GB2128090A

GB2128090A - New herbicidal method

Info

Publication number: GB2128090A
Application number: GB08326411A
Authority: GB
Inventors: Leslie Victor Hunt; Ponnan Veerasekaran
Original assignee: May and Baker Ltd
Current assignee: May and Baker Ltd
Priority date: 1982-10-05
Filing date: 1983-10-03
Publication date: 1984-04-26
Also published as: GB2128090B; GB8326411D0

Abstract

The trimethylamine and triethylamine salts of bromoxynil may be used to control selectively the growth of broad-leafed weeds by post-emergence application in maize and sorghum crops. Herbicidal compositions containing these salts and a process for their preparation are described.

Description

SPECIFICATION New herbicidal method This invention relates to a new method for the control of weeds in crops of maize and sorghum.

It is known, for example from British Patent No. 1,030,249 and British Patent No 1,067,032, that 3,5-dibromo-4-hydroxybenzonitrile (hereinafter referred to as 'bromoxynil') and its esters and alkali metal, alkaline earth metal, ammonium and amine salts, possess valuable herbicidal properties, more especially for the selective control of broad-leafed weeds in cereal crops by post-emergence application. (By the term 'post-emergence application', as used in the present specification, is meant application to the aerial or exposed portions of broad-leafed weeds after emergence above the surface of the soil).

Bromoxynil has been used extensively as a herbicide for many years, the vast preponderance of this usage being in the form of the octanoate ester or an alkali metal salt, especially the potassium salt, of bromoxynil, for the selective control of broad-leafed weeds in cereal crops by post-emergence application.

Bromoxynil esters, particularly the octanoate ester, have been used extensively for post-emergence broad-leafed weed control in small grain cereals, especially wheat, barley and oats, giving good control of the weeds without causing significant damage to the small grain cereal crop. However, the use of bromoxynil octanoate for post-emergence broad-leafed weed control in the wider-leafed cereals maize (Zea mays) and sorghum (Sorghum bicolor) has been restricted owing to transient phytotoxicity, which occurs in the form of necrosis of the sprayed leaves, caused to the crop plant. The margin of safety between the rate of application of bromoxynil octanoate required for effective control of broad-leafed weeds and the rate of application of bromoxynil octanoate which causes damage to crops of maize and sorghum is narrow.

Bromoxynil octanoate has, therefore, a narrow margin of selectivity or a low selectivity index (the ratio between the rate of application of a herbicide tolerated by the crop and the rate of appliction of the herbicide required for satisfactory weed control) when used to control the growth of broad-leafed weeds in maize and sorghum crops by post-emergence application. In marked contrast, bromoxynil octanoate has a high selectivity index in controlling the growth of broad-leafed weeds by post-emergence application in small grain crops, such as wheat, where it has been used successfully for many years.

Alkali metal salts of bromoxynil, particularly the potassium salt, are tolerated by small grain cereals and maize and sorghum at much higher rates of application than is the case with bromoxynil octanoate, but the control of the growth of broad-leafed weeds which is obtained is considerably poorer and less reliable than that produced by bromoxynil octanoate. For this reason, there has been no extensive use of bromoxynil potassium salt alone for weed control in cereals, although it has often been used admixed with other herbicides in herbicidal formulations used for the control of broad-leafed weeds in small grain cereal crops.

Accordingly, neither of the two bromoxynil derivatives which have hitherto been widely used for controlling the growth of broad-leafed weeds in small grain cereal crops, namely bromoxynil octanoate and bromoxynil potassium salt, are extensively used to control the growth of weeds in maize or sorghum crops.

Numerous amine salts of bromoxynil have been described as herbicides but none have hitherto been used extensively in agriculture.

As a result of research and experimentation, it has now been unexpectedly found that the trimethylamine and, more especially, the triethylamine salts of bromoxynil (hereinafter referred to collectively as the 'bromoxynil trimethyl- and triethyl-amine salts') are very much more active in the control of broad-leafed weeds than bromoxynil potassium salt while being substantially less damaging to maize (Zea mays) and sorghum (Sorghum bicolor) than bromoxynil octanoate.Accordingly, the bromoxynil trimethyl- and triethyl-amine salts as herein before defined have a much greater margin of selectivity or selectivity index than bromoxynil octanoate on the control of the-growth of broad-leafed weeds by post-emergence application in maize and sorghum crops and are substantially more active, with a greater margin of selectivity, in controlling the growth of broad-leafed weeds by post-emergence application in maize and sorghum crops than bromoxynil potassium salt, thereby representing a major advance in the control of broad-leafed weeds in crops of maize and sorghum.Bromoxynil trimethylamine and triethylamine salts are also more active, with a much greater margin of selectivity, in controlling the growth of broad-leafed weeds by post-emergence application in maize and sorghum crops than other amine salts of bromoxynil which have been tested, i.e bromoxynil triethanolamine, tri-n-propylamine, tri-n-butylamine, methyl-di-noctylamine and ammonium salts.The bromoxynil trimethyl- and triethyl-amine salts, and more especially bromoxynil triethylamine salt, are satisfactorily tolerated by maize or corn (Zea mays) and sorghum (Sorghum bicolor) at rates of application, in particularoffrom 100 to 10009 p.e./hectare, and more especially of from 150 to 6009 p.e./hectare, which provide satisfactory control of the growth of broad-leafed weeds by post-emergence application. (By the term 'p.e.' as used in the present specification is meant 'phenol equivalent' or the bromoxynil content of the trimethylamine or triethylamine salt of bromoxynil or other bromoxynil derivative applied).

Accordingly, the present invention provides a method for the selective control of broad-leafed weeds in an emerged crop of maize (Zea mays) or sorghum (Sorghum bicolor) which comprises the post-emergence application to the broad-leafed weeds in a crop of maize or sorghum of a herbicidally-effective amount which does not cause substantial permanent damage to the crop of the trimethylamine salt of bromoxynil or, preferably, the triethylamine salt of bromoxynil, particularly at a rate of application of from 100 to 10009 p.e./hectare and more especially at a rate of application of from 150 to 6009 p.e./hectare. Bromoxynil trimethyl- and triethyl-amine salts may, in particular, be used, according to the present invention, to control the growth of broad-leafed weed speciesAbutllon theophrasti, Amaranthus spp, e.g.Amaranthus retroflexus, Ambrosia artemisiifolia, Amsinkia intermedia, Anchusa arvensis, Anthems cotula, Ascelepias spp., Aethusa cynapium, Atriplex patula, Brassica kaber, Brassica nigra, Capsella bursa-pastoris, Centaurea cyanus, Chenopodium album, Chorispora tenella, Datura stramonium, Descurainea sophia, Fagopyrum tartaricum, Galinsoga parviflora, Helianthus annuus, lpomea spp., e.g. lpomea purpurea and Ipomea hederifolia, Kochia scoparia, Lapsana communis, Lithospermum arvense, Matricaria recutita, Matricaria inodora, Myosotis arvensis, Papaverrhoeas, Plantago media, Polygonum spp., e.g.Polygonum aviculare, Polygonum convolvulus, Polygonum lapathifolium, Polygonum persicaria, Polygonum pensylvanicum and Polygonum scab rum, Portulaca oleracea, Raphanus raphanistrum, Senecio vulgaris, Sida spinosa, Silene alba, Sinapis arvensis, Solanum nigrum, Solanum elaeagnifolium, Sonchus asper, Sonchus oleracea, Thlaspi arvense, Veronica persica and Xanthium spp., e.g. Xanthium strumarium, Xanthium pensylvanicum and Xanthium canadensis, in maize and sorghum crops by post-emergence application, and more especially to control the growth of Abutilon theophrasti, Amaranth us retroflexus, Chenopodium album, Ipomea purpurea, Polygonum lapathifolium, Solanum nigrum and Xanthium strumarium, which present particularly difficult problems of weed control in maize and sorghum crops.

It is to be understood that in carrying out the method of controlling the growth of broad-leafed weeds according to the present invention, mixtures of the trimethylamine salt of bromoxynil and the triethylamine salt of bromoxynil in any proportions may, if desired, be used.

Bromoxynil trimethyl- and triethyl-amine salts may be used alone to control the growth of broad-leafed weeds in maize or sorghum crops by post-emergence application or may be applied to control the growth of broad-leafed weeds in maize or sorghum crops by post-emergence application in conjunction with other herbicides which control the growth of monocotyledonous, e.g. grass, weeds and/or which are herbicidally active by residual or pre-emergence application and/or which possess persistent herbicidal activity and which are well tolerated by maize and sorghum. (By the terms 'residual application' and 'pre-emergence application' is meant application to the soil in which the weed seeds or seedlings are present before emergence of the weeds above the surface of the soil).Suitable herbicides include atrazine (2-chloro-4ethylamino-6-isopropylamino-1 ,3,5-triazine), simazine [2-chloro-4,6-bis(ethylamino)-1 ,3,5-triazinej, cyanazine [2-(4-chloro-6-ethylamino-1 ,3,5-triazin-2-ylam ino)-2-methyl propionitrile], propazine [2-chloro-4,6bis(isopropylamino)-1 ,3,5-triazine], terbuthylazine (2-tert-butylamino-4-chloro-6-ethylamino-1 ,3,5-triazine), linuron [3-(3,4-dichlorophenyl)-1 -methoxy-1 -methylurea], isoproturon [3-(4-isopropylphenyl)-1,1- dimethylurea], dinoseb acetate (2-sec-butyl-4,6-dinitrophenyl acetate), dinoseb amine (alkanolamine salts of 2-sec-butyl-4,6-dinitrophenol), dinoterb (2-tert-butyl-4,6-dinitrophenol), dicamba (3,6-dichloro-2methoxybenzoic acid) and salts thereof with metals, e.g. sodium or potassium, or amines, e.g.

dimethylamine, and the phenoxyacetic acid herbicides 2,4-D (2,4-dichlorophenoxyacetic acid) and MCPA (2-methyl-4-chlorophenoxyacetic acid) and their salts with metals, e.g. sodium or potassium, or amines, for example alkylamines, e.g. monomethylamine, dimethylamine, isopropylamine or triethylamine, or alkanolamines, e.g. diethanolamine, triethanolamine or mixed isopropanolamines, or their esters having low volatility, for example their esters with butoxyethanol, propylene glycol, tetrahydrofurfuryl alcohol, butoxypropanol, ethylhexanol or iso-octanol.

Bromoxynil trimethyl- and triethyl-amine salts may be applied alone or in combination with the other herbicides indicated above to control the growth of broad-leafed weeds in maize and sorghum crops by post-emergence application after the emergence of both the broad-leafed weeds and the crop. If desired, this post-emergence application of bromoxynil trimethyl- and triethyl-amine salts may follow the pre-emergence or pre-planting application to a locus which is an area planted with or to be planted with a maize or sorghum crop, if desired with incorporation into the soil, of one or more of the following herbicides::- alachlor [2-chloro-2',6'-diethyl-N-(methoxymethyl)acetanilide], metolachlor [2-chloro-6'-ethyl-N-(2-methoxy-1 - methylethyl)acet-o-toluidide], pendimethalin [N-(1 -ethylpropyl)-2,6-dinitro-3,4-xylidine], butylate (S-ethyl di-isobutylthiocarbamate), vernolate (S-propyl dipropylthiocarbamate), EPTC (S-ethyl dipropylthiocarbamate) or a mixture (12:1) of EPTC and N,N, diallyl-2,2-dichloroacetamide.

For use in the method of controlling the growth of broad-leafed weeds according to the present invention, the trimethylamine and triethylamine salts of bromoxynil may be applied in herbicidal compositions comprising at least one of the trimethylamine and triethylamine salts of bromoxynil in association with, and preferably homogeneously dispersed in, one or more compatible herbicidally-acceptable diluents or carriers or surface-active agents (i.e. diluents or carriers or surface-active agents of the type generally accepted in the art as being suitable for use in herbicidal compositions and which are compatible with the bromoxynil trimethyl- and triethyl-amine salts). The term "homogeneously dispersed" is used to include compositions in which the bromoxynil trimethyl- and triethyl-amine salts are dissolved in the 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 at least one of the trimethylamine and triethylamine salts of bromoxynil.

The herbicidal compositions may contain both a diluent or carrier and a 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 sulphoricinoleates, quaternary ammonium derivatives, products based on condensates of ethylene oxide with alkyl, e.g. nonyl or octyl, or polyaryl phenols, or carboxylic acid esters of anhydrosorbitols which have been rendered soluble by etherification of the free hydroxy groups by condensation with ethylene oxide, alkali and alkaline earth salts of sulphuric acid esters and sulphonic acids such as dinonyl- and dioctyl-sodium sulphono-succinates, alkali and alkaline earth metal salts of high molecular weight sulphonic acid derivatives such as sodium and calcium lignosulphonates and sodium and calcium alkyl benzene sulphonates.

Suitably, herbicidal compositions may comprise from 0.01 to 10% by weight of surface-active agent but, if desired, herbicidal compositions according to the present invention may comprise higher proportions of surface-active agent, for example up to 15% in liquid emulsifiable suspension concentrates and up to 25% in liquid water soluble concentrates.

Examples of suitable solid diluents or carriers are aluminium silicate, talc, calcined magnesia, kiesulguhr, tricalcium phosphate, powdered cork, adsorbent carbon black and clays such as kaolin and bentonite. The solid compositions (which may take the form of dusts, granules or wettable powders) are preferably prepared by grinding the bromoxynil trimethyl- and triethyl-amine salts with solid diluents or by impregnating the solid diluents or carriers with solutions of the bromoxynil trimethyl- and triethyl-amine salts 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 bromoxynil trimethyl- and triethyl-amine salts (dissolved in suitable solvents) onto the solid diluents or carriers in granular form and, if necessary, removing excess solvent, e.g. by evaporation, or by granulating compositions in powder form obtained as described above. Solid herbicidal compositions, particularly wettable powders and granules, may contain wetting or dispersing agent (for example of the types described above), which may also, when solid, serve as diluents or carriers.

Liquid compositions 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, tetrahydrofurfuryl alcohol, acetophenone, cyclohexanone, isophorone, toluene, xylene and mineral, animal and vegetable oils, e.g. light aromatic and naphthenic petroleum fractions (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.

Wettable 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 the bromoxynil trimethyl- and triethyl-amine salts may be used in the form of self-emulsifying concentrates comprising the active substances dissolved in the emulsifying agents or ii 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 may also contain, if desired, conventional adjuvants such as adhesives, protective colloids, thickeners, penetrating agents, stabilisers, sequestering agents, anti-caking agents, colouring agents and corrosion inhibitors. These adjuvants may also serve as carriers or diluents.

Preferred herbicidal compositions are wettable powders which comprise from 10 to 90% w/w of at least one of the trimethylamine and triethylamine salts of bromoxynil, from 2 to 10% w/w of surface-active agent and from 10 to 88% w/w of solid diluent or carrier; liquid water-miscible concentrates which comprise from 5 to 50% w/v of at least one of the trimethylamine and triethylamine salts of bromoxynil, from 5 to 25% w/v of surface-active agent and from 25 to 90% by volume of water-miscible solvent, e.g. dimethylformamide, or a mixture of water-miscible solvent and water; granules which comprise from 1 to 90% w/w of at least one of the trimethylamine and triethylamine salts of bromoxynil, from 0.5 to 2.5% w/w of surface-active agent and from 7.5 to 98.5% w/w of granular carrier, and emulsifiable concentrates which comprise from 0.05 to 90% w/v, and preferably from 1 to 60% w/v, of at least one of the trimethylamine and triethylamine salts of bromoxynil, from 0.01 to 10% w/v, and preferably from 1 to 10% w/v, of surface-active agent and from 9.99 to 99.94%, and preferably from 39 to 98.99%, by volume of organic solvent.

Herbicidal compositions may also comprise the bromoxynil trimethyl- and triethyl-amine salts in association with, and preferably homogenously dispersed in, one or more other herbicides as hereinbefore described which may be used in conjunction with the trimethylamine and triethylamine salts of bromoxynil and, if desired one or more compatible pesticidally acceptable diluents or carriers, surface-active agents and conventional adjuvants as hereinbefore described.

The bromoxynil trimethyl- and triethyl-amine salts may be prepared by reacting stoichiometric amounts of bromoxynil and trimethylamine or triethylamine in a suitable inert solvent, for example a liquid diluent suitable for incorporation in liquid herbicidal compositions according to the present invention as herein before described, or mixtures thereof, or a lower aliphatic alcohol, e.g. methanol or ethanol, or acetone, if necessary with heating. If desired, a stoichiometric amount of a mixture of trimethylamine and triethylamine may be used. The bromoxynil trimethyl- and triethyl-amine salts or mixtures thereof may, if desired, be isolated from the reaction mixture by conventional methods, for example by filtration, if necessary after the partial or complete removal of the solvent, e.g. by evaporation.However, it is frequently more convenient to use the solution of the trimethylamine or triethylamine salts of bromoxynil or mixtures thereof in a solvent which is obtained directly in the preparation of herbicidal compositions according to the present invention, particularly liquid herbicidal compositions, without isolating the bromoxynil trimethyland triethyl-amine salts.When reacting bromoxynil with trimethylamine or triethylamine or mixtures thereof in a solvent to give a solution of the trimethylamine or triethylamine salt of bromoxynii or mixtures thereof suitable for use directly in the preparation of herbicidal compositions, more especially liquid water-miscible concentrates and wettable powders, according to the present invention, without isolation of the bromoxynil trimethyl- and triethyl-amine salts or mixtures thereof, it is preferred to use a slight excess of trimethylamine or triethylamine or mixture thereof over the stoichiometric amount in order to give a solution of pH8.5 to pH9.5. If desired other components of herbicidal compositions, for example surface active agents, may be included in the solvent in which the trimethylamine or triethylamine salt of bromoxynil or mixtures thereof is prepared.

Bromoxynil triethylamine salt is a new compound which, together with its process of preparation and herbicidal compositions as herein before described which comprise it, form further features of the present invention. When a herbicidal composition comprises bromoxynil triethylamine salt and water or a common organic solvent a surface-active agent is preferably present.

The following Examples illusfrate herbicidal compositions according to the present invention.

Example 1 A water-miscible composition containing bromoxynil triethylamine salt was prepared from: bromoxynil . .. . . 34% w/v (weight/volume) triethylamine . . . 15%w/v Soprophor BSU (tristyrylphenol/ethylene oxide condensate containing 18 moles of ethylene oxide) . 1.5% w/v diethylene glycol . 25% w/v water.. . to 100% by volume, by mixing together a portion of the water, the diethylene glycol, the bromoxynil and the triethylamine (15% w/v of triethylamine represents a 2.6% by weight excess oftriethylamine over the stoichiometric amount required to form bromoxynil triethylamine salt) with heating and stirring. The Soprophor BSU was then added and the volume was made up to 100% by the addition of water.The resulting clear brown liquid of pH9 was completely miscible with water and may be diluted with water and applied at a rate of 0.5 litres of water miscible composition in 100 to 300 litres of spray fluid per hectare (an application of 170g of bromoxynil p.e. per hectare) to control the growth of broad-leafed weeds, e.g. Abutilon theophrasti, Amaranth us retroflexus, Chenopodium album, lpomea purpurea, Polygonum lapathifolium, Solanum nigrum and Xanthium strumarium, by post-emergence application in an emerged crop of maize or sorghum.

A similar water-miscible composition containing bromoxynil trimethylamine salt may be prepared as described above by replacing the triethylamine by the appropriate amount of trimethylamine and used in a similar manner.

Example 2 An emulsifiable composition containing bromoxynil triethylamine salt was prepared from: bromoxynil .... ..... .... 34% w/v triethylamine . ...... ............ .... 12.4% w/v Soprophor BSU ... ............ 5.25% w/v Arylan CA (70% solution of calcium dodecyl benzene sulphonate) ........ ..... ............ 2.25% w/v cyclohexanone . . 7.5% v/v (volume/volume) Solvesso 150 (aromatic Ci fraction of petroleum) . . . .......... to 100% by volume, by mixing together the cyclohexanone, the bromoxynil and the triethylamine and a portion of the Solvesso 150 with heating and stirring. The Soprophor BSU and the Arylan CA were then added and the volume was made up to 100% by the addition of Solvesso 150.The resulting clear brown liquid was self-emulsifiable in water and may be diluted with water and applied art a rate of 1.5 litres of emulsifiable composition in 100 to 300 litres of spray fluid per hectare (an application rate of 5109 of bromoxynil p.e. per hectare) to control the growth of broad-leafed weeds, e.g. Abutilon theophrasti, Amaranthus retroflexus, Chenopodium album, lpomea purpurea, Polygonum lapathifolium, Solanum nigrum and Xanthium strumarium, by postemergence application in an emerged crop of maize or sorghum.

A similar emulsifiable composition containing bromoxynil trimethylamine salt may be prepared as described above by replacing the triethylamine by the appropriate amount of trimethylamine and used in a similar manner.

Example 3 An emulsifiable composition containing bromoxynil triethylamine salt was prepared from: bromoxynil . . 34%w/v triethylamine . . 12.4%w/v Soprophor BSU . . 5.25%w/v Arylan CA . 2.25% w/v Solvesso 150 . to 100% by volume, by mixing together the bromoxynil, the triethylamine and a portion of the solvessor 150 with heating and stirring. The Soprophor BSU and the Arylan CA were then added and the volume was made up to 100% by the addition of Solvesso 150. The resulting clear brown liquid was self-emulsifying in water and may be diluted with water and applied at a rate of 1.5 litres of emulsifiable composition in 100 to 300 litres of spray fluid per hectare (an application rate of 510g of bromoxynil p.e. per hectare) to control the growth of broad-leafed weeds, e.g.Abutilon theophrasti, Amaranth us retroflexus, Chenopodium album, Ipomea purpurea, Polygonum lapathifolium, Solanum nigrum and Xanthium strumarium, by post-emergence application in an emerged crop of maize or sorghum.

Example 4 A wettable powder containing bromoxynil triethylamine salt was prepared from: bromoxynil . . 20%w/w triethylamine . . 8.8%w/w Soprophor BSU . ..... ...... 2.5% w/w diethylene glycol . 10% w/w Aerosil (silicon dioxide of microfine particle size) . to 100% by weight, by mixing together the bromoxynil, triethylamine (8.8% w/v of triethylamine represents a 2.5% by weight excess of triethylamine over the stoichiometric amount required to form bromxynil triethylamine salt), Soprophor BSU and diethylene glycol with heating and stirring, until a clear solution of pH9 was obtained.

The aerosil was then added with stirring until the liquid was fully absorbed and a free-flowing powder was obtained which may be diluted with water and applied at a rate of 0.75kg of wettable powder in 100 to 300 litres of spray fluid per hectare (an application rate of 1 50g of bromoxynil p.e. per hectare) to control the growth of broad-leafed weeds, e.g. Abutilon theophrastt Amaranthus retroflexus, Chenopodium album, Ipomea purpurea, Polygonum lapathifolium, Solanum nigrum and Xanthium strumarium, by postemergence application in an emerged crop of maize or sorghum.

A similar wettable powder composition containing bromoxynil trimethylamine salt may be prepared as described above by replacing the triethylamine by the appropriate amount of trimethylamine and used in a similar manner.

Example 5 Water-dispersible granules containing bromoxynil triethyiamine salt were prepared by mixing thoroughly the wettable powder containing bromoxynil triethylamine salt obtained as described with Example 4 with water (up to 5% volume/weight) to give a stiff paste or dough, which was then granulated by passage through an extruder and removal of excess water by drying to give water-dispersible granules which may be diluted with water and applied at a rate of 5kg of water-dispersible granules in 100 to 300 litres of spray fluid per hectare (an application rate of 10009 of bromoxynii p.e. per hectare) to control the growth of broad-leafed weeds, e.g.Abutilon theophrasti, Amaranthus retroflexus, Chenopodium album, Ipomea purpurea, Polygonum lapathifolium, Solanum nigrum and Xanthium strumarium, by post-emergence application in an emerged crop of maize or sorghum.

Similar water-dispersible granules containing bromoxynil trimethylamine salt may be prepared by replacing the triethylamine by the appropriate amount of trimethylamine.

Example 6 A water-miscible composition containing bromoxynil trimethylamine salt was prepared from: bromoxynil .......... ............ . . 34%w/v trimethylamine ..... ......... . . 7.25% w/v Soprophor BSU . . 1.5%w/v tetrahydrofurfuryl alcohol . . 25% w/v water ..... . to 100% by volume, by mixing together a portion of the water, the tetrahydrofurfuryl alcohol and the bromoxynil with stirring.

Trimethylamine was then bubbled through the solution by means of a dip tube until the pH of the solution was 8.0. The Soprophor BSU was then added and the volume was made up to 100% by volume by the addition of water. The resulting clear brown liquid was completely miscible with water and may be diluted with water and applied at a rate of 1 litre of water miscible composition in 100 to 300 litres of spray fluid per hectare (an application rate of 3409 of bromoxynil p.e. per hectare) to control the growth of broad-leafed weeds, e.g. Abutilon theophrasti, Armaranthus retroflexus, Chenopodium album, Ipomea purpurea, Polygonum lapathifolium, Solanum nigrum and Xanthium strumarium, by post-emergence application in an emerged crop of maize or sorghum.

Example 7 An emuisifiable composition containing bromoxynil trimethylamine salt was prepared from: bromoxynil . . 34%w/v trimethylamine . . 7.25% w/v Soprophor BSU . . 3.75% w/v Arylan CA .... 3.75 w/v a 1:1 by volume mixture of cyclohexanone and Solvesso 150 . . to 100% by volume, by mixing together the bromoxynil and a portion of the cyclohexanone/Solvesso 150 mixture with heating and stirring. Trimethylamine was then bubbled through the solution by means of a dip tube until all the bromoxynil had dissolved. The Soprophor BSU and Arylan CA were then added and the volume was then made up to 100% by volume with further cyclohexanone/Solvesso 150 mixture.The resulting clear brown liquid was self-emulsifying in water and may be diluted with water and applied at a rate of 1 litre of emulsifiable composition in 100 to 300 litres of spray fluid per hectare (an application rate of 340g of bromoxynil p.e. per hectare) to control the growth of Abutilon theophrasti, Amaranth us retroflexus, Chenopodium album, Ipomea purpurea, Polygonum lapathifolium, Solanum nigrum and Xanthium strumarium by post-emergence application in an emerged crop of maize or sorghum.

Example 8 A water-miscible composition containing bromoxynil triethylamine salt was prepared from: bromoxynil .. ............. ............. 34%w/v (weight/volume) triethylamine ..................................... 15% w/v Soprophor BSU (tristyrylphenol/ethylene oxide condensate containing 18 moles of ethylene oxide) .. 1.5% w/v tetrahydrofurfuryl alcohol ......... 25% w/v water ...... . to 100% byvolume, by mixing together a portion of the water, the tetrahydrofurfuryl alcohol, the bromoxynil and the triethylamine (15% w/v of triethylamine represents a 2.6% by weight excess of triethylamine over the stoichiometric amount required to form bromoxynil triethylamine salt) with heating and stirring.The Soprophor BSU was then added and the volume was made up to 100% by the addition of water. The resulting clear brown liquid of pH9 was completely miscible with water and may be diluted with water and applied at a rate of 0.5 litres of water miscible composition in 100 to 300 litres of spray fluid per hectare (an application rate of 170g of bromoxynil -p.e. per hectare) to control the growth of broad-leafed weeds, e.g.

Abutilon theophrasti, Amaranthus retroflexus, Chenopodium album, Ipomea purpurea, Polygonum lapathifolium, Solanum nigrum and Xanthium strumarium, by post-emergence application in an emerged crop of maize or sorghum.

Example 9 An emulsifiable composition containing bromoxynil triethylamine salt was prepared from: bromoxynil . . 34% w/v triethylamine . 12.4%w/v Soprophor BSU . . 3.75% w/v Arylan CA . 3.75% w/v a 1:1 by volume mixture cyclohexanone and Solvesso 150 . . to 100% by volume by mixing together a portion of the cyclohexanone/Solvesso 150 mixture, the bromoxynil and the triethylamine with heating and stirring. The Soprophor BSU and the Arylan CA were then added and the volume was made up to 100% by the addition of further cyclohexanone/Solvesso 150 mixture.The resulting clear brown liquid was self-emulsifiable in water and may be diluted with water and applied at a rate of 1.5 litres of emulsifiable composition in 100 to 300 litres of spray fluid per hectare (an application rate of 510g of bromoxynil p.e. per hectare) to control the growth of broad-leafed weeds, e.g.Abutilon theophrasti, Amaranthus retroflexus, Chenopodium album, Ipomea purpurea, Polygonum lapathifolium, Solanum nigrum and Xanthium strumarium, by post-emergence application in an emerged crop of maize or sorghum.

The method of controlling the growth of weeds according to the present invention and the advantageous selectivity of bromoxynil trimethyl- and triethyl-amine salts in controlling the growth of broad-leafed weeds in maize and sorghum by post-emergence application, in comparison with the widely-used bromoxynil derivatives bromoxynil octanoate and bromoxynil potassium salt and-other amine salts of bromoxynil, is demonstrated in the following experiments.

Experiment 1 The following formulations were tested: Formulation A: a water-miscible composition containing 34.0% (p.e.) w/v of bromoxynil triethylamine salt, prepared as described in Example 1.

B: an emusifiable composition containing 34.0% (p.e.) w/v of bromoxynil triethylamine salt, prepared as described in Example 3.

C: an emulsifiable composition containing 34% (p.e.) w/v of bromoxynil triethylamine salt, prepared as described in Example 2.

D: a water-miscible composition containing 34.0% (p.e.) w/v of bromoxynil trimethylamine salt, prepared as described in Example 1.

E: an emulsifiable composition containing 34.0% (p.e.) w/v of bromoxynil trimethylamine salt, prepared as described in Example 2.

F: a water-miscible composition containing 25% (p.e.) w/v of bromoxynil potassium salt, Soprophor BSU (1.1% w/v), tetrahydrofurfuryl alcohol (40% w/v) and water (to 100% by volume), prepared by the procedure described in Example 1 but replacing the bromoxynil triethylamine salt and the diethylene glycol by the appropriate amounts of, respectively, bromoxynil potassium salt and tetrahydrofurfuryl alcohol.

G: a commercially available emulsifiable composition containing 22.5% (p.e.) w/v of bromoxynil octanoate, a combined total of 7.5% w/v of Atlox 4855 and Agrilan A, and High Flash Naphtha CW (a high boiling point petroleum fraction) to 100% by volume, prepared by the general procedure described in Example 2, using the appropriate quantites of the ingredients indicated above. (Atlox 4855 and Agrilan A are each mixtures of nonionic surface active agent and calcium dodecyl benzene sulphonate).

Maize (Zea mays, sorghum (Sorghum bicolor) and wheat (Triticum aestivum) plants were grown in the greenhouse by directly sowing seeds in 13cm diameter plastic pots containing John Innes No 1 potting compost (7 parts by volume of sterilized loam, 3 parts by volume of peat and 2 parts by volume of fine grit).

Weed species were grown from seed in the greenhouse and transplanted at the seedling growth stage into 9cm diameter plastic pots containing John Innes No 1 potting compost. Three maize, sorghum, wheat or weed plants were grown per pot. The mean temperature in the greenhouse ranged from 1 50C at night to 270C during the day, with a daylength of 16 hours. Three replica pots, each containing three plants of uniform growth stage, were used for each spray treatment. Unsprayed pots, each containing three plants of uniform growth, were maintained as controls. The plants were at the following growth stages when sprayed.

Plant Leaves Maize 4 Sorghum 3 1/2 Wheat 3 (Broad-leafed Weeds) Amaranthus retroflexus (A.r.) 3 Polygonum lapathifolium (P.l.) 3 lpomeapurpurea (I.p.) 3 Chenopodium album (C.a.) 4 Solanum nigrum (S.a.) 4 Xanthium strumarium (X.s.) 4 Abutilon theophrasti (A.t.) 3 Appropriate quantities of Formulations A to G were diluted in somas of water to give spray fluids having concentrations equivalent to 85, 170,340, 680 and 13609 (p.e.) of bromoxynil per hectare when applied at a spray volume rate of 260 litres per hectare. The treatments were applied to the plants by means of a laboratory spraying apparatus using a flat fan jet (spray pressure 2.1 kgf/cm2), travelling at 2.6km/hour.After spraying, the pots were returned to the greenhouse and arranged in randomised blocks. The plants were watered by overhead watering 24 hours after spraying and daily thereafter.

Ten days after spraying, a visual assessment was made of the percentage reduction in top growth of each weed species for each replicate treatment in comparison with untreated control plants. The mean percentage control of each species at each rate of application and the mean percentage overall control of all tested weed species was calculated. The results obtained are presented in Table 1 below.

Visual assessment of injury to the maize, sorghum and wheat plants was also made 10 days after spraying and the percentage necrosis of the entire plant was recorded. These results are given in Table 2 below. TABLE 1 Formulation Application Mean percentage weed control rate of weed species [Bromoxynil g(p.e.)/ha] C.a. P.I. A.t. A.r. X.s. I.p. S.n.Overall (all species) A 85 33 100 83 100 60 70 100 78 (Bromoxynil 170 85 100 100 100 100 100 100 98 triethyl- 340 100 100 100 100 100 100 100 100 amine salt) 680 100 100 100 100 100 100 100 100 1360 100 100 100 100 100 100 100 100 B 85 40 100 75 100 53 80 100 78 (Bromoxynil 170 90 100 83 100 100 100 100 96 triethyl- 340 100 100 100 100 100 100 100 100 amine salt) 680 100 100 100 100 100 100 100 100 1360 100 100 100 100 100 100 100 100 C 85 23 80 80 100 80 80 97 77 (Bromoxynil 170 50 100 80 100 100 80 100 87 triethyl- 340 97 100 100 100 100 100 100 99.5 amine salt) 680 100 100 100 100 100 100 100 100 1360 100 100 100 100 100 100 100 100 D 85 10 90 47 100 40 50 100 62 (Bromoxynil 170 62 100 70 100 85 90 100 87 trimethyl- 340 97 100 90 100 90 100 100 97 amine salt) 680 100 100 100 100 100 100 100 100 1360 100 100 100 100 100 100 100 100 TABLE 1 (continued) Formulation Application Mean percentage weed control rate of weed species [Bromoxynil g(p.e.)/ha] C.a. P.I. A.t. A.r. X.s. I.p. S.n. Overall (all species) E 85 33 93 80 90 35 70 100 72 (Bromoxynil 170 73 100 83 100 60 75 100 84 trimethyl- 340 100 100 100 100 93 100 100 99 amine salt) 680 100 100 100 100 100 100 100 100 1360 100 100 100 100 100 100 100 100 F 85 0 30 45 80 10 10 50 32 (Bromoxynil 170 0 75 80 90 40 40 80 58 potassium 340 45 97 90 100 70 70 90 80 salt) 680 90 100 90 100 90 80 100 93 1360 100 100 100 100 100 100 100 100 G 85 45 93 90 100 80 80 90 83 (Bromoxynil 170 80 100 97 100 97 93 100 95 octonoate 340 100 100 100 100 100 100 100 100 680 100 100 100 100 100 100 100 100 1360 100 100 100 100 100 100 100 100 TABLE 2 Formulation Crop Necrotic leaf area (%) plant Application rate [Bromoxynil g(p.e.)/ha] 85 170 340 680 1360 A Maize 0 0 0 0 0 (Bromoxynil Sorghum 0 0 0 < 5 6 triethylamine salt) Wheat 0 0 0 0 0 B Maize 0 0 0 0 < 5 (Bromoxynil Sorghum 0 0 < 5 5 18 triethylamine salt) Wheat 0 0 0 0 0 C Maize 0 0 0 0 5 (Bromoxynil Sorghum 0 0 0 < 5 20 triethylaminesalt) Wheat 0 0 0 0 0 D Maize 0 0 0 0 < 5 (Bromoxynil Sorghum 0 0 < 5 5 15 trimethylamine salt) Wheat 0 0 0 0 0 E Maize 0 0 0 < 5 10 (Bromoxynil Sorghum 0 0 0 5 15 triethylamine salt) Wheat 0 0 0 0 < 5 F Maize 0 0 0 0 < 5 (Bromoxynil Sorghum 0 0 0 < 5 10 potassium salt) Wheat 0 0 0 0 0 G Maize 0 < 5 8 17 60 (Bromoxynil Sorghum 0 5 7 23 42 octanoate) Wheat 0 0 0 < 5 < 5 (' < ' means 'less than') The application rate for each of Formulations A to G required to give 95% overall control of all weed species was calculated by plotting the overall (all weed species) percentage controls against application rates on log/probability paper.These application rates giving 95% overall weed control are shown in Table 3 below and clearly demonstrates that bromoxynmil trimethylamine and triethylamine salts are from 3 to 5 1/2 times more active than bromoxynil potassium salt in controlling the growth of weeds and that in contrast to bromoxynil potassium salt, bromoxynil trimethylamine salt and triethylamine salts are equal to or, at worst, only 1.8 times less active than bromoxynil octanoate in controlling the growth of weeds.

The application rates for each of Formulations A to G which gave no more than 5% of damage (leaf necrosis) to the crop plants (maize, sorghum and wheat) were similarly calculated from the results given in Table 2. The application rates which gave no more than 5% of damage to the crop plant are also given in Table 3 below.

The selectivity index

application rate giving no more than 5% damage in crop plant application rate giving 95% overall weed control was calculated from these figures for each formulation in each crop and these indices are also given in Table 3. The selectivity indices clearly demonstrate that bromoxynil trimethylamine and triethylamine salts are from 2 to 5 1/2 times more selective than bromoxynil octanoate in the control of broad-leafed weeds by post-emergence application in maize crops, that bromoxynil trimethylamine and triethylamine salts are from 2 1/4 to 6 1/2 times more selective than bromoxynil octanoate in the control of broad-leafed weeds by post-emergence application in sorghum crops and that bromoxynil trimethylamine and triethylamine salts are 3 times more active than bromoxynil potassium salt in controlling the growth of broad-leafed weeds by post-emergence application and are more selective than bromoxynil potassium salt in the control of broad-leafed weeds by post-emergence application in maize and sorghum crops.These selectivity indices also indicate that bromoxynil trimethylamine and triethylamine salts are highly selective in wheat but that, in contrast to their selectivity indices in maize and sorghum crops, these salts show no advantage in selectivity over bromoxynil octanoate in controlling the growth of broad-leafed weeds by post-emergence application in wheat.

TABLE 3 Formulation Application rate Application rate Selectivity Index giving 95% overall producing no more weed control than 5% damage (leaf [Bromoxynil necrosis) on crop g (p.e.)/ha] plant [Bromoxynil g (p.e.)/ha] Maize Sorghum Wheat Maize Sorghum Wheat A (Bromoxynil 130 > 1360 1020 > 1360 > 10 7.8 > 10 triethylamine salt) B (Bromoxynil 140 > 1360 680 > 1360 > 9.7 4.8 > 9.7 triethylamine salt) C (Bromoxynil 190 1360 680 > 1360 7.1 3.6 > 7.1 triethylamine salt) D (Bromoxynil 250 1360 680 > 1360 > 5.4 2.7 > 5.4 trimethylamine salt) E (Bromoxynil 235 900 680 > 1360 3.8 2.9 > 5.8 trimethylamine salt) F (Bromoxynil 720 > 1360 1020 > 1360 > 1.9 1.4 > 1.9 potassium salt) G (Bromoxynil 140 250 170 1360 1.8 1.2 9.7 octanoate) (' > ' means 'greater than') Experiment2 The following formulations were tested Formulation H:: a water-miscible composition containing 34.0% (p.e.) w/v of bromoxynil trimethylamine salt, prepared as described in Example 6.

I: an emusifiable composition containing 34.0% (p.e.) w/v of bromoxynil trimethylamine salt, prepared as described in Example 7.

J: a water-miscible composition containing 34.0% (p.e.) w/v of bromoxynil triethylamine salt, prepared as described in Example 8.

K: an emulsifiable composition containing 34.0% (p.e.) w/v of bromoxynil triethylamine salt, prepared as described in Example 9.

L: a water-miscible composition containing 34.0% (p.e.) w/v of bromoxynil triethanolamine salt, prepared by the procedure described in Example 8 but replacing the triethylamine by the appropriate stoichiometric amount of triethanolamine.

M: an emusifiable composition containing 34.0% (p.e.) w/v of bromoxynil tri-n-propylamine salt, prepared by the procedure described in Example 9 but replacing the triethylamine by the appropriate stoichiometric amount of tri-n-propylamine.

N: an emulsifiable composition containing 34.0% (p.e.) w/v of bromoxynil tri-n-butylamine salt, prepared by the procedure described in Example 9 but replacing the triethylamine by the appropriate stoichiometric amount of tri-n-butylamine.

O: an emusifiable composition containing 34.0% (p.e.) w/v of bromoxynil methyl-di-n-octylamine salt, prepared by the procedure described in Example 9 but replacing the triethylamine by the appropriate stoichiometric amount of methyl-di-n-octylamine.

P: a water-miscible composition containing 17.0% (p.e.) w/v of bromoxynil potassium salt, prepared by the procedure described in Example 8 but replacing the bromoxynil and the triethylamine by the appropriate amount of bromoxynil potassium salt.

Q: a water-miscible composition containing 17.0% (p.e.) w/v of bromoxynil ammonium salt, prepared by the procedure described in Example 8 but replacing the triethylamine by concentrated aqueous ammonia and using the appropriate stoichiometric amounts of bromoxynil and ammonia.

R: an emulsifiable composition containing 34.0% (p.e.) w/v of bromoxynil octanoate, prepared by the procedure described in Example 9 but replacing the bromoxynil and the triethylamine by the appropriate amount of bromoxynil octanoate.

Maize, sorghum and broad leafed weeds were grown in the green house as described in Experiment 1. The plants were at the following growth stages when sprayed: Crop plants Leaves Maize 3 Sorghum 3 Weeds lpomeapurpurea (I.p.) cotyledons + 1 true leaf Abutilon theophrasti (A.t.) cotyledons + 1 true leaf Amaranthus retroflexus (A.r.) 2 Chenopodium album (C.a.) 4 Appropriate quantities of Formulations H to R were diluted in somas of water to give spray fluids having concentrations equivalent to 85, 170,340,680 and 13609 (p.e.) of bromoxynii per hectare when applied at a spray volume rate of 260 litres per hectare. The treatments were applied as described in Experiment 1.

Unsprayed pots were maintained as controls.

Ten days after spraying, a visual assessment was made of the percentage reduction in top growth of each weed species for each replicate treatment in comparison with untreated control plants. The mean percentage control of each species at each rate of application and the mean percentage overall control of all tested weed species was calculated. The results obtained are presented in Table 4 below.

Visual assessment of injury to the maize and sorghum plants was also made 10 days after spraying and the percentage necrosis of the entire plant was recorded. These results are given in Table 5 below.

TABLE 4 Formulation Application Mean percentage weed control rate of weed species [Bromoxynil I.p. A.t. A.r. C.a. Overall g(p.e)/ha] (all species) H 85 50 10 10 10 20 (Bromoxynil 170 95 70 30 62 64 trimethyl- 340 100 95 90 95 95 amine salt) 680 100 100 100 100 100 1360 100 100 100 100 100 I 85 75 35 30 35 42 (Bromoxynil 170 1007 75 60 75 78 trimethyl- 340 100 95 95 95 96 amine salt) 680 100 100 100 100 100 1360 100 100 100 100 100 J 85 85 30 40 35 47 (Bromoxynil 170 100 60 70 70 75 triethyl- 340 100 95 100 95 97 amine salt) 680 100 100 100 100 100 1360 100 100 100 100 100 K 85 95 40 43 50 57 (Bromoxynil 170 100 70 80 100 87 triethyl- 340 100 100 100 100 100 amine salt) 680 100 100 100 100 100 1360 100 100 100 100 100 L 85 60 20 10 20 27 (Bromoxynil 170 90 40 40 75 61 triethanol- 340 100 85 70 95 87 amine salt) 680 100 100 95 100 99 1360 100 100 100 100 100 M 85 60 0 0 0 15 (Bromoxynil 170 95 10 20 60 46 tri-n-propyl- 340 100 35 65 80 70 amine salt) 680 100 80 100 100 95 1360 100 100 100 100 100 TABLE 4 (continued) Formulation Application Mean percentage weed control rate of weed species [Bromoxynil g(p.e)/ha] I.p. A.t. A.r. C.a. Overall (all species) N 85 43 20 0 20 21 (Bromoxynil 170 100 45 30 70 61 tri-n-butyl- 340 100 80 65 100 86 amine salt) 680 100 95 100 100 98 1360 100 100 100 100 100 O 85 40 10 10 30 33 (Bromoxynil 170 100 30 30 70 57 methyl-di-n- 340 100 60 50 100 77 octylamine 680 100 98 100 100 99 salt) 1360 100 100 100 100 100 P 85 20 0 0 0 5 (Bromoxynil 170 40 10 10 20 20 potassium 340 100 20 30 50 50 salt) 680 100 50 60 90 75 1360 100 90 100 100 97 Q 85 40 0 0 0 10 (Bromoxynil 170 100 0 20 40 40 ammonium 340 100 30 56 90 69 salt) 680 100 70 90 100 90 1360 100 98 100 100 99 R 85 100 53 40 60 63 (Bromoxynil 170 100 80 85 90 91 octanoate) 340 100 100 100 100 100 680 100 100 100 100 100 1360 100 100 100 100 100 TABLE 5 Formulation Crop Necrotic leaf area (%) plant Application rate [Bromoxynil g(p.e.)/ha] 85 170 340 680 1360 H (Bromoxynil Maize 0 0 0 0 5 trimethylamine salt) Sorghum 0 0 0 0 5 I(Bromoxynil Maize 0 0 0 0 5 trimethylaminesalt) Sorghum 0 0 0 < 5 10 J (Bromoxynil Maize 0 0 0 0 0 (triethylaminesalt) Sorghum 0 0 0 0 5 K (Bromoxynil Maize 0 0 0 0 5 triethylaminesalt) Sorghum 0 0 0 < 5 10 L (Bromoxynil Maize 0 0 0 5 10 triethanolaminesalt) Sorghum 0 0 < 5 5 15 M (Bromoxynil tri-n- Maize 0 0 0 5 15 propylamine salt) Sorghum 0 0 0 5 25 N (Bromoxynil tri-n- Maize 0 0 < 5 10 20 butylamine salt) Sorghum 0 0 < 5 5 23 O (Bromoxynil methyl- Maize 0 0 5 17 30 di-n-octylamine salt) Sorghum 0 5 < 5 20 35 P (Bromoxynil Maize 0 0 0 0 0 potassium salt) Sorghum 0 0 0 0 5 Q (Bromoxynil Maize 0 0 0 0 0 ammonium salt) Sorghum 0 0 0 0 0 R (Bromoxynil Maize 0 0 8 19 40 octanoate) Sorghum 0 0 10 21 44 (' < 'means 'less than') The application rate for each of Formulations H to R required to give 95% overall control of all weed species tested was calculated as described in Experiment 1. These application rates giving 95% overall weed control are shown in Table 6 below and clearly demonstrate that bromoxynil trimethylamine and triethylamine salts are more active than bromoxynil triethanolamine, tri-n-propylamine, tri-n-butylamine and methyl-di-n-octylamine salts, from 3 1/2 to 4 times more active than bromoxynil potassium salt and from 2 to 3 times more active than bromoxynil ammonium salt, in controlling the growth of broad-leafed weeds by post-emergence application.Bromoxynil trimethylamine and triethylamine salts are shown to approach more closely the high level of activity shown by bromoxynil octanoate in controlling the growth of broad-leafed weeds by post-emergence application, than the other bromoxynil salts tested, and in particular bromoxynil potassium and ammonium salts, bromoxynil trimethylamine and trimethylamine salts being at worst only 1.6 times less active than bromoxynil octanoate in controlling the growth of weeds, whereas, in contrast, bromoxynil potassium and ammonium salts are less than 5 1/2 times and less than 4times, respectively, as active as bromoxynil octanoate.

The application rates for each of Formulations H to R which gave no more than 5% of damage (leaf necrosis) to the crop plants (maize and sorghum ) were similarly calculated from the results given in Table 5 and also are shown in Table 6 below. The selectivity index was calculated from these figure for each formulation in each crop and these indices are also given in Table 6. The selectivity indices clearly demonstrate that bromoxynil trimethylamine and triethylamine salts are highly selective in maize and sorghum, in contrast to bromoxynil triethanolamine, tri-n-propylamine, tri-n-butylamine, methyl-di-noctylamine, ammonium and potassium salts and bromoxynil octanoate.The selectivity indices indicate that bromoxynil trimethylamine and triethylamine salts are from 2.5 to 3.3 times more selective than bromoxynil octanoate in the control of broad-leafed weeds by post-emergence application in maize crops and that bromoxynil trimethylamine and triethylamine salts are from 2.8 to 3.1 times more selective than bromoxynil octanoate in the control of broad-leafed weeds by post-emergence application in sorghum crops. These selectivity indices also indicate that bromoxynil triethanolamine, tri-n-propylamine, tri-n-butylamine, methyl-di-n-octylamine, ammonium and potassium salts show no advantage in selectivity over bromoxynil octanoate in controlling the growth of broad-leafed weeds by post-emergence application in maize and sorghum crops.

TABLE 6 Formulation Application rate Application rate Selectivity Index giving 95% overall producing no more weed control than 5% damage (leaf [Bromoxynil necrosis) on crop g (p.e.)/ha] plant [Bromoxynil g(p.e.)/ha] Maize Sorghum Maize Sorghum H (Bromoxynil 340 1360 1360 4.0 4.0 trimethylamine salt) (Bromoxynil 290 1360 1200 4.7 4.1 trimethylamine salt) J (Bromoxynil 320 > 1360 1360 > 4.3 4.3 triethylamine salt) K (Bromoxynil 270 1360 1200 5.0 4.4 triethylamine salt) L (Bromoxynil 450 680 680 1.5 1.5 triethanolamine salt) M (Bromoxynil 520 680 680 1.3 1.3 tri-n-propylamine salt) N (Bromoxynil 400 560 680 1.4 1.7 tri-n-butylamine salt) 0 (Bromoxynil 600 340 340 < 1 < 1 methyl-di-noctylamine salt) P (Bromoxynil 1100 > 1360 1360 > 1.2 1.2 potassium salt) TABLE 6 (continued) Formulation Application rate Application rate Selectivity index giving 95% overall producing no more weed control than 5% damage (leaf [Bromoxynil necrosis) on crop g(p.e.)/ha] plant [Bromoxynil g(p.e.)/ha] Maize Sorghum Maize Sorghum 0 (Bromoxynil 800 > 1360 1360 > 1.7 1.7 ammonium salt) R (Bromoxynil 200 300 280 1.5 1.4 octanoate) (' > 'means 'greater than'; ' < 'means 'less 'less than') The following Example illustrates the preparation of bromoxynil trimethyl- and triethyl-amine salts.

Example 10 Triethylamine (5.50ml) was added to a stirred solution of 3,5-dibromo-4-hydroxybenzonitrile (5.549) in acetone (40ml). After 10 minutes, when the exothermic reaction had subsided, the mixture was filtered and the filtrate was evaporated to dryness to give a solid. The solid thus obtained was triturated with ethyl acetate and separated by filtration to give bromoxynil triethylamine salt (which may be alternatively named astriethylammonium 2,6-dibromo-4-cycanophenoxide) (5.19), in the form of a cream coloured solid, m.p.

56-58"C [Elemental analysis:- C,41.20; H,4.80; N,7.30%; calculated for C13H18Br2N2O :- C,41.30; H,4.76; N,7.40%].

By proceeding in a similar manner but replacing the triethylamine by trimethylamine and the acetone by ethanol, there was obtained bromoxynil trimethylamine salt (which may be alternatively named as trimethylammonium 2,6-dibromo-4-cyanophenoxide) in the form of a cream coloured solid, m.p. 97-99"C [Elemental analysis:- C,35.3; H,3.4; N,7.6%; calculated for C10H12Br2N20:- C,35.7; H,3.6; N,8.3%].

3,5-Dibromo-4-hydroxybenzonitrile (bromoxynil) may be prepared as described by Auwers and Reis, Ber., 29 (2), 2355-2360 (1896).

Claims

1. A method for the selective control of broad-leafed weeds in an emerged crop of maize or sorghum which comprises the post-emergence application to the broad-leafed weeds in a crop of maize or sorghum of a herbicidally-effective amount of the trimethylamine salt of 3,5-dibromo-4-hydroxybenzonitrile or the triethylamine salt of 3,5-dibromo-4-hydroxybenzonitrile at a rate of application of the trimethylamine salt of 3,5-dibromo-4-hydroxybenzonitrile or the triethylamine salt of 3,5-dibromo-4-hydroxybenzonitrile which controls the growth of the broad-leafed weeds without causing substantial permanent damage to the crop.

2. A method according to claim 1 wherein the broad-leafed weeds are at least one ofAbutilon theophrasti, Amaranthus spp, Ambrosia artemisiffolla, Amsinkia intermedia, Anchusa arvensis, Anthemis cotula, Ascelepias spp., Aethusa cynapium, Atriplexpatula, Brassica kaber, Brassica nigra, capsella bursa-pastoris, Centaurea cyan us, Chenopodium album, Chorispora tenella, Datura stramonium, Descurainea sophia, Fagopyrum tartaricum, Galinsoga parviflora, Helianthus annuus, Ipomea spp., Kochia scoparia, Lapsana communis, Lithospermum arvense, Matricaria recutita, Matricaria inodora, Myosotis arvensis, Papaverrhoeas, Plantago media, Polygonum spp., Portulaca oleracea, Raphanus raphanistrum, Senecio vulgaris, Sida spinosa, Silene alba, Sinapis arvensis, Solanum nigrum, Solanum elaeagnifolium, Sonchus asper, Sonchus oleracea, Thlaspi arvense, Veronica persica or Xanthium spp.

3. A method according to claim 1 wherein the broad-leafed weeds are at least one Abutilon theophrasti, Amaranthus retroflexus, Chenopodium album, lpomea purpurea, Polygonum lapathifolium, Solanum nigrum or Xanthium strumarium.

4. A method according to claim 1,2 or 3 wherein the rate of application of the trimethylamine salt of 3,5-dibromo-4-hydroxybenzonitrile or the triethylamine salt of 3,5-dibromo-4-hydroxy-benzonitrile is such as to apply from 100 to 10009 per hectare of bromoxynil.

5. A method according to claim 1,2 or 3 wherein the rate of application of the trimethylamine salt of 3,5-dibromo-4-hydroxybenzonitrile or the triethylamine salt of 3,5-dibromo-4-hydroxy-benzonitrile is such as to apply from 150 to 600g per hectare of bromoxynil.

6. A method according to any one of claims 1 to 5 wherein the trimethylamine salt of 3,5-dibromo-4hydroxybenzonitrile or the triethylamine salt of 3,5-dibromo-4-hydroxybenzonitrile is applied in conjunction with at least one other herbicide which controls the growth of monocotyledonous weeds and/or which controls the growth of monoctyledonous weeds and/or which is herbicidally active by residual or pre-emergence application and/or which possesses persisent herbicidal activity and which is well tolerated by maize or sorghum.

7. A method according to claim 6 in which the other herbicide is atrazine, simazine, cyanazine, propazine, terbuthylazine, linuron, isoproturon, dinoseb acetate, dinoseb amine, dinoterb, dicamba and salts thereof with metals or amines, 2,4-D and salts thereof with metals or amines and esters thereof, or MCPA and salts thereof with metals or amines and esters thereof.

8. A method according to any one of claims 1 to 7 wherein the post-emergence application to the broad-leafed weeds in maize or sorghum crops of the trimethylamine salt of 3,5-dibromo-4hydroxybenzonitrile or the triethylamine salt of 3,5-dibromo-4-hydroxybenzonitrile follows the preemergence or pre-planting application, to the area planted with or to be planted with the maize or sorghum crop, of alachlor, metolachlor, pendimethalin, butylate, vernolate, EPTC or a 12:1 mixture of EPTC and N,N-diallyl-2,2-dichloroacetamide.

9. A method according to any one of claims 1 to 8 wherein the triethylamine salt of 3,5-dibromo-4hydroxybenzonitrile is used.

10. A method according to claim 1 for controlling the growth of broad-leafed weeds in a crop of maize or sorghum substantially as hereinbefore described.

11. A method for controlling the growth of broad-leafed weeds in a crop of maize or sorghum substantially as described in any one of Examples 1 to 5.

12. A method for controlling the growth of broad-leafed weeds in a crop of maize or sorghum substantially as described in any one of Examples 6 to 9.

13. The triethylamine salt of 3,5-dibromo-4-hydoxybenzonitrile.

14. A process for the preparation of the triethylamine salt of 3,5-dibromo-4-hydroxybenzonitrile which comprises reacting stoichiometric amounts of 3,5-dibromo-4-hydroxybenzonitrile and triethylamine in a suitable inert solvent.

15. A process according to claim 14 wherein the inert solvent is a liquid diluent suitable for incorporation in liquid herbicidal compositions.

16. A process according to claim 14 or 15 substantially as hereinbefore described with especial reference to Example 10.

17. The triethylamine salt of 3,5-dibromo-4-hydroxybenzonitrile whenever prepared by a process according to claim 14, 15 or 16.

18. A solution of the triethylamine salt of 3,5-dibromo-4-hydroxybenzonitrile in an inert solvent obtained as the product of a process according to claim 15 or 16.

19. A herbicidal composition which comprises the triethylamine salt of 3,5-dibromo-4hydroxybenzonitrile and a herbicidally-acceptable diluent or carrier or surface-active agent.

20. A herbicidal composition according to claim 19 which contains from 0.05 to 90% by weight of the triethylamine salt of 3,5-dibromo-4-hydroxybenzonitrile.

21. A herbicidal composition according to claim 19 or 20 which contains from 0.01 to 10% by weight of surface-active agent.

22. A herbicidal composition according to claim 19 or 20 which contains from 0.01 to 25% by weight of surface-active agent.

23. A herbicidal composition according to any one of claims 19,20 or 21 in the form of dusts, granules or wettable powders.

24. A herbicidal composition according to any one of claims 19, 20, 21 or 22 in the form of aqueous, organic or aqueous-organic solutions, suspensions or emulsions.

25. A herbicidal composition according to any one of claims 19 to 22 or 24 in which the herbicidally-acceptable diluent is water.

26. A herbicidal composition according to claim 23 in the form of a wettable powder comprising from 10 to 90% w/w of the triethylamine salt of 3,5-dibromo-4-hydroxybenzonitrile, from 2 to 10% w/w of surface-active agent and from 10 to 88% w/w of solid diluent or carrier.

27. A herbicidal composition according to claim 24 or 25 in the form of a liquid water-miscible concentrate comprising from 5 to 50% w/v of the triethylamine salt of 3,5-dibromo-4-hydroxybenzonitrile, from 5 to 25% w/v of surface-active agent and from 25 to 90% by volume of water-miscible solvent or a mixture of water-miscible solvent and water.

28. A herbicidal composition according to claim 23 in the form of granules comprising from 1 to 90% w/w of the triethylamine salt of 3,5-dibromo-4-hydroxybenzonitrile, from 0.5 to 2.5% w/v of surface-active agent and from 7.5 to 98.5% w/v of granular carrier.

29. A herbicidal composition according to claim 24 in the form of an emulsifiable concentrate comprising from 0.05 to 90% w/v of the triethylamine salt of 3,5-dibromo-4-hydroxybenzonitrile, from 0.01 to 10% w/v of surface-active agent and from 9.99% to 99.94% by volume of organic solvent.

30. A herbicidal composition according to any one of claims 19 to 29 which contains at least one other herbicide which controls the growth of monocotyledonous weeds and/or which is herbicidally active by residual or pre-emergence application and/or which possesses persistent herbicidal activity and which is well tolerated by maize or sorghum.

31. A herbicidal composition according to claim 30 in which the other herbicide is atrazine, simazine, cyanazine, propazine, terbuthylazine, linuron, isoproturon, dinoseb acetate, dinoseb amine, dinoterb, dicamba and salts thereof with metals or amines, 2,4-D and salts thereof with metals or amines and esters thereof, or MCPA and salts thereof with metals or amines and esters thereof.

32. A herbicidal composition according to claim 19 substantially as hereinbefore described.

33. A herbicidal composition according to claim 19 substantially as described in any one of Examples 1 to 5.

34. A herbicidal composition according to claim 19 substantially as described in Example 8 or 9.