence the equilibrium state and accelerate the release of active ingredient from the granule and result in premature depletion of the active ingredient from the granule. Accordingly, the 10 concentration of pesticidal active ingredient in the soil may be insufficient to control the pest for the desired length of time. Examples of such CR formulations are described in Australian Patent specifications 554834 and 629411 and US Patent 4400374. However, the present invention is not limited to the formulations in these patents. These prior art 15 formulations are conveniently in the form of particles especially granules and pellets and have demonstrated good pesticidal efficacy over useful periods of time when applied to normal soils. However, at soil pH > 6.0 they can fail to maintain persistence of the released pesticide for the desired period of time. This is particularly evident for pesticidal active ingredients sensitive to high pH soil, such as 20 most of the class of pesticides known as organophosphates. These include chlorpyrifos, tebupirimphos, terbufos and phorate. This is also the case with other active ingredients such as the carbamate group of pesticides. Maintaining persistence for the desired time is also a problem where the microflora and microfauna population in the soil is at a level and/or type that rapidly degrade the 25 active ingredient. In cases where soils have both a relatively high pH as well as a high microflora or microfauna population the problems of adequate persistence are exacerbated. It has been found that the application of large amounts (> 150 Kg per hectare) of pH lowering chemical such as sulfur or ammonium sulfate applied in the 30 same furrow with the conventional CR granules can improve the persistence of the active by changing the general soil conditions. This will of course result in changed soil conditions in proximity to the granules as well as elsewhere. However, the use of such large amounts of pH adjusting chemicals is often not a cost effective or environmentally acceptable solution to the problem of maintaining the persistence of WO 98/48623 PCT/AU98/00299 3 active ingredients in difficult soils. Accordingly, there is a need for improved CR pesticidal formulations which will overcome the problem of inadequate persistence in difficult soils. 5 SUMMARY OF THE INVENTION Accordingly, this invention provides in one form a pesticidal controlled release granular formulation for soil application comprising a matrix and a pesticidal active ingredient wherein the formulation further comprises a protectant that in use is able to modify the soil properties in proximity to the granule such that the active 10 ingredient is not adversely degraded when released into the soil. Preferably the matrix is polymeric. Preferably the protectant comprises a material that reduces the alkalinity or increases the acidity of the soil in proximity to the granules. Preferably the protectant is a material which may generate hydrogen ions in 15 the presence of soil in proximity to the granules. Preferably the protectant is a coating of sulfur bound to the surface of the granules and wherein the coating is 1 - 80% by weight of the total composition. In an alternative form the protectant is a fatty acid distributed throughout the granule. 20 In a further alternative form the protectant is a biologically active compound that influences the microbial and/or the microflora population in proximity to the granule. In a still further form the protectant is a combination of one or more of a sulfur coating, fatty acid preferably distributed throughout the granule or a biologically 25 active compound that influences the microbial and/or the microflora population in proximity to the granule. DETAILED DESCRIPTION OF THE INVENTION Examples of protectants which may be used in this invention include fatty 30 acids, sulfur, ammonium sulfate, citric acid or other organic or inorganic acids or acidic salts or mixtures thereof. The protectant is normally selected so as to have low mobility in the soil. This can be achieved by the protectant having low water solubility or by of the protectant being able to absorb onto the soil particles. The protectant should preferably be compatible with the polymeric matrix so as to form a WO 98/48623 PCT/AU98/00299 4 stable non or low blooming product. The protectant is selected so as to not substantially adversely degrade or interfere with the pesticidal properties of the active ingredient. The fatty acids suitable for this invention can have a range of carbon chain length of C8 - C20 and can be saturated or unsaturated. Examples 5 include stearic acid and palmitic acid. The controlled release pesticidal compositions of this invention may be prepared using a number of methods. These include, but are not limited to: 1. The granule ingredients including a protectant are premixed. The mixture is then extruded and pelletised by conventional pelletising processes such as strand 10 pelletising or die face pelletising in air or underwater. In this first method the polymer, additives, fillers and protectant are usually individually metered to the extruder by gravimetric feeders, mixed and melted and then extruded through the extruder dies. Liquid pesticidal active ingredients such as molten chlorpyrifos may be injected into the extruder via a metering pump. This 15 latter technique is particularly suitable for incorporation of high melting point powdered protectants such as sulfur or citric acid. Alternatively, if the pesticide is soluble or compatible with the protectant such as chlorpyrifos and fatty acids, then the pesticide and the protectant can be mixed and injected into the extruder as a liquid via a metering pump at elevated temperature if necessary. The extrudate can 20 then be pelletised with the die face process or strand pelletising process. 2. The protectant is incorporated by post extrusion infusion into controlled release pellets or granules at elevated temperature and under mixing. This method is particularly suitable for liquid or low melting point protectants such as fatty acids. 3. Controlled release granules, containing active ingredient are coated with a 25 protectant by using a bonding agent to improve the adherence of the coating to the granule. This method is particularly suitable for the incorporation of high melting point powdered protectants such as sulfur which are insoluble in water. 4. A protectant may be incorporated into finely divided polymer in a high speed mixer and further mixed with other ingredients such as additives and fillers. The 30 mixture is then fed into an extruder barrel, while the pesticidal active ingredient such as chlorpyrifos is fed as a liquid at elevated temperature, for example 600C, via a metering pump. The tank, pump and transfer line may sometimes need to be heated. The extrudate can then be pelletised as in method 1. If a mixture of protectants is required, protectants may be incorporated by WO 98/48623 PCT/AU98/00299 5 one of the following two further methods that involve coating the granules. 5. Controlled release granules containing a liquid protectant are first prepared as per method 1 or 2 and then coated as in method 3 with the second protectant. 6. A first protectant is used with a preferable melting point 50 - 800C such as 5 organic fatty acids as a bonding agent and a second protectant with high melting point is bonded to the granule by the bonding agent. Of course the mixed protectants could also have been incorporated by methods 1 - 4. While not being limited to the following explanation, it is believed the 10 protectants in the preferred embodiments act by lowering the soil pH in proximity to the granule to pH conditions where hydrolysis or degradation of the active ingredient is slowed or reduced. Suitable protectants may be inorganic or organic acids or material selected to reduce the soil pH via either a buffering or neutralising action. They may also be materials which in the soil environment generate hydrogen ions 15 via actions of soil microbes on the material. It is believed in the case of certain protectants that they may alternatively also act by reducing microflora or microfauna populations in proximity to the granule and this may take place without the necessity for pH modification. Examples of suitable protectants for this alternate mechanism include fungicides, bacteriastat or soil sterilants. A combined mechanism of pH 20 modification and change in microbial population may take place in some cases. The need for the present invention is based on the observation that existing CR formulations release pesticide at different rates and over differing periods of time in soils with different pH. For example, a CR formulation containing chlorpyrifos continues to release active ingredient over a three year period of time in soils with 25 pH < 6.0, but the same CR formulation releases active ingredient for only 6 - 8 months in soils with pH > 7.0. It was found from chemical analysis that the concentration of chlorpyrifos in soil with pH < 6.0 is much higher than the concentration of chlorpyrifos in soil with pH > 7.0 at the same period to time, eg three months, even though much more of the active ingredient had been released 30 from the granules in the pH > 7.0 soil. As the solubility of chlorpyrifos in water is very low, 1.4 ppm, its mobility in the soil is also very low. Accordingly, only the soil within about 2mm of the granule requires the lowering of the pH to improve the stability of chlorpyrifos. Proximity to the granules means within about 4mm from the granule surface.

WO 98/48623 PCT/AU98/00299 6 It is important that the protectant has a beneficial effect within the proximity to the granule. However, lowering of pH or other beneficial effect beyond the proximity of the granule as well as within proximity of the granule is within the scope of the present invention. It will be appreciated that best results are achieved with the 5 present invention where the mobility of the active ingredient is such that efficacious amounts of active ingredient are within proximity to the granule surface where the protectant has a beneficial effect. Protectants with low solubility in water and hence low mobility in soil, such as organic acids, sulfur or both are preferred as it is believed they can adjust the soil 10 pH in proximity to the granules. The range of suitable organic acids vary in physical properties from liquid, semi solid and solid at ambient temperature. The effectiveness of organic acids as protectants may depend on their chemical and physical properties as well as the type of granule matrix. By selecting suitable organic acids and matrix the release 15 rate of the protectant from the granule may be adjusted to be similar to that of the pesticidal active ingredient, eg chlorpyrifos. In practice organic acids can be incorporated by using method 1, method 2, or method 3 in an amount from about 0.5-50wt. %, preferably between 3 to 25 wt. % of the total CR granule formulation; pesticide in an amount between about 0.1 - 50 20 wt. %, preferably between about 3 and about 20 wt. %; the matrix material for the granule may be a synthetic polymer as for example with poly vinyl chloride or poly(ethylene-vinyl acetate) copolymer and/or a natural or modified natural polymer as for example with starch. The matrix should be from 5 - 90% and when the matrix is polymeric consist of synthetic, natural polymers or mixtures thereof; each of the 25 synthetic and natural polymers are present in an amount between about 0 - 90 wt. %, preferably between about 20 and about 80 wt. %; The polymers may be thermoplastic or thermoset. Inorganic fillers such as inorganic salts such as ammonium sulfate and sodium sulfate, mineral fillers such as clays and calcium carbonate in an amount between about 0 - 80 wt. %, preferably between about 5 30 and about 60 wt. %; in some formulations improved results are achieved when ammonium sulfate is used at up to 50% of the protectant level; processing additives such as plasticisers, stabilisers and lubricants in an amount between about 0 - 30 wt. %, preferably between about 1 and about 10 wt. %. Other additives such as colorants and solvents may be incorporated without substantially changing the WO 98/48623 PCT/AU98/00299 7 efficacious properties of the granules. Sulfur is a particular preferred protectant. In the form of a powder it is practically insoluble in water. It is believed soil microorganisms convert the sulfur to sulphuric acid. As sulfur is released from CR granules at very low rates there may 5 be insufficient acid formed in the soil to lower the high soil pH. It has been found that generally better results can be achieved by coating the granules with sulfur rather than having it uniformly distributed throughout the granule. Sulfur may be incorporated by using method 3, as described above, in an amount between about 1 - 80 wt. % of the final product and more preferably between about 30 and 80 wt. %. 10 The bonding agents for the coating process may be chosen from a wide range of known materials including acrylic film forming emulsions at amounts typically between about 0.5 and 10 wt. % and, preferably between about 1 and 2 wt. %; polyvinyl alcohol in an amount preferably between 0.5 - 10 wt. %, and preferably between about 1 and 5 wt. %; pre-treatment additives such as fine, inorganic fillers 15 can be used in amounts up to about 1 wt. %, preferably between 0.1 and 0.5 wt. %. While the compositions of this invention are most useful in difficult soil it has been found that in normal soils of pH < 6.0 the persistence of the pesticidal compositions of the present invention may be improved over prior art formulations. 20 Soils with particularly high pH, pH > 8, may require more than one protectant to give best results. In this case both organic fatty acids and sulfur may be incorporated into CR granules and method 6 may be the most suitable manufacturing method. In addition, inorganic acids may also be used as protectants as well as bioactive agents such as fungicides, bacteriastats or soil sterilants. 25 These latter protectants adjust the microbial levels in the soil. When both an organic acid and sulfur are used as protectants the level of sulfur is typically between about 1 and 80 wt. % of the final product, preferably between about 15 and 80 wt. %. The organic acid (MP 50 - 800C) is used at typically about 1 - 20 wt. %, preferably between about 5 and 10 wt. %; polyvinyl alcohol as a final coating agent is used at 30 an amount up to about 5 wt. %, preferably up to about 2 wt. %. All percentages are by weight and expressed in terms of the final product composition. The invention is further described by reference to the following examples of preferred embodiments where all parts are expressed as parts by weight.

WO 98/48623 PCT/AU98/00299 8 EXAMPLES 1 - 4 These Examples illustrate the preparation of CR formulations according to the invention where a fatty acid protectant is incorporated by post extrusion infusion into CR granules. 5 Controlled release chlorpyrifos granular formulations based on an EVA copolymer matrix were prepared by an extrusion process using the ingredients set out above the heading "FATTY ACIDS" in the table below. The colour was a blue pigment dispersed in an EVA copolymer. A strand pelletising process was used to produce cylindrical granules of diameter and length approximately 2mm. 10 The granules and each of the protectant fatty acids of the type and quantity set out in the table were placed in a ribbon blender and mixed at a temperature between 60 0 C and 80 0 C for about 45 minutes or until the granules became dry. The composition of the overall CR formulations in each of these Examples are set out in the table below. Composition Example I Example 2 Example 3 Example 4 wt.% wt.% wt.% wt.% EVA Copolymer 64.4 64.4 64.4 64.4 Talc 10.0 10.0 10.0 10.0 Colour 0.6 0.6 0.6 0.6 Chlorpyrifos 10.0 10.0 10.0 10.0 FATTY ACIDS Palm Olein Acid 15.0 Palm Kernel Fatty Acid 15.0 Coconut Fatty Acid 15.0 Lauric Acid 15.0 15 EXAMPLES 5 AND 6 These Examples illustrate the use of sulfur as a protectant. A CR chlorpyrifos formulation based on EVA copolymer matrix was prepared as in the first part of Example 1. These granules were then coated with powdered sulfur as WO 98/48623 PCT/AU98/00299 9 follows: A slurry of Perlite (0.2 parts) and an acrylic film forming emulsion (0.8 parts) was prepared by stirring. The slurry (1.0 parts) was then blended slowly with the CR granules (46 parts) to coat the slurry evenly over the surface of the granules. The 5 coated granules were then dried at 250C for approximately 10 minutes to allow the emulsion to coalesce and form a film. These coated granules were then further coated with a 20% polyvinyl alcohol (88% hydrolysed) aqueous solution (4.4 parts). Powdered sulfur (12.5 parts) was then added to the polyvinyl alcohol coated granules in a gentle blender until no free sulfur remained in the blender. For 10 Example 5 the remaining powdered sulfur was then added in three equal amounts (12.5 parts) each as follows. A 10% polyvinyl (88% hydrolysed) aqueous alcohol solution (7 parts) was then added to the sulfur coated granules until they were quite damp but non clumping. A further portion (12.5 parts) of powdered sulfur was then added and the granules were coated again with a gentle tumbling action. This 15 process was repeated two more times. The remaining portion of the 10% polyvinyl alcohol solution (5.2 parts) was added after the last portion of powdered sulfur had been mostly incorporated such that the granules were damp but not sticky. The coated granules were then dried at 350C to give granules of the following overall compositions (non-volatile content). 20 This process was then repeated with appropriate adjustment of sulfur and polyvinyl alcohol levels to produce the granules in Example 6.

WO 98/48623 PCT/AU98/00299 10 Composition Example 5 Example wt.% 6 wt.% EVA Copolymer 33.7 51.5 Talc (Filler) 5.0 6.0 Colour (as in Example 1) 0.3 0.5 Chlorpyrifos 7.0 9.0 Acrylic emulsion 0.4 0.4 Perlite 0.1 0.1 Polyvinyl alcohol (88% hydrolysed) 3.5 2.5 Sulfur (powdered) 50.0 30.0 EXAMPLES 7 AND 8 These Examples illustrate the use of two different types of protectants in the 5 same granules. A CR chlorpyrifos formulation based on a PVC polymer and starch matrix was produced as in the first part of Example 1 except that an under water pelletising process was used to produce generally spherical granules of approximately 2mm diameter rather than the cylindrical granules of Example 1. These granules were 10 then coated with powdered sulfur by using fatty acids as the bonding agents. The fatty acid was first melted by heating and then applied as a coating to preheated granules with gentle agitation. Sulfur powder was then coated onto the granules by adding the sulfur gradually under gentle agitation. The sulfur coated granules were then cooled to room temperature.

WO 98/48623 PCT/AU98/00299 11 Composition Example 7 Example 8 wt.% wt.% PVC Polymer 13.0 13.0 Starch 6.0 6.0 Dibutyl Phthalate 8.0 8.0 Calcium Carbonate 30.0 30.0 Processing additives 4.0 4.0 Colour 0.5 0.5 Chlorpyrifos 10.0 10.0 Stearic Acid 6.0 Myristic Acid 6.0 Sulfur 22.5 22.5 EXAMPLES 9 AND 10 These Examples illustrate the preparation of further granules according to 5 the present invention. Granules were prepared with chlorpyrifos as the active ingredient using the method as described in Example VI, Table XIV of US Patent 4400374. These CR granules were then coated as in Example 5 above with powdered sulfur using polyvinyl alcohol as the binder material at two coating levels to give granules which 10 contained 27.5% sulfur by weight (Example 9) and 45.6% sulfur by weight (Example 10). EXAMPLE 11 This Example shows the comparative testing of Examples 9 and 10 15 compared to conventional CR granules. Samples of uncoated granules used to prepare the coated granules in Examples 9 and 10 were used as controls. Granule samples were then applied at a rate of 0.5g tol 00g soil in duplicate to a silty loam soil with a pH of 7.5. Uncoated WO 98/48623 PCT/AU98/00299 12 granules normally lose activity within 6 months in this soil and hence this soil is regarded as aggressive. Samples of the uncoated control were also added to the soil for comparison purposes with and without additions of sulfur to the soil (applied as a powdered form broadcast in the soil). The soil surrounding the granules was 5 analysed for chlorpyrifos content 6 months after application and the following results were obtained. Granules according to the present invention, particularly at the higher sulfur level, led to much higher chlorpyrifos levels in the soil after 6 months. Sample Added Sulfur pg Chlorpyrifos/ Number (g S/kg soil) Sulfur Form granule in the soil after 6 months Uncoated Control Nil Nil 3.1 Uncoated Control 1.17 Broadcast 4.0 Uncoated Control 2.34 Broadcast 6.3 Example 9 1.9 Coated (27.5% w/w) 14.5 Example 10 4.1 Coated (45.6% w/w) 32.2 10 EXAMPLES 12 -14 These Examples illustrate the preparation of further Examples of CR formulations according to the present invention. An unmodified CR granule formulation, referred to as the "Control", was 15 prepared as in Australian Patent No. 554,843 to produce granules with 14% w/w chlorpyrifos. A commercial fatty acid blend pristerene having a minimum of 70% stearic acid was then infused into the granules according to the method in Example 1.

WO 98/48623 PCT/AU98/00299 13 Composition (wt.%) Method of Preparation Example 12 Control (88) Pristerene (12) Method 2 Example 13 Control (53) Pretreatment latex (0.3) PVA (initial) (0.7) Method 3 PVA (final) (1.0) Sulfur (45) Example 14 Example 12 (53) Pretreatment latex (0.3) PVA (initial) (0.7) Method 5 PVA (final) (1.0) Sulfur (45) EXAMPLE 15 This Example illustrates the testing of Examples 12 - 14 compared to a 5 control as described in Examples 12 - 14 above. The release rate test was established in a controlled environment at a temperature of 300C and watering regimes to obtain medium soil moisture (moisture level from 6% to 20% wlw.). Two soils prone to extremely rapid degradation of chlorpyrifos and one standard soil with a much lesser rate of 10 chlorpyrifos degradation, were used for testing release rates of active ingredient from the granules and accumulation of chlorpyrifos in the soils. The aggressive soils were characterised as follows: Soil A was a silty loam with pH 7.4. Soil B was a clay loam with pH 6.9 - 7.0. The standard soil was a pale brown fine sandy loam with pH 5.3. 15 The test was conducted in two replicates and four recovery periods, over six months as follows: 28 day, 56 day, 84 day and 168 day. Each test sample was prepared by placing 50 grams of soil in a plastic container, followed by 60 granules of CR product and then another 50 grams of soil on top. A glass wool insert was then placed on top of the soil to prevent 20 soil disturbance during watering and also prevent the rapid loss of moisture.

WO 98/48623 PCT/AU98/00299 14 The samples were watered initially with 20ml of water and then weekly with 14ml of water to maintain moisture levels from within the range of 6% to 20%. The plastic containers were cylindrical andl20ml in volume (diameter 44 mm and height 108 mm), and had four holes for water drainage. A glass 5 wool insert was placed at the bottom of each container to prevent soil escape. At each recovery period the glass wool was removed from the top of the containers and soil left at 300C for 3 - 4 days to dry sufficiently to permit sieving to separate the granules from the soil. The granules were then analysed for chlorpyrifos and the soil samples analysed to determine total 10 chlorpyrifos in the soil. Results are set out below and expressed as micrograms of chlorpyrifos per granule (pg AI per granule). Higher concentrations of Al in the soil are present for Examples 12, 13 and 14 in the aggressive soil and after 168 days. Soil Time Control Example 12 Example 13 Example 14 Type Day pg Al per pg Al per pg Al per pg Al per Gran. Gran. Gran. Gran STD Soil 0 0 0 0 0 28 81.6 111 71.1 73.5 56 80.9 92.8 26.9 34.9 84 20.3 33.7 26.7 68.7 168 17.7 24.9 23.3 84.0 Soil A 0 0 0 0 0 28 68.5 72.2 60.3 57.8 56 54.0 57.2 29.3 27.3 84 3.1 10.3 19.1 39.2 168 4.7 9.5 23.0 69.3 Soil B 0 0, 0 0 0 28 50.1 45.3 53.3 46.2 56 54.0 35.0 34.6 27.2 84 3.4 17.6 24.2 36.4 168 4.8 11.7 19.4 76.0 WO 98/48623 PCT/AU98/00299 15 EXAMPLE 16 This example illustrates the field trial performance of composition according to the present invention. 5 Example 11 was repeated in a field trial in another aggressive soil characterised as a coarse sandy-loam soil of pH 6.5 to 7.0 at Gordonvale. The granules and soil were evaluated after nine and fifteen month intervals as in Example 15. The results are set out in the table below. Coated granules from Examples 9 and 10 showed much higher levels of soil borne chlorpyrifos 10 than the control after both 9 and 15 months. The amount of chlorpyrifos in the granules was much higher in the coated granules than for the controls after both 9 and 15 months. 9 Month 15 Months %AI in pg AI/ %AI in pg AI/ granules Granule granules Granule in soil in soil Uncoated Control (no added sulfur) 5.0 3.3 0.0 2.1 Uncoated Control (1.17g/Kg Sulfur broadcast) 4.7 2.5 0.0 2.2 Uncoated Control (2.34g/Kg Sulfur broadcast) 4.9 3.9 0.0 1.3 Example 10 9.3 60.6 9.8 51.3 Example 9 10.1 71.4 9.0 39.0 EXAMPLE 17 15 Example 16 was repeated in a further field trial in soil characterised as a red Kraznozem soil with pH was 6.1. The soil and granules were tested after nine and eighteen months as in Example 16 and the results are set out as follows. Example 9 and 10 again showed both higher levels of chlorpyrifos in the granules as well as higher concentrations of chlorpyrifos in the soil after 20 both 9 and 18 months.

WO 98/48623 PCT/AU98/00299 16 9 Month 18 Months %AI in pg AI/ %AI in pg All granules Granule granules Granule in soil in soil Uncoated Control (no added Sulfur) 7.0 11 4.5 13 Example 10 10.4 89 10.4 137 Example 9 10.6 69 10.7 130 Field trials of controlled release of similar chlorpyrifos formulations, with and without the sulfur and fatty acid protectants, were conducted in the Burdekin district of Far North Queensland, Australia on sugar cane farms with 5 soils known to be aggressive to the insecticide chlorpyrifos. The populations of the damaging pest greyback canegrubs (Dermolepida albohirtum) were assessed in the field 8 months after application. Plots treated with the controlled release chlorpyrifos formulations with the protectants (sulfur coating, fatty acids and sulfur coating), provided superior canegrub control to controlled 10 release chlorpyrifos formulations without the protectants, and to the nil insecticide treatments.

Claims (17)

1. A pesticidal controlled release granular formulation for soil application comprising a matrix and a pesticidal active ingredient wherein the formulation 5 further comprises a protectant that in use is able to modify the soil properties in proximity to the granule such that the active ingredient is not adversely degraded when released into the soil.

2. A pesticidal controlled release granular formulation as defined in Claim 1 wherein the matrix comprises a polymer. 10

3. A pesticidal formulation as defined in Claim 1 or Claim 2 wherein the protectant comprises a material that reduces the alkalinity or increases the acidity of the soil in proximity to the granules.

4. A pesticidal composition as defined in any one of Claims 1 - 3 wherein the protectant is selected from sulfur, fatty acid or biologically active 15 compound that influences the microbial or microflora populations in proximity to the granules.

5. A pesticidal composition as defined in any one of Claims 1 - 4 wherein the protectant is in the form of a coating on the granules.

6. A pesticidal composition as defined in any one of Claims 1 - 4 wherein 20 the protectant is distributed throughout the granules.

7. A pesticidal composition as defined in any one of Claims 1 - 6 wherein the protectant is sulfur.

8. A method of treating soil comprising treating the soil with an effective amount of a pesticidal composition as defined in any one of Claims 1 - 7. 25

9. A method of treating a soil as in Claim 8 wherein the soil is an aggressive soil.

10. A method of treating a soil as in Claim 9 wherein the pH of the soil is at least 7.0.

11. A method of controlling canegrub populations by applying an effective 30 amount of a pesticidal composition as defined in any one of Claims 1 - 7.

12. A method of preparing a pesticidal controlled release granular formulation for soil application by premixing granule ingredients including a protectant, extruding and pelletising the extrudate to form granules. WO 98/48623 PCT/AU98/00299 18

13. method of preparing a pesticidal controlled release granular formulation for soil application by post extrusion absorption or infusion of a protectant into the granules.

14. A method of preparing a pesticidal controlled release granular 5 formulation for soil application by coating the surface of the granule with a bonding agent prior to coating the granule with a protectant.

15. A method of preparing a pesticidal controlled release granular formulation for soil application by absorbing or infusing a protectant into finely divided polymer prior to mixing, extruding and granulating the formulation. 10

16. A method of preparing a pesticidal controlled release granular formulation for soil application as defined in Claim 14 wherein the bonding agent includes a protectant.

17. A method of preparing a pesticidal controlled release granular formulation for soil application as defined in either Claim 12 or Claim 15 which 15 further includes coating the granules with a protectant.