Oxyfluorfen dispersible granule formulations

Abstract: A dispersible granular formulation has been developed which contains oxyfluorfen herbicide. This formulation provides excellent suspensibility characteristics, and reduces post-emergent vapour phytotoxicity.

Description: This invention concerns novel dispersible granule formulations (hereinafter also referred to as dispersible granular compositions) of the herbicide oxyfluorfen (2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene), and processes for their preparation. In the context of this invention, a "dispersible granule" is one which will disperse when added to a liquid carrier. It does not include granules which do not disperse when added to water but which do ultimately disperse after some time in the environment. Water dispersible granular pesticide formulations are known. These formulations are desirable because they avoid the use of potentially toxic solvents and permit the use of easily-disposable paper containers or water soluble containers. Potential exposure of pesticide applicators and the general public to the pesticide or solvent is thereby reduced. Typical dispersible granular pesticide formulations are described for example in GB -A-1,433,882, EP-A-0,252,896 and U.S.-A-3,920,442. GB-A-1,433,882 describes a process for preparing dispersible granules by blending premilled, water-insoluble active ingredient, dispersing agents, disintegrating agents and wetting agents in an aqueous suspension. The aqueous mix is extruded to form granules which are then dried to yield the final product. U.S.-A- 3,920,442 describes water dispersible pesticide aggregates containing from 5 to 95% by weight of pesticide. The aggregates are prepared by contacting the finely divided solid ingredients in a fluidized bed with a fine spray of water or a solution of the binder-dispersant followed by drying. In attempts at making pesticide granules, it has often been found that granules or agglomerates prepared from the formulated wettable powders of the art using well-known agglomerating techniques and using water as the agglomerating agent, are not easily dispersible in water. On the other hand, agglomerates which are readily water-dispersible are often not sufficiently resistant to attrition and form a fine dust fraction upon handling and shipping. If conventional binders are added to make the granules strong, then they are not dispersible in water. Techniques such as tabletting, extrusion and rolling which involve high-pressure compaction of moistened mixtures containing finely divided pesticides, diluents, binder and dispersant, as described in U.S. -A-3,617,246, lead to dense pellets, tablets, plates, and rods which are subsequently dried and crushed. These latter techniques have also been used to form granules containing up to 50% of active pesticide, but the resulting granules are not rapidly or completely water dispersible and are not suitable for use in preparing sprayable suspensions. Low-melting solids such as oxyfluorfen present an especially difficult problem in the preparation of a dispersible granule formulation. The low-melting solid, herein defined as melting below 100° C., tends to melt or become sticky during or subsequent to the grinding process which is a necessary step in preparing dispersible granules. EP-A-0,252,896 describes a possible solution to this problem which requires micro-encapsulation of low-melting pesticides prior to granulation. However, microencapsulation involves additional processing steps and adds to the cost of the overall formulation. Conventional oxyfluorfen formulations also suffer from the loss of herbicide vapour at the site of application which is undesirable because of reduction of herbicide in the soil and also because of possible vapour injury to growing crops in or near the location to which the herbicide is applied. Oxyfluorfen is known to cause injury to soybeans by volatization under field conditions. Grabowski and Hopen, Weed Science 1985 , Vol. 33, pg. 306-309 show that emulsifiable concentrate, wettable powder and soil applied granular formulations of oxyfluorfen cause vapour injury to plants under greenhouse conditions. There is clearly a need for a dispersible granular oxyfluorfen formulation which can combine the features of a high active ingredient content, good suspensibility and dispersion properties as well as resistance to attrition thereby avoiding the formation of a dust. A dispersible granular herbicide composition designed for dispersion in a liquid carrier should ideally have a high content of active material, should be readily dispersible in the carrier and should then form a dispersion which is as stable as possible, requiring the minimum of subsequent agitation for homogeneity. The liquid carrier will, of course, for convenience normally be water. We have now succeeded in producing granules generally containing from 65% to 90% oxyfluorfen which readily break down when they are stirred into a liquid carrier to give a stable dispersion of the active ingredient. Accordingly in its broadest aspect the present invention provides a dispersible granular composition having at least 30% less vapour toxicity to growing plants compared with an equivalent emulsifiable concentrate or wettable powder formulation, and wherein substantially all of the granules have a mean particle size of at least 0.1 mm, said dispersible granular composition comprising 65 to 90% by weight, preferably at least 80% by weight, oxyfluorfen, 0.1 to 25% by weight of at least one surfactant component, 0 to 90% by weight flow aid, 0 to 5% by weight disintegrant, and 0 to 5% by weight defoaming agent. By granular, we mean granules substantially all of which have a mean particle size of at least 0.1 mm, which is a particle size much larger than the mean particle size of a powder, which is measured in microns. Oxyfluorfen is 2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene. Dispersible granular, also known as dry flowable, formulations are designated in agricultural literature as DC, DF or WG. The percentage active ingredient in the formulation is sometimes indicated, as for example, oxyfluorfen 80 DG or oxyfluorfen 60 DF. It has been found that the dispersible granule formulation of the invention causes significantly less vapour injury to growing plants compared with emulsifiable concentrate and wettable powder formulations of oxyfluorfen, without reducing preemergent herbicide activity. By "significantly less vapour injury" is meant at least a 30% reduction in injury by the dispersible granules of this invention compared with conventional formulations in an assay equivalent to the vapour bioassay described in Example 12. In addition to the active ingredient, oxyfluorfen, the mixture to be formed into dispersible granules contains one or more surfactants and, optionally, flow aid, disintegrant and/or defoaming agent. A satisfactory dispersible granular formulation should have a suitable suspensibility, so that the dispersed formulation remains stable and sufficiently homogeneous with minimum agitation. The suspensibility test is determined in accordance with a variation of the procedure of the Collaborative International Pesticides Analytical Council (CIPAC) Handbook, Vol. 1, Ed. G. R. Raw (1970), Method Number MT 15.1. Standard hard water (342 ppm as calcium carbonate) was prepared according to CIPAC method MT 18.1.4., also known as Army Hard Water. The suspensibility test is further described in Example 1. Preferably, the composition of the present invention has a suspensibility of at least 70%. The term "surfactant" is used in the broad sense to include materials which may be referred to as emulsifying agents, dispersing agents and wetting agents, and the surfactant component may comprise one or more surfactants selected from the anionic, cationic and nonionic types. Examples of surfactants of the anionic type include soaps, salts of aliphatic monoesters of sulfuric acid such as sodium lauryl sulfate, salts of sulfonated aromatic compounds, for example sodium dodecylbenzene sulfonate, sodium or ammonium lignosulfonate or butylnaphthalene sulfonate, and a mixture of the sodium salts of diisopropyl- and triiso-propylnaphthalene sulfonates. Suitable agents of the non-ionic type include, for example, the condensation products of ethylene oxide with fatty alcohols such as oleoyl alcohol or cetyl alcohol, or with alkyl phenols such as octyl phenol, nonyl phenol and octyl cresol. Other non-ionic agents are the partial esters with ethylene oxide and the lecithins. Preferably the surfactant component will comprise at least one wetting agent such as those selected from alkyl naphthalene sulfonates, alkylaryl polyoxyethylene ammonium sulfonates, sulfosuccinates and nonionics such as tridecyl alcohol ethoxylate; or at least one dispersing agent such as those selected from the group of naphthalene sulfonates, lignosulfonates and polyacrylates. The total surfactant component will comprise from 0.1 to 25% and preferably from 1 to 15% by weight of the dry weight of the composition. In the context of this specification, a dispersing agent is a surfactant which facilitates the dispersion of the pesticide particles when the product is added to a liquid, for example water. The dispersing agents used are preferably water-soluble ones. Phosphate esters, polycarbonate/acrylates and calcium lignosulfonates produced granules with poor suspensibility. Examples of dispersants preferred for the dispersible granule formulations of this invention include: Polyfon H, Polyfon O, Reax 88B, Morwet D-425, Reax 45A, Polyfon T, Polyfon F, Lignosol XD-65, Reax 45L, Reax 85A, Reax 910, Polyfon OD, PC-825, many of which are described in Table 1. Most preferred dispersants are: Reax 85A, Polyfon H and Morwet D425. Examples of surfactants preferred as wetting agents for the dispersible granule formulations of this invention include Morwet B, Morwet EFW, Sellogen DFL, Morwet IP, Igepon AC-78, Igepon T-77, Aerosol OT-B, and Triton XN-45S, described in Table 1. Most preferred wetting agents are Morwet B and Triton XN-45S. Preferably, the composition of the present invention comprises 0 - 25% by weight dispersant, and 0 - 25% by weight wetting agent. All surfactants act as dispersing agents in some degree, and also in some degree as wetting agents; most surface-active agents are however, more efficient in one capacity than the other. The worker of ordinary skill in the formulation art can select a surfactant most suitable for the purpose in view. Small particles of a low-melting solid such as oxyfluorfen often tend to stick together thereby causing flow problems in processing the material. Flow enhancing agents also called flow aids such as clays or silica particles may be used to minimize these problems. Flow aids preferred for the oxyfluorfen dispersible granular include HiSil 233, Wessalon 50S, Cab-O-Sil M-5, Wessalon S, Barden Clay, and Microcel E. Most preferred is HiSil 233, a silicate flow aid. The flow aid is present in the dispersible granule in an amount of from 0 to 90%, and preferably from 1 to 8%. Addition of a silicon containing antifoaming agent is desirable to aid in the processing and use of oxyfluorfen dispersible granules. Defoaming agents are present in amounts of 0% to 5%, for example 0.1% to 5%, with a preferred range being 0.2% to 1.0%. The preferred defoaming agent is Mazu DF-1300. Disintegrants, which are water soluble organic compounds such as starch or sugar or water soluble inorganic salts such as sodium acetate or sodium bicarbonate, are sometimes used in dispersible granule formulations. See GB-A-1,433,882 for example. We have found that certain disintegrants have different effects on the oxyfluorfen dispersible granules of this invention; formulations containing sodium bicarbonate were found to disperse less effectively. On the other hand, Primojel disintegrant, a sodium starch glycolate provided a dispersible granule with good physical properties and biological activity. In one embodiment of the composition of the present invention said dispersant is a sulfonated lignin, and/or said flow aid is a silica compound, and/or said wetting agent is a naphthalene sulfonate, and/or said defoaming agent is a silicone or silica compound, and/or said disintegrant is a sodium starch glycolate. The most preferred composition of this invention comprises by weight percent: oxyfluorfen 80.4%; dispersant, Reax 85A, 17.5%; flow aid, HiSil 233, 1.6%; defoaming agent, Mazu DF-1300, 0.5%; and water, less than 1%. Examples of dispersant, wetting agents, flow aids and defoaming agents useful in this invention are shown in Table I. According to the present invention there is also provided a process for producing a dispersible granular composition according to the invention, comprising: (a). combining a flow aid with oxyfluorfen and milling to a particle size of less than 20 microns; (b). adding less than 25 percent by weight water and a dispersant to the product of step (a) and mixing until a paste is obtained; (c). converting said paste into granules; and (d). drying said granules whereby granules are produced substantially all of which have a mean particle size of at least 0.1 mm. Conversion of the paste into granules may be accomplished by agglomeration. Agglomeration or granulation may be accomplished by any operable means such as wet granulation, tabletting, pan agglomeration, fluid bed agglomeration or extrusion. Extrusion is the preferred method. The preferred amount of water to be added to the mixture to be agglomerated is 18 to 25 parts per 100 parts by weight. After conversion of the paste into granules, e.g. by extrusion, the dispersible granules are dried. For storage stability, it is preferred to reduce the residual water to at least 2% and preferably below 1% by weight. Drying temperatures above about 100°C are injurious to the product. The preferred drying temperature is less than 60°C. and more preferably less than 50°C. Drying may be accomplished by any suitable drying means preferably one which supplies inert gas at a controlled temperature. A two stage fluid bed dryer is preferred. A preferred process for producing the oxyfluorfen dispersible granules of this invention comprises: (a) milling a mixture of oxyfluorfen, and flow aid to a particle size between 3 and 15 microns; (b) adding a surfactant, e.g. a dispersant, and 18-25% water (based on the total weight of ingredients) to the milled mixture of step (a) and mixing until a homogeneous, extrudable paste is obtained; (c) extruding the paste obtained in step (b); (d) drying the extruded granules at a temperature of less than 60° C. to a moisture content of less than 2% by weight. The present invention further provides a method of controlling weeds, comprising applying a pre-emergent herbicidally effective amount of a composition according to the invention, or a composition made by the process of the invention. The following Examples describe the preparation of the oxyfluorfen dispersible granules of this invention and are intended only to illustrate the invention and not intended to limit the scope of the invention which is defined by the claims. EXAMPLE 1 Preparation of Oxyfluorfen 80 DG by Extrusion Technical oxyfluorfen (97% purity by weight) was melted by heating at 100°C. for 24 hours. The molten material was then poured into aluminum foil lined trays to a depth of about one inch (25 mm). After cooling at room temperature for 24 hours, the solid was broken up and milled in a coffee mill. The coarse milled oxyfluorfen was blended with HiSil 233 flow aid in a Marion mixer (manufactured for Rapid Machinery Co., Marion, Iowa by Texas Div. Tranter Inc. Old Burk Road, Wichita Falls, TX) in the following ratio of ingredients in parts by weight: oxyfluorfen 80.4; HiSil 1.6 and mixed for 20 minutes. The above blend was milled in a Bantam micropulverizer, (manufactured by Mikropul, 10 Chantaur Road, Summit, NJ 07901) fitted with a 0.042 inch (1 mm) screen and automatic feeder. The mean particle size of micropulverized product was about 40 microns. The micropulverized product was then air milled in an 8" (20 cm) horizontal (pancake) jet mill (manufactured by Fluid Energy Processing and Equipment Co., 153 Penn Energy, Hatfield, PA 19440). An Accu-Rate feeder (made by Accu-Rate, 746 E. Milwaukee Street, White Water, WI 53190) was fitted with a 2" (50mm) screw feed nozzle positioned to deliver micropulverized material to the air mill. High pressure nitrogen was used for both feeding and grinding to maintain an oxygen concentration below 10%. The ground material was collected in the air bag. The air mill was operated at a nitrogen feed pressure of 65 psig (4.58 N/cm 2 ), a nitrogen grind pressure of 60 psig (4.23 N/cm 2 ), and an accurate-rate setting of 100. Under these conditions the milling rate was 8-10 lbs (4-5 kg)/hour. The mean particle size was about 5 microns. The above blend (82.0 parts by weight), Reax 85A dispersant (17.5 parts by weight), Mazu DF 1300 antifoam (0.5 parts by weight) and water (25 parts by weight) were mixed in a Kitchen Aid mixer (made by Hobart, Kitchen Aid Div., Troy, Ohio) for approximately 2 to 3 minutes. The mixture was transferred to a KAR 130 extruder (made by Tsu Tsui Rikagaku Kikai Co., Ltd., japan) fitted with a 1.0 mm screen. After extrusion, the extrudate was air dried to a moisture content of 1 to 2% by weight at a temperature of less than 40° C. Suspensibility (variation of CIPAC method) Two grams of oxyfluorfen DG was placed in a glass-stoppered graduated cylinder containing 248 ml of Army Hard Water at 25°C. The cylinder was inverted 30 times over a period of 90 seconds and allowed to stand for 30 minutes. The bottom 25 ml was separated, evaporated and dried for 16 hours at 60°C; and the resulting residue was used to calculate the percent suspensibility by the following formula. % suspensibility = 2 - weight of residue in grams 2 x 111 Examples 2-8 A number of formulations of oxyfluorfen DG were prepared following the general procedure of Example 1 using variations of dispersants, wetting agents, disintegrants, defoaming agents and flow aids. The components and results are shown in Table 2 below. Example 9 Preparation of Oxyfluorfen DG by Granulation Oxyfluorfen (77.9 parts by weight) and HiSil 233 (1.6 parts by weight) were milled to a particle size of approximately 5 microns. Reax 85A (20.0 parts by weight) and Mazu DF 1300 (0.5 parts by weight) were added to the oxyfluorfen and HiSil and mixed in a Hobart blender until the mixture was well blended. Water was added slowly to the powder while mixing. When the mixture began to granulate, addition of water was stopped and stirring was continued until granulation was complete. The resulting granules were dried under vacuum and screened to remove fines and oversized particles. Example 10 Pre-emergent herbicide test procedure The following test procedure was employed to assess the herbicidal activity of the formulations of the invention. Seeds of selected plants were planted in flats or pots. The test compound was sprayed directly onto the soil surface immediately after planting. The flats or pots were then placed in a greenhouse and watered by subirrigation and overhead. Subsequently, only overhead watering was used. Test species employed are listed in Tables 3 and 4. Each formulation to be evaluated was suspended in water and sprayed over the flats or pots using a carrier volume equivalent to 25 gallons per acre (233.84 liters per hectare) at the rate of application in grams per hectare (g/Ha) specified in the tables. About two or three weeks after application of the test formulation, the state of growth of the plants was observed. Each species was evaluated on a scale of 0 to 100 in which 0 equals no control and 100 equals total control of the species. Tables 3 and 4 show the pre-emergent herbicide activity of the oxyfluorfen dispersible granule formulations of this invention compared with oxyfluorfen emulsifiable concentrate (1.6 E), a commercial formulation of Rohm and Haas Company, Philadelphia, PA 19105. Example 11 Vapour Bioassay : The vapour assay was designed to detect herbicidal injury that can occur only from vapourized herbicides. Unsprayed plants were exposed to potential vapours within an enclosed system as follows. Typical greenhouse soil (50:50 of soil to Redi Earth) was added to an eight inch (20.32 cms) diameter circular pot six inches (15.24 cms) tall to within one inch (2.54 cms) of the top and then covered with a 2:1 soil and sand mix. The pot was sprayed with a herbicide in the conventional manner. The sprayed pot was immediately placed in the greenhouse and the soil wetted from the bottom up using a water-filled saucer. After wetting the soil, a 2 inch (5 cm) pot of velvetleaf was placed in a small petri dish in the center of the pot. After placing the untreated plants on the treated soil, a one gallon clear plastic bag was inverted over the eight inch pot forming a tightly sealed tent over the entire system. The pot/tent system was left in the greenhouse for four days at which time injury evaluations were made using a scale of 0 (no injuries) to 100 (complete kill). Tables 5 and 6 show the vapour injury caused by dispersible granule formulations of this invention in comparison to the oxyfluorfen emulsifiable concentrate (1.6 E) and oxyflourfen wettable powder (25 WP) commercial formulations of Rohm and Haas Company, Philadelphia, PA 19105. Oxyfluorfen DG Vapour Test 300 g/Hectare Active Ingredient (Velvetleaf) 4 Days after Application Formulation % Injury Oxyfluorfen DG (Example 1) 30 Oxyfluorfen DG (Example 2) 25 Oxyfluorfen DG (Example 3) 35 Oxyfluorfen Emulsifiable Concentrate (1.6 E) 100 Untreated 0 Oxyfluorfen DG Vapour Test 300 g/Hectare Active Ingredient Velvetleaf 4 Days after Application Formulation % Injury Oxyfluorfen DG Example 2 40 Oxyfluorfen DG Example 4 45 Oxyfluorfen DG Example 5 50 Oxyfluorfen Emulsifiable Concentrate (1.6 E) 90 Untreated 0 Oxyfluorfen 25 WP 80 Oxyfluorfen Emulsifiable Concentrate (1.6 E) 100 Untreated 0 "Polyfon", "Reax", "Morwet", "Lignosol", "Triton", "Sellogen", "Igepon", "HiSil", "Wessalon", "Cab-O-Sil", "Barden", "Microcel", "Primojel", "RediEarth", "Orzan", "Aerosol" and "Mazu" are trademarks which may be registered in one or more of the designated states.

Claims: A dispersible granular composition having at least 30% less vapour toxicity to growing plants compared with an equivalent emulsifiable concentrate or wettable powder formulation, and wherein substantially all of the granules have a mean particle size of at least 0.1 mm, said dispersible granular composition comprising 65 to 90% by weight oxyfluorfen, 0.1 to 25% by weight of at least one surfactant component, 0 to 90% by weight flow aid, 0 to 5% by weight disintegrant, and 0 to 5% by weight defoaming agent. A composition as claimed in claim 1 having a suspensibility of at least 70 %. A composition as claimed in claim 1 or 2, wherein the surfactant component comprises a wetting agent and/or dispersant, and which further comprises one or more of said flow aid, defoaming agent and disintegrant. A composition as claimed in any of claims 1 to 3, comprising 0-25% by weight dispersant, and 0-25% by weight wetting agent. A composition as claimed in claim 4, comprising 1 to 8% by weight flow aid. A composition as claimed in claim 4, comprising 0.2 to 1.0% by weight defoaming agent. A composition as claimed in any of claims 3 to 6 wherein said dispersant is a sulfonated lignin, and/or said flow aid is a silica compound, and/or said wetting agent is a naphthalene sulfonate, and/or said defoaming agent is a silicone or silica compound, and/or said disintegrant is a sodium starch glycolate. A composition as claimed in any of claims 1 to 7, wherein the amount of oxyfluorfen is at least 80% by weight. A composition as claimed in any of claims 1 to 8, wherein the total amount of surfactant component is 1 to 15% by weight. A process for producing a dispersible granular composition according to claim 1, comprising: a) combining a flow aid with oxyfluorfen and milling to a particle size of less than 20 microns; b) adding less than 25 percent by weight water and a dispersant to the product of step (a) and mixing until a paste is obtained; c) converting said paste into granules; and d) drying said granules whereby granules are produced substantially all of which have a mean particle size of at least 0.1 mm. A process as claimed in claim 10 wherein: in step a) said mixture of oxyfluorfen and flow aid are milled to a particle size of between 3 and 15 microns; in step b) 18-25 percent by weight water plus dispersant are added to the milled mixture of step (a) and mixed until a homogeneous, extrudable paste is obtained; in step c) said granules are formed by extruding the paste; and in step d) said granules are dried at a temperature of less than 60°C to a moisture content of less than 2% by weight. A method of controlling weeds, comprising applying a pre-emergent herbicidally effective amount of a dispersible granule composition as defined in any of claims 1 to 9 or a composition made by a process according to claim 10 or 11.

Inventors: CAYER CHRISTINE MARY, MUSCO VINCENT ANGELO, PETERSON ROBERT FREDERICK JR, CAYER, CHRISTINE MARY, MUSCO, VINCENT ANGELO, PETERSON, ROBERT FREDERICK, JR.
Applicants: ROHM & HAAS, ROHM AND HAAS COMPANY
Application year: 1992
Main classification: A01N33
IPC codes: A01N25, A01N33