Abstract:
A method of selectively controlling undesirable vegetation in crops by using a postemergent application of an herbicidally effective amount of a metal chelate of a 2-(substituted benzoyl)-1,3-cyclohexanedione compound to the locus of such undesirable vegetation.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention is directed to the use of metal chelates as a delivery system to improve the selectivity of 2-(substituted benzoyl)-1,3-cyclohexanedione compounds as post-emergence herbicides in crops.  
         BACKGROUND OF THE INVENTION  
         [0002]    The protection of crops from weeds and other undesirable vegetation which inhibit crop growth is a constantly recurring problem in agriculture. To help combat this problem researchers in the field of synthetic chemistry have produced an extensive variety of chemicals and chemical formulations effective in the control of such unwanted growth. Chemical herbicides of many types have been disclosed in the literature and a large number are in commercial use.  
           [0003]    Unfortunately, many of such herbicides exhibit phytotoxicity to the desired crop as well as to the weeds sought to be controlled. Thus, there is a long-standing need for selective herbicides which will control frequently occurring weeds but which will not adversely affect the crop plants when applied at herbicidally effective levels.  
           [0004]    U.S. Pat. Nos. 4,780,127, 4,938,796, 5,006,158 and 5,089,046 disclose 2-(substituted benzoyl)-1,3-cyclohexanedione compounds having the general structure:  
                         
 
           [0005]    wherein X, Q and Z have the meanings set forth hereinafter. These dione compounds have proved to be effective pre-emergent and postemergent herbicides against a wide variety of grasses, broadleaf weeds and sedges. Moreover, PCT Application No. 97/27748 discloses that metal chelates of 2-(substituted benzoyl)- 1,3 -cyclohexanedione compounds have proved to be chemically stable for long periods of time under normal as well as extreme temperature conditions.  
           [0006]    The parent cyclohexanedione exhibits a substantial phytotoxic effect. In contrast, it has now been discovered that metal chelates of 2-(substituted benzoyl)-1,3-cyclohexanedione compounds will effectively control a broad range of weeds without exhibiting any substantial phytotoxic effect on the crop itself.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention is directed to methods of selectively controlling weeds and other undesirable vegetation in a given crop such as wheat. In one embodiment of this invention, the method comprises the postemergent application of an herbicidally effective amount of a metal chelate of a 2-(substituted benzoyl)-1,3-cyclohexanedione to the locus of such weeds and other vegetation. In another embodiment of this invention, the method comprises the postemergent application of an herbicidally effective amount of a metal chelate of a 2-(substituted benzoyl)-1,3-cyclohexanedione to the locus of such weeds and other vegetation, said metal chelate having been formulated as a microcapsule.  
           [0008]    As is employed herein, the term “herbicide” is used to denote a compound which controls or modifies the growth of plants. The term “herbicidally effective amount” is used to indicate the quantity of such compound which is capable of producing a controlling or modifying effect. Controlling or modifying effects include all deviations from natural development, for example: killing, retardation, leaf burn, albinism, dwarfing, and the like. The term “plants” refers to all physical parts of a plant, including seeds, seedlings, saplings, roots, tubers, stems, stalks, foliage, and fruits.  
         DETAILED DESCRIPTION OF THE INVENTION  
         [0009]    The present invention relates to the use of metal chelates of herbicidal dione compounds to selectively control weeds and other undesirable vegetation in a given crop such as wheat. These herbicidal dione compounds have the general formula (I):  
                         
 
           [0010]    wherein X represents a halogen atom; a straight- or branched-chain alkyl or alkoxy group containing up to six carbon atoms which is optionally substituted by one or more groups —OR 1  or one or more halogen atoms; or a group selected from nitro, cyano, —CO 2  R 2  —S(O) m R 1 , —O(CH 2 ) r OR 1 , —COR 2 , —OSO 2 R 4 , —NR 2 R 3 , —SO 2 NR 2 R 3 , —CONR 2 R 3  and —CSNR 2 R 3 ;  
           [0011]    R 1  represents a straight- or branched-chain alkyl group containing up to six carbon atoms which is optionally substituted by one or more halogen atoms;  
           [0012]    R 2  and R 3  each independently represents a hydrogen atom; or a straight- or branched-chain alkyl group containing up to six carbon atoms which is optionally substituted by one or more halogen atoms;  
           [0013]    R 4  represents a straight- or branched-chain alkyl, alkenyl or alkynyl group containing up to six carbon atoms optionally substituted by one or more halogen atoms; or a cycloalkyl group containing from three to six carbon atoms;  
           [0014]    each Z independently represents halo, nitro, cyano, S(O) m R 5 , OS(O) m R 5 , (C 1 -C 6 )alkyl, (C 1 -C 6 )alkoxy, (C 1 -C 6 )haloalkyl, (C 1 -C 6 )haloalkoxy, carboxy, (C 1 -C 6 )alkylcarbonyloxy, (C 1 -C 6 )alkoxycarbonyl, (C 1 -C 6 )alkylcarbonyl, amino, (C 1 -C 6 )alkylamino, (C 1 -C 6 )dialkylamino having independently the stated number of carbon atoms in each alkyl group, (C 1 -C 6 )alkylcarbonylamino, (C 1 -C 6 )alkoxycarbonylamino, (C 1 -C 6 )alkylaminocarbonylamino, (C 1 -C 6 )dialkylaminocarbonylamino having independently the stated number of carbon atoms in each alkyl group, (C 1 -C 6 )alkoxycarbonyloxy, (C 1 -C 6 )alkylaminocarbonyloxy, (C 1 -C 6 )dialkylaminocarbonyloxy, phenylcarbonyl, substituted phenylcarbonyl, phenylcarbonyloxy, substituted phenylcarbonyloxy, phenylcarbonylamino, substituted phenylcarbonylamino, phenoxy or substituted phenoxy;  
           [0015]    R 5  represents cyano; —COR 6 ; —CO 2 R 6 ; or —S(O) m R 7 ;  
           [0016]    R 6  represents hydrogen or straight- or branched-chain alkyl group containing up to six carbon atoms;  
           [0017]    R 7  represents (C 1 -C 6 )alkyl, (C 1 -C 6 )haloalkyl, (C 1 -C 6 )cyanoalkyl (C 3 -C 8 )cycloalkyl optionally substituted with halogen, cyano or (C 1 -C 4 )alkyl; or phenyl optionally substituted with one to three of the same or different halogen, nitro, cyano, (C 1 -C 4 )haloalkyl, (C 1 -C 4  alkyl, (C 1 -C 4 )alkoxy or —S(O) m R 8 ;  
           [0018]    R 8  represents (C 1 -C 4 )alkyl, (C 1 -C 4 )alkyl substituted with halogen or cyano, phenyl or benzyl;  
           [0019]    each Q independently represents C 1 -C 4  alkyl or -CO 2 R 9  wherein R 9  is C 1 -C 4  alkyl;  
           [0020]    m is zero, one or two;  
           [0021]    n is zero or an integer from one to four;  
           [0022]    r is one, two or three; and  
           [0023]    z is 0 or an integer from 1 to 6.  
           [0024]    As used herein, the terms “halogen” and “halo” include fluorine, chlorine, bromine and iodine atoms. In polyhalogenated groups, the halogens may be the same or different. The term “substituted” in terms of “substituted phenylcarbonyl,” “substituted phenylcarbonyloxy,” “substituted phenylcarbonylamino” and “substituted phenoxy” means having one to five substituents, which may be the same or different, selected from the following: halo, nitro, cyano, S(O) m R 2 , (C 1 -C 6 )alkyl, (C 1 -C 6 )alkoxy, (C 1 -C 6 )haloalkyl, (C 1 -C 6 )haloalkoxy, carboxy, (C 1 -C 6 )alkylcarbonyloxy, (C 1 -C 6 )alkylcarbonyl, (C 1 -C 6 )alkoxycarbonyl, (C 1 -C 6 )alkylcarbonylamino, amino, (C 1 -C 6 )alkylamino and (C 1 -C 6 )dialkylamino having independently the stated number of carbon atoms in each group.  
           [0025]    The 2-(substituted benzoyl)-1,3-cyclohexanedione compounds of formula I are described, inter alia, in U.S. Pat. Nos. 4,780,127, 4,938,796, 5,006,158 and 5,089,046, the disclosures of which are incorporated herein by reference. Herbicidal 2-(substituted benzoyl)-1,3-cyclohexanedione compounds for use in this invention may be prepared by the methods described in the aforementioned patent publications, or by the application and adaptation of known methods used or described in the chemical literature.  
           [0026]    2-(substituted benzoyl)-1,3-cyclohexanedione compounds especially useful in the present invention include those in which z is zero; X is chloro, bromo, nitro, cyano, C 1 -C 4  alkyl, —CF 3 , —S(O) m R 1  or —OR 1 ; n is one or two; and each Z is independently chloro, bromo, nitro, cyano, C 1 -C 4  alkyl, —CF 3 , —OR 1 , —OS(O) m R 5  or —S(O) m R 5 . Examples of preferred cyclohexanedione compounds are 2-(2′-nitro-4′-methylsulfonylbenzoyl)-1,3-cyclohexanedione, 2-(2′-nitro-4′- methylsulfonyloxybenzoyl)-1,3-cyclohexanedione and 2-(2′-chloro-4′-methylsulfonylbenzoyl)-1,3-cyclohexanedione.  
           [0027]    Compounds of formula (I) may exist in enolic tautomeric forms that may give rise to geometric isomers. Furthermore, in certain cases, the various substituents may contribute to optical isomerism and/or stereoisomerism. All such forms are embraced within compounds useful in the present invention.  
           [0028]    Metal chelates of 2-(substituted benzoyl)- 1,3-cyclohexanedione compounds of formula I are described, inter alia, in PCT Application No. 97/27748, the disclosures of which are incorporated herein by reference. Metal chelates of 2-(substituted benzoyl)-1,3-cyclohexanedione compounds have the general structure:  
                         
 
           [0029]    wherein X, Q and Z have the meanings set forth above, and Me represents a di- or trivalent metal ion such as Cu +2 , Co +2 , Zn +2 , Ni +2 , Ca +2 , Al +3 , Ti +3  and Fe +3.    
           [0030]    Herbicidal metal chelates of 2-(substituted benzoyl)-1,3-cyclohexanedione compounds for use in this invention may be prepared by the methods described in the aforementioned PCT application, or by the application and adaptation of known methods used or described in the chemical literature.  
           [0031]    Metal ions which may be useful in forming the metal chelate compounds of the present invention include di- or trivalent metal ions such as Cu +2 , Co +2 , Zn +2 , Ni +2 , Ca +2 , Al +3 , Ti +3  and Fe +3 . The selection of a particular metal ion to form the metal chelate compound will depend upon the dione compound to be chelated and the strength of the metal chelate complex. Without being bound by theory, it appears as if the strength of the metal chelate complex is directly related to the release rate of the triketone from the metal chelate complex, which in turn is related to the selectivity of the metal chelate compounds of this invention. Those skilled in the art will be able to readily determine the appropriate metal ion for use with a specific dione compound without undue experimentation. The preferred metal ions are divalent transition metal ions, particularly Cu +2 , Ni +2 , Zn +2  and Co +2 , with Cu +2  being especially preferred.  
           [0032]    Any appropriate salt which would be a source of a di- or trivalent metal ion may be used to form the metal chelate of the dione compound in accordance with this invention. Particularly suitable salts include: chlorides, sulfates, nitrates, carbonates, phosphates and acetates.  
           [0033]    It also has been found that the stability and the activity of the herbicidal metal chelate compositions of the present invention is pH dependent. The pH of the metal chelate compositions should be between about 2 and about 10, preferably between about 3 and about 7. Generally, it is believed that for Cu +2  chelate compositions the pH should be between about 4 and 6; for Co +2  between about 3 and 5; and for Ni +2  and Zn +2  about 5. The optimum pH for a particular metal chelate composition can be determined using routine experimental techniques.  
           [0034]    The metal chelate of the herbicidal 2-(substituted benzoyl)-1,3-cyclohexanedione compounds can be formulated in the same manner in which herbicides are generally formulated. The choice of formulation and mode of application for any given herbicidal compound may affect its activity, and selection must be made accordingly. Herbicidal compositions may thus be formulated as water dispersible granules, as wettable powders, as powders or dusts, as suspensions, or as controlled release forms such as microcapsules. The formulation of the metal chelate of the herbicidal 2-(substituted benzoyl)-1,3-cyclohexanedione compounds for use in this invention may be prepared by the methods described in the aforementioned patent application or by the application and adaptation of known methods used or described in the chemical literature. Processes for microencapsulating the herbicidal composition specifically have been described in U.S. Pat. Nos. 4,285,720 and 4,956,129 and U.S. application Ser. No. 08/354,409, and may also be prepared by the application and adaptation of known methods used or described in the chemical literature. The object of the formulation, however, is to apply the compositions to the locus where control is desired by a convenient method (i.e., postemergent application). The “locus” is intended to include soil, as well as established vegetation.  
           [0035]    Formulations containing the metal chelates of the herbicidal dione compounds of formula (I) can be applied by conventional methods to the areas where control is desired. The formulations containing an herbicidal metal chelate according to the invention can also be produced as premixes with other herbicides, or can be tank-mixed with one or more additional herbicidal or other agricultural compositions. Specific examples of other herbicides which may be incorporated in an herbicidal formulation with the metal chelates according the invention include acetanilides, tralkoxydim, bromoxynil and its esters, thiafluamide, MCPA and its esters, 2,4-D and its esters, and fluroxypyr meptyl.  
           [0036]    In the practice of the present invention, the metal chelate of the herbicidal 2-(substituted benzoyl)-1,3-cyclohexanedione compounds is applied postemergent to the locus of the undesirable vegetation to be controlled. Application rates will depend on the particular plant species and degree of control desired. In general, application rates of between about 5 and about 500 g/ha may be employed.  
           [0037]    The following examples are for illustrative purposes only and are not intended as necessarily representative of the overall testing performed and are not intended to limit the invention in any way. 
       
    
    
     SPECIFIC EMBODIMENTS OF THE INVENTION  
     EXAMPLE 1  
       [0038]    All of the metal chelate compounds used in the 1,3-cyclohexanedione formulations of this example were prepared using a mix and mill process except for Formulation C which was formulated using a precipitation process. Both the mix and mill process and the precipitation process are described in more detail in PCT Application No. 97/27748, the disclosure of which has been incorporated herein by reference.  
         [0039]    Twelve days after the seeds were sown in aluminum flats (containing soil comprising 2 parts sandy loam to 1 part peat), the 1,3-cyclohexanedione suspension formulations (at the rates listed in Table 1 below) were applied postemergence to the following plant species: Galium aparine (catchweed bedstraw) (“GALAP”); Chenopodium album (lambsquarters) (“CHEAL”); Matricaria inodora (scentless flase chamomile) (“MATIN”); and wheat.  
         [0040]    The flats were placed in a greenhouse and evaluated 6 and 21 days after application (“DAA”). Injury was evaluated as percent control, with percent control being the total injury to the plants due to all factors including: Inhibited emergence, stunting, malformation, albinism, chlorisis, and other types of plant injury. The control rating range from 0 to 100 percent, where 0% represents no effect with growth equal to the untreated control and where 100% represents a complete kill.  
         [0041]    The results observed (as a mean of 3 replications) are summarized in Table 1 below.  
                                                                                                                           TABLE I                           Bioactivity of Various Metal Chelates of 1,3-Cyclohexanedione Formulations                Weed Control Activity, %                Molar Ratio   Appl. Rate   Phytotoxicity to Wheat, %   GALAP   CHEAL   MATIN            Formulation   Dione/Metal   g a.i./ha   6 days   21 days   21 days   21 days   21 days                    Control 1       12.5   38   10   75   100   99       (Unchelated)       25   45   14   54   100   100               50   53   22   99   100   100               100   65   58   100   100   100       Formulation A   2/5   12.5   0   0   64   100   0       (Cu Chelate)       25   2   0   75   100   44               50   2   0   83   100   72               100   2   4   98   100   85       Formulation B   2/1   12.5   0   0   83   100   18       (Cu Chelate)       25   2   0   87   100   45               50   0   0   84   100   73               100   2   6   99   100   90       Formulation C   2/1   12.5   0   0   93   100   84       (Cu Chelate)       25   0   0   94   100   79               50   0   0   68   100   100               100   8   7   99   100   100       Formulation D   2/5   12.5   5   0   44   100   100       (Co Chelate)       25   8   2   61   100   88               50   25   10   84   100   55               100   33   14   100   100   99       Formulation E   2/1   12.5   23   2   63   100   99       (Co Chelate)       25   33   2   66   100   100               50   38   20   94   100   100               100   43   38   99   100   100       Formulation F   2/5   12.5   20   2   66   100   100       (Zn Chelate)       25   28   8   71   100   100               50   35   17   99   100   93               100   40   18   98   100   100       Formulation G   2/1   12.5   28   3   64   100   65       (Zn Chelate)       25   35   10   89   100   99               50   40   19   84   100   100               100   45   35   100   100   100       Formulation H   2/5   12.5   20   3   85   100   100       (Ni Chelate)       25   30   3   59   100   100               50   40   9   100   100   100               100   45   31   98   100   100       Formulation I   2/5   12.5   30   6   78   100   100       (Ca Chelate)       25   40   9   83   100   100               50   45   25   100   100   100               100   53   48   94   100   100                  
 
         [0042]    From these results, it is clear that the phytotoxicity of the 1,3-cyclohexanedione formulations to wheat was reduced by chelation. In contrast, however, the herbicidal activity of the 1,3-cyclohexanedione formulations on the weeds and other undesirable vegetation was only slightly affected by chelation. In addition, it is also apparent from these results that the activity of the 1,3-cyclohexanedione formulation varied depending on the metal ion used to form the metal chelate compound.  
       EXAMPLE 2  
       [0043]    The metal chelate compounds used in the 1,3-cyclohexanedione suspension formulations of this example were prepared using the mix and mill process as described in Example 1. Moreover, a procedure essentially identical to that described in Example 1 was employed for the postemergent application of the 1,3-cyclohexanedione suspension formulations (at the rates listed in Table II below) to aluminum flats containing the following plant species: CHEAL;  Amaranthus retroflexus  (redroot pigweed)(“AMARE”);  Polygonum convolvulus  (wild buckwheat)(“POLCO”);  Brassica kaber  (wild mustard)(“SINAR”);  Thlaspi arventse  (field pennycress)(“THLAR”);  Brassica canpestris  (oilseed rape)(“BRSNN”); wheat (“TRZAS”); and barley (“HORVS”). Injury was evaluated at 8 and 32 DAA.  
         [0044]    The results observed (as a mean of 4 replications) are summarized in Table II below.  
                                                                                                                                                                           TABLE II                           Comparison of Activity and Phytotoxicity of Chelated and Unchelated 1,3-Cyclohexanedione(a.i.) Formulations                Phytotoxicity to Wheat (TRZAS)               and Barley (HORVS), %   Weed Control Activity, % (32 days)                Rate   TRZAS   HORVS   AMARE   BRSNN   CHEAL   POLCO   SINAR   THLAR            Formulation   g a.i./ha   8 days   32 days   8 days   32 days   32 days   32 days   32 days   32 days   32 days   32 days                    Control 2   3.125   4   1   0   0   80   69   100   4   92   85       (Unchelated)   6.25   14   5   4   0   88   86   100   53   99   91           12.5   19   1   6   0   97   89   100   81   98   99           25   24   12   6   0   98   97   100   94   97   100           50   34   15   11   4   100   100   100   100   100   100           100   44   59   18   6   100   100   100   100   100   100       Formulation J   6.25   0   0   0   1   100   90   100   100   100   99       (Cu Chelate)   12.5   0   0   0   1   98   82   100   98   99   94           25   0   0   0   0   99   89   100   66   100   99           50   0   0   0   1   100   89   100   88   100   100           100   4   34   1   3   100   95   100   100   100   100           200   11   64   0   4   100   100   100   100   99   100                  
 
         [0045]    These data indicate that the copper chelate of 2-(substituted benzoyl)-1,3-cyclohexanedione, Formulation J, showed an 16× increase in wheat selectivity at early assessment compared to the unchelated formulation (Control 2). Weed control activity of the copper chelate formulation was approximately the same as that of the unchelated formulation.  
       EXAMPLE 3  
       [0046]    The metal chelate compounds used in the 1,3-cyclohexanedione formulations of this example were prepared using the mix and mill process as described in Example 1. Control 3 and Formulation K were formulated as suspension formulations and Formulation L was formulated as microcapsules.  
         [0047]    Employing a procedure essentially identical to that described in Example 1, the 1,3-cyclohexanedione formulations were applied postemergence at the rates listed in Table III below to aluminum flats containing the following plant species: AMARE, BRSNS, POLCO, SINAR and TRZAS. Injury was evaluated at 6 and 22 DAA.  
         [0048]    The results observed (as a mean of 4 replications) are summarized in Table III below.  
                                                                                                                                                   TABLE III                           Comparison of Activity and Phytotoxicity of Unchelated, Chelated and Microencapsulated       1,3-Cyclohexandedione(a.i.) Formulations                Phytotoxicity to Wheat, %   Weed Control Activity, %                Rate   TRZAS(K)   TRZAS(R)   AMARE   BRSNN   POLCO   SINAR            Formulation   g a.i./ha   6 days   22 days   6 days   22 days   22 days   22 days   22 days   22 days                    Control 3   2.5   —   —   —   —   56   38   48   87       (Unchelated)   5   —   —   —   —   85   48   65   85           10   —   —   —   —   90   81   83   97           20   23   10   26   8   97   88   97   100           40   29   9   40   18   99   96   88   100           80   34   18   50   25   —   —   —   —           160   60   58   58   59   —   —   —   —           320   61   80   61   80   —   —   —   —       Formulation K   2.5   —   —   —   —   41   65   55   97       (Cu Chelate)   5   —   —   —   —   72   56   67   92           10   —   —   —   —   61   65   62   93           20   4   3   16   14   88   73   89   95           40   10   17   6   31   97   90   92   96           80   0   8   12   21   —   —   —   —           160   6   33   7   33   —   —   —   —           320   39   74   49   69   —   —   —   —       Formulation L   2.5   —   —   —   —   20   39   25   88       (Cu Chelate/   5   —   —   —   —   26   10   28   78       Microcapsule)   10   —   —   —   —   45   16   45   88           20   1   1   6   5   75   31   66   99           40   0   3   1   6   95   71   84   98           80   1   13   0   10   —   —   —   —           160   0   38   4   33   —   —   —   —           320   39   66   15   58   —   —   —   —                  
 
         [0049]    The above data indicates that the copper chelate of 2-(substituted benzoyl)-1,3-cyclohexanedione (Formulation K) showed improved selectivity over the unchelated formulation (Control 3). These data also indicate that the selectivity of the copper chelate of 2-(substituted benzoyl)-1,3-cyclohexanedione was further improved by microencapsulation (Formulation L).  
         [0050]    The foregoing description and example are for the purpose of illustration only and does not limit the scope of protection which should be accorded this invention.