CA1118222A - Microencapsulated trifluoralin - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Microcapsules of a size ranging from about 10 to about 100 microns and containing an organic solvent solution of a trifluoro-2, 6-dinitro-N, N-(C1-C?)dialkyl-p-toluidine wherein said microcapsules are prepared by interfacial polycondensation to form a polycondensate capsule wall selected from polyurea and amide-urea copolymera which may be cross-linked are disclosed herein to provide improved aqueous herbicidal composition especially for large scale application to crop producing areas.

Description

T~lis inventlon re1ates to an encapsulatec! seltctive l1erbicide wherein thc! capsule walls are speci~ically definec1 an(l the herbicide is dissolved in a specifiec1 amount of a specified organic solvent. ~lore particularly, it relates to microcapsules formed with a polycondensate wall structure ~polyurea or an amide-urea copolymer resin) encapsulating a trifluoro -2, 6-dinitro -N, N-dialkyl -p -to]uidine compound clissolved ln the specified solvent.
Trifluralin is the generic name for alpha, alpha, alpha- trifluoro-2, 6-dinitro-N, N-dipropyl-p -toluidine, a product of the Elanco Division of Eli Lilly and Company sold in a pre-emergent herbicide composition under the trade-mark "Treflan". This product is one of the foremost herbicides in use today.~s a selective pre-emergent type herbicide, it has applications on many crops including cottOn, soyb(!an~, safElower, sunfLower, beans, peas, sugar beets, castor beans, rapeseed, established ornaméntals; transplants of cabbage, cauli-flower, broccoli, brussels sprouts, tomatoes and pepper; non bearing vineyards;
citrus trees; established alfalfa, carrots and potatoes. Its use to eliminate erminating and seedling weed grasses is covered by ~nited States Patent ~o.
3,257,190.
Trifluralin, as a pre-emergent herbicide, is available as an emulsi-fiable concentrate (E.C.) or as 5~ granules. 'lo be effectlve, both fo1-ms must be worlced inio the soiL i;urrace Ifter apl~licatiol-l. Ihe granular product is used at the recomnlended rate of 80 lbs./acre, applied by conventional tractor driven equipmènt and it is simultaneously incorporated into the top 2-3 inches of the soil. The E.C., on the other hand, is preferably applied by aerial spraying since vast acreage can be sprayed quickly and economically. Appli-cations of the E.C., however, must be incorporated within four (4) hours after spraying (as stated on the product label) in order to prevent loss of effectiveness of the treatment. It has been shown that vapor losses for un-incorporated trifluralin, only three (3) hours after spraying, can be as muchas 30% . Thus, the great advantage of aerial spraying, rapid coverage of vast acreage, is lost due to the inability of the farmer to incorporate the treat-ment before it is dissipated by vaporization. It is apparent that a need exists for a sprayable formulation of trifluralin that will not lose its active ingredient so rapidly by vaporization. This would allow the speed and economy of aerial application while the longer period for the incorporation process would be more convenient for the farmer.
Microencapsulation has been described as a procedure which avoids premature volatilization or other deterioration of the encapsulated material (U.K. Spec. No. 1,371,179). It would be expected that the activity of insecti-cides and herbicides in encapsulated form would be greatly prolonged and, indeed, microeocapsulation of pesticides has been used for and is known to increase the persistency of the encapsulated product (U.S. 3,577,515;
U.S. 3,959,464; U.K. Spec. 1,371,179; and W.A. Gentner et al., Publication of U.S.D.A. "The Interference of Microencapsulation on the Herbicidal Performance of Chlorpropham" September, 1976).
Trifluralin and closely related derivatives, however, do not suffer from the lack of persistence after incorporation into the soil and, because of their established and approved persistency and selectivlty for use in connection with crop food seeds, seedlings and established plants, it is considered un-desirable to increaæe or delay their activity by microencapsulation or otherwise.
This inven~ion provides an encapsulated trifluoro-2, 6-dinitro-N, N-dialkyl -p-toluidine which demonstrates decreased volatility outside the soil but which has substantially unchanged activity when incorporated in the soil compared to unencapsulated trifluralin.
Thus, this invention comprises microcapsules of a solution of alpha, 1. Parochetti, J.V. and Hein, E.R., Weed Science, Volume 21, Issue 5 (September) 1973.
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ila, .lLI~lnl- trif~ ro-, (~ ;nilro--N, N--d~ 5) a~l-yl-p -tol.uLcline di~s--solvc(l in at l.eas~ i'0' Up ~:0 about ~071 ol an aromaLic petroleum solvent based on tl~c ~e:il~llt of thc solu~:i.on, sa.id so:Lution microencapsulated wit~li.n a resinous po:lycondellsate ~all se.lecte(l rrom tlle gro-lE) cons:ist~ g of polyurea and amide-urea copolylmers, and at least a major proportion of said microcapsules having a size ranging from about 10 to about 100 m.icrons, said polycolldensate wall prepared by the rcacti.on of first and second polyurea or amide-urea copolymer-forming intermediates, at least one of said first and second intermediates containing from 0 to 100 percent, based on the weight of the intermediate, of a polyfunctional reactant which is (a) complementary to the other of said intermediates and effectivc for crosslinking reaction and (b) has at least tllrcc reactivc groll~)s tllat arc cffcct:ively functional in said reaction, said groups selected from the class consisting of amine, isocyanate9 -COCl and -S02Cl groups. The alkyl group of the toluidine compound include, for example, methyl, ethyl, n-propyl, isopropyl9 n~butyl, isoamyl, l-methylisobutyl and the lil;e.
'Lhe term "crosslinking" as uscd hcrein refers to intermolecular connections or l.inks between strands of linear polymer molecules resulting from the amount of functional reactant, having at :I.e;lst thrc~c effectivel.y :Eunctional reactivc ~roups, whicll rcplac~s at :I.e~l.st a por~ion oE one or more similarly reactive diEImctional condensati.on reactants in the polycondensation recipe. For example, when all of the difunctional acid derived component is replaced with a polyfunctional reactant, e.g., polyfunctional isocyanate, in a polycondensation rccil)e which might normally consist of a difunctional amine and a difunctional acid dcrived component, the resulting polycondensate is considered to be a 100% crosslinked polyurea. When a total of only 50% of the difunctional component is replaced with the polyfunctional reactant9 the poly-condensate is considered to be 50~ crosslinked.

~ ik~1-ot11 oi- s.ai(1 first and sceol1d inte1-rl1ec1iL1tes can consist ei1~ire1y (1()0~) of ~)o1ytur1ct-i()r1al reactants, as descri1)ed above, whereby each reactant wilL be able to crossli1lk with a complimentary crosslinking group on a11 adjacer1t polymer chaill to obtai1l what may be termed as a polycondensate wall wllich can be 2()07' crosslinked, it is preferred that only one of said first and seconcl intermediates contain up to lO0 percent of said polyfunctional reactant. ~er. only one of the intermediates eontains a polyf~mctional reactant and that polyfunctional reactant is 100~ of said intermediate the polycondensate resin is referred to as 100~ crosslinked.
In general, the microeneapsulation proeedure as used herein is deseribed in U.S. 3,429,827 (1~. P~uus) allcl U.S. 3,577,515 (J. E. Vandegaer) anc1 involves an interfaeia:L polymerization proeedure to obtain a polyeon-densate eapsule wall material whie11 is preferably erosslinked. Important variables in the proeedure whie11 may affeet the rate of volatilization or release of trifluralin from the mieroeapsule include the degree of eross~
linking of the polycondensate wal], wall thickness, identity of polyeondensate and capsule partiele size. The proeedure eon1prises (1) establishing, by agitation, a dispersion of to-be-eneapsulated droplets eontaining a first of said intermediates in a body of liquid which is in eontL111~ous p11ase nnd is in~iseible with t11e drop:Lets ar1d :Ls essenLiaLLy frec Or ar1y reaetc1nt eomple-mentary to said first intemlediate, and (2) thereafter bringing a seeond of said intermediates, i.e., complementary to the first intermediate, into the eontLnuous llquid phase so that the first and seeond intermediates reaet at interfaees between the droplets and the eontinuous phase to eneapsulate the droplets within a skin of said polyeondensate.
~1ere erosslinking is desired, at least one of said first and seeond intermediates eomprises at least in part a polyfunctional reaetant whicll ~a) is cc~ )lc~ elltarv to Lhe otllcr of sa:id :interniediates and effective ~o{ crosslinkillg rcaction an(:l (b~ has at Icast tl)ree reactive groups that are the salile as each othel- and that are selectccl from the c:lass consisting of amine, isocyanate, -COCl and -SO2CI groups, salcl first and second inter-mediates thereby reacting to encapsulate the droplets within the aforesaid polycondensate ski.n havin~ crosslinlcillg therei.n.
~ xamples of suitable diamine ancl polyamine reactants are ethylene diamine, phenylene dia~line, toluene diamine, hexamethylene diamine, diethylene triamine, piperazine, 1,3,5-benzenetriamine trihydrochloride, 2,4,6-triamino-toluene trihydrochloride, tetraethylene pentamine, pentaethyl.ene hexamine, polyetilyleneamine, 1,3,6-trianlinonapl~thlelle,3,4,5,8-tetra aminoanthraquinone.
Ixamp]es of difullctiollal alld polyfullc~:ioncl:L acicl derived compounds providing -COCl and -SO2Cl reactive groups are sebacoyl chloride, ethylene-bis-chloro-formate, phosgene, azelaoyl chloride, adipoyl chloride, terephthaloy] chloride, dodecanedioic aci.d ehloride, dimer aeid chloride, 1,3-benzene tetra acid chloride, 1,3,5-benzene trischloroformate. Interm~diates useful in providing reactive isoeyanate groups are represented by sueh eompo~mds as paraphenylene diisocyanate, meta-pllenylenc-~. diisocyanate naphtllalene -1,5-di:isoeyanate,

2,G)-toluene diisocyanate, 4,4-(lipl)enyl diisocy;lllltc~, tll(! d:iClll01'0 d.Lpllellyl methane di.lsocyanates, b:i.l)ellzyl cl:i.i.s(cy<ln.J~e, I-:iLol.y:lc-ne (I:ii.socyanclte, the diphenyl ether diisoeyanates, the di.methyldiphenyl dl:i.soeyanates, the poly-methy].ene polypheny:L isoeyanates, triphenylmetharle -4,4~4~ -triisoeyanate, isopropyl bellzene ~(-diisoc:yanate ancl the like.
When cross]inlcing is desi.red, suffieient polyfunetional reaetant (i.e., trifunetional or greater) i.C!., a reaetant llaving at least 3 funetional groups thereon as above-deseribed, is provided in the polycondensation reeipe to produee mieroeapsules wherein the po].ycondensed eaps-lle wall can erosslink np t~ 100,`, that is~ up to 100~ of one of the polycondensate forming inter-me(liates (reactan~s) is polyfunctioll.l1. In the prefcrred embodiments, the polycolldellsate wall will be prepared with about 5 to about 50% polyfunctional reactant as a component of one of said intermediates. Microcapsules of poly-condensates with no crosslinking would, graphically speaking, be made Up of strands of linear polymer molecules not connected to each other. By cross-linking the polymer, these strands are linked together at various spots along their length making a much "tighter" network.
Tlle ratio of wall polymer to active ingredient controls the capsule wall thickness. The preferred range for wall percentage is from 5 to 15% but the product is functional with walls Or 2.5~ to 40% based on the weight of the microcupsules. Tt is nlost economica] to uC;e a lower wall percentage as the capsule payload can tllen be higher whicll allows for a product containing a higher concentration of active ingredient.
The particle size (largest linear dimension) of the microcapsule also effects its wall thickness and thereby the rate of release of active ingredient. The major proportion of said microcapsules may range from below 10 to several hundred microns. The preferred particle size range, however, is from 25 microns to 50 m;crc)ns. Larger partic]es over ~00 Illlcrorls will cause screell clog~inr, an(ll)articles ullcler l() miclolls nlny lncrease the drift of the particles during aerial application. Small particles will have a more rapid release rate than larger particles since the wall thickness of small particles is less than that of large particles.
~ suspension or sl~rry of the microcapsules in water is the normal embocliment for shipping, storing, and ultimately the application of the herbicide composition in the field. A convenient water dispersion, suspension or slurry of the encapsulated herbicide for shipping and storage will consist of fro~ out 10 ~o 30~ by weigl~t, pref~erably ilbotlt 257~ of the herbicide, WhiCil w.ill be diluted to al)out O.J - 2.0~ ror apl)liccition. Ihis slurry, suspension or disper-;ion ol ~he microcapsu:les in water may have included therein suspendillg a.gent:s, for example, crosslinked acrylic acid interpolymers as discussed ;n U.S. Patent NO. 3~426~004; xanthan p,um as disclosed in U.S.
Patent NO. 4,107,292; other suspending agents such as hydroxethyl cellulose, gums, clays, sub-micron size silica and other inorganic materials; and wetting agents and dispersants sucll as detergents, polyvinyl alcoho]s, gelatin, methyl cellulose, casein and clays.
An exemplary recipe for preparing the polycondensate encapsulating resin wall for the or~anic solvent solutlon of trifluralin is as follows:
Polyfunctional isocyanate (such as polymethylene polyphenyllsocyanate known as "PAPI"), x moles, wllere x equals 0 to 1; Diacid chloride (such as sebacoyl dicllloride) or difunctional isocyanate (such as toluene diisocyanate), 1 -x moles; Difunctional amine (such as ethylene diamine), n - y moles, where n equals 1 to 3; Diethylene triamine (a difunctional polyamine), y moles, where y = 0 to 1.5; in addition, a base such as sodium hydroxide may be included in the recipe to neutrali~e the hydrochloric aci(l generated durin~ the poly-condensation reactioll. ~xcess allline may be presellL In ~he t'ecipe. rhe diacid cllloride and/or isocyanate are added to tlle trlfluralin solution whicll acts as a water-insoluble organic solvent, this organic mixture is dispersed in water and the amine is charged to the reaction as an aqueous solution.
In addition to tl-le critical nature of the microcapsule wall, it has beell found necessary to use a solvent to Eorm a so]ution oE trifluralin before encapsulation to provide effective release rates. The choice and amount oi the solvent used has been found to have a profound effect on the rate of release of trifluralin from the capsule.

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Solvents which can be used for this invention are very limited in number for three reasons. First, the solvent must be approved as an inert ingredient for use on growing crops and as such listed in the code of U.S.
Federal Regulations, Title 40 part l~Q.1001. Second, the solvent must be compatible with and dissolve the active ingredient without effecting its selective herbicidal activity. Third, because of encapsulation requirements>
the solvent must not be water soluble. Typical aromatic petroleum solvents which are useful for this invention include xylene, toluene, naphtha and the like. The amount of solvent in the solution will range from about 20 to about 60 percent, preferably from 30 to 50 percent, based on the weight of the solution.
The microcapsules are at times depicted hereinafter by reference to a set of numbers which may also include letter designations. For example, in the set 5/10/SX50, the number 5 refers to a microcapsule having a wall weight of 5 percent based on the weight of the microcapsule, the number 10 refers to the use of lO percent polyfunctional reactant to replace a di-functional reactant in the polycondensation recipe to thereby effect cross-linking, the letter S refers to a polycondensate wall prepared using sebacoyl chloride in the polycondensation recipe and the letter-number X50 refers to a solution of trifluralin in xylene within the microcapsule at a concentration of 50 percent by weight.
The effect of the solvent on the volatility of encapsulated tri-fluralin can be demonstrated by the following data:

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TABLE
Sample Wall Solvent Volatility % tri-No. Formulations Type Amount fluralin lost after (hours) 1 A xylene 30~ 19 22 30 --2 A Panasol AN-2* 30~ .4 .7 -- 8.5

3 B xylene 80% 80 -- -- --(5 hrs.)

4 B Panasol AN-2* 30% 57 67 68 --E.C. --- --- 90.3 94.5 __ __ *Panasol AN-2 - Registered trademark of the Amoco Chemicals Corporation for an aromatic petroleum (naphtha) solvent.
The test data in the above table was developed in a test procedure wherein the microencapsulated products or E.C. (emulsifiable concentrate of trifluralin) were placed on filter paper in an oven heated to 54C. and having a conventional forced air draft.
The microencapsulated trifluralin used to obtain the above data was prepared in accordance with the encapsulation procedure of the following Example except that Wall Formulation A was derived by using 50~ polymethylene polyphenylisocyanate (FAPI) based on the weight of the non-water soluble reactants and the wall weight was ad~usted by using an amount of reactants (relative to the solution of trifluralin) to provide a wall of 10 percent based on the total weight of the microcapsule (10/50/SP70 where P-Panasol An-2).Wall formulation B was also derived in accordance with the same procedure except that an amount of reactants were used to provide a wall of 10 percent based on the total weight of the microcapsule (10/5/SP70). Samples 1 and 3 were prepared with xylene replacing Panasol AN-2 in the amounts indicated.

1`11e follQwing cxalllple is set fortll to delllo~ trte the procedure for preparcltion of the mi,crot~nc~-lpsu1ilted procluct of Lh:is invention.
~XA~LL
Tile Prepar_t ~n of ~icroencap~,ulated Triflu_alin To prepare a sample of nicroencapsulated triflura],in having a 15~
wall witll 5~ crosslinking i.e., 5% of difunctiorlal reactallt is replaced with polyfunctional crosslinking reactant, and whercin trifluralin at a concentra tion of 70% is dissolved in Panasol (15/5/SP70) the fo]lowing recipe was used:
10g of trifluralin was warmed with 4.3g of Panasol ~N-2 and stirred until the mixture was homogeneous (solutioll concentration of 70~ trifluralin).
Sebacoy] chloricle t2.43g) and PAPI (0.14g or 5~ based on the weight of the non-water soluble reactants) was added to the above to give the complete organic mix.
The organic mix was then dispersed by a high speed stirrer into an aqueous so]ution of 0.25~ Gelvatol (polyvinyl alcohol) for 15 seconds.
A mixture of ethylenediamine (0.64g), diethylenetriamine (0.74g) and sodium hydroxide (0.~2g) in 10 ml of water was then added to accomplish the polymerization.
The slurry was stirre(l ~or two l~our:i, neutrallze(l wLth conc. ~ICl to pll 7.0 and passed through a 50 mesh screen to remove over-size particles.
Some of the water was removed by cdecantation and the resulting mixture was thickene(l with a xantllall g,um to prevent sett]in~. The final mixture had a concentration of 22~ or about 2 lbs./gallon of active ingredient.
To provide for application to the field, such as by aerial spray, water is added to this mixture to ad~just the concentration as required.
The following table shows volatility and herbicidal activity data ~118Z2Z

for several samples of microencapsulated trifluralin having differing wall thicknesses. These samples were prepared in accordance with the procedure of the foregoing Example except that 1) amounts of reactants were employed to produce microcapsules wherein the walls of samples C, D and E were respec-tively 10, 20 and 30% based on the total weight of the microcapsule, 2) additional polymethylene polyphenylisocyanate was used to increase the cross-linking of the polycondensate wall (25% PAPI based on the weight of the non-water soluble reactants) and 3) adipoyl chloride was used to replace sebacoyl chloride. Volatility data was obtained using the same test procedure used for the data of Table 1. The herbicidal activity data was obtained from field tests in which the herbicide products were applied by spraying at the rate of 1/2 pound per acre and then raked (incorporated) into the top 1-3 inches of soil at the given number of days.

Volatili o (hrs.) Rye Grass Counts Incorporated at (days) Sample 1 2 3 4 16 20 0 1 2 3 Total D -- 20.5 -- -- 32.637.3 14 6 19 13 52 E 15.3 --16.8 -- --- 15.8 2438 32 19 103 E.C. 90.3 94.5 -- -- -- -- 1835 34 40 127 Check (no herbicide) 75 78 84 86 323 This data shows the decreased volatility of encapsulated samples of trifluralin as well as dependence of the rate of volatilization on the type of capsule wall as compared to the emulsifiable concentrate (E.C.) of trifluralin. The second table shows the tendency of the E.C. to permit more grass germination as incorporation is delayed, whereas the samples of encap-sulated trifluralin, particularly Sample D (20/25/A), do not show such a trend.

The data also shows that the activity of the encapsulated formulation and of the emulsifiable concentrate are essentially the same when both are immediately lncorporated in the soil after application.
~ s previously stated, it has been found necessary to use a solvent to form a solution of trifluralin before encapsulation to provide effective release rates. The amount of solvent in the solution will range from about 20 to about 60 percent, preferably from 30 to 50 percent, based on the weight of the solution. Ordinarily, this will allow for a solution containing from about 80 to about 40 percent dissolved trifluralin. ~owever~ it is contem-plated that one may replace a minor portion of the trifluralin with another active pesticide whereby a dual, additive or even synergistic effect may be obtained.
To determine the comparative herbicidal activity of emulsifiable concentrates (E.C.) of trifluralin and experimental formulations of tri-fluralin encapsulated in different wall systems designed for delayed incor-poration with the use of a grain sorghum and oat bioassay, when applied to a moist soil surface and incorporated immediately or after seven days, a test procedure was used in accordance with the following description:
Metal flats having a depth of three inches were filled with non-sterilized medium textured greenhouse 90il and subirrigated with an excess amount of water. Each of the E.C. and encapsulated herbicides, formulated in water, was sprayed on the soil surface of three different flats at a rate of 0.75 pounds of trifluralin per acre. In one E.C. treatment of the E.C.
formulation was immediately incorporated into the soil, i.e., the soil for three flats was placed in a rotary mixer and the E.C. formulation was sprayed onto the soil as it tumbled; after incorporation was complete, the treated soil was then placed back in the flats and subirrigated.

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~ fter treatment, the fla~s were moved into a growth room wh:ich was maintained to simu1ate crop growing conditions and had a ]arge air excnange capacity to enhclnce the volatility of the applied Iormulations. The flats were allowed to remain in the growth room for several days during wilich no additional water was added to the soil. ~fter seven days, except for those three flats for which the E.C. formulation had been immediately incorporated, tlle formulations were incorporated into the soil of each flat by mixing in a rotary mixer. The eafter each flat plus an untreated control was planted with twenty-five (25) grain sorghum seeds and twenty (20) cultivated oat seeds, the soil was moistened with an aqueous solution of soluble fertilizer and the flats were moved into a greenhouse. ~ourteen days after planting, the fresh Weigllt was harveste(l allcl recorcled. 'I`he percerlt inhibition of grain sorghum and oats growtll compared against the control is reported in Table 3.
The E.C. formulation which was incorporated immediately (Sample No.
30) provided 100 percent growth inhibition of both grain sorghum and culti-vated oats whereas when incorporation of the r..c. formulation was delayed for seven days (Sample No.'s 27, 28 and 29), the percent inhibition for grain sorghum was 38, 52 and 69 and for oats 22, 27 and 59 percent. The following encapsulated trifluralin formulation6 l~rovided 90 plus percc~rlt inhlbition of both grain sorgl-1um ancl oats: SnmpLe:; 3, fi, 8, 13, 16, 22 and 23.
The remaining encapsulated formulations except for Samples 1, 7, 20 and 25 also provided much improved inhibition of both grain sorghum and oats over the I.(,. formulation.
Sample No.~s l and 7 show percent inhibition of grain sorghum and oats to about the same general extent as the ~.C. formulation. The encapsu-lation formulations of Samples No.'s ] ancl 7 are the same and would be expected to show similar inhibition results. These encapsulated products have no c~ross]. inli;llg of tlle ~ yCOll~.'nSatC t~all and llave l:ight wcigl--t walls re]ative to the weigllt oi the microc.lpsules. Tlle percent inhibition oi the encapsu-lated trifl.ural:in is increased when, as in thc preferred embodimentt the polycondensate wall is crosslinked or, as in the case of Sample No.'s 10, 15, 17 an(l 22, the walls have a higller weigllt proportion relative to the weight of the microcapsule. Sample No. 20 is a replicate of Sample No. 19 whicl shows comparative]y good inhibition for both sorgh-ml and oats. The poor performance of Sample No. 20 is therefore unexplainable. Sample No. 25 rcpresents an encapsulated product whereill insufficient solvent was used with the trifluralin, i.e., 10% solvent - 90~ trifluralin.
When the encapsulated trifluralin formulations were sprayed on the soil surface (i.e., witllout incorporation) tiley caused no greater injury to cotton and corn plant:ings than the l.C. formulation and generally exhibited, in most cases, about the same degree of control of crabgrass, pigweed and foxtail millet as the ~.C. formulation.

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Delay d Incorporation Test Percent Inhibition Sample No. Formulation Grain Sorghum Oats 15~0/ST50 45 41 610/10/SP7~ 97 99 915/5tSP60 74 92 1212.5/5/SP70 85 94 15lS/0/SP70 83 94 .

~ - 15 -~1~8Z;Z;Z

TABLE 3 (Cont.) -Delayed Incorporation Test Percent Inhibition Sample No. Formulation Grain Sor~hum Oats 21 10/50/S(HMDA)*P70 79 86 22 15tO/SX70 92 99 15/10/St**90 67 93 26 10/l00/X70 97 98 EC
(immed. incorp.) 100 100 31 Control O O

* = terephthaloyl chloride.
*~IDA = hexamethylene diamine replaced usual amines in formulation.
** t = Tenneco solvent (aromatic petroleum solvent).

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The solvents employed ln the capsule formulations for the above table were Panasol AN-2 represented by P, xylene represent by X, toluene represented by T and Tenneco solvent represented by t.
The data set forth in the foregoing table indicates that a micro-encapsulated trifluralin product having a wall weight within the range of from 5 to 15 percent, based on the weight of the microcapsule, and amount of a polyfunctional reactant replacing from 5 to 50 percent of a difunctional reactant in the polycondensation recipe, and an amount of solvent for the trifluralin solution ranging from 30 to 50 percent is the preferred embodiment of this invention. Furthermore, the data shows that if no polyfunctional reactant is used in the polycondensation recipe, the microcapsule wall weight should be about 15 percent of the weight of the microcapsule. Still, further, the data shows that, in general microencapsulated trifluralin of this invention unexpectedly demonstrate decreased volatility outside the soil but substan-tially unchanged activity when thereafter incorporated in the soil compared to unencapsulated trifluralin.

Claims (14)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A herbicide product comprising microcapsules of a solution of alpha, alpha, alpha- trirluoro-2, 6-dinitro-N, N-di(CI-C5) alkyl-p-toluidine dissolved in at least 20% up to about 60% of an aromatic petroleum solvent based on the weight of the solution, said solution microencapsulated within a resinous polycondensate wall selected from the group consisting of poly-urea and amide-urea copolymers, and at least a major proportion of said microcapsule having a size ranging from about 10 to about 100 microns, said polycondensate wall prepared by the reaction of first and second polyurea or amide-urea copolymcr-forming intermecliates, at least one of said first and second intermediates containing from 0 to 100 percent, based on the weight of the intermediate, of a polyfunctional reactant which is (a) complementary to the other of said intermediates and effective for crosslink-ing reaction and (b) has at least three reactive groups that are effectively functional in said reaction, said reactive groups selected from the class consisting of amine, isocyanate, -COCl and -S02Cl groups.

2. The herbicide product of c1aim 1 wherein only one or said first and second intermediates consists of from 0 to 100 percent, based on the weight of said intermediate, of said polyfunctional reactant.

3. The product of claim 2 wherein the (Cl-C5) alkyl group is n-propyl.

4. The product of claim 3 wherein the encapsulating wall is an amide-urea copolymer.

5. The product of claim 3 wherein from about 5 to about 50 percent of said intermediate is said polyfunctional reactant.

6. The product of claim 5 wherein the solvent is naphtha.

7. The product of claim 5 wherein the solvent is xylene.

8. The product of claim 5 wherein the solvent is toluene.

9. The product of claim 5 wherein said wall has a weight percent range of from about 5 to about 15 percent based on the weight of the micro-capsules .

10. The product of claim 4 wherein said amide-urea copolymer is the product of the interfacial polycondensation of a difunctional amine, sebacoyl chloride and polymethylene polyphenylisocyanate wherein said polyphenyli-socyanate replace from about 5 to ahout 50% of said sebacoyl chloride in the polycondensation reaction.

11. The product of claim 10 wherein the weight percent of said encapsulating wall is about 5 and about 15 percent based on the weight of the microcapsules.

12. The product of claim 1 in the form of a sprayable aqueous dispersion.

13. A method of selectively destroying germinating weed seeds and seedlings comprising spraying the area to be treated with an effective amount of the aqueous dispersion of claim 12 having a phytotoxic concentration of herbicid and, thereafter, incorporating the microcapsules into the surface of the soil.

14. The method of claim 13 wherein said spraying is accomplished by aerial spraying.