GB2115283A

GB2115283A - Herbicidal composition

Info

Publication number: GB2115283A
Application number: GB08302822A
Authority: GB
Inventors: Alistair Naismith Reid; Christopher Thomas Lake; Brian Bonney
Original assignee: Albright and Wilson Ltd
Current assignee: Solvay Solutions UK Ltd
Priority date: 1982-02-11
Filing date: 1983-02-02
Publication date: 1983-09-07
Also published as: GB2115283B; GB8302822D0

Abstract

Combinations of linuron and one or more phenoxy alkanoic acids have been found to exhibit a synergistic interaction when used as herbicides. Especially useful acids are those known as 2,4DB, MCPB and MCPA. The active ingredients may be applied separately or as a single formulation. The preferred formulations take the form of an emulsifiable concentrate of the acid in an organic solvent medium.

Description

SPECIFICATION Herbicidal composition This invention relates to novel combinations of known herbicides, to compositions containing these combinations, to methods for the preparation of such compositions and to methods of applying such combinations to the land.

The application of various synthetic chemicals to the land as herbicidal agents is accepted as part of the agricultural industry. In order to gain acceptance such chemicals must be effective in suppressing or preventing the growth of one or more types of weeds whilst not affecting the growth of the desired crop to any significant extent.

There is a constant demand in the industry for compositions which are more effective or cheaper or both and which can be formulated so asto be easily applied to the land in controlled quantities.

One group of chemicals which have been found to be useful as herbicides comprises the phenoxy alkanoicacidsoftheformula:

wherein n is an integer having a value offrom 1 to 4, R1 represents a hydrogen atom ora methyl group and R2, R3, R4 and R5which may be the same or different represent a hydrogen atom a halogen atom or, an alkyl group having from 1 to 4 carbon atoms and salts and ester derivatives thereof.

These phenoxy alkanoic acids (which term will hereinafterfor convenience be used to include salts and esters derived therefrom) have been found to be useful in varying degrees as herbicides for application to grasslands. They are not entirely effective even when used in carefully selected combinations in that certain weeds especially chickweeds are not controlled by the application of the herbicides at dosage levels which do not damagethegrass crops.

Another compound which is widely used as a herbicide is 3-(3,4 dichloro - phenyl) - 1 - methoxy -1 methylurea commonly known and for convenience hereinafter referred to as linuron. Linuron is widely applied to cereal and potatoes as a herbicide and has been proposed for application to grassland although it is not widely used in this area.

The application of more than one herbicidal agent either consecutively or in admixture to the land is common practice in the art. The combination of two or more known herbicides will give a result equal to the aggregate of the properties of the separate herbicides which result is predicted by means of what is known as the Colby formula.This formula can best be illustrated by reference to a hypothetical example employingtwoknown herbicidesAand B. Nowifthe application of A (at a particular dosage level) is known to provide 80% weed control (and hence leave 20% live weeds) and similarly the application of B (at a particular dosage level) is known to provide 70% weed control (and hence leave 30% live weeds) the Colby formula predicts that the application of those particular dosage levels of A and B in combination will leave a proportion of X% live weeds where 20 x 30% X= 100 = 6% Thus the combination is expected to provide 94% weed control.

We have now discovered the application of a combination of linuron with at least one phenoxy alkanoic acid of the type defined above or suitable derivative thereof provides a greater degree of weed control than would be predicted by the Colby formula i.e. that such a combination of herbicides appears to provide a synergistic interaction. Thus from one aspect our invention provides a method for controlling the growth of weeds on the land which comprises applying an effective quantity of linuron and at least one phenoxy alkanoic acid or a salt or ester derivative thereof as defined above thereto.

The greater degree of control which can be achieved using this novel combination of herbicides enables the grower to achieve improved weed control by applying the conventional dosage levels of these herbicides to his land and thereby avoiding damage to the crop or less preferably to achieve the conventional degree of weed control whilst applying a lower dosage of each herbicide than would normally be required.

Preferred phenoxy alkanoic acids for present use include those having the above formula wherein at least one and preferably no more than two ofthe substituents R2, R3, R4 or R5, more preferably R2 and/or R5 represents a chlorine atom whilst the remainder represent hydrogen atoms. Also preferred arethose phenoxyalkanoicacidswhereinthose substituents which represent alkyl groups represent methyl groups and particularlythosewherein one of R2 or R5 represents a methyl group. In this case R3 and R4 preferably represent hydrogen atoms. In both cases R1 also preferably represents a hydrogen atom.

Particular phenoxy alkanoic acids for use according to the present invention include 4 - (2,4 dichloro phenoxy) butyric acid commonly known and hereinafter referred to as 24DB, (4chloro-2-methyl phenoxy) butyric acid commonly known and hereinafter referred as MCPB; (4-chloro-2-methyl phenoxy) acetic acid commonly known and hereinafter referred to as MCPA, 2,4,5 trichloro phenoxyacetic acid, 2-(4-chloro-2 methyl phenoxy) propionic acid, 2-(2,4-dichloro phenoxy) propionic acid, 2, (2,4,5 trichloro phenoxy) propionic acid, 4(4-chloro-2methyl phenoxy) butyric acid, 4 (2,4 dichlorophenoxy) butyric acid and 4-(2,4,5 trichloro phenoxy) butyric acid.

Preferred phenoxy alkanoic acids are 2,4DB, MCPA and MCPB. A particuiarly preferred phenoxy alkanoic acid for present use is a combination of 2,4DB with at least one of MCPA and MPCB, the combination of 2,4DB and MCPA being especially preferred.

The phenoxy alkanoic acid may be applied to the land as such or as a salt or an ester derivative thereof.

The most commonly employed salts are the alkali metal ammonium amine and alkanolamine salts especially the sodium and potassium or mixed sodium/potassium salts and the dimethylamine trimethyiamine, diethylamine, triethylamine and mono-ethanolamine salts although other salts e.g.

the calcium or magnesium salts may be preferred for use in particular methods of application. The ester derivatives which are useful are those derived from alcohols which preferablycompriseatleastfour carbon atoms. The preferred esters for present use arethe butyl iso-octyl and butoxy-ethyl esters. For reasons of convenience, this specification usesthe term phenoxy alkanoic acids to include the salts or ester derived therefrom where appropriate.

The herbicidal activity of the phenoxy alkanoic acids varies according to the form in which it is supplied. In general the ester derivatives are from 1.2 to 1.5 times more effective than the corresponding salt derivatives or the free acids from which they are derived. As a consequence of this variation in activity the quantities and relative proportions of the phenoxy alkanoic acids may be appropriately adjusted where the ester derivative is employed.

The synergism between linuron and the phenoxy alkanoic acid is observed through all possible ranges of proportions. In general, the weight ration of linuron to phenoxy aklanoic acid will be in range 1:200 to 50:1 more preferably in the range 1:70 to 7:1. The weight ratio of linuron to the total weight of phenoxyalkanoic acid preferably in the ratio 1:20 to 1:1.

The quantities of the active ingredient applied to the land will vary according to the degree of weed control described and the need to minimise any damageto the desired crop. In general, the methods ofthis invention will be carried out by the application offrom lotto 250 gms preferablyfrom 30to 200 gms and most preferably from 75 to 150 gms per hectare of linuron and from 100 to 5000 preferablyfrom 200 to 3000 and most preferablyfrom 600 to 2000 gms per hectare of phenoxy aklanoic acid. In its preferred embodiment wherein the phenoxy aklanoic acid comprises a mixture of 2,4DB with at least one of MCPA or MCPB our invention involves the application offrom 400 to 1800 gms of 2,4DB per hectare and from 30to 250 gms of MCPAand/or MCPB per hectare.

The active ingredients may be applied to the land using any of the conventional techniques known in the art.

The active ingredients may be applied to the land either separately or preferably may be formulated into a single composition which can be applied to the land in a single step. The active ingredients are normally formulated as concentrates which are diluted immediately prior to their application to the land. Where a single composition containing two or more active ingredients is formulated the relative proportions of those active ingredients will normally be the same as is intended to be applied to the land so that the composition can be prepared for use by means of a single dilution step.

The formulation of the active herbicidal ingredients and the application of such formulations to the land may be achieved using a wide variety of conventional techniques involving the addition of the active ingredients to a suitable carrier. Thus for example the active ingredients may be absorbed upon the surface of a finely divided solid and applied to the land as a dust. Suitable solids include attapulgite kieselguhr Fullers earth, talc etc.

Alternativelythe active ingredients may beformulated as wettable powders by absorption upon the surface of a finely divided solid together with a suitable wetting agent so as to form a particulate material. The solid materials used may be any of those which are useful in the formulation of dusts but usually they will be more finely divided. The particulate material is added to an appropriate solvent usuallywaterto provide a solution or suspension of the active ingredients.

Athird alternative is the formulation of an aerosol composition by admixing the active ingredients with a propellant e.g. a polyhalogenated alkane and possibly with an appropriate solvent.

Another alternative is the preparation of a flowable suspension as a concentrate for dilution at the point of use by grinding the active ingredients with a liquid suspension medium which is usuallywater a thickening agent and a suspending agent. Suitable thickening agents include polysaccharide gums, xanthan gum, carboxymethylcellulose, guar gum, alginates, mineral clays, bentonites, attapulgites etc. Suitable suspending agents include anonic, nonionic and cationic surfactants, emulsifiers and dispersing agents. Flowable suspensions may optionally include other additives such as preservatives, anti-foaming agents and freezing point depressants.

Another alternative istheformation of a solution or emulsion with a liquid solvent or carrier. The active ingredients can be dispersed in an appropriate liquid vehicle. This vehicle may be water or an organic solvent or a mixture of solvents. The choice of liquid vehicle will depend upon the nature ofthe active ingredient. Thus ingredients which are soluble in or emulsifiable in waterwill usually be dispersed in waterfor reasons of economy. Alternatively organic solvents may be employed. The most preferred organic solvents are the hydrocarbons derived from petroleum although it may be necessaryto incorporate a co-solvent in certain instances in order to completely dissolve the active material.

Compounds useful as wetting agents, dispersing agents emulsifying agents and surfactants include all those compounds which are termed as surface active agents in the art. Such compounds are well known in the art. Suitable materials include anionic surface active agents, for example soaps, mono- or di-esters of phosphoric acid with fatty alcohol ethoxylates or salts of such esters, fatty alcohol sulphates such as sodium dodecyl sulphate, sodium octadecyl sulphate or sodium cetyl sulphate, ethoxylated fatty alcohol sulphates, ethoxylated alkylphenol sulphates, lignin sulphonates, petroleum sulphonates, alkyl-aryl sul phonates, such as alkyl-benzene sulphonates or loweralkylnaphthalenesulphonatese.g. butylnapthalene sulphonate, salts of sulphonated naphthalene-formaldehyde condensates, salts of sulphon ated phenol-formaldehyde condensates, or more complexsulphonatessuch astheamidesulphonates e.g. the sulphonated condensation product of oleic acid and N-methyl taurine of the dialkyl sulphosuccinatese.g. the sodium sulphonate of dioctyl succinate.

Another class of surface active agents which are useful are the nonionicagents,forexample condensation products of fatty acid esters, fatty alcohols, fatty acid am ides or fatty-, alkyl- or alkenyl-substituted phenols with ethylene oxide, fatty esters of polyhydric alcohol esters e.g. sorbitan fatty acid esters, condensation products of such esters with ethylene oxide e.g. polyoxyethylene sorbitan fatty acid esters, blockcopolymers of ethylene oxide and propylene oxide, acetylenic glycols such as 2,4,7,9tetramethyl-5-decyn-4,7-diol, or ethoxylated acetylenic glycols.

The surface active agents may also comprise cationic agents, for example alkyl- and/or arylsubstituted quaternary ammonium compounds such as cetyl trimethylammoniu m bromide or ethoxylated tertiaryfatty amines.

Preferred surface active agents for present use includeethoxylatedfattyalcoholsulphates, lignin sulphonates, alkyl-aryl sulphonates, salts of sulphonated naphthalene-formaldehyde condensates, salts of sulphonated phenol-formaldehyde condensates, dialkyl sulphosuccinates, alkyl phenol ethoxylates and fatty alkyl ethoxylates.

Combination ofnonionicand anionic dispersing agents offer advantages in terms of improved dispersing power and such combinations are more preferably employed in mostformulations. Linuron is substantially insoluble in water and is conventionally applied in the form of an emulsifiable concentrate in an appropriate solvent e.g. which composition may obtain other ingredients such as surfactants or combined with solid diluents and wetting agents.

The combination of linuron and the phenoxy alkanoic acids is preferably made up into a single formulation incorporating a carrierwhich can be applied to the land in a single operation. Such formulations are believed to be novel and thus from anotheraspect our invention provides a herbicidal composition which comprises an active ingredient of amixtureoflinuron and at least one phenoxy alkanoic acid having the formula

wherein n is an integer having a value of from 1 to 4, R1 represents a hydrogen atom or a methyl group and R2, R3, R4 and R5which may be the same or different represent a hydrogen atom a halogen atom, or an alkyl group having from 1 to 4 carbon atoms or a salt or an ester derivative thereof together with a suitable carrier.

The novel compositions can be made up in any of the forms referred to above. The precise content of these compositions will be varied according to known criteria in accordance with conventional techniques which are well known in the art. Thus since linuron is not sufficiently water soluble to be formulated as an aqueous solution it can only be suspended in aqueous media or dissolved in an organic solvent.

The phenoxy-alkanoic acids can either be used in the form of their salts which can be dissolved in an aqueous medium orintheform oftheirorganicester derivatives which can be dissolved in an organic solvent. These restrictions are well known in the art and the novel compositions are prepared taking them into account in the normal way. They may be made up in a novel form e.g. as a suspension of a salt of a phenoxy alkanoic acid in an organicsolvent contain- ing linuron or as a suspension of linuron in an aqueous solution ofthe salt ofthe phenoxy alkanoic acid. The preferred form of the novel composition is an emulsifiable concentrate of linuron and a solvent soluble ester of one or more phenoxy alkanoic acids since this can be diluted and sprayed onto the land in a single operation.Preferred solvents for use according to this aspect of our invention include aliphatic hydrocarbons such as kerosene, gas oil or white spirit; aromatic hydrocarbons such as heavy aromatic naptha, andxylene. Wherearomaticsolventsform the majority orthe whole of the solvent medium or a concentrate, it may be necessary to add a suitable co-solventin orderto dissolve all of the linuron.

Suitable co-solvents include cyclohexanone and isophorone.

These preferred compositions may contain from 10 to 100 gms/litre of linuron and from 100 to 500 gms litre of a phenoxy alkanoic acid when manufactured as a concentrate. At the point of application they are preferably diluted 20 to 200 or preferably 40 to 100 times with water in order to simplify their application to the land at the level of application of active ingredients which is desired.

Such compositions may advantageously include a surface active agent. Preferably a blend of anionic and non-ionic surface active agents are employed eg.

a blend of an alkyl benzene sulphonate and an ethoxylated alcohol or alkyl phenol.

The novel active ingredients may be applied in a single or in consecutive steps to a variety of crops where it is desired to suppress weed growth. As noted above they find particular application to cereal crops and to newly sown and established grassland, including clover. Thus they can usefully be applied to land bearing winter sown barley oats and wheat, spring sown barley oats and wheat, undersown cereals and direct sown leys. When applied in appropriate dosages at the appropriate stage of crop development the novel combination of herbicides is especially effective in suppressing the growth of Black-bindweed, Charlock, Common Chickweed, Common Fumitory, Common Orache, Common Poppy, Corn Buttercup, Fat-hen, Field Penny-cress, Knotgrass, Pale Persicaria, Redshank, Shepherd's-purse, Small Nettle, Smooth Sow-thistle, Wild Radish.The novel methods and compositions are especially valuable in controlling the growth of Chickweed and Shepherd's purse. The dosage levels mayvarf through a wide range depending upon the particular application, upon the degree of weed growth control which is desired, and upon the particular phenoxy alkanoic acid or acid mixture which is employed. The novel combination of herbicides may also be employed in combination with other known herbicides.

In general the dosage of linuron applied is in the range 1 Oto 5000 gms/hectare preferably20 to 1000 and most preferably50to 500 gms-hectare. The dosage of phenoxy alkanoic acid mayvaryfrom 50to 10,000 gmsShectare e.g. 250 to 7000 preferably 5000 and most preferably 500 to 3000 gms/hectare.

The invention is illustrated by the following examples: Example I A novel composition according to the invention was made up as an organic solution according to the following formulation.

LINURON (Technical Grade) 25 gms 24DB Butyl ester 320 gms MCPA Iso-octyl ester 56 gms Isophorone 30 gms NANSAEVM7O 30gms Empilan KA5* 70 gms Xylene made up to 1 litre *a proprietary brand of a fatty alcohol ethoxylate sold byAlbright & ilson Limited which is a 5 mole ethoxylate of a predominantly C10-C12 straight chain alcohol which contains no significant quantity of water.

Example2 A novel composition was made up as an organic solution according to the following formulation:- Linuron Technical 31.6 gil 2,4-DB Butyl ester 275 gil MCPA Iso-octyl ester 47.6 gil Cyclohexanone 20 g/l Sandozol LDR. 30 9/l Sandozol LMN 50 g/l Shellsol A to 1 litre SANDOZOL LC)R is a proprietory brand of a blend of anionic and nonionic surfactants sold by the Sandoz Products Limited.

SANDOZOL LMM is a proprietory brand of aliphatic polyoxyethylene blend of surfactants sold by the Sandoz Products Limited.

SHELLSOLAisa proprietory brand of a high aromatic content hydrocarbon solvent containing 31.3% 1,2,4 trimethylbenzene and 47.5% of other C9 aromatics.

Example 3 Atrial was carried out at a single grassland location involving the application of (a) linuron (b) a mixture of phenoxy alkanoic acids and (c) a combination of linuron and the same phenoxy alkanoic acids. Each treatment was applied to four separate strips. The overall weed control was assessed as a percentage as compared with untreated control strips.

The specific formulations applied were as followed (a) LINURQN 15--a soluaicn containing 150 gms/litre sf linuron inxyleneand isophorone (b) FP -a a solution containing 220 gms/litre of 2,4-DB (in the form of the butyl ester) and 30 gms/l itre of MCPA (in the form ofthe iso-octyl ester) in kerosene as solvent.

(c) FP 252 - a solution containing 30 gmsilitre linuron 220 gms/litreof 2,4-DB (intheform of the butyl ester) and 30 gmsilitre of MCPA in the form of the iso-octyl ester) in kerosene as solvent.

The results shown in the following table together with the % mean control predicted by the Colby formula for the weed control expected from the application of both linuron and the phenoxy aikanoic acids on the basis of the performances of the treatments (a) and (b).

Treatment Rate/HA Dosage Mean Weed (litres) (gms) Control % (a) Linuron 15 1.0 150 85.0 (b) FP 251 5.0 1250 72.5 (c) FP 252 5.0 150+1250 99.5 Colby Prediction {a: b) 95.9 Thus the mean weed control achieved is greater than predicted indicating synergism between the active ingredients.

Example 4 Trials were carried out at seven grassland locations involving the application of each of the specific formulations (a), (b) and (c) described in Example 3, to four strips of each trial The control of Common Chickweed was asessed as a percentage as compared ss ith untreated control strips.The results are shown in thelEollowing table:- Treatment Rate/HA Dosage Mean Chickweed (litres) (grams) Control % (a) Linuron 15 0.5 75 47.8 (b) FP 251 2.5 625 27.5 (c) FP 252 2.5 75+625 81.0 Colby Production (a+b) 62.2 Example 5 Atrial was carried out at a single grassland location involving the application of each of the specific formulations (a), (b) and (c) described in Example 3, to four separate strips. The control of Shepherdspurse was assessed as a percentage compared with untreated control strips. The results are shown in the following table: Treatment Rate/HA Dosage Mean Shepherds (litres) (grams) purse Control % (a) Linuron 15 0.5 75 35.0 (b) FP 251 2.5 625 40.0 (c) FP 252 2.5 75+625 95.0 Colby Production (a+b) 61.0

Claims

1. A method for controlling the growth of weeds ontheland,whichcomprisesapplying an effective quantity of linuron and at least one phenoxy alkanoic acid oftheformula

wherein n is an integer having a value offrom 1 to 4, R1 represents a hydrogen atom ora methyl group R2, R3, R4 and R5 which may be the same or different, represent a hydrogen atom, a halogen atom or an aklyl group having from 1 to 4 carbon atoms in the form ofthe acid, or a salt or an ester derivative thereof to the land.

2. A method according to claim 1, which comprises applying a quantity offrom 10 to 5000 gms per hectare of linuron and from 50 to 10,000 gms per hectare of phenoxy alkanoic acid to the land.

3. A method according to claim 2 which comprises applying 30to 200 gms per hectare of linuron to the land.

4. A method according to claim 3 which comprises applying from 75to 150 gms per hectare of linuron.

5. A method according to any of the preceding claims, which comprises applying from 100 to 5000 gms per hectare of phenoxy alkanoic acid.

6. A method according to claim 5, which comprises applying from 200 to 3000 gms per hectare of phenoxy alkanoic acid.

7. A method according to claim 6, which comprises applying from 600 to 2000 gms per hectare of phenoxy alkanoic acid to the land.

8. A method according to any of the preceding claims wherein the ratio of the weight of linuron applied to the land to the weight of phenoxy alkanoic acid which is applied to the land is in the range 1:200 to 50:1.

9. A method according to claim 8, wherein said ratio is in the range 1 :7to 7:1.

10. A method according to claim 9, wherein said ratioisintherange1:20to1:1.

11. A method according to any of the preceding claimswhernin the phenoxy alkanoic acid is ofthe formula 1, wherein at least one ofthe substituents, R2, R3, R4 and R5 represents a chlorine atom.

12. A method according to claim 11, wherein no morethantwoofthesubstituents, R2, R3, R4and R5 represent chlorine atoms.

13. A method according to either of claims 11 or 12, wherein the substituents, R2, R3, R4 and R5, which do not represent chlorine atoms, represent hydrogen atoms.

14. A method according to any of claims 1 to 10, wherein the substituents, R2, R3, R4 and R5 which represent alkyl groups represent methyl groups.

15. A method according to claim 14, wherein one of R2 or R5 represents a methyl group and the other represents a hydrogen atom.

16. A method according to either of claims 14 or 15, wherein R3 and R4 represent hydrogen atoms.

17. A method accordingto any of the preceding claims wherein R1 represents a hydrogen atom.

18. A method according to any of claims 1 to 16 wherein the phenoxy alkanoic acid is selected from the group comprising 4- (2,4dichloro phenoxy) butyric acid, 4-(4 chloro -2-methyl phenoxy) butyric acid; (4chloro -2-methyl phenoxy) acetic acid, 2,4,5 trichloro phenoxy acetic acid, 2-(L4-ch I o 2-(4-chloro-2-methyl phenoxy) acetic acid; 2,4,5 tri chloro phenoxy acetic acid, 2-(4-chloro-2-methyl phenoxy) propionic acid, 2,(2,4,5 trichloro phenoxy) propionic acid; 4(4-chloro2-methyl phenoxy) butyric acid, 4(2,4-dichlorophe- noxy) butyric acid and 4-(2,4,5 trichloro phenoxy) butyric acid.

19. A method according to claim 18,wherein the phenoxy alkanoic acid is selected from the group comprising 4-(2,4 dichlorophenoxy) butyric acid; 4-(4 chloro-2-methyl phenoxy) butyric acid, (4-chloro-2methyl phenoxy) butyric acid and (4 chloro-2-methyl phenoxy) acetic acid.

20. A method according to claim 19, wherein the phenoxy aklanoic acid is a combination of 4-(2,4, dichlorophenoxy) butyric acid with at least one of 4-(4-chloro-2-methyl phenoxy) butyric acid and (4chloro-2-methyl phenoxy) acetic acid.

21. A method according to claim 20, wherein the 4-(2,4 dichlorophenoxy) butyric acid is combined with {4-chloro-2-methyl phenoxy) acetic acid

22. A herbicidal composition which comprises active ingredients and a carrierwherein the active ingredient comprises a mixture of linuron with at least one phenoxy alkanoic acid having the formula

wherein n is an integer having a value of from 1 to 4, R represents a hydrogen atom or a methyl group, R2, R3, R4and Which may be the same or different, represent a hydrogen atom, a halogen atom or an alkyl group having from 1 to 4 carbon atoms, or a salt or an ester derivative thereof.

23. A composition according to claim 22, wherein at least one of the substituents R2, R3, R4 or R5 represents a chlorine atom.

24. A composition according to claim 23, wherein those ofthesubstitutents, R2, R3, R4and R5which do not represent chlorine atoms, represent hydrogen atoms.

25. A composition according to claim 22, wherein at least one ofthe substituents, R2, R3, R4 and R5 representga methyl group.

26. A composition according to claim 25, wherein one ofthe substituents, R2 or R5 represents a methyl group and the other represents a hydrogen atom.

27. A composition according to claim 26, wherein R3 and R4 represent hydrogen atoms.

28. Acomposition according to any of claims 22 to 27, wherein R1 represents a hydrogen atom.

29. Acomposition according any of claims 22 to 27, wherein the phenoxy alkanoic acid is selected from the group comprising 4-(2, 4 dichloro phenoxy) butyric acid, 4-(4 chloro -2-methyl phenoxy) butyric acid; (4 chloro-2- methyl phenoxy) acetic acid; 2,4,5 tri chloro phenoxy adcetic acid, 2-(4-chloro-2-methyl phenoxy) acetic acid, 2,4,5 trichloro phenoxy acetic acid, 2-(4-chloro-2-methyl phenoxy) propionic acid 2(2,4,5 trichloro phenoxy) propionic acid; 4(4-chloro2-methyl phenoxy) butyric acid 4-(2,4-dichlorophenoxy) butyric acid and 4-(2,4,5 trichloro phenoxy (butyric acid).

30. A composition according to claim 29, wherein the phenoxy alkanoic acid is selected from the group comprising 4-(2,4 dichlorophenoxy) butyric acid; 4-(4 chloro-2-methyl phenoxy) butyricacid and (4chloro2-methyl phenoxy) acetic acid.

31. Acomposition according to claim 30, wherein the phenoxy alkanoic acid is a combination of 4-(2,4 dichlorophenoxy) butyric acid with at least one of 4-(4-chloro-2-methyl phenoxy) butyric acid and (4chloro-2-methyl phenoxy acetic acid.

32. Acomposition according to claim 31, wherein the 4(2,4 dichlorophenoxy) butyric acid is combined with (4chlorn-2-methyl phenoxy) acetic acid.

33. A composition according to any of claims 22 to 32 wherein the phenoxy alkanoic is present in the form of an ester.

34. A composition according to any of claims 33 wherein the ester is formed with an alcohol having at leastfourcarbon atoms.

35. A composition according to either of claims 33 or 34, wherein the ester is selected from the group comprising the butyl, iso-octyl and butoxy-ethyl esters.

36. Acomposition according to any of claims 33 to 35, which comprises a solvent; a solvent soluble ester ofthe phenoxy alkanoic acid, linuron and an emulsifying agent.

37. A composition according to claim 36, wherein the solvent is selected from the group comprising kerosene, gas oil, white spirit, heavy aromatic naptha andxylene.

38. A composition according to any of claims 22 to 37, which comprises from lotto 100 gms per litre of linuron and from 100 to 500 gms of phenoxy alkanoic acid.

39. Amethodaccordingto anyofclaims 1 to 21 substantially as hereinbefore described with refer ence to the foregoing examples.

40. A herbicidal composition according to any of claims 22 to 38 substantially as hereinbefore described with reference to the foregoing examples.