the synergistic herbicidal compositions of this invention contain ( a ) a compound of formula ( i ) and ( b ) a compound of formula ( ii ), wherein formulae ( i ) and ( ii ) are defined above ; and an agriculturally acceptable carrier therefor . preferably , component ( a ) is nmsc and component ( b ) is acetochlor , alachlor or metolachlor , with acetochlor being especially preferred . the synergistic composition contains an herbicidally effective amount of a combination of component ( a ) and component ( b ). the term &# 34 ; herbicide &# 34 ; as used herein denotes a compound which controls or modifies the growth of plants . the term &# 34 ; herbicidally effective amount &# 34 ; indicates the quantity of such a compound or combination of such compounds which is capable of producing a controlling or modifying effect on the growth of plants . controlling or modifying effects include all deviation from natural development , for example : killing , retardation , leaf burn , albinism , dwarfing and the like . the term &# 34 ; plants &# 34 ; refers to all physical pars of a plant , including seeds , seedlings , saplings , roots , tubers , stems , stalks , foliage , and fruits . in the compositions of this invention , the weight ratio of component ( a ) to component ( b ) at which the herbicidal effect is synergistic lies within the range of between about 32 : 1 and about 1 : 20 . preferably , the weight ratio of component ( a ) to component ( b ) is between about 8 : 1 and 1 : 15 , with a weight ratio of between about 4 : 1 and about 1 : 10 being especially preferred . the rate at which the synergistic composition of the invention is applied will depend upon the particular type of weed to be controlled , the degree of control required , and the timing and method of application . in general , the compositions of the invention can be applied at an application rate of between about 0 . 005 kilograms / hectare ( kg / ha ) and about 5 . 0 kg / ha , based on the total amount of active ingredient ( component ( a )+ component ( b )) in the composition . an application rate of between about 0 . 5 kg / ha and 3 . 0 kg / ha is preferred . in an especially preferred embodiment of this invention , the composition contains components ( a ) and ( b ) in relative amounts sufficient to provide an application rate of at least 1 . 0 kg / ha , of which component ( a ) provides at least 0 . 04 kg / ha . the compositions of this invention are useful as herbicides , demonstrating synergistic activity for the control of undesirable vegetation . the compositions can be formulated in the same manner in which herbicides are generally formulated . the compounds may be applied either separately or combined as part of a two - part herbicidal system . the object of the formulation is to apply the compositions to the locus where control is desired by a convenient method . the &# 34 ; locus &# 34 ; is intended to include soil , seeds , and seedlings , as well as established vegetation . the composition employed in the practice of the present invention can be applied in a variety of ways known to those skilled in the art , at various concentrations . the composition is useful in controlling the growth of undesirable vegetation by preemergence or postemergence application to the locus where control is desired . the compositions of the present invention are particularly effective when applied preemergence . in practice , the composition is applied as a formulation containing the various adjuvants and carriers known to or used in the industry for facilitating dispersion . the choice of formulation and mode of application for any given compound may affect its activity , and selection will be made accordingly . the compositions of the invention may thus be formulated as granules , as wettable powders , as emulsifiable concentrates , as powders or dusts , as flowables , as solutions , as suspensions or emulsions , or as controlled release forms such as microcapsules . these formulations may contain as little as about 0 . 5 % to as much as about 95 % or more by weight of active ingredient . the optimum amount for any given compound will depend upon formulation , application equipment , and nature of the plants to be controlled . wettable powders are in the form of finely divided particles which disperse readily in water or other liquid carriers . the particles contain the active ingredient retained in a solid matrix . typical solid matrices include fuller &# 39 ; s earth . kaolin clays , silicas and other readily wet organic or inorganic solids . wettable powders normally contain about 5 % to about 95 % of the active ingredient plus a small amount of wetting , dispersing , or emulsifying agent . emulsifiable concentrates are homogeneous liquid compositions dispersible in water or other liquid , and may consist entirely of the active compound with a liquid or solid emulsifying agent , or may also contain a liquid carrier , such as xylene , heavy aromatic naphthas , isophorone and other non - volatile organic solvents . in use , these concentrates are dispersed in water or other liquid and normally applied as a spray to the area to be treated . the amount of active ingredient may range from about 0 . 5 % to about 95 % of the concentrate . granular formulations include both extrudates and relatively coarse particles , and are usually applied without dilution to the area in which suppression of vegetation is desired . typical carriers for granular formulations include sand , fuller &# 39 ; s earth . attapulgite clay , bentonite clays , montmorillonite clay , vermiculite , perlite and other organic or inorganic materials which absorb or which can be coated with the active compound . granular formulations normally contain about 5 % to about 25 % active ingredients which may include surface - active agents such as heavy aromatic naphthas , kerosene and other petroleum fractions , or vegetable oils ; and / or stickers such as dextrins , glue or synthetic resins . dusts are flee - flowing admixtures of the active ingredient with finely divided solids such as talc , clays , flours and other organic and inorganic solids which act as dispersants and carriers . microcapsules are typically droplets or granules of the active material enclosed in an inert porous shell which allows escape of the enclosed material to the surroundings at controlled rates . encapsulated droplets are typically about 1 to 50 microns in diameter . the enclosed liquid typically constitutes about 50 to 95 % of the weight of the capsule , and may include solvent in addition to the active compound . encapsulated granules are generally porous granules with porous membranes sealing the granule pore openings , retaining the active species in liquid form inside the granule pores . granules typically range from 1 millimeter to 1 centimeter , preferably 1 to 2 millimeters in diameter . granules are formed by extrusion , agglomeration or prilling , or are naturally occurring . examples of such materials are vermiculite , sintered clay , kaolin , attapulgite clay , sawdust and granular carbon . shell or membrane materials include natural and synthetic rubbers , cellulosic materials , styrene - butadiene copolymers , polyacrylonitriles , polyacrylates , polysters , polyamides , polyureas , polyurethanes and starch xanthates . other useful formulations for herbicidal applications include simple solutions of the active ingredient in a solvent in which it is completely soluble at the desired concentration , such as acetone , alkylated naphthalenes , xylene and other organic solvents . pressurized sprayers , wherein the active ingredient is dispersed in finely - divided form as a result of vaporization of a low boiling dispersant solvent carrier , may also be used . many of these formulations include wetting , dispersing or emulsifying agents . examples are alkyl and alkylaryl sulfonates and sulfates and their salts ; polyhydric alcohols ; polyethoxylated alcohols ; esters and fatty amines . these agents , when used , normally comprise from 0 . 1 % to 15 % by weight of the formulation . each of the above formulations can be prepared as a package containing the herbicide together with other ingredients of the formulation ( diluents , emulsifiers , surfactants , etc .). the formulations can also be prepared by a tank mix method , in which the ingredients are obtained separately and combined at the grower site . these formulations can be applied to the areas where control is desired by conventional methods . dust and liquid compositions , for example , can be applied by the use of power - dusters , broom and hand sprayers and spray dusters . the formulations can also be applied from airplanes as a dust or a spray or by rope wick applications . to modify or control growth of germinating seeds or emerging seedlings , dust and liquid formulations can be distributed in the soil to a depth of at least one - half inch below the soil surface or applied to the soil surface only , by spraying or sprinkling . the formulations can also be applied by addition to irrigation water . this permits penetration of the formulations into the soil together with the irrigation water . dust compositions , granular compositions or liquid formulations applied to the surface of the soil can be distributed below the surface of the soil by conventional means such as discing , dragging or mixing operations . an important factor influencing the usefulness of a given herbicide is its selectivity towards crops . in some cases , a beneficial crop is susceptible to the effects of the herbicide . to be effective , an herbicide must cause minimal damage ( preferably no damage ) to the beneficial crop while maximizing damage to weed species which infest the locus of the crop . it is known that chloroacetanilide compounds of formula ( ii ) may cause undesirable damage to certain crop species , particularly corn , at relatively high application rates . to preserve the beneficial aspects of herbicide use and to minimize crop damage , it is known to apply chloroacetanilide herbicides in combination with an antidote . as used herein , &# 34 ; antidote &# 34 ; describes a compound which has the effect of establishing herbicide , selectivity , i . e ., continued herbicidal phytotoxicity to weed species by the herbicide , and reduced or non - phytotoxicity to the cultivated crop species . the term &# 34 ; antidotally effective amount &# 34 ; describes an amount of an antidote compound which counteracts to some degree a phytotoxic response of a beneficial crop to an herbicide . if necessary or desired for a particular application or crop , the composition of the present invention may contain an antidotally effective amount of an antidote for component ( b ). those skilled in the art will be familiar with antidotes which are suitable for use with chloroacetanilide compounds of formula ( ii ) and can readily determine an antidotally effective amount for a particular compound and application . further , other biocidally active ingredients or compositions may be combined with the synergistic herbicidal composition of this invention . for example , the compositions may contain , in addition to components ( a ) and ( b ), insecticides , fungicides , bactericides , acaracides or nematicides , in order to broaden the spectrum of activity . the following example is for illustrative purposes only . this example is not intended as necessarily representative of the overall testing performed and is not intended to limit the invention in any way . as one skilled in the art is aware , in herbicidal testing , a significant number of factors that are not readily controllable can affect the results of individual tests and render them non - reproducible . for example , the results may vary depending on environmental factors , such as amount of sunlight and water , soil type , ph of the soil , temperature , and humidity , among other factors . also , the depth of planting , the application rate of individual and combined herbicides , the application rate of any antidote , and the ratio of the individual herbicides to one another and / or to an antidote , as well as the nature of crops or weeds being tested , can affect the results of the test . results may vary from crop to crop within the crop varieties . seeds of the following six different weed species were sown into 1 liter aluminum flats containing sandy loam soil : barnyardgrass ( echinochloa crusgalli ) (&# 34 ; echcg &# 34 ;), goosegrass ( eleusine indica ) (&# 34 ; elein &# 34 ;), wild - proso millet ( panicum miliaceum ) (&# 34 ; panmi &# 34 ;), large crabgrass ( digitaria sanguinalis ) (&# 34 ; digsa &# 34 ;), broadleaf signalgrass ( brachiaria platphylla ) (&# 34 ; brapp &# 34 ;), and porol . seeding depths ranged from 0 . 5 to 1 . 5 cm and plant densities ranged from 3 to 25 plants per row depending on individual plant species . seeds of ivyleaf morningglory ( ipomoea hederacea ) (&# 34 ; ipohe &# 34 ;) were sown into 400 ml plastic cups containing sandy loam soil . water dispersible formulations of nmsc and acetochlor were applied to the soil surface in a complete factorial treatment design with seven ( 7 ) levels of each . nmsc was applied at 0 , 5 , 10 , 20 , 40 , 80 and 160 grams per hectare ( g / ha ) to the flats and to the cups . acetochlor was applied at 0 , 5 , 10 , 20 , 40 , 80 and 160 g / ha to the flats and at 0 , 50 , 100 , 200 , 400 , 800 and 1600 g / ha to the cups . after application , the flats and cups were placed in a glasshouse and maintained under good growing conditions . the degree of weed control was visually evaluated and recorded 25 days after treatment as a percentage of weed control . percent control is the total injury to the plants due to all factors including : inhibited emergence , stunting , malformation , chlorosis and other types of plant injury . the control ratings range from 0 to 100 percent , where 0 represents no injury and 100 represents complete kill . the combination of nmsc and acetochlor was effective against the tested weed species at varying rates of application . the combinations of nmsc and acetochlor gave various results against panmi , echcg , digsa , elein , brapp and ipohe , showing antagonism , additivity and synergy or an indication of potential synergy at different levels of application . however , it was found that combinations of nmsc and acetochlor exhibited unexpected and surprising synergistic action in the control of porol , at rates at which neither compound alone exhibits control of this weed species . table i below shows the actual results of the above described preemergence testing of combinations of nmsc and acetochlor on porol . table i also shows the expected weed control for the tested combinations of nmsc and acetochlor against porol , calculated according to the colby method ( s . r . colby . &# 34 ; calculating synergistic and antagonistic response of herbicide combinations .&# 34 ; weeds 15 ( i ): 20 - 23 , 1967 ). the colby method represents a direct approach to measuring the synergistic activity of two herbicides . according to the colby method : wherein e is the expected percent weed control for a combination of a first herbicide h1 and a second herbicide h2 at an application rate of p + q g / ha ; x is the percent weed control observed for h1 at application rate p g / ha : and y is the percent weed control observed for h2 at application rate q g / ha . table i__________________________________________________________________________weed control of porol by combinations of nmsc and acetochlor acetochlor ( g / ha ) 0 5 10 20 40 80 160nmsc ( g / ha ) a . sup . 1 e . sup . 2 a e a e a e a e a e a e__________________________________________________________________________ 0 0 0 0 0 0 0 0 0 0 0 12 12 45 45 5 0 0 0 0 0 0 0 0 0 0 17 12 45 4510 0 0 0 0 0 0 0 0 0 0 17 12 70 4520 0 0 0 0 0 0 0 0 0 0 22 12 33 4540 0 0 0 0 0 0 0 0 5 0 77 12 88 4580 5 5 0 5 83 5 60 5 77 5 100 16 100 48160 5 5 55 5 47 5 62 5 72 5 100 16 100 48__________________________________________________________________________ . sup . 1 actual percent weed control . sup . 2 expected percent weed control the results shown in table i demonstrate the synergistic herbicidal efficacy achieved by compositions of this invention . although the invention has been described with reference to preferred embodiments and examples thereof , the scope of the present invention is not limited only to those described embodiments . as will be apparent to persons skilled in the art , modifications and adaptations to the above - described invention can be made without departing from the spirit and scope of the invention , which is defined and circumscribed by the appended claims .
a synergistic herbicidal composition containing a cyclohexanedione compound of formula : ## str1 ## wherein n is 0 or 1 ; and a chloroacetanilide compound of the formula : ## str2 ## wherein r 1 is hydrogen , methyl or ethyl ; r 2 is hydrogen or ethyl ; r 3 is hydrogen or methyl ; and r 4 is methyl , methoxy , methoxymethyl , ethoxy or butoxy . a method of controlling the growth of undesirable vegetation , particularly in crops , using this synergistic composition is also disclosed .