Abstract:
There are provided compositions comprising a concentrated amount of an herbicidally active agent, or combination of agents, in a solid state suspended in a water immiscible solvent containing an anionic surfactant and a nonionic surfactant and optionally containing an antifoam agent and a suspending or thickening agent. Upon dilution with hard or soft water, said compositions readily form sprayable herbicidal emulsions.

Description:
This is a divisional of application Ser. No. 07/797,523, filed on Nov. 25, 1991, now U.S. Pat. No. 5,268,352, which is a continuation of application Ser. No. 07/440,179, filed on Nov. 22, 1989, abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to novel and useful agricultural formulations of herbicidal agents which exhibit poor solubility characteristics in both aqueous and organic media. 
     Emulsifiable suspension concentrate compositions (or oil flowable dispersions) are compositions which consist essentially of an active agent in a solid state suspended in a non-aqueous liquid containing a surfactant or a mixture of surfactants and said compositions having the property of forming an emulsion when diluted with water. 
     Emulsifiable suspension concentrate compositions containing pesticides such as herbicides and fungicides as the active agent and paraffinic oils as the non-aqueous liquid are described in European Patent Applications EP-A1-243872 and EP-A2-142670. However, said patent applications do not describe the use of aromatic solvents as the non-aqueous liquid. 
     Herbicidal agents, such as N-phosphonomethylglycine (glyphosate) and 2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)nicotinic acid (imazapyr), are especially useful for controlling undesirable plant species when applied postemergence. In addition to being highly effective herbicides, said compounds are zwitterionic in nature and generally relatively insoluble in both aqueous and non-aqueous media. Therefore, these types of herbicidal agents are routinely formulated as the corresponding salts as described in European Patent Application EP-A2-220902 and U.S. Pat. No. 4,816,060. 
     It is an object of this invention to provide an emulsifiable suspension concentrate composition of the free acids of a herbicidal agent, such as N-phosphonomethylglycine and 2-(imidazolin-2-yl)pyridine carboxylic acids, without the pre-formulation of the corresponding herbicidal salts. It is an object of this invention to produce herbicidal compositions which are physically stable and readily dilutable in hard or soft water to give a sprayable herbicidal emulsion. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a novel emulsifiable suspension concentrate composition of a herbicidal agent characterized by a relative degree of insolubility in both aqueous and non-aqueous media. The emulsifiable suspension concentrate composition of the invention is comprised of an active herbicidal agent, or combination of agents, in a solid state suspended in a water immiscible solvent containing an anionic surfactant and a nonionic surfactant and optionally containing an antifoam agent and a suspending or thickening agent. 
     The water immiscible solvent is a non-paraffinic heavy aromatic solvent consisting of a mixture of aromatic hydrocarbons, such as naphthalenes and alkylnapthalenes, having a distillation range of about 118° to 305° C. 
     The above-described compositions allow the formulation of active herbicidal agents such as amino acids and imidazolinylnicotinic acids without further chemical modifications, such as salt or ester formation. The above compositions provide a stable, concentrated, readily dilutable form of a herbicide suitable for spray application. The compositions also exhibit surprising herbicidal efficacy comparable to the efficacy of the corresponding salts. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention also relates to an emulsifiable suspension concentrate composition of a herbicidal agent comprising an amino acid or imidazolinylpyridine carboxylic acid (alone or in combination) in a solid state suspended in a water immiscible liquid containing an anionic surfactant and an ethoxylated fatty acid surfactant and optionally containing an antifoam agent and a thickening or suspending agent. 
     The herbicidal agent is usually sold in a concentrated form either as a solid or a liquid and, just prior to application, the concentrate is diluted with water, or water containing adjuvants, and sprayed on fields of soil and/or actively growing plants. Solid concentrate formulations, such as granulars, wettable powders and dusts, may also be used. 
     Since not all solid concentrate formulations of the free acid form of herbicidal agents, such as N-phosphonomethylglycine, exhibit the same high magnitude of efficacy and further since certain highly effective herbicidal compounds, such as N-phosphonomethylglycine and imidazolinylnicotinic acids, are relatively insoluble in water and conventional organic solvents, they are not readily amenable to commercial formulation. Chemical modification of said compounds to give the corresponding salts is required to improve their solubility characteristics. Surprisingly, it has been found that compounds, such as amino acids and imidazolinylnicotinic acids, may be formulated as liquid concentrates without further chemical modifications of said compounds and with a high degree of retention of efficacy. 
     The emulsifiable suspension concentrate compositions of the present invention are comprised of about 10% to 50% of a herbicidal agent, such as N-phosphonomethylglycine or an imidazolinylnicotinic acid, alone or in combination, suspended in about 29% to 84% of a non-paraffinic aromatic solvent mixture having a distillation range of 118° to 305° C. containing about 3% to 10% of an anionic surfactant, about 3% to 10% of an ethoxylated fatty acid surfactant, 0 to about 0.10% of an antifoam agent and 0 to about 2.0% of a suspending or thickening agent. 
     One preferred composition comprises about 30% to 50% of an active herbicidal agent or combination of agents, about 40% to 57% of a non-paraffinic aromatic solvent mixture having a distillation range of 118° to 305° C., about 5.0% to 7.0% of an anionic surfacant, about 5.0% to 7.0% of an ethoxylated fatty acid surfactant, about 0.02% to 0.15% of an antifoam agent and 0.5 to 2% of a suspending agent. 
     Among the herbicidal agents suitable for use in the compositions of the invention are amino acids such as glyphosate and imidazolinylpyridine carboxylic acids such as imazapyr and combinations thereof. A preferred herbicidal agent is glyphosate, alone or in combination with an imidazolinylnicotinic acid. 
     Solvents suitable for use in the compositions of the invention include heavy aromatic solvent mixtures having a distillation range of 118° to 305° C. Preferred solvents include those mixtures of aromatics having a distillation range of about 183° to 285° C., and the most preferred aromatic solvent mixtures is that which distills in a range of about 225° to 280° C. Anionic surfactants suitable for use in the present invention include alkylarylsulfonic acids such as C 8  -C 18  alkylbenzenesulfonic acid, with dodecylbenzenesulfonic acid being the preferred anionic surfactant. 
     Among the ethoxylated fatty acid surfactants which may be employed are ethoxylated castor oils with about 15-60 ethylene oxide units per molecule. Preferred ethoxylated castor oils are those which have about 36-40 ethylene oxide units per molecule. Suitable antifoam agents include silicone polymers containing silica such as dimethylsilicone polymer plus silica, and suitable suspending or thickening agents include hydrated fumed silica or attapulgite clays or amine treated attapulgite clays. 
     The herbicidal emulsifiable suspension concentrate compositions may be prepared by dissolving an anionic surfactant in an aromatic solvent and adding a solid herbicidal agent or combination of agents, with vigorous agitation to form a suspension. This suspension is milled to the required particle size distribution. A median particle diameter of 1-2 microns provides suitable physical properties. The milled suspension is treated with an ethoxylated fatty acid surfactant and, optionally, an antifoam agent and a suspending or thickening agent and mixed thoroughly. Alternatively, the herbicidal agent is milled as a dry powder and is added to a solution of the anionic surfactant in the aromatic solvent with vigorous agitation to ensure complete dispersion and the remaining components are added with stirring. 
     The above-prepared emulsifiable suspension concentrate compositions are physically stable and demonstrate excellent dilution properties in hard and soft waters to produce a sprayable herbicidal emulsion. In practice, it is generally preferable to dilute the compositions of the invention in water containing about 0.25% of an adjuvant such as a polyoxyethylene sorbitan laurate surfactant to obtain an especially high degree of herbicidal activity. 
     In order to facilitate a further understanding of the invention, the following examples are presented primarily for the purpose of illustrating certain more specific details thereof. The invention is not to be deemed limited thereby except as defined in the claims. Unless otherwise noted, all parts are by weight. 
     EXAMPLE 1 
     
         ______________________________________Component               %______________________________________N-phosphonomethylglycine                   41.90Dodecylbenzenesulfonic acid                   6.00Ethoxylated castor oil, 36 C..sup.1                   6.00Dimethylsilicone polymer with silica.sup.2                   0.10Mixture of aromatic hydrocarbons with                   46.00a distillation range of 226°-279° C..sup.3                   100.00______________________________________ .sup.1 36 units of ethylene oxide per molecule Flomo ® 36 C., manufactured by DeSoto .sup.2 TH 100IND ® antifoam, manufactured by ThompsonHayward .sup.3 Aromatic 200°, manufactured by EXXON 
    
     Method 1 
     An anionic surfactant, dodecylbenzenesulfonic acid, is dissolved in a water immiscible solvent, Aromatic 200®, with stirring. This solution is treated with the herbicidal agent, N-phosphonomethylglycine, in a crystalline or powder state with vigorous stirring to give a dispersion. The resultant dispersion is milled until a median particle size of 1-2 microns is obtained. 
     The milled dispersion is treated with an ethoxylated fatty acid surfactant, castor oil, 36C 1 , and an antifoam agent, dimethylsilicone polymer with silica 2  and mixed thoroughly. 
     Method 2 
     The herbicidal agent, N-phosphonomethylglycine, is milled to give a median particle size of 1-2 microns and then added to a solution of an anionic surfactant, dodecylbenzenesulfonic acid in a water immiscible solvent, Aromatic 200®, with vigorous agitation. The resultant dispersion is treated with an ethoxylated fatty acid surfactant, castor oil, 36C 1 , and an antifoam agent, dimethylsilicone polymer plus silica 2 , and mixed thoroughly. 
     Physical Properties 
     The physical characteristics of the above-described N-phosphonomethylglycine emulsifiable concentrate composition are shown below. 
     
         ______________________________________Viscosity (Brookfield LVT at 22° C.                  500-600 cPspindle #2, speed 30 rpm)Density at 20° C.                  1.41 g/mLParticle size (Horiba CAPA 700)                  1.21 microns                  (median)pH, 2% diluted in deionized water                  2.0-2.4Dispersibility in water (in both                  Good emulsifica-standard hard and soft waters),                  tion, no oil sep-2.5 g in 100 ml total volume.                  aration after 24                  hours.______________________________________ 
    
     EXAMPLE 2 
     
         ______________________________________Components            A       B______________________________________Imazethapyr           --      33.3Imazapyr              33.33   --Dodecylbenzenesulfonic acid                 5.00    5.00Ethoxylated castor oil, 36 C..sup.1                 5.00    5.00Dimethylsilicone polymer with                 0.03    0.03silica.sup.2Mixture of aromatic hydrocarbons                 56.64   56.64with a distillation range of226°-279° C.                 100.00  100.00______________________________________ .sup.1 36 units of ethylene oxide per molecule Flomo ® 36 C., manufactured by DeSoto .sup.2 TH IND30 ® antifoam, manufactured by ThompsonHayward .sup.3 Aromatic 200 ®, manufactured by EXXON 
    
     Method 
     The herbicidal agent, as a finely divided powder, is added to a rapidly stirred solution of the anionic surfactant, dodecylbenzenesulfonic acid, in the aromatic solvent, Aromatic 200®. The resultant dispersion is treated with the remaining components and placed on a high shear mixer for 3 minutes. 
     Optionally the solid herbicidal agent is milled to a median particle size of 1-2 microns prior to use in the above-described preparation. 
     
         ______________________________________Physical Properties            A           B______________________________________Dispersibility in water,            Good emulsi-                        Good emulsi-4.0 g in 100 ml total            fication,   fication,volume.          slight settl-                        slight settl-            ing after 24                        ing after 24            hours, easily                        hours, easily            resuspended resuspended______________________________________ 
    
     EXAMPLE 3 
     
         ______________________________________Preparation of combination emulsifiable suspension con-centrate compositionsComponents           C       D______________________________________Glyphosate           37.69   32.89Imazapyr             4.20    9.00Dodecylbenezenesulfonic acid                6.00    6.00Flomo ® 36 C..sup.1                6.00    6.00TH 100IND ® antifoam.sup.1                0.10    0.10Aromatic 200 ®.sup.1                46.01   46.01                100.00  100.00______________________________________ .sup.1 As described in Example 1. 
    
     Method 
     A solution of dodecylbenzene in Aromatic 200® is treated with glyphosate with rapid stirring. The resultant dispersion is treated with the remaining components and placed on a high shear mixer for 3 minutes. 
     Optionally, a dispersion of glyphosate and the imidazolinylnicotinic acid solid in a solution of dodecylbenzenesulfonic acid in Aromatic 200® is milled to give a median particle size of 1-2 microns prior to the addition of the remaining components. 
     
         ______________________________________Physical Properties            C           D______________________________________Dispersibility in water,            Good emulsi-                        Good emulsi-4.0 g in 100 ml total            fication,   fication,volume.          slight oil  slight oil            separation  separation            after 24    after 24            hours, easily                        hours, easily            resuspended resuspended______________________________________ 
    
     EXAMPLE 4 
     Greenhouse Postemergent Herbicidal Evaluation 
     This is an evaluation of the postemergent herbicidal activity of the emulsifiable suspension concentrate composition of N-phosphonomethylglycine as compared to a commercial aqueous solution composition of the isopropylammonium salt of N-phosphonomethylglycine. 
     The test compositions used for this evaluation are the emulsifiable suspension concentrate composition of N-phosphonomethylglycine which is described in Example 1 and referred to herein as Glyphosate 40 ESC and an aqueous soluble composition of the isopropylammonium salt of N-phosphonomethylglycine which is commercially sold by Monsanto under the trademark ROUNDUP® and referred to herein as Glyphosate Salt. 
     Seedling plants are grown in jiffy flats for about 2 weeks. The glyphosate 40 ESC composition is dispersed in water containing 0.25% TWEEN-20®, a polyoxyethylene sorbitan monolaurate surfactant manufactured by Atlas Chemical Industries in sufficient quantity to provide the equivalent of about 0.063 kg to 0.500 kg per hectare of N-phosphonomethylglycine to the plants when applied through a spray nozzle operating at 40 psi for a predetermined time. The Glysphosate Salt is dispersed in water according to the label directions and applied to the plants as described above. After spraying, the plants are placed on greenhouse benches and cared for in the usual manner commensurate with conventional greenhouse practices. The plants are evaluated at 7 and 14 days after treatment and rated according to the rating system shown below. 
     
         ______________________________________Rating System      % Control______________________________________No effect           0Possible effect     1-10Slight effect      11-25Moderate effect    26-40Definite injury    41-60Herbicidal effect  61-75Good Herbicidal effect              76-90Approaching complete kill              91-99Complete kill      100______________________________________ 
    
     
         ______________________________________Plant Species UsedCommon Name       Scientific Name______________________________________Mustard Wild      Brassica kaberCotton            Gossypium hirsustumCorn              Zea maysMorningglory      Ipomoea purpureaSoybean           Glycine maxBarnyard Grass    Echinochloa crus-galliLambsquaters      Chenopidium albumRagweed           Ambrosia artemisifoliaGreen Foxtail     Setaria veridis______________________________________ 
    
     The data obtained at 14 days after treatment are reported in Table I below. 
     
                                           TABLE I__________________________________________________________________________Postemergence Herbicidal Evaluation                                  Grn   Rate       Must          Cot             Field                Morn                    Soy                       Barn                           Lambs                               Rag                                  FoxComposition   (ka/ha)       ard          ton             Corn                glry                    bean                       yardg                           quart                               weed                                  tail__________________________________________________________________________Glyphosate Salt   0.500       80.0          80.0             90.0                66.7                    78.3                       98.7                           99.3                               38.3                                  100.0Glyphosate ESC   0.500       60.0          50.0             95.0                71.7                    80.0                       94.3                           96.3                               40.0                                  91.7Glyphosate Salt   0.250       38.3          35.0             58.3                63.3                    63.3                       71.0                           83.3                               33.3                                  85.0Glyphosate ESC   0.250       33.3          40.0             85.3                75.3                    71.7                       78.3                           100.0                               53.3                                  93.3Glyphosate Salt   0.125       13.3          20.0             18.3                30.0                    20.0                       23.3                           61.7                               6.7                                  46.7Glyphosate ESC   0.125       26.7          3.3             71.7                30.0                    50.0                       48.3                           83.3                               23.3                                  81.7Glyphosate Salt   0.063       0.0          3.3             3.3                15.0                    6.7                       16.7                           36.7                               0.0                                  20.0Glyphosate ESC   0.063       6.7          0.0             61.7                10.0                    20.0                       35.0                           70.0                               13.3                                  40.0__________________________________________________________________________ 
    
     EXAMPLE 5 
     Field Postemergent Herbicidal Evaluation 
     The test compositions used are Glyphosate 40 ESC and Glyphosate Salt, and are as described in Example 4. 
     A field containing established, actively growing plants is divided into plots of 10 meters×30 meters and is sprayed with a tractor mounted compressed air sprayer with a delivery of 200 liters per hectare. The Glyphosate 40 ESC composition is dispersed in water containing 0.25% TWEEN-20® in sufficient quantity to provide the equivalent of 2.0 kg to 0.5 kg per hectare to the plants. Glyphosate Salt is dispersed in water according to the label directions and applied to the plants as described hereinabove. The plots are evaluated at 7 and 14 days after treatment. Each treatment is replicated once. The data obtained for 14 days after treatment is reported in Table II. 
     
         ______________________________________Plant SpeciesCommon Name       Scientific Name______________________________________Redroot pigweed   Amoranthus retroflexusCommon lambsquarters             Chenopodium albumCommon purslore   Portulara oleraceaCommon ragweed    Ambrosia artemisiifolaLarge crabgrass   Digitaria sanguiralisFall panicum      Panicum diclotomiflorumBarnyard grass    Echirochloa curs-galliFoxtail millet    Setaria italica______________________________________ 
    
     
                                           TABLE II__________________________________________________________________________Postemergence Field Evaluation        Red        Root                  Fox    Rate        Pig Lambs                Rag                   Crab                       Fall                          Bard                              tailComposition    kg/ha        weed            quart                weed                   gras                       pani                          yardq                              millet__________________________________________________________________________Glyphosate Salt    0.5 100  80  98                   100  95                          100 100Glyphosate ESC    0.5 100 100  85                   100  98                          100 100Glyphosate Salt    1.0 100 100 100                   100 100                          100 100Glyphosate ESC    1.0 100 100 100                   100 100                          100 100Glyphosate Salt    2.0 100 100 100                   100 100                          100 100Glyphosate ESC    2.0 100 100 100                   100 100                          100 100__________________________________________________________________________