Plant protecting and regulating compositions – Plant growth regulating compositions – Plural active ingredients
Reexamination Certificate
2000-08-04
2002-04-09
Clardy, S. Mark (Department: 1616)
Plant protecting and regulating compositions
Plant growth regulating compositions
Plural active ingredients
C504S363000, C504S128000
Reexamination Certificate
active
06369001
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to compositions useful in agriculture comprising at least two herbicidal active ingredients, one of which is a selective graminicide of the cyclohexenone class or the aryloxyphenoxypropionate class and the other of which is a water-soluble herbicide. In particular, the present invention relates to stable liquid concentrate compositions of such active ingredients.
BACKGROUND OF THE INVENTION
As a means of killing or otherwise controlling unwanted plants, especially weeds, in agriculture and related endeavors, it is desirable to treat such plants or the locus thereof with chemical herbicides. Commonly such treatment has to be done in presence of plants, especially crop plants, which it is desired not to injure to an unacceptable degree. For this reason selective herbicides, that is, compounds having useful herbicidal activity against certain species of weeds but acceptably non-injurious to the particular crop in which these weeds occur, have been developed for a wide range of agricultural applications. In addition, certain crop plants have been developed by conventional breeding methods and by methods involving genetic transformation to tolerate certain herbicides that would otherwise injure or kill them.
A common problem with a selective herbicide is that its weed control spectrum, that is, the range of weed species effectively controlled by the herbicide, does not embrace the full diversity of weeds present in a crop. It has therefore been common to apply two or more herbicides simultaneously in order to achieve the desired spectrum of control. Two or more different herbicides, separately packaged as concentrate formulations, can be admixed with water in a spray tank by the end user, a method known as tank-mixing. More conveniently, however, the different herbicides can be coformulated in a single concentrate formulation, requiring only dilution in water by the end user prior to application by spraying. Such a formulation is often known as a package-mix.
Package-mix formulations present numerous challenges to the formulator of agricultural chemicals such as herbicides. For example, the formulation should contain the herbicidal active ingredients at as high a total concentration as possible, for maximum convenience to the end user and to minimize packaging and shipping costs, while keeping the active ingredients in the desired weight ratio one to the other. Most importantly, the package-mix formulation must exhibit sufficient physical and chemical stability to have an effective shelf life of at least a few months, preferably at least a year, ideally at least two years.
Where the package-mix formulation contains a first herbicide that is oil-soluble and that undergoes chemical degradation, even at a slow rate, in water, and a second herbicide that is water-soluble, the challenge of providing a storage-stable liquid concentrate formulation is particularly acute. Water used as the solvent for the second herbicide acts as a degradation medium for the first herbicide. Hydrolysis is the most common water-mediated degradation mechanism.
Graminicides are selective herbicides having strong herbicidal activity against many grass species but generally relatively non-phytotoxic to dicotyledonous species, including dicotyledonous crops such as cotton, rapeseed (including canola), soybeans and sugar beet. There are two main classes of selective graminicides in widespread use in agriculture: cyclohexenones, sometimes called “dims”, and aryloxyphenoxypropionates, sometimes called “fops”. Among commercially significant oil-soluble “dims” are butroxydim, clethodim, cycloxydim, sethoxydim, tepraloxydim and tralkoxydim. Among commercially significant “fops” are clodinafop-propargyl, cyhalofop-butyl, diclofop-methyl, fluazifop-butyl, fluazifop-P-butyl, haloxyfop, propaquizafop, quizalofop and quizalofop-P.
Because the spectrum of herbicidal activity of “dims” and “fops” is largely restricted to grasses, there is often great complementarity in a package-mix of a “dim” or “fop” with a second herbicide that has strong broadleaf herbicidal activity. Many such herbicides are most conveniently formulated as water-soluble salts in aqueous solution. Examples are salts of clopyralid, 2,4-D, dicamba, imazethapyr, MCPA and triclopyr.
Another situation where a “dim” or “fop” is a useful component of a package-mix is where the second herbicide has broad-spectrum or essentially non-selective herbicidal activity and where gramineous crops such as wheat, maize or rice have been bred to tolerate high doses of that herbicide. “Volunteer” plants of such herbicide-tolerant gramineous crops can become troublesome weeds in a succeeding broadleaf crop that is tolerant of the same herbicide. For example, in a crop rotation where glyphosate-tolerant soybeans follow glyphosate-tolerant corn (maize), “volunteer” corn cannot be controlled by glyphosate alone in the soybean crop. There is therefore advantage in adding a “dim” or “fop” to the glyphosate to ensure control of“volunteer” corn along with all the other weed species. Glyphosate is most conveniently formulated as a water-soluble salt in aqueous solution; the same is true of several other broad-spectrum herbicides including glufosinate.
Thus among the most desirable package-mix partner herbicides for a “dim” or “fop” are a number of water-soluble herbicides. It is often possible to formulate the package-mix as a dry particulate, for example granular, product; however for many purposes in agriculture a liquid concentrate formulation is preferred. Where the partner herbicide is water-soluble, as in the case of the salts mentioned above, such a liquid concentrate is preferably water-based.
A major problem is that most “dims” and “fops” exhibit some degree of chemical instability, primarily in the form of hydrolysis, in an aqueous medium; in the majority of cases this instability is pH-dependent. For example, tralkoxydim is especially unstable in an acid medium, whereas diclofop-methyl undergoes hydrolysis more readily in an alkaline medium.
It would therefore be a major advance in the art to provide a water-based liquid concentrate composition comprising a first herbicide that is a graminicide that degrades in an aqueous medium, and a second herbicide that is water-soluble, yet wherein the graminicide has acceptable long-term chemical stability.
As examples of a graminicide and a water-soluble herbicide, consider quizalofop-P and a salt of glyphosate respectively.
Quizalofop is a racemic mixture of R- and S-isomers of 2-[4-[(6-chloro-2-quinoxalinyl)oxy]phenoxy]propanoic acid and is most commonly used in the form of the ethyl ester (quizalofop-ethyl). Quizalofop-P is the R-isomer and is available in several ester forms of which the most widely used is the ethyl ester (quizalofop-P-ethyl). In water, quizalofop-P-ethyl exhibits hydrolytic instability, hydrolysis occurring most rapidly when pH is in the alkaline range.
Glyphosate (N-phosphonomethylglycine) in its strict sense is an acid compound, but the word “glyphosate” is herein used in a less restrictive sense, except where the context dictates otherwise, to encompass not only glyphosate acid but also salts, adducts and esters thereof, and compounds which are converted to glyphosate in plant tissues or which otherwise provide glyphosate ions. In most commercial formulations of glyphosate, the glyphosate is present as a water-soluble salt. In this respect, glyphosate is typical of most exogenous chemical substances that are acids or that form anions.
Herbicidal salts of glyphosate are disclosed, for example, in U.S. Pat. No. 3,799,758 to Franz, U.S. Pat. No. 3,853,530 to Franz, U.S. Pat. No. 4,140,513 to Prill, U.S. Pat. No. 4,315,765 to Large, U.S. Pat. No. 4,405,531 to Franz, U.S. Pat. No. 4,481,026 to Prisbylla and U.S. Pat. No. 4,507,250 to Bakel. In most of the salts disclosed, the counterion to glyphosate anion is a relatively low molecular weight, non-amphiphilic cation. Typical of such salts are alkali metal, for example sodium and potassium,
Clardy S. Mark
Monsanto Technology LLC
Schaper Joseph A.
Senniger Powers Leavitt & Roedel
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