WO2003013248A1

WO2003013248A1 - Weed control

Info

Publication number: WO2003013248A1
Application number: PCT/EP2002/008321
Authority: WO
Inventors: Sylvie Lavault
Original assignee: Bayer CropScience SA
Current assignee: Bayer CropScience SA
Priority date: 2001-08-08
Filing date: 2002-07-26
Publication date: 2003-02-20
Anticipated expiration: 2004-02-08
Also published as: AR034981A1

Abstract

A method for controlling the growth of weeds at a locus in a growing medium, which comprises treating the locus with a delayed-release composition comprising oxadiargyl to provide progressive release of oxadiargyl herbicide into the growing medium.

Description

Weed Control

This invention relates to a method for controlling the growth of weeds by the progressive release of oxadiargyl into the surface layer of a growing medium and to compositions for use in the method.

Background of the invention

It is known that many herbicides injure crop plants at herbicide application rates needed to control weed growth. This renders many herbicides unsuitable for controlling weeds in the presence of certain crops. Where weed growth in crops is uncontrolled however, this results in lower crop yield and reduced crop quality, as weeds will compete with crops for nutrients, light and water. Reduction in herbicidal injury to crops without an unacceptable reduction in the herbicidal action can be accomplished by use of crop protectants known as "antidotes", also sometimes referred to as "safeners" or "antagonists". The safening effect of a compound is generally specific to the herbicidal partner and the crop where the active ingredients are applied.

The use of oxadiargyl which is for controlling weeds has been disclosed in, for example, Japanese Patent Application No. 61 297457. In addition, the use of this herbicide in the presence of certain antidotes is described in Japanese Patent Publication No. 97 132506. Commercial formulations of oxadiargyl (typically emulsion concentrates) may, in some instances, adversely affect or interfere with the development of crop plants, especially rice crops. Such a risk of phytotoxicity caused by oxadiargyl has lead to the routine application of commercial formulations of oxadiargyl with an antidote.

It has been found that by modifying the mode in which oxadiargyl is applied to a crop locus the dose rate of oxadiargyl can be maintained in the growing medium, for example, during the period from application of oxadiargyl to establishment of a crop. It has been found that by maintaining a uniform concentration of oxadiargyl in the growing medium, during the period from application of the oxadiargyl to establishment of a crop, improved crop selectivity may be obtained. Furthermore, herbicidal efficacy may be improved.

The present invention provides a method for controlling the growth of weeds at a locus in a growing medium, which comprises treating the locus with a delayed- release composition comprising oxadiargyl to provide progressive release of oxadiargyl herbicide into the growing medium.

The growing medium includes composts, preferably soil, which may be substantially covered by an aqueous layer, which may or may not contain particulate organic matter. The locus is preferably a crop-growing locus, typically where a crop is sown and cultivated, for example a paddy field.

According to a feature of the invention the method comprises applying to the locus, for example where the crop is sown and cultivated, sequential low doses of oxadiargyl. For example by treating the locus with a delayed release composition comprising oxadiargyl.

The delayed release composition, which constitutes a feature of the invention, may comprise, for example, an encapsulated composition comprising oxadiargyl itself or a composition containing it. The delayed release compositions may be prepared by known methods.

The encapsulated product may have a solid, outer wall, said wall comprising an inert material (a protective coating), generally having no substantial herbicidal activity.

The encapsulated product according to the present invention may comprise granules comprising oxadiargyl, each of these granules being encapsulated with a solid film comprising an inert protective coating material itself having no substantial herbicidal activity. Preferably the coating material is made from at least a barrier material and a surface active agent and/or plasticizer. The combination of both types of material result in the production of encapsulations which are capable of providing the required release properties.

Examples of barrier materials which may be selected from, and are not limited to, the following : fatty acids, polyglycerol esters of fatty acids, monoglycerides, diglycerides, gelatins, starches derived from corn, wheat, potato or milo vegetables, zein proteins, sucroesters, sucroglycerides, cellulose ethers, cellulose esters, chitin, chitosan, amylopectin or hydrocolloids and mixtures thereof.

Specific barrier materials include the following generic materials, along with, where appropriate, trade names that the materials are presently sold under: glyceryl esters of long chain fatty acids such as glyceryl monopalmitostearate (Geleol - Gattefosse Company), glyceryl palmitostearate (Biogapress - Gattefosse Company) and (Plurol WL1009 - Gattefosse Company); acetylated monoglycerides such as monoacetylated monoglycerides (Myvacet 5-07 - Eastman Kodak Company); hemisynthetic glycerides (Suppocire A and Suppocire D - Gattefosse Company); sucroglycerides derived from fatty oils such as coprah oil (Celynol LMO - Rhone- Poulenc SA), palm oil (Clynol MSPO 11 - Rhone Poulenc SA), and hydrogenated soybean oil and palm oil; cellulose acetate phthalate (Aquateric CD910 - FMC Corp.); modified celluloses such as ethylcellulose aqueous dispersions (Aquacoat - FMC Corp.), and hydroxyl propylcellulose (klucel EF - Aqualon Company); sucrose esters of fatty acids having an HLB value of from 7 to15 such as palmitate (Sucroester 15 - Gattefosse Company), and distearate (Sucroester 11 - Gattefosse Company); mixture of ethylcellulose, coconut oil, ammonium hydroxide and oleic acid (Surelease - Colorcon Company); gelatin (100, 175 and 250 bloom strength); starches such as high amylose corn starch (Hylon VII), pregelatinized corn starch (Ultratex 1 ), modified corn starch (Ultracet LT), waxy maize starch (Colflo 67), pregelatinized waxy maize starch (Instant Clearjel), modified waxy maize starch (Purity Gum 1773); gums such as carrageenan gum (Carrageenan IOTA), pectin gum (Unipectin HMI), guar gum, locust bean gum, and xanthan gum; long chain fatty acids having carbon chain length of from 9 to 21 carbon atoms such as capric acid, lauric acid, myristic acid, thdecylclic acid; gelatins having a bloom strength of greater than 100 (e.g., 100, 175, 250) and mixtures thereof.

Particularly preferred is the use of gelatin, chitosan, stearic acid and glyceryl monopalmitostearate.

The other component of the coating is a surface active agent or plasticizer material. These materials can function to reduce the thickness and provide flexibility to the coating material when applied to oxadiargyl and thereby enable the production of a controlled release material. The key criteria to be considered when selecting such materials is that they provide an optimally sized coating.

More particularly, the surface active agent functions to provide a uniformly distributed layer of the coating material to produce a strong thin coating whereas the plasticizer functions to help provide coatings which are thin, strong and do not easily break. Particularly preferred is the use of both surface active agents and plasticizer materials.

Examples of surface active agents which may be selected include the following: sucroesters, sucroglycerides, propylene glycol monoesters, ethoxylated monoglycerides, ethoxylated diglycerides, glycerol lacto esters of fatty acids, lecithin, polyoxyethylene sorbitan esters, sorbitan esters of fatty acids, stearoyl-2-lactylate, polyoxyethylene esters of fatty acids such as stearic acid, acetylated monoglycerides and mixtures thereof. Particularly preferred are sucroesters, polyoxyethylene sorbitan esters, specifically polyoxyethylene sorbate monooleate and mixtures thereof. Such materials are commercially available under the names of Sucroester 7 from the Gattefosse Company (sucrose distearate) and Tween 80 (polyoxyethylene sorbate monooleate). Several of the barrier materials, particularly the sucroesters can additionally function as the surface active agents. Other materials which have multiple functions include mono and diglycerides, polyoxyethylene esters of long chain fatty acids such as polyoxyethylene sorbate monooleate, sorbitan monoesters of long chain fatty acids and gelatins.

Preferred plasticizers include acetyl tributyl citrate (Citroflex A4), acetyl triethyl citrate (Citroflex A2), tricalcium phosphate, dicalcium phosphate or diethylphthalate and mixtures thereof. These materials function to produce very thin coatings, i.e., the entire coating comprising no more than from 2 to 10 percent by weight of the entire core material.

In practice, the barrier material is between from 80 to 100 percent by weight of the coating material, more preferably between from 90 to 95 percent by weight of the coating material. Further, the coating typically has a thickness ranging between from 3 to 20 microns, more preferably between from 5 to 10 microns.

To apply the coating to oxadiargyl any method which is commonly used to encapsulate herbicide materials may be selected. Examples of such methods include fluidized bed coating, coacervation, interfacial polycondensation polymerization, spray coating, pan coating or solvent film coating. Particularly preferred is the use of fluidized bed coating.

Under such a coating method, the oxadiargyl typically in the form of a powder is placed in a fluidized bed apparatus, (e.g. GLATT GPC G1 ) preferably equipped with top or bottom spray nozzles. A dispersion containing the coating material is then pumped into and atomised in the apparatus on the fluidized particle bed, typically by a hot air current. In practice, the solvent used to form the coating dispersion is typically water, although other solvents such as alcohols and glycols could be used.

The application of the dispersion to the powder typically takes from 15 to 240 minutes, depending on the thickness of the coating film desired. The coated material powder is then dried, typically from 1 to 60 minutes, resulting in the production of a coating of the coating material onto all external surfaces of the oxadiargyl.

In practice the core does not react with the coating and therefore, two discrete phases (e.g., core/shell particle morphology) are produced.

The granules of encapsulated oxadiargyl according to the present invention may be for example, in a powdered state or in a liquid or solid formulation, in association with an agriculturally acceptable diluent or carrier.

Compositions of the present invention provide a method for controlling the release of a herbicide in a range of soil types and edaphic conditions by modification of the ratios of oxadiargyl : carrier material, in order to achieve the most favourable release rates for optimal efficacy and selectivity.

Compositions of the present invention provide a method for reducing the release rate of herbicides, such as oxadiargyl, in soil thereby slowing the overall rate of degradation. Encapsulation in a matrix carrier increases the stability of the herbicide as it is protected from the components which may promote degradation, such as moisture or microbial activity.

By the term "pre-emergence application" is meant an application to the soil in which the weed seeds or seedlings are present before emergence of the crop. One example of a pre-emergence application is known as "pre-plant incorporated" (PPI), where the herbicide is incorporated into the soil before planting the crop. Another is where the herbicide is applied to the soil surface after sowing the crop. By the term "foliar activity" is meant herbicidal activity produced by application to the aerial or exposed portions of the weeds which have emerged above the surface of the soil. ln general, the application rate of oxadiargyl in compositions of the present invention is from 0.05 kg to 0.150 kg herbicidally active compound, preferably from 0.05 kg to 0.075 kg herbicidally active compound per hectare.

The compositions of the invention are generally applied to a locus pre-emergence of the weeds and crop plant, or early post-emergence. Preferably the compositions of the invention are applied pre-emergence.

According to a further feature of the present invention, there are provided compositions suitable for herbicidal use in the method of the invention comprising oxadiargyl (which may be encapsulated as hereinbefore described), in association with, and preferably homogeneously dispersed in, one or more compatible agriculturally-acceptable diluents or carrier and/or surface active agents [i.e. diluents or carriers and/or surface active agents of the type generally accepted in the art as being suitable for use on herbicidal compositions and which are compatible with oxadiargyl]. The term "homogeneously dispersed" is used to include compositions in which oxadiargyl is dissolved in other components. The term "herbicidal compositions" is used in a broad sense to include not only compositions which are ready for use as herbicides but also concentrates which must be diluted before use. Preferably, the compositions contain from 0.05 to 90% by weight of oxadiargyl. The herbicidal compositions may contain both a diluent or carrier and surface-active (e.g. wetting, dispersing, or emulsifying) agent. Surface-active agents which may be present in herbicidal compositions of the present invention may be of the ionic or non-ionic types, for example sulpho cinoleates, quaternary ammonium derivatives, products based on condensates of ethythene oxide with alkyl and polyaryl phenols, e.g. nonyl- or octyl-phenols, tristyryl phenols, condensates of ethylene oxide with alcohols, or carboxylic acid esters of anyhydrosorbitols which have been rendered soluble by etherification of the free hydroxy groups by condensation with ethylene oxide, alkali and alkaline earth metal salts of sulphuric acid esters and sulphonic acids such as dinonyl- and dioctyl-sodium sulphonosuccinates and alkali and alkaline earth metal salts of high molecular weight sulphonic acid derivatives such as sodium and calcium lignosulphonates and sodium and calcium alkylbenzene sulphonates.

Suitably, the herbicidal compositions according to the present invention may comprise up to 10% by weight, e.g. from 0.05% to 10% by weight, of surface-active agent but, if desired, herbicidal compositions according to the present invention may comprise higher portions of surface-active agent, for example up to 15% by weight in liquid emulsifiable suspension concentrates and up to 25% by weight in liquid water soluble concentrates.

Examples of suitable solid diluents or carriers are aluminium silicate, microfine silicon dioxide, talc, chalk, calcined magnesia, kieselguhr, tricalcium phosphate, powdered cork, adsorbent carbon black and clays such as kaolin, attapulgite, diatomaceous earth, mica, alumina oxide, titanium oxide and bentonite. The solid compositions (which may take the form of dusts, granules or wettable powders) are preferably prepared by grinding oxadiargyl with solid diluents or by impregnating the solid diluents or carriers with solutions of oxadiargyl in volatile solvents, evaporating the solvents and if necessary, grinding the products so as to obtain powders. Granular formulations may be prepared by absorbing the oxadiargyl dissolved in suitable solvents, (which may, if desired, be volatile) onto the solid diluents or carriers in granular form and, if desired, evaporating the solvents, or by granulating compositions in powder form obtained as described above. Solid herbicidal compositions, particularly wettable powders and granules, may contain wetting or dispersing agents (for example of the types described above), which may also, when solid, serve as diluents or carriers.

Liquid compositions according to the invention may take the form of aqueous, organic or aqueous-organic solutions, suspensions and emulsions which may incorporate a surface-active agent. Suitable liquid diluents for incorporation in the liquid compositions include water, glycols, glycol ethers, tetrahydrofurfuyl alcohol, acetophenone, cyclohexanone, isophorone, alkyl pyrrolidones, butylolactone, chlorinated toluene, xylene, mineral, animal and vegetable oils, esterified vegetable oils and light aromatic and naphthenic fractions of petroleum (and mixtures of these diluents). Surface-active agents, which may be present in the liquid compositions, may be ionic or non-ionic (for example of the types described above) and may, when liquid, also serve as diluents or carriers.

Powders, dispersible granules and liquid compositions in the form of concentrates may be diluted with water or other suitable diluents, for example mineral or vegetable oils, particularly in the case of liquid concentrates in which the diluent or carrier is an oil, to give compositions ready for use.

When desired, liquid compositions of oxadiargyl may be used in the form of self- emulsifying concentrates containing the active substances dissolved in the emulsifying agents or in solvents containing emulsifying agents compatible with the active substances, the simple addition of such concentrates to water producing compositions ready for use.

Liquid concentrates in which the diluent or carrier is an oil may be used without further dilution using the electrostatic spray technique. Herbicidal compositions according to the present invention may also contain, if desired, conventional adjuvants such as adhesives, protective colloids, thickeners, penetrating agents, spreading agents, stabilisers, buffers, sequestering agents, anti- caking agents, colouring agents and corrosion inhibitors. These adjuvants may also serve as carriers or diluents.

Unless otherwise specified, the following percentages are by weight. Preferred herbicidal compositions according to the present invention are encapsulations containing water dispersible granules which comprise from 1 to 90%, e.g. 25 to 75% of oxadiargyl, from 1 to 15%, e.g. 2 to 10%, of surface-active agent and from 5 to 95%, e.g. 20 to 60%, of solid diluent, e.g. clay, granulated with the addition of water to form a paste and then dried; aqueous suspension concentrates which comprise from 5 to 70% of oxadiargyl, from 2 to 10% of surface-active agent, from 0.1 to 5% of thickener and from 15 to 87.9% of water; wettable powders which comprise from 5 to 90% of oxadiargyl, from 2 to 10% of surface-active agent and from 8 to 88% of solid diluent or carrier; water soluble or water dispersible powders which comprise from 5 to 90% of oxadiargyl, from 2 to 40% of sodium carbonate and from 0 to 88% of solid diluent; liquid water soluble concentrates which comprise from 5 to 50%, e.g. 10 to 30% of oxadiargyl, from 0 to 25% of surface-active agent and from 10 to 90%, e.g. 45 to

85%, of water miscible solvent, e.g. triethylene glycol, or a mixture or water-miscible solvent and water; liquid emulsifiable suspension concentrates which comprise from 5 to 70% of oxadiargyl from 5 to 15% of surface-active agent, from 0.1 to 5% of thickener and from 10 to 84% of organic solvent, e.g. mineral oil; and emulsifiable concentrates which comprise 0.05 to 90%, and preferably from 1 to

60% of oxadiargyl, from 0.01 to 10%, and preferably from 39 to 98.99%, of organic solvent.

The water dispersible granules comprising oxadiargyl have a particle size of generally 10-2000 μm, preferably 300-1500 μm.

Herbicidal compositions according to the present invention may also comprise oxadiargyl in association with, and preferably homogeneously dispersed in, one or more other pesticidally active compounds and, if desired, one or more compatible pesticidally diluents or carriers, surface-active agents and conventional adjuvants as hereinbefore described.

Examples of other pesticidally active compounds which may be included in, or used in conjunction with, the herbicidal compositions of the present invention include herbicides, for example to increase the range of weed species controlled, for example those listed in the Pesticide Manual 11^th Edition (British Crop Protection

Council).

Pesticidally active compounds and other biologically active materials which may be included in, or used in conjunction with, the herbicidal compositions of the present invention, for example those hereinbefore mentioned, and which are acids, may, if desired, be utilised in the form of conventional derivatives, for example alkali metal and amine salts and esters.

The following Examples illustrate herbicidal compositions which may be used for the purpose of comparison in the present invention. Example C1 :

An emulsifiable concentrate is formed from:

Oxadiargyl 20% w/v

N-Methylpyrrolidinone (NMP) 25% w/v

Calcium dodecylbenzenesulphonate 4% w/v

(CaDDBS)

Nonylphenol ethylene oxide propylene oxide

Condensate (NPEOPO) 4% w/v

Aromatic solvent to 100 volumes by stirring NMP, oxadiargyl, CaDDBS, NPEOPO and Aromatic solvent until a clear solution is formed, and adjusting to volume with Aromatic solvent.

Example C2

A wettable powder is formed from:

Oxadiargyl 50% w/w

Sodium dodecylbenzenesulphonate 3% w/w

Sodium methyl oleoyl taurate 5% w/w

Sodium polycarboxylate 1 % w/w

Microfine silicon dioxide 3% w/w

China clay 38% w/w by blending the above ingredients together and grinding the mixture in an air jet mill.

Example C3

A suspension concentrate is formed from:

Oxadiargyl 50% w/v

Antifreeze (Propylene glycol) 5% w/v

Ethoxylated tristyrylphenol phosphate 0.5% w/v

Nonyl phenol 9 mole ethoxylate 0.05% w/v

Sodium polycarboxylate 0.02% w/v

Attaclay 1.5% w/v

Antifoam 0.003% w/v

Water to 100 volumes by stirring the above ingredients together and milling in a bead mill.

Example C4

A water dispersible granule is formed from:

Oxadiargyl 50% w/w

Sodium dodecylbenzenesulphonate 3% w/w

Sodium methyl oleoyl taurate 5% w/w

Sodium polycarboxylate 1 % w/w

Binder (Sodium lignosulphonate) 8% w/w china clay 30% w/w

Microfine silicon dioxide 3% w/w by blending the above ingredients together, grinding the mixture in an air jet mill and granulating by addition of water in a suitable granulation plant (e.g. Fluid bed drier) and drying. Optionally the active ingredient may be ground either on its own or admixed with some or all of the other ingredients.

The following non-limiting Examples illustrate the invention.

Unless otherwise stated percentages are by weight, and active ingredients were used as technical materials.

EXAMPLE 1

Compositions comprising 0.15ppm oxadiargyl were prepared and their stability in water analysed. To determine the release kinetics of oxadiargyl from different formulation types in water, the formulations were placed in petri dishes (with a depth of 3cm), sealed to prevent any solvent loss; stored at 25°C for the specified length of time then sampled (at a depth of 1cm) and analysed. The method of analysis was as follows. Each formulation mixture was analysed for the proportion of oxadiargyl released into water using standard High Performance Liquid Chromatography (HPLC) technology. This involves weighing a known amount of sample into a solvent system of 65:35, acetonitrile:distilled water (containing 0.07% of phosphoric acid) followed by injecting a known aliquot into the HPLC system. If the method calls for an internal standard with which to calibrate accuracy, then the internal standard is added to the extracted aliquot. The extracted sample is passed through a column (for example a TOSOH TSK-gel ODS-80TM column) packed with sorbent. Following elution the various components of the compositions are separated depending upon varying sorption capacities/hydrophilicity. The amount of the component is determined by the amount of ultraviolet light absorbed at specific wavelengths of the ultraviolet light. The amount of oxadiargyl released is calculated as the concentration of compound present in the water sample.

Table 1 Concentration of oxadiargyl in water (ppm)

Wherein WG represents a wettable granule formulation, and EC represents the commercial emulsifiable concentrate formulation "Raft™". Different profiles of the release of oxadiargyl from wettable granules and emulsifiable concentrates were obtained. The release of uniform concentrations of oxadiargyl from the WG formulation was observed from 1 to 288 hours. In comparison, oxadiargyl from the EC formulation appeared to be concentrated within the top 1cm of the water surface (the sampling point) initially, decreasing gradually over time. [Such high concentrations located within the surface layer of water may cause phytotoxicity in developing rice plants]. EXAMPLE 2

3g of each sample formulation (WG) were weighed into glass bottles with 350ml of water. The bottles were rolled on rollers at 100 revolutions per minute (rpm) for 15 minutes, after which the contents were poured onto a sieve (160μm pore size) and washed under running water for 5 minutes. Residual material on the sieve was dried at 60°C for 12 hours then weighed. The results are expressed as the percentage disintegration of the granules;

wherein M₀ represents the initial weight of the granules, and Mi represents the weight of non-disintegrated granules.

Table 2 Physical stability of WG formulations of oxadiargyl in the presence of a coating

Table 3 Physical stability of WG formulations of oxadiargyl in the presence of a binder

The presence of coatings on the wettable granules or binding materials within the granules containing oxadiargyl improve the physical stability of the formulation.

EXAMPLE 3

The experimental protocol as described in Example 1 was conducted using wettable granule formulations with different coatings or containing different binding agents (as defined in Example 2). The amount of oxadiargyl released from the formulations into solution was determined at several time intervals.

Table 4 Release of oxadiargyl from wettable granules with different coatings

Table 5 Release of oxadiargyl from wettable granules with different binders

EXAMPLE 4

Weed seeds of Echinochloa oryzicola, (ECHOR), Monochoria vaginalis (MOOVA) and Scirpus juncoides (SCPJU) were sown and formulations of oxadiargyl (as described in Example 2) applied at 6.3, 12.5, 25, 50, 75, 100 and 200g per hectare, five days after sowing. The efficacy of the oxadiargyl formulations on the weed species was observed 18 days after treatment and is expressed as percentage leaf sheath browning in the following tables:-

Table 6 Efficiency of oxadiargyl at 18 DAT on Scirpus juncoides (SCPJU)

Table 7 Efficiency of oxadiargyl at 18 DAT on Monochoria vaginalis (MOOVA)

Table 8 Efficiency of oxadiargyl at 18 DAT on Echinochloa oryzicola (ECHOR)

Wherein EC represents the commercial emulsifiable concentrate formulation, "Raft™".

The efficacy of oxadiargyl, when applied in compositions of the present invention, on SCPJU, MOOVA and ECHOR is comparable with that of the commercial EC formulation.

EXAMPLE 5

Seeds of transplanted rice (ORYSA) were sown in compost in a glasshouse with supplementary illumination (14 hours). Rice plants, were transplanted into paddy pots containing puddled light clay (organic matter 1 %, clay 29.0%, sand 30.0%, silt 40.0%, pH 6.9). 5 days after sowing the paddies were treated with oxadiargyl formulations at 6.3, 12.5 and 25g per hectare. The paddies were watered as necessary and the rice visually assessed for the percentage reduction in growth 5, 7 and 18 DAT.

Table 9 Selectivity (on transplanted rice) 5 DAT

Table 10 Selectivity (on transplanted rice) 7 DAT

Table 11 Selectivity (on transplanted rice) 18 DAT

Compositions of the present invention show good selectivity on transplanted rice from 5 to 18 DAT and at high application rates compared to the commercial EC formulation.

EXAMPLE 6

Seeds of ORYSA (transplanted rice), and weed species Echinochloa oryzicola (ECHOR), Monochoria vaginalis (MOOVA) and Lindernia Pyxidaria (LIDPY) were sown in concrete paddy pots containing puddled clay loam. The paddies were then treated with WG formulations of oxadiargyl encapsulated with coatings and/or containing a binding material, and a suspension concentrate (SC) formulation, at an application rate of 50g per hectare.

Table 12 Efficacy of WG formulations of oxadiargyl

Compositions of the present invention show good efficacy on ECHOR, MOOVA and LIDPY and are selective on transplanted rice.

Claims

1. A method for controlling the growth of weeds at a locus in a growing medium, which comprises treating the locus with a delayed-release composition comprising oxadiargyl to provide progressive release of oxadiargyl herbicide into the growing medium.

2. A method according to Claim 1 in which the delayed release composition comprises an encapsulated composition.

3. A method according to Claim 1 or 2 in which encapsulated water dispersible granules of oxadiargyl are used.

4. A method according to Claim 1 , 2 or 3 in which the granules of oxadiargyl have a particle size of from 10 to 2000μm.

5. A method according to any one of the preceding Claims in which the growing medium is soil.

6. A method according to any one of the preceding Claims in which the locus is a crop-growing locus.

7. A method according to Claim 6 in which the crop is rice.

8. A delayed release composition comprising oxadiargyl.

9. A composition according to Claim 8 in which encapsulated water dispersible granules of oxadiargyl are used.

10. A composition according to Claim 8 or 9 in which the granules of oxadiargyl have a particle size of from 10 to 2000μm.

11. A method according to Claim 1 substantially as hereinbefore described.

12. A composition according to Claim 8 substantially as hereinbefore described.