Aqueous concentrate formulations of pesticidal and plant growth modifying chemicals are widely used in agricultural, industrial, recreational and residential areas worldwide. The active ingredients of such concentrates frequently contain acid functional groups such as carboxylic or phosphonic acids, more commonly in the form of their water soluble salts. An aqueous concentrate is essentially a solution of the active ingredient in water at relatively high concentration, intended for dilution in water prior to application by spraying or other means. Typically the aqueous concentrate is diluted in about 10 to about 500 times its own volume of water prior to application.
2,4-D and glyphosate (N-(phosphonomethyl)glycine) are members of the phenoxyacetic acid and organophosphonic acid classes of herbicides, respectively. They have limited solubility in water in their acid forms and therefore must be converted into water-soluble salts in order to be formulated as soluble aqueous concentrates. Salts of these herbicidal acids commonly used for preparing these aqueous herbicide concentrates include organo ammonium cations such as, for example, isopropyl ammonium, dimethyl ammonium, triethyl ammonium, monoethanol ammonium, diethanol ammonium, triethanol ammonium, triisopropanol ammonium and N,N,N-trimethylethanol ammonium (choline). In addition, glyphosate is often formulated in an aqueous concentrate as the sesquisodium salt, the mono-potassium salt or the mono- or di-ammonium salt.
In today's agrochemical market with the continued demand for improved productivity it becomes increasingly common to combine more than one formulated product in a spray tank in order to achieve the optimal spectrum of control, efficacy, and delivery efficiency of the products. In doing this, however, spray tank incompatibilities between products can occur at times leading to product performance issues and difficulty in the field application of the products.
Spray tank incompatibility occurs when components of an aqueous pesticide spray tank mixture or solution chemically or physically interact thereby reducing the effectiveness of the spray applied product. The incompatibility of a pesticide spray tank mixture or solution may physically manifest itself through the formation of crystalline precipitates, surface scum, oily droplets, gels, excessive foam or clumps of solid matter, and may result in clogged spray nozzles or screens.
Compatible aqueous pesticide mixtures or solutions are defined as those mixtures or solutions that, when formed by the combination or mixing of one or more pesticide products and/or other commonly used ingredients, result in little or no solids precipitation or phase separation and the retention of their full biological efficacy.
It is well known that aqueous solutions of salts of 2,4-D can have compatibility issues leading to the formation of precipitated solids under the following combination of conditions: (1) a 2,4-D acid equivalent (ae) concentration of about 0.3 weight percent or higher, (2) a pH of about 6 or lower, and (3) the presence of inorganic cations such as, for example, K+, Na+, Ca2+, Mg2+, NH4+, Fe2+, Fe3+ and the like. The exact conditions necessary for the on-set of the crystallization of solids from these solutions of 2,4-D salts will also depend on the temperature and hardness of the water used, pH of the mixture and the actual composition and concentrations of the components in the solution. For example, a spray tank mixture made from concentrates of DMA-6® herbicide (registered trademark of Dow AgroSciences LLC; 2,4-D dimethyl ammonium salt solution with a pH value of about 7) at a rate of 800 g ae/hectare and Roundup WeatherMax® herbicide (registered trademark of Monsanto; glyphosate potassium salt solution with a pH value of about 4.7) at 840 g ae/hectare and a spray volume of about 47 liters/hectare would have a pH value of about 5 and will be incompatible and result in the significant formation of solids.
The common practice of adding ammonium sulfate to aqueous herbicide spray mixtures containing glyphosate to improve herbicide performance may also lead to compatibility problems. If an herbicide such as 2,4-D dimethyl ammonium (DMA) is present in a spray mixture containing glyphosate to which ammonium sulfate has been added, crystallization of solids will occur if the pH and the 2,4-D concentration are in the critical ranges discussed herein.
A number of solutions to the spray tank compatibility issues discussed herein have been proposed and are disclosed, for example, in WO 2006/127501A2, WO 2007/147208A1 and WO 2008/069826A1. These proposed solutions involve the use of additives such as, for example, surfactant based compatibility agents that inhibit the formation of solids or the use of greater than about 10% molar excesses of organic amines, with respect to 2,4-D, to modify the pH of the spray solution and thereby improve spray tank compatibility.
Considering the wide use of glyphosate and 2,4-D aqueous herbicide concentrates, and the development and expected commercial introduction of crops tolerant to both glyphosate and 2,4-D products, there is an increasing need for herbicide formulations of these two herbicidal active ingredients that are compatible when tank mixed together and used under a wide range of field conditions.
The present invention provides a novel solution to the compatibility problems encountered between aqueous solutions of water soluble salts of 2,4-D and glyphosate in the presence of inorganic cations.