GB2082069A - The control of weeds by application of a benzenesulphonylcarbamate and paraquat - Google Patents

Abstract

The control of the growth of monocotyledonous and dicotyledonous weeds is achieved by the application to a locus of weed infestation after emergence of the weeds above the surface of the soil of asulam (i.e. methyl 4- aminobenzenesulphonylcarbamate) or an agriculturally acceptable salt thereof in association with paraquat (i.e. an agriculturally acceptable (bis) salt of the 1,1'-dimethyl-4,4'-bipyridyldiylium ion) at application rates of from 1.5 kg to 3.0 kg asulam equivalent per sprayed hectare and of from 50 g to 150g paraquat equivalent per sprayed hectare, in the ratio of asulam equivalent to paraquat equivalent by weight of 10:1 to 30:1. Herbicidal compositions comprising asulam, or an agriculturally acceptable salt thereof, in association with paraquat are described.

Description

SPECIFICATION The control of weeds by application of a benzenesulphonylcarbamate and paraquat This invention relates to a new method for the control of the growth of weeds and to new herbicidal compositions for use in the method.

It is known, interalia from the specifications of our British Patents Nos. 1040541 and 1052881,that methyl 4 - aminobenzenesulphonylcarbamate of the formula:

which is known as 'asulam', and its agriculturally acceptable salts, i.e. its alkali metal (particularly sodium and potassium), ammonium, amine (particularly diethanolamine, triethanolamine, octylamine, morpholine and dioctylmethylamine) and alkaline earth metal (particularly calcium and magnesium) salts, possess herbicidal properties. Asulam, which is active against monocotyledonous and dicotyledonous weeds, is of substantial commercial importance, particularly because of its low toxicity to mammals, birds, fish and wild life in general, and has a short soil persistence.

Asulam and 'Asulox' (a commercial formulation of the sodium salt of asulam) have hitherto been used to control the growth of many grasses and certain perennial weeds.

Asulam or agriculturally acceptable salts thereof as hereinbefore described may be used, for example under tropical and sub-tropical conditions, at rates of application of from 3.0to4.0 kg asulam equivalent/sprayed hectare by post-emergence application to control the growth of grass and broad-leafed weeds in plantation crops by overall spray application, e.g. in sugar cane and date palms, or directed spray application, e.g. in bananas. Asulam and its agriculturally acceptable salts are translocated within the weeds to which they are applied, exerting systemic herbicidal activity and persistent control of the growth of the weeds. Asulam and its agriculturally acceptable salts inhibit cell division in the weeds to which they are applied and prevent further meristematic growth.After a period of time, which may be from two to six weeks, the weeds become chlorotic and then slowly decay. In consequence, visual maninfestation of control of the growth of the weeds, e.g.

the commencement of chlorosis, may not become apparant for several weeks after the application of asulam and its agriculturally acceptable salts to the weeds. However, at the rates of application indicated above, satisfactory persistent control of several annual broad-leafed weeds, for example Achyranthes indica, may not be achieved.

It is also known that paraquat (the 1,1' - dimethyl 4,4' - bipyridyldiylium ion), in the form of the dich chloride or other agriculturally acceptable (bis) salt, may be used by post-emergence application to control the growth of a broad spectrum of weeds by directed spray application in vines, orchards and plantation crops or by overall spray application to loci of weed infestation which are not crop-growing areas, for which purposes rates of application of from 250 to 600 g paraquat equivalent/sprayed hectare are generally suitable. [It is to be understood that the unqualified term 'paraquat' as used hereinafter in the present specification means the agriculturally acceptable (bis) salts of the 1,1 ' dimethyl - 4,4' - bipyridyldiylium ion unless the contrary is indicated.By the term 'post-emergence application' is meant application to the aerial or exposed portions of the weeds which have emerged above the surface of the soil. By the term 'asulam and its agriculturally acceptable salts' is meant asulam or one or more of its agriculturally acceptable salts as herein before described. By the term 'asulam equivalent' is meant the amount of methyl 4 - aminobenzenesulphonylcarbamate or the methyl 4 - aminobenzenesulphonylcarbamate content of the asulam salt in question. By the term 'paraquat equivalent' is meant the 1,1' - dimethyl - 4,4' - bipyridyldiylium ion content of the 1,1' - dimethyl - 4,4' bipyridyldiylium (bis) salt in question. By the term sprayed hectare' is meant the surface area of ground in hectares to which asulam and its agriculturally acceptable salts are applied in association with paraquat].

The application of paraquatto plants causes rapid necrosis and destruction of plant tissue to which it is applied, resulting in control of the growth of the plants but not necessarily total kill of the plant because the very rapidity of onset of necrosis limits the extent to which paraquat is translocated through the plant. Under conditions inducive of vigorous plant growth, for example under tropical or subtropical conditions, regeneration of plants which have been treated with paraquat results in the break-down of weed control within relatively short periods of time and necessitates repeated applications of paraquat to achieve effective long-term control of the growth of weeds, more especially of vigorous grass weeds and perennial grass and broadleafed weeds.

Efforts to combine the rapid control of the growth of weeds obtained by the post-emergence application of paraquat with the persistence of weed control obtained by the post-emergence application of asulam and its agriculturally acceptable salts by associated application of asulam and its agriculturally acceptable salts at the rates of application indicated above, i.e. 3.0 to 4.0 kg asulam equivalent/sprayed ha, and paraquat at the rates of application indicated above, i.e. 250 to 600 g paraquat equivalent/sprayed ha, fail to achieve any improvement in control of the growth of weeds obtained by the application of asulam and its agriculturally acceptable salts alone or paraquat alone at the rates of application indicated above.It is believed that this is due to the prevention of the effective absorption and translocation of asu lam and its agriculturally acceptable salts in plant tissue by the rapid necrosis of the plant tissue produced by the paraquat.

As a result of research and experimentation, it has now been found that the antagonistic effect produced by the associated application of asulam or an agriculturally acceptable salt thereof and paraquat at the rates of application herein before indicated may be overcome and improved control of the growth of weeds (i.e. undesired vegetation) may be obtained by the associated post-emergence application of asulam or an agriculturally acceptable salt thereof at rates of application which are somewhat lower than those normally utilized for controlling the growth of weeds and paraquat at relatively low doses.

Improvements in the control of the growth of weeds by the application of asulam or an agriculturally acceptable salt thereof in association with paraquat provided according to the present invention are obtained in terms of potency, i.e. reduction in the amount of herbicide which needs to be applied to achieve satisfactory control of the growth of weeds, reduction in frequency of application of the herbicides required to prevent the breakdown of weed control and an increase in the spectrum of weeds which may be controlled by a given rate of herbicide application.

Excellent and persistent control of the growth of weeds, without the antagonistic effect produced by the associated application of asulam and its agriculturally acceptable salts and paraquat at the rates of application hereinbefore described, is achieved by the application of from 1.5 to 3.0 kg asulam equivalent/sprayed ha in association with from 50 to 150 g paraquat equivalent/sprayed ha in the ratio of asulam equivalent to paraquat equivalent by weight of 10:1 to 30:1, especially 15:1 to 25:1 and more especially 20:1.

Accordingly, the present invention providers a method forthe control of the growth of monocotyledonous, e.g. grass, and dicotyledonous, i.e.

broad-leafed weeds (i.e. undesired vegetation), for example Commmellna elegans, Borreria verticllliata, Borreria latifolla, Sida acuta, Amaranthus dubius, Pteridium aquilinum, Peperomia sp., Ipomea spp., Momordica charantia, Euphorbia hypericifolia, Xanthium spp.,Achyranthes indica, Caladium spp., Tridax spp., Digitaria ciliaris, Digitaria sanguinalis, Paspalum fasciculatum, Setaria barbata, Panicum muticum, Panicum fasciculatum, Panicum maximum, Panicum trichoides, Eleusine indica, and Sorghume halepense, at a locus of weed infestation which comprises the post-emergence application of asulam or an agriculturally acceptable salt thereof as hereinbefore described in association with paraquat at application rates of from 1.5 to 3.0 kg asulam equivalent per sprayed hectare and of from 50 to 150 g paraquat equivalent per sprayed hectare, in the ratio of asulam equivalent to paraquat equivalent by weight of 10:1 to 30:1, especially 15:1 to 25:1 and more especially 20:1.Application may be by directed application, e.g. directed spray, to control the growth of weeds in vines, orchards and plantation crops, e.g. sugar cane, coffee, date palm or bananas, where application to the crop plant is undesirable, or by overall, non-directed application, e.g. overall, non directed spray, in a locus of weed infestation which is not a crop-growing area and in which a total herb icidal effect is desired. Bananas are a preferred crop wherein the method according to the present inven tion may be used to control the growth of weeds by directed application, e.g. directed spray, avoiding application to the banana trees.Loci of weed infesta tion which are not crop-growing areas but in which the control of weeds is nevertheless desirable include airfields, industrial sites, railways, roadside verges, the verges of rivers, irrigation and other waterways, scrubland and fallow or uncultivated land, in particular where it is desired to control the growth of weeds in order to reduce fire risks.

According to a preferred feature of the present invention, there is provided a method for the control of weeds as hereinbefore described which is particu larly suitable for use in situations in which the weeds to be controlled are growing in areas shaded, for example by established trees (e.g. bananas), which comprises the application of asulam or an agricul turally acceptable salt thereof in association with paraquat at application rates of from 1.75 to 2.25 kg asulam equivalent per sprayed hectare and of from 87.5 gto 112.5 g paraquat equivalent per sprayed hectare, the ratio of asulam to paraquat equivalent by weight being 20:1.

According to a further preferred feature of the present invention there is provided a method for the control of weeds as hereinbefore described which is particularly suitable for use in situations in which the weeds to be controlled are growing in areas which are not shaded, which comprises the application of asulam or an agriculturally acceptable salt thereof in association with paraquat at application rates of from 2.25 to 3.0 kg asulam equivalent per sprayed hectare and of from 112.5 to 150 g paraquat equival ent per sprayed hectare, the ratio of asulam equival ent to paraquat equivalent by weight being 20:1.

In carrying out the method of controlling the growth of weeds according to the present invention, asulam and its agriculturally acceptable salts may be applied in association with paraquat by separate but nearly simultaneous applications or, as it preferred, by the application of formulations containing both asulam and its agriculturally acceptable salts and paraquat, for example obtained by mixing concen trated formulations containing asulam and its agriculturally acceptable salts and concentrated formulations containing paraquat, e.g. by tank mixing, or by using concentrated formulations con taining both asulam and its agriculturally acceptable salts and paraquat, and, if necessary, diluting with suitable diluents (e.g. water or oils) to give formula tions suitable for application.

In carrying out the herbicidal method of the pres ent invention, the associations of asulam and agriculturally acceptable salts thereof as hereinbe fore described and paraquat are normally applied as spray fluids, and such spray fluids may, if desired, contain from about 0.1% to about 1% w/v of surfac tant or surface-active agent. Suitable surfactants may be of the ionic or non-ionic types, for example sulphoricinoleates, quaternary ammonium deriva tives, products based on condensates of ethylene 5 oxide with nonyl- or octyl-phenols, or carboxylic acid esters of anhydrosorbitols which have been rendered soluble by etherification of the free hyd- roxy groups by condensation with ethylene oxide, alkali and alkaline earth metal salts of sulphuric acid ) esters and sulphonic acids such as dinonyl- and di-octyl-sodium sulpho-succinates and alkali and alkaline earth metal salts of high molecularweight sulphonic acid derivatives, e.g. sodium and calcium lignosulphates.

According to a further feature of the present invention, there are provided compositions suitable for herbicidal use according to the method herein before described comprising asulam or an agriculturally acceptable salt thereof as herein before described in association with paraquat,the ratio of asulam equivalent to paraquat equivalent (as hereinbefore defined) in the composition being within the range 10:1 to 30:1, especially 15:1 to 25:1 and more especially 20::1, by weight, with or without, and preferably homogeneously dispersed in, one or more compatible herbicidally-acceptable diluents or carriers (i.e. diluents or carriers of the type generally accepted in the art as being suitable for use in herbicidal compositions and which are compatible with asulam and or an agriculturally acceptable salt thereof as herein before described and the paraquat salt) and suitable, if necessary after dilution (e.g.

with water or an oil) to give application rates of from 1.5 to 3.0 kg asu lam equivalent per sprayed hectare and from 50 to 150 g paraquat equivalent per sprayed hectare. 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 100% by weight of asu lam, or an agriculturally acceptable saltthereof as hereinbefore described, and paraquat together. The compositions according to the invention may, if desired, contain from about 0.01 to about 10% of surfactant.Compositions suitable for immediate application as herbicides without dilution may, for example, contain from about 0.01% to about 1% of surfactant, e.g. from about 0.01% to about 1% w/v of surfactant in spray fluids. Compositions according to the present invention in the form of concentrates which are to be diluted, e.g. with water or oil before use as herbicides may, for example, contain from about 0.05% to about 10% of surfactant, e.g. from about 0.05% to about 10% w/w of surfactant in the case of solid concentrates and from about 0.05% to about 10% w/v of surfactant in the case of liquid concentrates.

The herbicidal compositions may contain both diluents or carriers and surfactants or surface-active (e.g. wetting, dispersing, suspending or emulsifying) agents. Suitable surface-active agents which may be present in herbicidal compositions of the present invention may be those hereinbefore described.

Examples of suitable solid diluents or carriers are water-soluble alkali metal (e.g. sodium or potassium) chlorides (e.g. sodium chloride), carbonates, bicarbonates and sulphates, and urea. The solid compositions (which may take the form of water solube powders or granules) are preferably prepared by grinding the active ingredient with solid diluents.

Granular formulations may be prepared by granulating compositions in powder form obtained as described above.

Liquid compositions according to the invention may take the form of aqueous solutions or suspensions in oil which may incorporate surfactants. Suitable liquid diluents for incorporation in the liquid compositions include water and aliphatic and aromatic hydrocarbons. Surfactants, which may be present in the liquid compositions, may be of the types described above and may, when liquid, also serve as diluents or carriers. Liquid compositions in the form of concentrates may be diluted with water or an oil, e.g. kerosene, to give compositions ready for use.

Spray solutions for use in the method of the present invention may also be prepared in an extemporaneous fashion by mixing asulam or an agriculturally acceptable salt thereof as hereinbefore described, or asulam and a suitable salt of sodium, potassium or magnesium, for example sodium or potassium carbonate or bicarbonate or magnesium carbonate, the paraquat and, if desired, surfactants, with water in the spray tank.

Herbicidal compositions according to the present invention may also contain, if desired, conventional adjuvants such as adhesives, colouring agents and corrosion inhibitors. These adjuvants may also serve as carriers or diluents.

According to a further feature of the present invention there is provided an article of manufacture comprising a herbicidal composition as hereinbefore described, and preferably a herbicidal concentrate which must be diluted before use, within a container for the aforesaid herbicidal commpositions, and instructions physically associated with the aforesaid container setting out the manner in which the aforesaid herbicidal composition contained therein is to be used to control the growth of weeds.The containers will normally be of the types conventionally used for the storage of chemical substances which are solids at normal ambient temperatures and herbicidal compositions, particularly in the form of concentrates, for example cans and drums of metal, which may be internally-lacquered, and plastics materials, bottles of glass and plastics materials, and, when the contents of the container is a solid, for example granular herbicidal compositions, boxes, for example of cardboard, piastics materials and metal, or sacks. The containers will normally be of sufficient capacity to contain amounts of the herbicidal compositions sufficient to treat at least one acre of ground to control the growth of weeds therein but will not exceed a size which is convenient for conventional methods of handling.The instructions will be physically associated with the container, for example by being printed directly thereon or on a label or tag affixed thereto. The directions will normally indicate that the contents of the container, after dilution if necessary, are to be applied to control the growth of weeds in the manner and for the purposes hereinbefore described.

The following Examples illustrate herbicidal compositions and methods for the control of the growth of weeds according to the present invention.

EXAMPLE 1 An aqueous concentrate containing: Asulam (as sodium salt) 35% w/v (asulam equivalent) Paraquat (as dichloride) 1.75% w/v (paraquat equivalent) Water to 100% by volume is prepared by dissolving the asulam salt and paraquat in a portion of the water and then adding, with stirring, the remainder of the water.

The aqueous concentrate thus obtained may be diluted with water and applied at a rate of 6 litres of formulation (corresponding to 2.1 kg of asulam equivalent and 105 g of paraquat equivalent) in 400 litres of spray fluid per sprayed hectare to a cropgrowing area planted with bananas to control the growth of the weeds hereinbefore described by post-emergence directed spray application to the foliage of the weeds, taking care to avoid spraying the crop foliage.

EXAMPLE2 An aqueous concentrate containing: Asulam (as sodium salt) 40% w/v (asulam equivalent) Paraquat (as dichloride) 2%w/v (paraquat equivalent) Water to 100% by volume is prepared in a similar manner to that hereinbefore described in Example 1.

The aqueous concentrate thus obtained may be diluted with water and applied at a rate of 5 litres of formulation (corresponding to 2.0 kg of asulam equivalent and 100 g of paraquat equivalent) in 400 litres of spray fluid per sprayed hectare to a cropgrowing area planted with bananas to control the growth of the weeds hereinbefore described by post-emergence directed spray application to the foliage of the weeds, taking care to avoid spraying the crop foliage.

EXAMPLE 3 A water soluble powder or granule formulation con taining Asulam (as sodium salt) 85.5 wlw (asulam equivalent) (94.1% w/w asulam sodium salt) Paraquat (as dichloride) 4.27% w/w (paraquat equivalent) (5.9% wlw paraquat dichloride) is prepared by grinding the components, together or individually, through suitable milling equipment, followed if necessary by thorough mixing and then, if desired, granulating the powder thus obtained by known methods, for example compaction, extrusion and pan granulation.

The water soluble powder and granule formulations thus obtained may be dissolved in water and applied at a rate of 3.0 kg of formulation (corres ponding to 2.57 kg asulam equivalent and 128 g paraquat equivalent) in 400 litres of spray fluid per sprayed hectare to a crop-growing area planted with bananas to control the growth of the weeds hereinbefore described by post-emergence directed spray application to the foliage of the weeds, taking care to avoid spraying the crop foliage.

EXAMPLE 4 A water soluble powder or granule formulation containing: Asulam (as sodium salt) 50% w/w (asulam equivalent) Paraquat (as dichloride) 2.5% w7w (paraqttat equivalent) Sodium chloride to 100% buy weight is prepared by the procedure herein described in Example 3.

The water soluble powder and granule formulations thus obtained may be dissolved in water and applied art a rate of 6 kg of formulation (corresponding to 3.0 kg asulam equivalent and 150 g paraquat equivalent) in 400 litres of spray fluid per sprayed hectare to a crop-growing area planted with sugar cane to control the growth of the weeds hereinbefore described by post-emergence directed spray application to the foliage of the weeds, taking care to avoid spraying the crop foliage.

EXAMPLE 5 An oil suspension formulation containing: Asulam (as sodium salt) 50% w/v (asulam equivalent) Paraquat (as dichloride) 2.5% w/v (paraquat equivalent) Ethylan 55 (nonylphenol ethylene oxide condensate containing 5.5 moles of ethylene oxide per mole of nonylphenol) 2% w/v Atlox 4856B (surfactant blend of polyoxyethylene triglyceride and alkyl aryl sulphonates) 5% w/v Deodorised kerosene to 100% by volume is prepared by suspending the asulam salt and paraquat in a solution of the Ethylan 55 and Atlox 4856B in a portion of the deodorised kerosene and then adding, with stirring, the remainder of the deodor ised kerosene.

The oil suspension formulation thus obtained may be diluted with water and applied at a rate of4 litres of formulation (corresponding to 2 kg asulam equivalent and 100 g paraquat equivalent) in 400 litres of spray fluid per sprayed hectare to a crop-growing area planted with bananas to control the growth of the weeds hereinbefore described by post emergence directed spray application to the foliage of the weeds, taking care to avoid spraying the crop foliage.

The oil suspension formulation may also be diluted into deodorised kerosene and applied at a rate of 4 litres of formulation (corresponding to 2 kg asulam equivalent and 100 g paraquat equivalent) in 30 litres of spray fluid per sprayed hectare to a crop-growing area planted with bananas to control the growth of the weeds herein before described by post-emergence directed spray application to the foliage of the weeds, taking care to avoid spraying the crop foliage.

The following representative experiments illus trate the method of the present invention:- EXPERIMENT 1 Plots of area 0.0186 hectare in a randomised block design in a plantation of established banana trees (variety Robusta) whose weed flora comprised Commelina elegans, Sida acuta, Eleusine indica, Borreria verticilliata, Borreria latiflora, Setaria barbata andAchyranthes indica, at growth stages of 15 to 30 cm high, were treated as hereinafter indicated.

Treatments were applied by directed spray, using a knapsack sprayer, to the weeds, taking care to avoid application to the banana foliage. Treatments 1,2 and 3 were prepared by diluting amounts of the aqueous concentrate prepared as hereinbefore indicated in Example 1 corresponding to the indicated volume of concentrate per sprayed hectare, with water and applied at an application rate corresponding to 448 litres of spray fluid per sprayed hectare. Treatment 4 was prepared by diluting an amount of a 20% w/v aqueous paraquat (as dichloride) concentrate corresponding to the indicated volume of concentrate per sprayed hectare, with water and applied at an application rate corresponding to 448 litres of spray fluid per sprayed hectare.

Treatment 1 5.6 litres of the aqueous concentrate prepared as described in Example 1 (1.96 kg asulam equivalent and 98 g paraquat equivalent) per sprayed hectare.

Treatment2 7.0 litres of the aqueous concentrate prepared as described in Example 1 (2.45 kg asulam equivalent and 122.5 g paraquat equivalent) per sprayed hectare.

Treatment3 8.4 litres of the aqueous concentrate prepared as described in Example 1 (3.0 kg asulam equivalent and 150 g paraquat equivalent) per sprayed hectare.

Treatment 2.8 litres of 20% w/v aqueous paraquat (as dichloride) concentrate (560 g paraquat equivalent) per sprayed hectare.

Each treatment was replicated three times.

Assessment of weed control and the effect of the treatments on the banana plant was carried out one week after treatment and fortnightly thereafter according to the scale of ratings indicated in Table I.

TABLEI: European Weed Research Council Scale of Rating (Rawle 1978)

Scale Symptoms of Weed of Phytotoxicity Control General Rating on the crop % Appraisal 1 None 100 Excellent 2 Very slight symptoms 98 Very good 3 Slight symptoms 95 Good 4 Heavy symptoms 90 Satisfactory 5 Doubtful 82 Uncertain 6 Evident damage 70 Unsatisfactory 7 Heavy damage 55 Bad 8 Very heavy damage 30 Very bad 9 Complete kill O Absolutely useless The following results were obtained: RESULTS Safety of Treatments to Bananas The results presented in Table II show that there was no phytotoxicity to the banana plants due to any of the test treatments.

STABLE!!: Effect of Treatments of Bananas

Weeks after spraying Treatment 1 1 3 5 7 9 11 13 15 17 Treatment 1 1 1 1 1 1 1 1 1 Treatment2 1 1 1 1 1 1 1 1 1 Treatment 3 1 1 1 1 1 1 1 1 1 Treatment4 1 1 1 1 1 1 1 1 1 Overall Weed Control The overall weed control over the trial period is given in Table Ill.

TABLEIII: Effect of Treatments on Overall Weed Control

Weeks after spraying Treatment 1 3 5 7 9 11 13 15 17 Treatment 1 7.0 6.0 5.7 4.3 3.7 4.0 4.0 4.7 5.0 Treatment 2 6.0 5.0 5.7 5.0 3.7 3.7 3.0 4.7 4.7 Treatment3 6.7 4.7 3.7 3.7 2.7 3.0 2.7 2.7 3.7 Treatment 4 3.6 4.0 4.7 4.7 5.7 6.0 6.0 6.3 6.7 The results given in Table Ill show that the herbicidal effects of Treatments 1,2 and 3 manifested themselves visually relatively slowly over the first five to nine weeks after spraying which is, as hereinbefore described, characteristic of the herbicidal properties of asulam and its agriculturally acceptable salts. Thereafter, a high level of weed control, including growth ofAchyranthes indica, was obtained up to seventeen weeks after spraying, more especially with Treatment 3. In contrast, although Treatment 4 produced a rapid control of weeds characteristic of paraquat, this weed control had broken down about five weeks after spraying.

EXPERIMENT 2 Plots of 100 square metres area in a randomized block design in two plantations (Sites 1 and 2) of approximately six months old banana trees (variety Plant Crop Valery) in Jamaica were treated as hereinafter indicated. At Site 1, the soil type was heavy clay, derived from yellow limestone, and at Site 2, the soil type was mainly alluvial deposit. Both sites were on flat land with an annual rainfall of approximately 1778 mm. Spraying coincided with the onset of the rainy season. An assessment of emerged weed species observed at the sites prior to treatment revealed that broad-leafed species were more common than grasses and grassy weeds at both sites.The weed populations comprised: Site 7:- Cynodon dactylon, Digitaria ciliaris, Panicum maximum, Cyperus rotundus, Digitaria decumbens, Amaranthus dubius, Bidens pilosa, Mimosa pudica, Physalis angulata, Sida acuta, Desmodium adscendens and Wild Mustard (Brassica Kaber or Sinapis arvensis).

Site 2r Cynodon dactylon, Digitaria ciliaris, Panicum maximum, Cyperus rotundus, Cyperus ferax, Amaranth us dubius, Bidens pilosa, Sida acuta, Brassica Kaber, Mimosa pudica, and Desmodium adscendens.

Treatments 1,2 and 3 were prepared by diluting amounts of the aqueous concentrate prepared as hereinbefore indicated in Example 1 corresponding to the indicated volume of concentrate per sprayed hectare, with water and applied at an application rate corresponding to 450 litres of spray fluid per sprayed hectare.-Treatment 4 was prepared by diluting an amount of 20% w/v aqueous paraquat (as dichloride) concentrate corresponding to the indicated volume of concentrate per sprayed hectare, with water and applied at an application rate corresponding to 337.5 litres of spray fluid per sprayed hectare.Treatments 5 and 6 were prepared by diluting amounts of 40% w/v aqueous asulam (as sodium salt) concentrate cor responding to the indicated volume of concentrate per sprayed hectare, with water and applied at an application rate corresponding to 450 litres of spray fluid per sprayed hectare. Application was made by knapsack sprayer, care being taken to avoid application to the banana plants.

Treatment 1 6 litres of the aqueous concentrate prepared as described in Example 1(2.1 kg asulam equivalent and 105g paraquat equivalent) per sprayed hectare.

Treatment2 8 litres of the aqueous concentrate prepared as described in Example 1(2.8 kg asulam equivalent and 140 g paraquat equivalent) per sprayed hectare.

Treatment3 10 litres of the aqueous concentrate prepared as described in Example 1(3.5 kg asulam equivalent and 175 g paraquat equivalent) per sprayed hectare.

Treatment 1.41 litres of 20% w/v aqueous paraquat (as dichloride) concentrate (280 g paraquat equivalent) per sprayed hectare.

Treatment 5 8.46 litres of 40% w/v aqueous asulam (as sodium salt) concentrate (3.4 kg asulam equivalent) per sprayed hectare.

Treatment 6 11.28 litres of 40% w/v aqueous asulam (as sodium salt) concentrate (4.5 kg asulam equivalent) per sprayed hectare.

Each treatment was replicated three times and untreated plots were retained as controls.

Assessment of weed control and the effects of the treatments on the banana plants was carried out at weekly intervals after treatment. The time between treatment and the achievement of effective weed control ('Time (days) to achieve weed control') and the time between treatment and reinfestation of weeds to a level requiring further weed control measures ('Duration (days) of effective weed control') were recorded.

The following results were obtained: RESULTS Safety of Treatments to Bananas No phytotoxic effects were observed in the banana plants in any of the treated plots at either Site. The plants were uniform in size and colour and exhibited no signs of chlorosis or necrosis.

WEED CONTROL The weed control obtained at Sites 1 and 2 with the treatments is given in Table IV.

TA BLE IV Weed Control

Time (days) Duration (days) to achieve of effective Weeds not Treatment weed control control controlled 1 4-10 130 None (No weeds survived treatment) 2 2-7 130 None (No weeds survived treatment) 3 2-5 150 None (No weeds survived treatment) 4 2-5 80 Desmodium adscendens Side acute 5 14-19 150 None (No weeds survived treatment) 6 14-17 150 None (No weeds survived treatment) The results given in Table IV show that the treatments according to the present invention (Treatments 1 and 2) produced both a rapid control of weeds characteristic of paraquat at application rates (105 to 140 g per hectare) lowerthan those generally used for paraquat alone, combined with the maintenance of a high level of weed control for upto 130 days after treatment at application rates of asulam (2.1 to 2.8 kg per hectare) lowerthan those generally used for asulam alone. In contrast, Treatment 3 showed no improvement over the results obtained using asulam alone (Treatments 5 and 6) and Treat ment4, although producing a rapid control of weeds characteristic of paraquat, gave effective weed control only up to 80 days after treatment.

Claims (27)

1. A method for the control of the growth of monocotyledonous and dicotyledonous weeds which comprises the post-emergence application to a locus of weed infestation of asulam (i.e. methyl 4 aminobenzene - sulphonylcarbamate) or an agriculturally acceptible salt thereof in association with paraquat (i.e. an agriculturally acceptable (bis) salt of the 1,1' - dimethyl - 4,4' - bipyridyldiylium ion) at application rates of from 1.5 kg to 3.0 kg asulam equivalent per sprayed hectare and of from 50 g to 150 g paraquat equivalent per sprayed hectare, in the ratio of asulam equivalent to paraquat equivalent by weight of 10:1 to 30:1.

2. A method according to claim 1 in which the ratio of asulam equivalent to paraquat equivalent by weight applied to the locus of weed infestation is 15:1 to 25:1.

3. A method according to claim 1 in which the ratio of asulam equivalent to paraquat equivalent by weight applied to the locus of weed infestation is 20:1.

4. A method according to claim 1,2 or3 in which asulam, or an agriculturally acceptable salt thereof, and paraquat are applied in association by directed application to control the growth of weeds in vines, orchards or plantation crops.

5. A method according to claim 4 in which the locus of infestation is in a sugar cane, coffee, date palm or banana plantation.

6. A method according to any of claims 1 to 5 for the control of weeds in a locus in shade which comprises the post-emergence application to the shaded locus of weed infestation of asulam, or an agriculturally acceptable salt thereof, in association with paraquat at application rates of from 1.75 kg to 2.25 kg asulam equivalent per sprayed hectare and of from 87.5 g to 112.5 g paraquat equivalent per sprayed hectare, in the ratio of asulam equivalent to paraquat equivalent by weight of 20:1.

7. A method according to claim 6 in which the locus of weed infestation in shade is in a banana plantation.

8. A method according to claim 1, 2 or 3 for the control of weeds in an area not in shade which comprises the post-emergence application to such an area of weed infestation of asulam, or an agriculturally acceptable salt thereof, in association with paraquat at application rates of from 2.25 kg to 3.0 kg asulam equivalent per sprayed hectare and of from 112.5 gto 150 g paraquat equivalent per sprayed hectare, in the ratio of asulam equivalent to paraquat equivalent by weight of 20:1.

9. A method according to any one of claims 1 to 8 in which the weeds controlled are one or more of Commelina elegans, Borreria verticilliata, Borreria latifolia, Sida acuta, Amaranthus dubius, Pteridium aqullinium, Peperomia s p., Ipomea spp., Momordica charantia, Euphorbia hypericifolia, Xanthium spp., Achyranthes indica, Caladium spp., Tridax spp., Digitaria ciliaris, Digitaria sanguinalls, Paspalum fasciculatum, Setaria barbata, Panicum muticum, Panicum fasciculatum, Panicum maximum, Panicum trichoides, Eleusine indica, and Sorghume halepense.

10. A method according to any one of claims 1 to 9 in which asulam, or an agriculturally acceptable salt thereof, and paraquat are applied to the locus of weed infestation separately but nearly simultaneously.

11. A method according to any one of claims 1 to 9 in which asulam, or an agriculturally acceptable salt thereof, and paraquat are applied to the locus of weed infestation simultaneously by means of a formulation containing both asulam, or an agriculturally acceptable salt thereof, and paraquat.

12. A method according to claim 11 in which the herbicides are applied to the locus of weed infestation simultaneously by means of a tank-mix prepared from concentrated formulations containing asulam, oran agriculturally acceptable salt thereof, and concentrated formulations containing paraquat, optionally diluted with suitable diluent(s).

13. A method according to claim 12 in which a liquid diluent selected from water or oils is used to give formulations suitable for application.

14. A method according to any one of the preceding claims in which the association of asulam, or an agriculturally acceptable salt thereof, and paraquat are applied to the locus of weed infestation as spray fluid(s).

15. A method according to claim 14 in which the spray fluid(s) contain from 0.1% to 1% (w/v) of surfactant.

16. A herbicidal composition forthe control of the growth of monocotyledonous or dicotyledonous weeds which comprises asulam or an agriculturally acceptable salt thereof in association with paraquat, the ratio of asulam equivalent to paraquat equivalent in the composition being within the range 10:1 to 30:1 by weight

17. A herbicidal composition according to claim 16 which includes one or more herbicidallyacceptable diluents or carriers.

18. A herbicidal composition according to claim 16 or 17 in which the ratio of asulam equivalent to paraquat equivalent in the composition is 15:1 to 25:1.

19. A herbicidal composition according to claim 16 or 17 in which the ratio of asulam equivalent to paraquat equivalent in the composition is 20:1.

20. A herbicidal composition according to claim 17,18 or 19 capable of giving application rates of from 1.5 kg to 3 kg asulam equivalent per sprayed hectare and from 50 to 150 g paraquat equivalent per sprayed hectare.

21. A herbicidal composition according to any one of claims 16 to 20 which contains from 0.05 to 100% by weight of asulam, or an agriculturally acceptable salt thereof, and paraquat.

22. A herbicidal composition according to any one of claims 16 to 21 which contains from 0.01 to 10% of surfactant.

23. A herbicidal composition according to any one of claims 16 to 22 in the form of a spray fluid containing from 0.01% to 1% w/v of surfactant.

24. A herbicidal composition according to claim' 22 in the form of a concentrate, which is to be diluted before use as a herbicide, containing from 0.05% to 10% to surfactant.

25. A herbicidal composition according to any one of claims 17 to 24 in which the diluent is water.

26. A herbicidal composition according to any one of claims 17 to 24 in which the diluent is an oil.

27. A herbicidal composition according to claim 16 substantially as hereinbefore described with especial reference to any one of Example 1 to 5.