COMPOSITION AND METHOD FOR TREATING PLANTS WITH EXOGENOUS CHEMICALS

Abstract: Methods and compositions are disclosed wherein exogenous chemicals are applied to plants to generate a desired biological response. One embodiment of the present invention is a plant treatment composition that comprises (a) an exogenous chemical and (b) a first excipient substance which forms liposomes in aqueous dispersion and which consists of one or more compounds each having (i) a hydrophilic moiety comprising a cationic group and (ii) a hydrophobic moiety comprising two hydrocarbyl or acyl chains, wherein about 40 to 100 percent of said chains in the composition are saturated linear alkyl or alkanoyl groups having about 8 to about 22 carbon atoms, preferably about 12 to about 18 carbon atoms.

Description: COMPOSITION AND METHOD FOR TREATING PLANTS WITH EXOGENOUS CHEMICALS BACKGROUND OF THE INVENTION This invention relates to formulations and methods for enhancing the efficacy of exogenous chemicals used in treating plants. An exogenous chemical, as defined herein, is any chemical substance, whether naturally or synthetically derived, which (a) has biological activity or is capable of releasing in a plant an ion, moiety or derivative which has biological activity, and (b) is applied to a plant with the intent or result that the chemical substance or its biologically active ion, moiety or derivative enter living cells or tissues of the plant and elicit a stimulatory, inhibitory, regulatory, therapeutic, toxic or lethal response in the plant itself or in a pathogen, parasite or feeding organism present in or on the plant. Examples of exogenous chemical substances include, but are not limited to, chemical pesticides (such as herbicides, algicides, fungicides, bactericides, viricides, insecticides, aphicides, miticides, nematicides, molluscicides, and the like), plant growth regulators, fertilizers and nutrients, gametocides, defoliants, desiccants, mixtures thereof, and the like. Exogenous chemicals, including foliar-applied herbicides, have at times been formulated with surfactants, so that when water is added, the resulting sprayable composition is more easily and effectively retained on the foliage (e.g., the leaves or other photosynthesizing organs) of plants. Surfactants can also bring other benefits, including improved contact of spray droplets with a waxy leaf surface and, in some cases, improved penetration of the accompanying exogenous chemical into the interior of leaves. Through these and perhaps other effects, surfactants have long been known to increase the biological effectiveness of herbicide compositions, or other compositions of exogenous chemicals, when added to or included in such compositions. Thus, for example, the herbicide glyphosate (N- phosphonomethylglycine) has been formulated with surfactants such as polyoxyalkylene-type surfactants including, among other surfactants, polyoxyalkylene alkylamines. Commercial formulations of glyphosate herbicide marketed under the trademark ROUNDUP® have been formulated with a surfactant composition based on such a polyoxyalkylene alkylamine, in particular a polyethoxylated tallowamine, this surfactant composition being identified as MON 0818. Surfactants have generally been combined with glyphosate or other exogenous chemicals either in a commercial concentrate (herein referred to as a "coformulation"), or in a diluted mixture that is prepared from separate compositions, one comprising an exogenous chemical (e.g. glyphosate) and another comprising surfactant, prior to use in the field (i.e., a tank mix). Various combinations of exogenous chemicals and surfactants or other adjuvants have been tested in the past. In some instances, the addition of a particular surfactant has not produced uniformly positive or negative changes in the effect of the exogenous chemical on the plant (e.g., a surfactant that may enhance the activity of a particular herbicide on certain weeds may interfere with, or antagonize, the herbicidal efficacy on another weed species). Some surfactants tend to degrade fairly rapidly in aqueous solutions. As a result, surfactants that exhibit this property can only be used effectively in tank mixes (i.e., mixed with the other ingredients in solution or dispersion in the tank soon before spraying is to occur), rather than being cofoπnulated in an aqueous composition with the other ingredients in the first instance. This lack of stability, or inadequate shelf-life, has hindered the use of certain surfactants in some exogenous chemical formulations. Other surfactants, though chemically stable, are physically incompatible with certain exogenous chemicals, particularly in concentrate coformulations. For example, most classes of nonionic surfactant, including polyoxyethylene alkylether surfactants, do not tolerate solutions of high ionic strength, as for example in a concentrated aqueous solution of a salt of glyphosate. Physical incompatibility can also lead to inadequate shelf-life. Other problems that can arise from such incompatibility include the formation of aggregates large enough to interfere with commercial handling and application, for example by blocking spray nozzles. Another problem that has been observed in the past is the effect of environmental conditions on uptake of an exogenous chemical composition into foliage of a plant. For example, conditions such as temperature, relative humidity, presence or absence of sunlight, and health of the plant to be treated, can affect the uptake of a herbicide into the plant. As a result, spraying exactly the same herbicidal composition in two different situations can result in different herbicidal control of the sprayed plants. One consequence of the above-described variability is that often a higher rate of herbicide per unit area is applied than might actually be required in that situation, in order to be certain that adequate control of undesired plants will be achieved. For similar reasons, other foliar-applied exogenous chemicals are also typically applied at significantly higher rates than needed to give the desired biological effect in the particular situation where they are used, to allow for the natural variability that exists in efficiency of foliar uptake. A need therefore exists for compositions of exogenous chemicals that, through more efficient uptake into plant foliage, allow reduced use rates. Many exogenous chemicals are commercially packaged as a liquid concentrate that contains a significant amount of water. The packaged concentrate is shipped to distributors or retailers. Ultimately the packaged concentrate ends up in the hands of an end user, who further dilutes the concentrate by adding water in accordance with label instructions on the package. The dilute composition thus prepared is then sprayed on plants. A significant portion of the cost of such packaged concentrates is the cost of transporting the concentrate from the manufacturing site to the location where the end user purchases it. Any liquid concentrate formulation that contained relatively less water and thus more exogenous chemical would reduce the cost per unit amount of exogenous chemical. However, one important limit on the ability of the manufacturer to increase the loading of the exogenous chemical in the concentrate is the stability of that formulation. With some combinations of ingredients, a limit will be reached at which any further reduction of water content in the concentrate will cause it to become unstable (e.g., to separate into discrete layers), which may make it commercially unacceptable. Accordingly, a need exists for improved formulations of exogenous chemicals, particularly herbicides, that are stable, effective, less sensitive to environmental conditions, and permit the use of reduced amounts of exogenous chemical to achieve the desired biological effect in or on plants. A need also exists for stable liquid concentrate formulations of exogenous chemicals that contain less water and more exogenous chemical than prior art concentrates. SUMMARY OF THE INVENTION The present invention relates to novel methods and compositions wherein exogenous chemicals are applied to plants to generate a desired biological response. One embodiment of the present invention is a plant treatment composition that comprises (a) an exogenous chemical and (b) a first excipient substance which forms liposomes in aqueous dispersion and which consists of one or more compounds each having (i) a hydrophilic moiety comprising a cationic group and (ii) a hydrophobic moiety comprising two hydrocarbyl or acyl chains, wherein about 40 to 100 percent of said chains in the composition are saturated linear alkyl or acyl groups having about 8 to about 22 carbon atoms, preferably about 12 to about 18 carbon atoms. Preferably the cationic group is an amine or ammonium group. An "excipient substance" as that term is used in this patent is any substance other than the exogenous chemical and water that is added to the composition, and that satisfies the other conditions described. "Excipient substances" include inert ingredients, although an excipient substance useful in the present invention does not have to be devoid of biological activity. In a preferred embodiment, the first excipient substance comprises one or more phospholipids selected from the group consisting of di-C 8-22 -acylphosphatidylcholines and di-C 8 . 22 - acylphosphatidylethanolamines, wherein about 40 to 100 percent of all acyl chains in said phospholipids are saturated alkanoyl chains. In a more specific embodiment, the first excipient substance is a phospholipid or mixture of phospholipids, about 40 to 100 percent of which consists of a dipalmitoyl or distearoyl ester of phosphatidylcholine or a mixture thereof. In one preferred embodiment, the weight/weight ratio of the first excipient substance to the exogenous chemical is about 1 :3 to about 1 : 100. A wide variety of exogenous chemicals can be used in the compositions and methods of the present invention. A preferred class is foliar-applied exogenous chemicals, i.e. exogenous chemicals that are normally applied post-emergence to foliage of plants. A preferred subclass of foliar-applied exogenous chemicals is those that are water-soluble. By "water-soluble" in this context is meant having a solubility in distilled water at 25°C greater than about 1% by weight. Especially preferred water- soluble exogenous chemicals are salts that have an anion portion and a cation portion. In one embodiment of the invention, at least one of the anion and cation portions is biologically active and has a molecular weight of less than about 300. Particular examples of such exogenous chemicals where the cation portion is biologically active are paraquat, diquat and chlormequat. More commonly it is the anion portion that is biologically active. Another preferred subclass of exogenous chemicals is those that exhibit systemic biological activity in the plant. Within this subclass, an especially preferred group of exogenous chemicals is N- phosphonomethylglycine and its herbicidal derivatives. N-phosphonomethylglycine, often referred to by its common name glyphosate, can be used in its acid form, but is more preferably used in the form of a salt. Any water-soluble salt of glyphosate can be used in the practice of this invention. Some preferred salts include the sodium, potassium, ammonium, mono-, di-, tri- and tetra-C 1-4 -alkylammonium, mono-, di- and tri-C]. -alkanolammonium, mono-, di- and tri-C^-alkylsulfonium and sulfoxonium salts. The ammonium, monoisopropylammonium and trimethylsulfonium salts of glyphosate are especially preferred. Mixtures of salts can also be useful in certain situations. A composition of the present invention comprising an exogenous chemical and a first excipient substance as described above can have a number of different physical forms. For example, the composition can further comprise water in an amount effective to make the composition a dilute aqueous composition ready for application to foliage of a plant. Such a composition typically contains about 0.02 to about 2 percent by weight of the exogenous chemical, but for some purposes can contain up to about 10 percent by weight or even more of the exogenous chemical. Alternatively, the composition can be a shelf-stable concentrate composition comprising the exogenous chemical substance in an amount of about 10 to about 90 percent by weight. Such shelf- stable concentrates can be, for example, (1) a solid composition comprising the exogenous chemical substance in an amount of about 30 to about 90 percent by weight, such as a water-soluble or water- dispersible granular formulation, or (2) a composition that further comprises a liquid diluent, wherein the composition comprises the exogenous chemical substance in an amount of about 10 to about 60 percent by weight. In this latter embodiment, it is especially preferred for the exogenous chemical substance to be water-soluble and present in an aqueous phase of the composition in an amount of about 15 to about 45 percent by weight of the composition. In particular, such a composition can be, for example, an aqueous solution concentrate or an emulsion having an oil phase. If it is an emulsion, it can more specifically be, for example, an oil-in-water emulsion, a water-in-oil emulsion, or a water-in-oil-in-water multiple emulsion. As described above, one embodiment of the invention is a sprayable composition. The term "spray composition" is sometimes used herein to mean a sprayable composition. In a related embodiment of the invention, a concentrate composition is provided which, upon dilution, dispersion or dissolution in water forms the sprayable composition just described. The concentrate composition contains a reduced amount of the aqueous diluent, or, in a particular embodiment, is a dry composition having less than about 5% water by weight. Typically a concentrate composition of the invention contains at least about 10% by weight of the exogenous chemical, preferably at least about 15%. The weight ratio of the first excipient substance to the exogenous chemical preferably is between about 1 :3 and about 1 : 100. We have been surprised by the high level of biological effectiveness, specifically herbicidal effectiveness of a glyphosate composition, exhibited at such low ratios of first excipient substance to exogenous chemical. Higher ratios can also be effective but are likely to be uneconomic in most situations and increase the risk of producing an antagonistic effect on effectiveness of the exogenous chemical. Prior art exogenous chemical compositions that have included liposome-forming excipient substances have typically contained a higher percentage of the liposome-forming excipient substance than of the exogenous chemical. Compositions of the present invention can contain less of the excipient substance than the exogenous chemical, and in some embodiments much less. This makes such compositions of the present invention much less expensive than the above-described prior art compositions. It is surprising that the enhancement of biological activity that has been observed when using the present invention can be achieved with the addition of relatively small amounts of such excipient substances. As indicated above, the first excipient substance comprises a liposome-forming compound having a hydrophilic moiety that comprises a cationic group and a hydrophobic moiety that comprises two independently saturated or unsaturated hydrocarbyl or acyl chains. Liposome-forming compounds useful in the invention can illustratively be represented as in formulas I-IV below. All such compounds 1 2 have two hydrocarbyl chains R and R each independently having about 7 to about 21 carbon atoms. A number of subclasses of such liposome-forming compounds are known. One subclass has the formula N + (CH 2 R 1 )(CH 2 R 2 )(R 3 )(R 4 ) Z " I wherein R and R are independently hydrogen, C 1- alkyl or C 1- hydroxyalkyl and Z is a suitable agriculturally acceptable anion. A second subclass has the formula N + (R 5 )(R 6 )(R 7 )CH 2 CH(OCH 2 R 1 )CH 2 (OCH 2 R 2 ) Z " II wherein R , R and R are independently hydrogen, Cι. alkyl or C 1 -4 hydroxyalkyl and Z is a suitable anion. A third subclass has the formula N + (R 5 )(R 6 )(R 7 )CH 2 CH(OCOR 1 )CH 2 (OCOR 2 ) Z " III wherein R 3 , R , R and Z are as defined above. A fourth subclass has the formula N + (R 5 )(R 6 )(R 7 )CH 2 CH 2 OPO(0 " )OCH 2 CH(OCOR 1 )CH 2 (OCOR 2 ) IV wherein R\ R , and R are as defined above. Compounds of formulas I-IV will have the indicated formulas in an acid medium, for example at a pH of 4 and may have the same formulas at other pH's as well. It should be understood, however, that compositions of the present invention are not limited to use at a pH of 4. ι 2 It is preferred that about 40 to 100 percent of the R and R chains in the composition are saturated straight-chain alkyl groups each having about 7 to about 21 carbon atoms. Examples of suitable agriculturally acceptable anions Z include hydroxide, chloride, bromide, iodide, sulfate, phosphate and acetate. In all of the above subclasses of liposome-forming substances, the hydrophilic moiety comprises a cationic group, specifically an amine or ammonium group. The compound as a whole is in some cases cationic (as in I, II and III) and in some cases neutral (as in IV). Where the amine group is quaternary, it behaves as a cationic group independently of pH. Where the amine group is secondary or tertiary, it behaves as a cationic group when protonated, i.e. in an acid medium, for example at a pH of 4. In a preferred embodiment, the composition further comprises a second excipient substance that is an amphiphilic quaternary ammonium compound or mixture of such compounds. The hydrophobic moiety of the quaternary ammonium compound is a saturated alkyl or haloalkyl group having about 6 to about 22 carbon atoms. Preferred quaternary ammonium compounds (other than those which are liposome-forming and have two hydrocarbyl chains) for use as the second excipient substance in compositions of the invention have the formula R 8 -W a -X-Y b -(CH 2 ) n -N + (R 9 )(R 10 )(R π ) T " V wherein R represents the hydrophobic moiety and is a hydrocarbyl or haloalkyl group having from about 6 to about 22 carbon atoms, W and Y are independently O or NH, a and b are independently 0 or 1 but at least one of a and b is 1 , X is CO, SO or S0 2 , n is 2 to 4, R , R and R are independently C alkyl, g and T is a suitable anion. R in one particular embodiment is hydrocarbyl having about 12 to about 18 carbon atoms. R can also be fluorinated. In one specific embodiment, R is perfluorinated, and preferably has about 6 to about 12 carbon atoms. Suitable agriculturally acceptable anions T include hydroxide, chloride, bromide, iodide, sulfate, phosphate and acetate. In one particularly preferred embodiment, R is saturated perfluoroalkyl having about 6 to about 12 carbon atoms, X is CO or S0 , Y is NH, a is 0, b is 1 , n is 3, R , R and R are methyl, and T is selected from the group consisting of chloride, bromide and iodide. In another preferred embodiment, the composition further comprises a second excipient substance which is a compound or mixture of compounds of formula R 14 -CO-A-R 15 VII wherein R is a hydrocarbyl group having about 5 to about 21 carbon atoms, R 3 is a hydrocarbyl group having 1 to about 14 carbon atoms, the total number of carbon atoms in R and R is about 1 1 to about 27, and A is O or NH. R preferably has about 1 1 to about 21 carbon atoms, R preferably has 1 to about 6 carbon atoms and A is preferably O. In another, the second excipient substance is a C 1-4 alkyl ester of a C 1 2 - 18 fatty acid, for example a propyl, isopropyl or butyl ester of a C 1 _ι 8 fatty acid. Butyl stearate is an especially preferred example. The aqueous composition in embodiments comprising a compound of formula VII can be an emulsion comprising an oil phase that comprises said second excipient substance, for example a water-in-oil-in-water multiple emulsion or an oil-in-water emulsion. In any of the above particular embodiments, the exogenous chemical and/or second excipient substance can be encapsulated within or associated with the liposomes formed by the first excipient substance, but do not necessarily have to be so encapsulated or associated. "Associated" in this context means bound to or at least partly intercalated in some fashion in a vesicle wall, as opposed to being encapsulated. In yet another embodiment of the invention, the exogenous chemical and/or second excipient substance is not encapsulated in or associated with the liposomes at all. Although the present invention does not exclude the possibility of so encapsulating or associating the exogenous chemical, a presently preferred dilute sprayable liposomal composition encapsulates less than 5% by weight of the exogenous chemical that is present in the overall composition. Another dilute sprayable liposomal embodiment of the present invention has no substantial amount (i.e., less than 1 % by weight) of the exogenous chemical encapsulated in the liposomes. As a droplet of such a liposomal composition dries on foliage of a plant, the proportion of the exogenous chemical that is encapsulated in the liposomes may change. Compositions of the present invention that include an exogenous chemical can be applied to foliage of plants in an amount that is effective to achieve the desired biological effect of the exogenous chemical. For example, when the exogenous chemical is a postemergent herbicide, the composition can be applied to a plant in a herbicidal ly effective amount. The compositions and methods of the present invention have a number of advantages. They provide enhanced biological activity of exogenous chemicals in or on plants in comparison with prior formulations, either in terms of greater ultimate biological effect, or obtaining an equivalent biological effect while using a reduced application rate of exogenous chemical. Certain herbicide formulations of the present invention can avoid antagonism that has been observed in some prior art herbicide formulations, and can minimize quick production of necrotic lesions on leaves that in some situations hinder overall translocation of herbicide in the plant. Certain herbicide compositions of the invention modify the spectrum of activity of the herbicide across a range of plant species. For example, certain formulations of the present invention containing glyphosate can provide good herbicidal activity against broadleaf weeds while not losing any herbicidal effectiveness on narrowleaf weeds. Others can enhance herbicidal effectiveness on narrowleaf weeds to a greater extent than on broadleaf weeds. Still others can have enhanced effectiveness which is specific to a narrow range of species or even a single species. Another advantage of the present invention is that it generally employs relatively small amounts of the excipient substances in relation to the amount of exogenous chemical employed. This makes the compositions and methods of the present invention relatively inexpensive, and also tends to reduce instability problems in specific compositions where one or both excipient substances are physically incompatible with the exogenous chemical. Further, compositions of the present invention are less sensitive in some instances to environmental conditions such as relative humidity at the time of application to the plant. Also, the present invention allows the use of smaller amounts of herbicides or other pesticides, while still obtaining the required degree of control of weeds or other undesired organisms. DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS Examples of exogenous chemical substances that can be included in compositions of the present invention include, but are not limited to, chemical pesticides (such as herbicides, algicides, fungicides, bactericides, viricides, insecticides, aphicides, miticides, nematicides, molluscicides and the like), plant growth regulators, fertilizers and nutrients, gametocides, defoliants, desiccants, mixtures thereof and the like. In one embodiment of the invention, the exogenous chemical is polar. A preferred group of exogenous chemicals are those that are normally applied post-emergence to the foliage of plants, i.e. foliar-applied exogenous chemicals. Some exogenous chemicals useful in the present invention are water-soluble, for example salts that comprise biologically active ions, and also comprise counterions, which may be biologically inert or relatively inactive. A particularly preferred group of these water-soluble exogenous chemicals or their biologically active ions or moieties are systemic in plants, that is, they are to some extent translocated from the point of entry in the foliage to other parts of the plant where they can exert their desired biological effect. Especially preferred among these are herbicides, plant growth regulators and nematicides, particularly those that have a molecular weight, excluding counterions, of less than about 300. More especially preferred among these are exogenous chemical compounds having one or more functional groups selected from amine, carboxylate, phosphonate and phosphinate groups. Among such compounds, an even more preferred group are herbicidal or plant growth regulating exogenous chemical compounds having at least one of each of amine, carboxylate, and either phosphonate or phosphinate functional groups. Salts of N-phosphonomethylglycine are examples of this group of exogenous chemicals. Further examples include salts of glufosinate, for instance the ammonium salt (ammonium DL-homoalanin-4-yl (methyl) phosphinate). Another preferred group of exogenous chemicals which can be applied by the method of the invention are nematicides such as those disclosed in U.S. Patent No. 5,389,680, the disclosure of which is incoφorated herein by reference. Preferred nematicides of this group are salts of 3,4,4-trifluoro-3- butenoic acid or of N-(3,4,4-trifluoro-l -oxo-3-butenyl)glycine. Exogenous chemicals which can usefully be applied by the method of the present invention are normally, but not exclusively, those which are expected to have a beneficial effect on the overall growth or yield of desired plants such as crops, or a deleterious or lethal effect on the growth of undesirable plants such as weeds. The method of the present invention is particularly useful for herbicides, especially those that are normally applied post-emergence to the foliage of unwanted vegetation. Herbicides which can be applied by the method of the present invention include but are not limited to any listed in standard reference works such as the "Herbicide Handbook," Weed Science Society of America, 1994, 7th Edition, or the "Farm Chemicals Handbook," Meister Publishing Company, 1997 Edition. Illustratively these herbicides include acetanilides such as acetochlor, alachlor and metolachlor, aminotriazole, asulam, bentazon, bialaphos, bipyridyls such as paraquat, bromacil, cyclohexenones such as clethodim and sethoxydim, dicamba, diflufenican, dinitroanilines such as pendimethalin, diphenylethers such as acifluorfen, fomesafen and oxyfluorfen, fatty acids such as Cα^o fatty acids, fosamine, flupoxam, glufosinate, glyphosate, hydroxybenzonitriles such as bromoxynil, imidazolinones such as imazaquin and imazethapyr, isoxaben, norflurazon, phenoxies such as 2,4-D, phenoxypropionates such as diclofop, fluazifop and quizalofop, picloram, propanil, substituted ureas such as fluometuron and isoproturon, sulfonylureas such as chlorimuron, chlorsulfuron, halosulfuron, metsulfuron, primisulfuron, sulfometuron and sulfosulfuron, thiocarbamates such as triallate, triazines such as atrazine and metribuzin, and triclopyr. Herbicidally active derivatives of any known herbicide are also within the scope of the present invention. A herbicidally active derivative is any compound which is a minor structural modification, most commonly but not restrictively a salt or ester, of a known herbicide. These compounds retain the essential activity of the parent herbicide, but may not necessarily have a potency equal to that of the parent herbicide. These compounds may convert to the parent herbicide before or after they enter the treated plant. Mixtures or coformulations of a herbicide with other ingredients, or of more than one herbicide, may likewise be employed. An especially preferred herbicide is N-phosphonomethylglycine (glyphosate), a salt, adduct or ester thereof, or a compound which is converted to glyphosate in plant tissues or which otherwise provides glyphosate ion. Glyphosate salts that can be used according to this invention include but are not restricted to alkali metal, for example sodium and potassium, salts; ammonium salt; alkylamine, for example dimethylamine and isopropylamine, salts; alkanolamine, for example ethanolamine, salts; alkylsulfonium, for example trimethylsulfonium, salts; sulfoxonium salts; and mixtures thereof. The herbicidal compositions sold by Monsanto Company as ROUNDUP® and ACCORD® contain the monoisopropylamine (IPA) salt of N-phosphonomethylglycine. The herbicidal compositions sold by Monsanto Company as ROUNDUP® Dry and RIVAL® contain the monoammonium salt of N-phosphonomethylglycine. The herbicidal composition sold by Monsanto Company as ROUNDUP® Geoforce contains the monosodium salt of N-phosphonomethylglycine. The herbicidal composition sold by Zeneca as TOUCHDOWN® contains the trimethylsulfonium salt of N-phosphonomethylglycine. The herbicidal properties of N-phosphonomethylglycine and its derivatives were first discovered by Franz, then disclosed and patented in U.S. Patent 3,799,758, issued March 26, 1974. A number of herbicidal salts of N-phosphonomethylglycine were patented by Franz in U.S. Patent 4,405,531, issued September 20, 1983. The disclosures of both of these patents are hereby incorporated by reference. Because the commercially most important herbicidal derivatives of N-phosphonomethylglycine are certain salts thereof, the glyphosate compositions useful in the present invention will be described in more detail with respect to such salts. These salts are well known and include ammonium, IPA, alkali metal (such as the mono-, di-, and trisodium salts, and the mono-, di-, and tripotassium salts), and trimethylsulfonium salts. Salts of N-phosphonomethylglycine are commercially significant in part because they are water soluble. The salts listed immediately above are highly water soluble, thereby allowing for highly concentrated solutions that can be diluted at the site of use. In accordance with the method of this invention as it pertains to glyphosate herbicide, an aqueous solution containing a herbicidally effective amount of glyphosate and other components in accordance with the invention is applied to foliage of plants. Such an aqueous solution can be obtained by dilution of a concentrated glyphosate salt solution with water, or dissolution or dispersion in water of a dry (e.g. granular, powder, tablet or briquette) glyphosate formulation. Exogenous chemicals should be applied to plants at a rate sufficient to give the desired biological effect. These application rates are usually expressed as amount of exogenous chemical per unit area treated, e.g. grams per hectare (g/ha). What constitutes a "desired effect" varies according to the standards and practice of those who investigate, develop, market and use a specific class of exogenous chemicals. For example, in the case of a herbicide, the amount applied per unit area to give 85% control of a plant species as measured by growth reduction or mortality is often used to define a commercially effective rate. Herbicidal effectiveness is one of the biological effects that can be enhanced through this invention. "Herbicidal effectiveness," as used herein, refers to any observable measure of control of plant growth, which can include one or more of the actions of (1) killing, (2) inhibiting growth, reproduction or proliferation, and (3) removing, destroying, or otherwise diminishing the occurrence and activity of plants. The herbicidal effectiveness data set forth herein report "inhibition" as a percentage following a standard procedure in the art which reflects a visual assessment of plant mortality and growth reduction by comparison with untreated plants, made by technicians specially trained to make and record such observations. In all cases, a single technician makes all assessments of percent inhibition within any one experiment or trial. Such measurements are relied upon and regularly reported by Monsanto Company in the course of its herbicide business. The selection of application rates that are biologically effective for a specific exogenous chemical is within the skill of the ordinary agricultural scientist. Those of skill in the art will likewise recognize that individual plant conditions, weather and growing conditions, as well as the specific exogenous chemical and formulation thereof selected, will affect the efficacy achieved in practicing this invention. Useful application rates for exogenous chemicals employed can depend upon all of the above conditions. With respect to the use of the method of this invention for glyphosate herbicide, much information is known about appropriate application rates. Over two decades of glyphosate use and published studies relating to such use have provided abundant information from which a weed control practitioner can select glyphosate application rates that are herbicidally effective on particular species at particular growth stages in particular environmental conditions. Herbicidal compositions of glyphosate or derivatives thereof are used to control a very wide variety of plants worldwide. Such compositions can be applied to a plant in a herbicidally effective amount, and can effectively control one or more plant species of one or more of the following genera without restriction: Abutilon, Amaranthus, Artemisia, Asclepias, Avena, Axonopus, Borreria, Brachiaria, Brassica, Bromus, Chenopodium, Cirsium, Commelina, Convolvulus, Cynodon, Cyperus, Digitaria, Echinochloa, Eleusine, Elymus, Equisetum, Erodium, Helianthus, Imperata, Ipomoea, Kochia, Lolium, Malva, Oryza, Ottochloa, Panicum, Paspalum, Phalaris, Phragmites, Polygonum, Portulaca, Pteridium, Pueraria, Rubus, Salsola, Setaria, Sida, Sinapis, Sorghum, Triticum, Typha, Ulex, Xanthium, and Zea. Particularly important species for which glyphosate compositions are used are exemplified without limitation by the following: Annual broadleaves: velvetleaf (Abutilon theophrasti) pigweed (Amaranthus spp.) buttonweed (Borreria spp.) oilseed rape, canola, indian mustard, etc. (Brassica spp.) commelina (Commelina spp.) filaree (Erodium spp.) sunflower (Helianthus spp.) morningglory (Ipomoea spp.) kochia (Kochia scoparia) mallow (Malva spp.) wild buckwheat, smartweed, etc. (Polygonum spp.) purslane (Portulaca spp.) russian thistle (Salsola spp.) sida (Sida spp.) wild mustard (Sinapis arvensis) cocklebur (Xanthium spp.) Annual narrowleaves: wild oat (Avena fatua) carpetgrass (Axonopus spp.) downy brome (Bromus tectorum) crabgrass (Digitaria spp.) barnyardgrass (Echinochloa crus-galli) goosegrass (Eleusine indica) annual ryegrass (Lolium multiflorum) rice (Oryza sativa) ottochloa (Ottochloa nodosa) bahiagrass (Paspalum notatum) canarygrass (Phalaris spp.) foxtail (Setaria spp.) wheat (Triticum aestivum) corn (Zea mays) Perennial broadleaves: mugwort (Artemisia spp.) milkweed (Asclepias spp.) Canada thistle (Cirsium arvense) field bindweed (Convolvulus arvensis) kudzu (Pueraria spp.) Perennial narrowleaves: brachiaria (Brachiaria spp.) bermudagrass (Cynodon dactylon) yellow nutsedge (Cyperus esculentus) purple nutsedge (C. rotundus) quackgrass (Elymus repens) lalang (Imperata cylindrica) perennial ryegrass (Lolium perenne) guineagrass (Panicum maximum) dallisgrass (Paspalum dilatatum) reed (Phragmites spp.) johnsongrass (Sorghum halepense) cattail (Typha spp.) Other perennials: horsetail (Equisetum spp.) bracken (Pteridium aquilinum) blackberry (Rubus spp.) gorse (Ulex europaeus) Thus, the method of the present invention, as it pertains to glyphosate herbicide, can be useful on any of the above species. Effectiveness in greenhouse tests, usually at exogenous chemical rates lower than those normally effective in the field, is a proven indicator of consistency of field performance at normal use rates. However, even the most promising composition sometimes fails to exhibit enhanced performance in individual greenhouse tests. As illustrated in the Examples herein, a pattern of enhancement emerges over a series of greenhouse tests; when such a pattern is identified this is strong evidence of biological enhancement that will be useful in the field. The first excipient substance in compositions of the present invention is selected from the class of amphiphilic liposome-forming substances. These include various lipids of synthetic, animal, or plant origin, including phospholipids, ceramides, sphingolipids, dialkyl surfactants, and polymeric surfactants. A variety of these materials are known to those skilled in the art, and are commercially available. Lecithins are particularly rich in phospholipids and can be derived from a number of plant and animal sources. Soybean lecithin is one particular example of a relatively inexpensive commercially available material that includes such substances. Many other substances have been described which can be used to form liposomes; the present invention includes compositions comprising any such liposome-forming substances, so long as other requirements set out above are met, and use of such compositions for enhancing biological effectiveness of exogenous chemicals applied to foliage of plants. For example, US Patent No. 5,580,859, incorporated here by reference, discloses liposome-forming substances having a cationic group, including N-(2,3-di-(9-(Z)-octadecenyloxy))-prop-l -yl-N,N,N-trimethylammonium chloride (DOTMA) and l,2-bis(oleoyloxy)-3-(trimethylammonio)propane (DOTAP). Liposome-forming substances which are not themselves cationic, but do contain a cationic group as part of the hydrophilic moiety, include for example dioleoylphosphatidylcholine (DOPC) and dioleoylphosphatidylethanolamine (DOPE). Any of these liposome-forming substances can be used with or without the addition of cholesterol. These substances contain portions that are hydrophilic and hydrophobic within the same molecule. They have the ability to self-assemble in aqueous solution or dispersion into structures that are more complex than simple micelles. The nature of the aggregate that will be formed can be related to the critical packing parameter P by the following equation: P = V HA where V is the volume of the hydrophobic tail of the molecule, / is the effective length of the hydrophobic tail, and A is the area occupied by the hydrophilic headgroup in the surface of the aggregate. The most probable self-assembled structures are spherical micelles when P is less than 1/3, rodlike micelles when P is between 1/3 and ' , lamellar when P is between 1 and ] Λ, and inverse structures when P is greater than 1. The preferred materials in the present invention have P greater than 1/3. Cationic liposome-forming substances having a hydrophobic moiety comprising two hydrocarbyl chains are accompanied by a counterion (anion), identified as Z in formulas I, II and III above. Any suitable anion can be used, including agriculturally acceptable anions such as hydroxide, chloride, bromide, iodide, sulfate, phosphate and acetate. In a specific embodiment where the exogenous chemical has a biologically active anion, that anion can serve as the counterion for the liposome-forming substance. For example, glyphosate can be used in its acid form together with the hydroxide of a cationic liposome-forming substance such as a compound of formula I. Compounds of formula I known in the art to be liposome-forming include distearyldimethylammonium chloride and bromide (also known in the art as DODAC and DODAB respectively). Compounds of formula II known in the art to be liposome-forming include DOTMA referenced above and dimyristooxypropyldimethylhydroxyethylammonium bromide (DMRIE). Compounds of formula III known in the art to be liposome-forming include dioleoyloxy-3- (dimethylammonio)propane (DODAP) and DOTAP referenced above. Compounds of formula IV known in the art to be liposome-forming include DOPC and DOPE, both referenced above. In many liposome-forming substances known in the art, the hydrophobic hydrocarbyl chains are unsaturated, having one or more double bonds. Particularly commonly used in the pharmaceutical art are dioleyl or dioleoyl compounds. A potential problem with these is that in an oxidizing environment they become oxidized at the site of the double bond. This can be inhibited by including in the formulation an antioxidant such as ascorbic acid. Alternatively the problem can be avoided by use of liposome-forming substances wherein a high proportion of the hydrophobic hydrocarbyl chains are fully saturated. Thus in a composition of the present invention, from about 40 to 100 percent of the hydrocarbyl chains (R and R in formulas I-IV) in the composition are saturated straight-chain alkyl groups. Particularly preferred 1 7 compositions use liposome-forming substances in which R and R , together with the adjacent CH 2 or CO groups shown in formulas I-IV, both form palmityl (cetyl) or palmitoyl or, alternatively, both form stearyl or stearoyl groups. Phospholipids, because of their low cost and favorable environmental properties, are particularly favored among liposome-forming substances in the method and compositions of the invention. Vegetable lecithins, such as soybean lecithin, are a rich source of phospholipids; however in vegetable lecithins a high proportion of the hydrophobic hydrocarbyl chains of the phospholipid compounds are typically unsaturated. One embodiment of compositions in accordance with the present invention comprises both saturated phospholipid and unsaturated phospholipid, with the weight ratio of saturated phospholipid to unsaturated phospholipid being greater than about 1 :2. In various particularly preferred embodiments, (1) at least 50% by weight of the phospholipids are di-C 12 . 22 -saturated alkanoyl phospholipid, (2) at least 50% by weight of the phospholipids are di-C 16-18 -saturated alkanoyl phospholipid, (3) at least 50% by weight of the phospholipids are distearoyl phospholipid, (4) at least 50% by weight of the phospholipids are dipalmitoyl phospholipid, or (5) at least 50% by weight of the phospholipids are distearoyl phosphatidylcholine, dipalmitoyl phosphatidylcholine, or a mixture thereof. Higher proportions of saturated alkanoyl phospholipids are generally found in lecithins of animal origin, such as for example egg yolk lecithin, than in vegetable lecithins. Illustratively, analysis of samples of egg yolk lecithin and soybean lecithin has shown 45% of acyl chains in egg yolk lecithin, and only 22% of acyl chains in soybean lecithin to be saturated alkanoyl chains. Phospholipids are known to be chemically unstable, at least in acid media, where they tend to degrade to their lyso-counterparts. Thus where phospholipids rather than more stable liposome-forming substances are used, it is usually preferable to adjust the pH of the composition upward. In the case of glyphosate compositions, the pH of a composition based on a mono-salt such as the monoisopropylammonium (IPA) salt is typically around 5 or lower. When phospholipids are used as the first excipient substance in a glyphosate composition of the invention, it will therefore be preferable to raise the pH of the composition, for example to around 7. Any convenient base can be used for this purpose; it will often be most convenient to use the same base as used in the glyphosate salt, for example isopropylamine in the case of glyphosate IPA salt. Compounds useful as the second excipient substance herein include quaternary ammonium compounds having formula V above. In compounds of formula V, R unless perfluorinated preferably has from about 12 to about 18 carbon atoms. R is preferably perfluorinated, in which case it preferably has from about 6 to about 12 carbon atoms. Preferably n is 3. R groups are preferably methyl. Sulfonylamino compounds of formula V are especially preferred. Suitable examples include 3-(((heptadecafluorooctyl)sulfonyl)amino)-N,N,N-trimethyl-l -propaminium iodide, available for example as Fluorad FC-135 from 3M Company, and the corresponding chloride. It is believed that Fluorad FC-754 of 3M Company is the corresponding chloride. Derivatives of Fluorad FC-754, herein described as "FC-acetate" and "FC-salicylate," have been prepared by the following procedure. (1) The solvent in a sample of Fluorad FC-754 is gently evaporated off by heating in a glass beaker at 70-80°C, to leave a solid residue. (2) The solid residue is allowed to cool to room temperature. (3) A 1 g aliquot of the residue is placed in a centrifuge tube and dissolved in 5 ml isopropanol. (4) A saturated solution of potassium hydroxide (KOH) is prepared in isopropanol. (5) This solution is added drop by drop to the solution of FC-754 residue; this results in formation of a precipitate and addition of KOH solution continues until no further precipitate forms. (6) The tube is centrifuged at 4000 rpm for 5 minutes. (7) More KOH solution is added to check if precipitation is complete; if not, the tube is centrifuged again. (8) The supernatant is decanted into another glass tube. (9) A saturated solution of acetic acid (or salicylic acid) is prepared in isopropanol. (10) This solution is added to the supernatant in an amount sufficient to lower pH to 7. (1 1) Isopropanol is evaporated from this neutralized solution by heating at 60°C until completely dry. (12) The residue (either the acetate or salicylate salt) is dissolved in a suitable amount of water and is then ready for use. Another class of quaternary ammonium compounds useful as the second excipient substance in the present invention has the formula N + (R , 6 )(R 17 )(R 18 )(R 19 ) Q " VIII where R , R , R and R are independently C 3 _ 6 alkyl groups and Q is a suitable anion, such as for example hydroxide, chloride, bromide, iodide, sulfate, phosphate or acetate. In preferred compounds of formula VIII all R groups are the same. Particularly preferred compounds of formula VIII are tetrabutylammonium salts. Where the exogenous chemical comprises a biologically active anion, a salt of formula VIII where Q is that anion is an option providing both the exogenous chemical and second excipient substance. An example is the tetrabutylammonium salt of glyphosate. Other quaternary ammonium compounds that may be useful include compounds having a single Ci 2-22 hydrocarbyl group and three groups selected from benzyl or C 1-4 alkyl groups attached to the quaternary nitrogen atom. Specific examples include cetyltrimethylammonium bromide and benzalkonium chloride. Another class of compound useful as the second excipient substance is an amide or ester of formula VII above. R in formula VII is preferably aliphatic and has about 7 to about 21 carbon atoms, more preferably about 13 to about 21 carbon atoms. It is especially preferred that R be a saturated straight- chain alkyl group. R is preferably an aliphatic group having 1-6 carbon atoms, more preferably alkyl or alkenyl having 2-4 carbon atoms. An especially preferred compound of formula VII for use as the second excipient substance is butyl stearate. As compounds of formula VII, including butyl stearate, are generally oily liquids, aqueous compositions containing them are typically emulsions having at least one aqueous phase and at least one oil phase, with the compound of formula VII being present predominantly in the oil phase. Such emulsions may be water-in-oil, oil-in-water or water-in-oil-in-water (W/O/W) multiple emulsions. Compositions in accordance with the present invention are typically prepared by combining water, the exogenous chemical and the first excipient substance. Where the first excipient substance is one that disperses readily in water, simple mixing with mild agitation may be sufficient. However, most liposome-forming substances including most forms of lecithin require high shear to disperse in water, and in such cases it is presently preferred to sonicate or microfluidize the liposome-forming first excipient substance in water. This can be done before or after a second excipient substance and/or the exogenous chemical is added. The sonication or microfluidization will generally produce liposomes or other aggregate structures other than simple micelles. The precise nature, including average size, of liposomes or other aggregates depends among other things on the energy input during sonication or microfluidization. Higher energy input generally results in smaller liposomes. Although it is possible to entrap or otherwise bind loosely or tightly the exogenous chemical in or on liposomes or with other supramolecular aggregates, the exogenous chemical does not need to be so entrapped or bound, and in fact the present invention is effective when the exogenous chemical is not entrapped or bound in the aggregates at all. In a particular embodiment of the invention, the liposomes or other aggregates have an average diameter of at least 20 nm, more preferably at least 30 nm. Average liposome diameters can be determined by light scattering techniques. The concentrations of the various components will vary, in part depending on whether a concentrate is being prepared that will be further diluted before spraying onto a plant, or whether a solution or dispersion is being prepared that can be sprayed without further dilution. In an aqueous glyphosate formulation that includes a dialkyl surfactant, for example a cationic dialkyl surfactant of formula I, suitable concentration ranges are: glyphosate 0.1 - 400 grams acid equivalent (a.e.)/liter, and dialkyl surfactant 0.001 - 10% by weight. In an aqueous glyphosate formulation using a cationic fluoro-organic surfactant and lecithin, suitable concentrations can be: glyphosate 0.1 - 400 g a.e./l, fluoro-organic surfactant 0.001 - 10% by weight, and egg yolk lecithin 0.001 - 10% by weight. In solid glyphosate formulations, higher concentrations of ingredients are possible because of the elimination of most of the water. Weight/weight ratios of ingredients may be more important than absolute concentrations. For example, in a glyphosate formulation containing egg yolk lecithin and a cationic fluoro-organic surfactant, the ratio of lecithin to glyphosate a.e. is preferably in the range from about 1 :3 to about 1 : 100. It is generally preferred to use a ratio of lecithin to glyphosate a.e. close to as high as can be incorporated in the formulation while maintaining stability, in the presence of an amount of the fluoro-organic surfactant sufficient to give the desired enhancement of herbicidal effectiveness. For example, a lecithin/glyphosate a.e. ratio in the range from about 1 :3 to about 1 : 10 will generally be found useful, although lower ratios, from about 1 : 10 to about 1 :100 can have benefits on particular weed species in particular situations. The ratio of fluoro-organic surfactant, when present, to glyphosate a.e. is likewise preferably in the range from about 1 :3 to about 1 : 100. Because fluoro-organic surfactants tend to have relatively high cost, it will generally be desirable to keep this ratio as low as possible consistent with achieving the desired herbicidal effectiveness.. The ratio of fluoro-organic surfactant, where present, to lecithin is preferably in the range from about 1 :10 to about 10: 1, more preferably in the range from about 1 :3 to about 3: 1 and most preferably around 1 : 1. The ranges disclosed herein can be used by one of skill in the art to prepare compositions of the invention having suitable concentrations and ratios of ingredients. Preferred or optimum concentrations and ratios of ingredients for any particular use or situation can be determined by routine experimentation. Although the combination of the components might be done in a tank mix, it is preferred in the present invention that the combination be made further in advance of the application to the plant, in order to simplify the tasks required of the person who applies the material to plants. We have found, however, that in some cases the biological effectiveness of a liposome-containing composition prepared from scratch as a dilute spray composition is superior to that of a composition having the same ingredients at the same concentrations but diluted from a previously prepared concentrate formulation. Although various compositions of the present invention are described herein as comprising certain listed materials, in some preferred embodiments of the invention the compositions consist essentially of the indicated materials. Optionally, other agriculturally acceptable materials can be included in the compositions. For example, more than one exogenous chemical can be included. Also, various agriculturally acceptable adjuvants can be included, whether or not their purpose is to directly contribute to the effect of the exogenous chemical on a plant. For example, when the exogenous chemical is a herbicide, liquid nitrogen fertilizer or ammonium sulfate might be included in the composition. As another example, stabilizers can be added to the composition. In some instances it might be desirable to include microencapsulated acid in the composition, to lower the pH of a spray solution on contact with a leaf. One or more surfactants can also be included. Surfactants mentioned here by trade name, and other surfactants that can be useful in the method of the invention, are indexed in standard reference works such as McCutcheon's Emulsifiers and Detergents, 1997 edition, Handbook of Industrial Surfactants, 2nd Edition, 1997, published by Gower, and International Cosmetic Ingredient Dictionary, 6th Edition, 1995. The compositions of the present invention can be applied to plants by spraying, using any conventional means for spraying liquids, such as spray nozzles, atomizers, or the like. Compositions of the present invention can be used in precision farming techniques, in which apparatus is employed to vary the amount of exogenous chemical applied to different parts of a field, depending on variables such as the particular plant species present, soil composition, and the like. In one embodiment of such techniques, a global positioning system operated with the spraying apparatus can be used to apply the desired amount of the composition to different parts of a field. The composition at the time of application to plants is preferably dilute enough to be readily sprayed using standard agricultural spray equipment. Preferred application rates for the present invention vary depending upon a number of factors, including the type and concentration of active ingredient and the plant species involved. Useful rates for applying an aqueous composition to a field of foliage can range from about 25 to about 1 ,000 liters per hectare (1/ha) by spray application. The preferred application rates for aqueous solutions are in the range from about 50 to about 300 1/ha. Many exogenous chemicals (including glyphosate herbicide) must be taken up by living tissues of the plant and translocated within the plant in order to produce the desired biological (e.g., herbicidal) effect. Thus, it is important that a herbicidal composition not be applied in such a manner as to excessively injure and interrupt the normal functioning of the local tissue of the plant so quickly that translocation is reduced. However, some limited degree of local injury can be insignificant, or even beneficial, in its impact on the biological effectiveness of certain exogenous chemicals. EXAMPLES In the following Examples illustrative of the invention, greenhouse tests were conducted to evaluate relative herbicidal effectiveness of glyphosate compositions. Compositions included for comparative purposes included the following: Formulation B: which consists of 41% by weight of glyphosate IPA salt in aqueous solution. This formulation is sold in the USA by Monsanto Company under the ACCORD® trademark. Formulation C: which consists of 41% by weight of glyphosate IPA salt in aqueous solution with a coformulant (15% by weight) of a surfactant (MON 0818 of Monsanto Company) based on polyoxyethylene (15) tallowamine. This formulation is sold in Canada by Monsanto Company under the ROUNDUP® trademark. Formulation J: which consists of 41% by weight of glyphosate IPA salt in aqueous solution, together with surfactant. This formulation is sold in the USA by Monsanto Company under the ROUNDUP® ULTRA trademark. Formulations B, C and J contain 356 grams of glyphosate acid equivalent per liter (g a.e./l). Various proprietary excipients were used in compositions of the Examples. They may be identified as follows: Fluorad FC-135, though defined only generically as above in 3M product literature and in standard directories, has been specifically identified as C 8 F 17 S0 2 NH(CH 2 ) 3 N + (CH 3 ) 3 F in a paper by J. Linert & J. N. Chasman of 3M, titled "The effects of fluorochemical surfactants on recoatability" in the December 20, 1993 issue of American Paint & Coatings Journal, and reprinted as a trade brochure by 3M. Where a proprietary excipient is a surfactant supplied as a solution in water or other solvent, the amount to be used was calculated on a true surfactant basis, not an "as is" basis. For example, Fluorad FC-135 is supplied as 50% true surfactant, together with 33% isopropanol and 17% water; thus to provide a composition containing 0.1% w/w Fluorad FC-135 as reported herein, 0.2 g of the product as supplied was included in 100 g of the composition. The amount of lecithin, however, is always reported herein on an "as is" basis, regardless of the content of phospholipid in the lecithin sample used. Spray compositions of the Examples contained an exogenous chemical, such as glyphosate IPA salt, in addition to the excipient ingredients listed. The amount of exogenous chemical was selected to provide the desired rate in grams per hectare (g/ha) when applied in a spray volume of 93 1/ha. Several exogenous chemical rates were applied for each composition. Thus, except where otherwise indicated, when spray compositions were tested, the concentration of exogenous chemical varied in direct proportion to exogenous chemical rate, but the concentration of excipient ingredients was held constant across different exogenous chemical rates. Concentrate compositions were tested by dilution, dissolution or dispersion in water to form spray compositions. In these spray compositions prepared from concentrates, the concentration of excipient ingredients varied with that of exogenous chemical. The following procedure was used for testing compositions of the Examples, except where otherwise indicated. Seeds of the plant species indicated were planted in 85 mm square pots in a soil mix which was previously steam sterilized and prefertilized with a 14- 14- 14 NPK slow release fertilizer at a rate of 3.6 kg/m . The pots were placed in a greenhouse with sub- irrigation. About one week after emergence, seedlings were thinned as needed, including removal of any unhealthy or abnormal plants, to create a uniform series of test pots. The plants were maintained for the duration of the test in the greenhouse where they received a minimum of 14 hours of light per day. If natural light was insufficient to achieve the daily requirement, artificial light with an intensity of approximately 475 microeinsteins was used to make up the difference. Exposure temperatures were not precisely controlled but averaged about 27°C during the day and about 18°C during the night. Plants were sub-irrigated throughout the test to ensure adequate soil moisture levels. Pots were assigned to different treatments in a fully randomized experimental design with 3 replications. A set of pots was left untreated as a reference against which effects of the treatments could later be evaluated. Application of glyphosate compositions was made by spraying with a track sprayer fitted with a 950 IE nozzle calibrated to deliver a spray volume of 93 liters per hectare (1/ha) at a pressure of 166 kilopascals (kPa). After treatment, pots were returned to the greenhouse until ready for evaluation. Treatments were made using dilute aqueous compositions. These could be prepared as spray compositions directly from their ingredients, or by dilution with water of preformulated concentrate compositions. For evaluation of herbicidal effectiveness, all plants in the test were examined by a single practiced technician, who recorded percent inhibition, a visual measurement of the effectiveness of each treatment by comparison with untreated plants. Inhibition of 0% indicates no effect, and inhibition of 100% indicates that all of the plants are completely dead. Inhibition of 85% or more is in most cases considered acceptable for normal herbicidal use; however in greenhouse tests such as those of the Examples it is normal to apply compositions at rates which give less than 85% inhibition, as this makes it easier to discriminate among compositions having different levels of effectiveness. EXAMPLE 1 Spray compositions were prepared having excipient ingredients as shown in Table 1 a. Lecithins used were sourced from Avanti. In addition to the excipient ingredients shown, all spray compositions contained glyphosate IPA salt. Three different glyphosate concentrations were used for each composition listed in Table la, selected to provide glyphosate a.e. rates as indicated in Table lb. Compositions were prepared by the following procedure. The required amount of the selected lecithin, in powder form, was dispersed in 50 ml water by sonicating in a Fisher Sonic Dismembrator, Model 550, set at output level 8, for 3 minutes. The other ingredients, including glyphosate, were added after sonication. The pH of the spray composition was adjusted to 7 by addition of isopropylamine. The compositions were freshly prepared when applied in the greenhouse test of this Example. Table la Velvetleaf (Abutilon theophrasti, ABUTH) and Japanese millet (Echinochloa crus-galli, ECHCF) plants were grown and treated by the standard procedures given above. Applications of spray compositions were made 16 days after planting ABUTH and 19 days after planting ECHCF, and evaluation of herbicidal inhibition was done 15 days after application. As comparative treatments, Formulation B and Formulation C were applied alone and in tank- mix with Fluorad FC-135. Results, averaged for all replicates of each treatment, are shown in Table lb. Table lb In this test, glyphosate compositions containing egg yolk lecithin (1-01 to 1 -03) performed similarly to those containing soybean lecithin (1-04 to 1-06) on ABUTH but were generally more effective than those containing soybean lecithin on ECHCF, at least in the absence of Fluorad FC-135. Addition of Fluorad FC-135, as in compositions 1-07 to 1-12, enhanced effectiveness of all compositions. EXAMPLE 2 Spray compositions were prepared having excipient ingredients as shown in Table 2a. Phospholipids used were sourced from Avanti and had a purity of 98%o or greater. In addition to the excipient ingredients shown, all spray compositions contained glyphosate IPA salt. Four different glyphosate concentrations were used for each composition listed in Table 2a, selected to provide glyphosate a.e. rates as indicated in Table 2b. Compositions were prepared by the following procedure. The required amount of the selected phospholipid, in powder form, was dispersed in 50 ml water by sonicating in a Fisher Sonic Dismembrator, Model 550, set at output level 8, for 3 minutes. Cholesterol, if included, was added before sonication. Glyphosate was added after sonication. The compositions were freshly prepared when applied in the greenhouse test of this Example. Table 2a Velvetleaf (Abutilon theophrasti, ABUTH) and Japanese millet (Echinochloa crus-galli, ECHCF) plants were grown and treated by the standard procedures given above. Applications of spray compositions were made 15 days after planting ABUTH and ECHCF, and evaluation of herbicidal inhibition was done 15 days after application. As comparative treatments, Formulation B, Formulation C and Formulation J were applied alone; Formulation B was also applied in tank-mix with soybean lecithin (45%, Avanti). Results, averaged for all replicates of each treatment, are shown in Table 2b. Table 2b In this test, a glyphosate composition (2-01) containing phosphatidylcholine (98% purity) from soybean lecithin showed greater herbicidal effectiveness on ABUTH than a tank-mix of Formulation B with soybean lecithin (45% phospholipid). Even greater effectiveness was evident with distearoylphosphatidylcholine (2-06) and L-dipalmitoylphosphatidylcholine (2-09). EXAMPLE 3 Spray compositions were prepared having excipient ingredients as shown in Table 3a. Phospholipids used were sourced from Avanti and had a purity of 98%> or greater. In addition to the excipient ingredients shown, all spray compositions contained glyphosate IPA salt. Four different glyphosate concentrations were used for each composition listed in Table 3a, selected to provide glyphosate a.e. rates as indicated in Table 3b. Compositions were prepared by the following procedure. The required amount of the selected phospholipid, in powder form, was dispersed in 50 ml water by sonicating in a Fisher Sonic Dismembrator, Model 550, set at output level 8, for 3 minutes. Cholesterol, if included, was added before sonication. Glyphosate was added after sonication. The compositions were freshly prepared when applied in the greenhouse test of this Example. Table 3a Velvetleaf (Abutilon theophrasti, ABUTH) and Japanese millet (Echinochloa crus-galli, ECHCF) plants were grown and treated by the standard procedures given above. Applications of spray compositions were made 14 days after planting ABUTH and ECHCF, and evaluation of herbicidal inhibition was done 19 days after application. As comparative treatments, Formulation B and Formulation J were applied alone; Formulation B was also applied in tank-mix with soybean lecithin (45%, Avanti). Results, averaged for all replicates of each treatment, are shown in Table 3b. Table 3b In this test, glyphosate compositions containing the shorter alkanoyl chain phospholipids (3-01 to 3-03) tended to show the greatest herbicidal effectiveness. No great or consistent difference was observed in this test between saturated and unsaturated C 18 alkanoyl phospholipids (L-stearoyl, 3-10, versus L-oleoyl, 3-14, or L-linoleoyl, 3-15). EXAMPLE 4 Spray compositions were prepared having excipient ingredients as shown in Table 4a. Soybean lecithin (45% phospholipid) and pure (>98%) phospholipids used were sourced from Avanti. In addition to the excipient ingredients shown, all spray compositions contained glyphosate IPA salt. Four different glyphosate concentrations were used for each composition listed in Table 4a, selected to provide glyphosate a.e. rates as indicated in Table 4b. Compositions were prepared by the following procedure. The required amount of the selected phospholipid, in powder form, was dispersed in 50 ml water by sonicating in a Fisher Sonic Dismembrator, Model 550, set at output level 8, for 3 minutes. Cholesterol or sitosterol, if included, was added before sonication. Glyphosate was added after sonication. The compositions were freshly prepared when applied in the greenhouse test of this Example. Table 4a Velvetleaf (Abutilon theophrasti, ABUTH) and Japanese millet (Echinochloa crus-galli, ECHCF) plants were grown and treated by the standard procedures given above. Applications of spray compositions were made 19 days after planting ABUTH and ECHCF, and evaluation of herbicidal inhibition was done 16 days after application. As comparative treatments, Formulation B and Formulation J were applied alone; Formulation B was also applied in tank-mix with soybean lecithin (45% phospholipid, Avanti). Results, averaged for all replicates of each treatment, are shown in Table 4b. Table 4b In this test, glyphosate compositions containing purified L- or D-dipalmitoylphosphatidylcholine (4-06 to 4-15) generally showed greater herbicidal effectiveness than those containing soybean lecithin (4-01 to 4-05). EXAMPLE 5 Spray compositions were prepared having excipient ingredients as shown in Table 5a. Soybean lecithin (45% phospholipid) and pure (>98%) phospholipids used were sourced from Avanti. In addition to the excipient ingredients shown, all spray compositions contained glyphosate IPA salt. Four different glyphosate concentrations were used for each composition listed in Table 5a, selected to provide glyphosate a.e. rates as indicated in Table 5b. Compositions were prepared by the following procedure. The required amount of the selected phospholipid, in powder form, was dispersed in 50 ml water by sonicating in a Fisher Sonic Dismembrator, Model 550, set at output level 8, for 3 minutes. Sitosterol, if included, was added before sonication. Other ingredients, including glyphosate, were added after sonication. The compositions were freshly prepared when applied in the greenhouse test of this Example. Table 5a Velvetleaf (Abutilon theophrasti, ABUTH) and Japanese millet (Echinochloa crus-galli, ECHCF) plants were grown and treated by the standard procedures given above. Applications of spray compositions were made 17 days after planting ABUTH and ECHCF, and evaluation of herbicidal inhibition was done 17 days after application. As comparative treatments, Formulation B and Formulation J were applied alone. Results, averaged for all replicates of each treatment, are shown in Table 5b. Table 5b In this test, glyphosate compositions containing purified L- or D-dipalmitoylphosphatidylcholine (5-05 to 5-12) generally showed greater herbicidal effectiveness than those containing soybean lecithin (5-01 to 5-04). The preceding description of specific embodiments of the present invention is not intended to be a complete list of every possible embodiment of the invention. Persons skilled in this field will recognize that modifications can be made to the specific embodiments described here that would be within the scope of the present invention.

Claims: WHAT IS CLAIMED IS: 1. A plant treatment composition comprising (a) an exogenous chemical and (b) a first excipient substance which forms liposomes in aqueous dispersion and which consists of one or more compounds each having (i) a hydrophilic moiety comprising a cationic group and (ii) a hydrophobic moiety comprising two hydrocarbyl or acyl chains, wherein about 40 to 100 percent of said chains in the composition are saturated linear alkyl or alkanoyl groups having about 8 to about 22 carbon atoms. 2. The composition of claim 1 wherein about 40 to 100 percent of said chains in the composition are saturated linear alkyl or alkanoyl groups having about 12 to about 18 carbon atoms. 3. The composition of claim 1, wherein the first excipient substance comprises a liposome-forming compound having a hydrophobic moiety comprising two independently saturated or unsaturated hydrocarbyl groups R and R each independently having about 7 to about 21 carbon atoms, said liposome-forming compound having a formula selected from the group consisting of: (a) N + (CH 2 R 1 )(CH 2 R 2 )(R 3 )(R 4 ) Z " wherein R and R are independently hydrogen, C 1 -4 alkyl or C,_ 4 hydroxyalkyl and Z is a suitable anion; (b) N + (R 5 )(R 6 )(R 7 )CH 2 CH(OCH 2 R')CH 2 (OCH 2 R 2 ) Z " wherein R , R and R are independently hydrogen, C 1 -4 alkyl or C 1- hydroxyalkyl and Z is a suitable anion; (c) N + (R 5 )(R 6 )(R 7 )CH 2 CH(OCOR' )CH 2 (OCOR 2 ) Z " wherein R , R , R and Z are as defined above; and (d) N + (R 5 )(R l ;fR 7 )CH 2 CH 2 OPO(0 " )OCH 2 CH(OCOR 1 )CH 2 (OCOR 2 ) wherein R , R , and R are as defined above. 4. The composition of claim 3, wherein Z is selected from the group consisting of hydroxide, chloride, bromide, iodide, sulfate, phosphate and acetate. 1 1 5. The composition of claim 3, wherein R and R are independently saturated straight-chain alkyl groups each having about 7 to about 21 carbon atoms. 6. The composition of claim 3, wherein the first excipient substance is a phospholipid selected from the group consisting of di-C . 22 -alkanoylphosphatidylcholines and di-C 8 . 22 - alkanoylphosphatidylethanolamines. 7. The composition of claim 6, wherein the first excipient substance is a dipalmitoyl or distearoyl ester of phosphatidylcholine or a mixture thereof. 8. The composition of claim 1 wherein the first excipient substance is a phospholipid or mixture of phospholipids selected from the group consisting of di-C 8- 2 -acylphosphatidylcholines and di-C 8 . 2 - acylphosphatidylethanolamines, wherein about 40 to 100 percent of the acyl chains are saturated alkanoyl chains. 9. The composition of claim 1 wherein the first excipient substance is a phospholipid or mixture of phospholipids, about 40 to 100 percent of which consists of a dipalmitoyl or distearoyl ester of phosphatidylcholine or a mixture thereof. 10. The composition of claim 1 wherein the weight/weight ratio of the first excipient substance to the exogenous chemical is about 1 :3 to about 1 : 100. 1 1. The composition of claim 1 wherein the first excipient substance is a lecithin of animal origin. 12. The composition of claim 1 1 wherein the lecithin is derived from egg yolk. 13. The composition of claim 1 wherein the exogenous chemical is a foliar-applied exogenous chemical. 14. The composition of claim 13 wherein the exogenous chemical is a pesticide, gametocide or plant growth regulator. 15. The composition of claim 14 wherein the exogenous chemical is a herbicide, nematicide or plant growth regulator. 16. The composition of claim 15 wherein the exogenous chemical is a herbicide. 17. The composition of claim 16 wherein the herbicide is selected from the group consisting of acetanilides, bipyridyls, cyclohexenones, dinitroanilines, diphenylethers, fatty acids, hydroxybenzonitriles, imidazolinones, phenoxies, phenoxypropionates, substituted ureas, sulfonylureas, thiocarbamates and triazines. 18. The composition of claim 16 wherein the herbicide is selected from the group consisting of acetochlor, alachlor, metolachlor, aminotriazole, asulam, bentazon, bialaphos, diquat, paraquat, bromacil, clethodim, sethoxydim, dicamba, diflufenican, pendimethalin, acifluorfen, C 9- ιo fatty acids, fomesafen, oxyfluorfen, fosamine, flupoxam, glufosinate, glyphosate, bromoxynil, imazaquin, imazethapyr, isoxaben, norflurazon, 2,4-D, diclofop, fluazifop, quizalofop, picloram, propanil, fluometuron, isoproturon, chlorimuron, chlorsulfuron, halosulfuron, metsulfuron, primisulfuron, sulfometuron, sulfosulfuron, triallate, atrazine, metribuzin, triclopyr and herbicidal derivatives thereof. 19. The composition of claim 18 wherein the herbicide is glyphosate or a herbicidal derivative thereof. 20. The composition of claim 19 wherein the herbicide is glyphosate in its acid form. 21. The composition of claim 15 wherein the exogenous chemical is water-soluble. 22. The composition of claim 21 wherein the exogenous chemical is a salt having an anion portion and a cation portion. 23. The composition of claim 22 wherein at least one of said anion and cation portions is biologically active and has a molecular weight of less than about 300. 24. The composition of claim 23 wherein the exogenous chemical is paraquat or diquat. 25. The composition of claim 23 wherein the exogenous chemical exhibits systemic biological activity in the plant. 26. The composition of claim 25 wherein the exogenous chemical has one or more functional groups selected from the group consisting of amine, amide, carboxylate, phosphonate and phosphinate groups. 27. The composition of claim 26 wherein the exogenous chemical is a salt of 3,4,4-trifluoro-3- butenoic acid or of N-(3,4,4-trifluoro- l-oxo-3-butenyl)glycine that exhibits nematicidal activity. 28. The composition of claim 26 wherein the exogenous chemical is a herbicidal or plant growth regulating compound having at least one of each of amine, carboxylate and either phosphonate or phosphinate functional groups. 29. The composition of claim 28 wherein the herbicidal or plant growth regulating compound is a salt of glufosinate. 30. The composition of claim 29 wherein the salt of glufosinate is the ammonium salt. 31. The composition of claim 28 wherein the herbicidal or plant growth regulating compound is a salt of N-phosphonomethylglycine. 32. The composition of claim 31 wherein the salt of N-phosphonomethylglycine is selected from the group consisting of sodium, potassium, ammonium, mono-, di-, tri- and tetra-C 1-4 -alkylammonium, mono-, di- and tri-C 1 -4 -alkanolammonium, mono-, di- and tri-Ci -4 -alkylsulfonium and sulfoxonium salts. 33. The composition of claim 32 wherein the salt of N-phosphonomethylglycine is the ammonium, monoisopropylammonium or trimethylsulfonium salt. 34. The composition of claim 1, further comprising a second excipient substance that is an amphiphilic quaternary ammonium compound or mixture of such compounds having the formula R 8 - W a -X- Y b -(CH 2 ) n -N + (R 9 )(R 1 ^(R 1 ' ) T " wherein R is a hydrocarbyl or haloalkyl group having from about 6 to about 22 carbon atoms, W and Y are independently O or NH, a and b are independently 0 or 1 but at least one of a and b is 1 , X is CO, SO or S0 2 , n is 2 to 4, R , R and R are independently C 1 -4 alkyl, and T is a suitable anion. 35. The composition of claim 34 wherein the weight/weight ratio of the second excipient substance to the exogenous chemical is between about 1 :3 and about 1 : 100. 36. The composition of claim 34, where R is hydrocarbyl and has about 12 to about 18 carbon atoms. 37. The composition of claim 34, where R is fluorinated. 38. The composition of claim 34, where R is perfluorinated. 39. The composition of claim 38, where R has about 6 to about 12 carbon atoms. 40. The composition of claim 34, where T is selected from the group consisting of hydroxide, chloride, bromide, iodide, sulfate, phosphate and acetate. 41. The composition of claim 34, where R is saturated perfluoroalkyl having about 6 to about 12 carbon atoms, X is CO or S0 2 , Y is NH, a is 0, b is 1, R , R and R are methyl, and T is selected from the group consisting of hydroxide, chloride, bromide, iodide, sulfate, phosphate and acetate. 42. The composition of claim 41, where X is S0 2 , n is 3 and T is chloride, bromide or iodide. 43. The composition of claim 1, further comprising a second excipient substance which is a compound or mixture of compounds having the formula R l4 -CO-A-R 15 wherein R 1 is a hydrocarbyl group having about 5 to about 21 carbon atoms, R 1S is a hydrocarbyl group having 1 to about 14 carbon atoms, the total number of carbon atoms in R 14 and R 15 is about 1 1 to about 27, and A is O or NH. 44. The composition of claim 43 wherein the weight/weight ratio of second excipient substance to the exogenous chemical is from about 1 :3 to about 1 : 100. 45. The composition of claim 43 wherein R is saturated in from about 40 to 100 percent by weight of all compounds having the stated formula present in the composition. 46. The composition of claim 43 wherein R has about 1 1 to about 21 carbon atoms, R has 1 to about 6 carbon atoms and A is O. 47. The composition of claim 43 wherein the second excipient substance is a C alkyl ester of a C 12 . 18 fatty acid. 48. The composition of claim 43 wherein the second excipient substance is a C 1-4 alkyl ester of a C 1 - ι 8 saturated fatty acid. 49. The composition of claim 43 wherein the second excipient substance is a propyl, isopropyl or butyl ester of a Cι 2-18 fatty acid. 50. The composition of Claim 1, further comprising water in an amount effective to make the composition a dilute aqueous composition ready for application to foliage of a plant. 51. The composition of Claim 50, wherein the composition is a shelf-stable concentrate composition comprising the exogenous chemical substance in an amount of about 15 to about 90 percent by weight. 52. The composition of Claim 51, wherein the composition is a solid composition comprising the exogenous chemical substance in an amount of about 30 to about 90 percent by weight. 53. The composition of Claim 52, wherein the composition is a water-soluble or water-dispersible granular formulation. 54. The composition of Claim 51, further comprising a liquid diluent, and wherein the composition comprises the exogenous chemical substance in an amount of about 15 to about 60 percent by weight. 55. The composition of Claim 54 wherein the exogenous chemical substance is water-soluble and is present in an aqueous phase of the composition in an amount of about 15 to about 45 percent by weight of the composition. 56. The composition of Claim 55, wherein the composition is an aqueous solution concentrate. 57. The composition of Claim 55, wherein the composition is an emulsion having an oil phase. 58. The composition of Claim 57, wherein the composition is an oil-in-water emulsion. 59. The composition of Claim 57, wherein the composition is a water-in-oil emulsion. 60. The composition of Claim 57, wherein the composition is a water-in-oil-in-water multiple emulsion. 61. A herbicidal composition that comprises (a) N-phosphonomethylglycine or a herbicidal derivative thereof, and (b) at least one phospholipid, wherein about 40 to 100 percent of the phospholipids are a dipalmitoyl or distearoyl ester of phosphatidylcholine or a mixture thereof. 62. A plant treatment method, comprising contacting foliage of a plant with a biologically effective amount of a composition according to any of claims 1 to 50 or 61.

Inventors: WARD ANTHONY J I, WARD, ANTHONY, J., I.
Applicants: MONSANTO CO, MONSANTO COMPANY
Application year: 1997
Main classification: A01N25
IPC codes: A01N25, A01N35, A01N37, A01N41, A01N43, A01N47, A01N57, G01N33