BACKGROUND OF THE INVENTION The control of undesired vegetation is extremely important in achieving high crop efficiency. Achievement of selective control of the growth of weeds especially in such useful crops as rice, soybean, sugar beet, corn (maize), potato, wheat, barley, tomato and plantation crops, among others, is very desirable. Unchecked weed growth in such useful crops can cause significant reduction in productivity and thereby result in increased costs to the consumer. The control of undesired vegetation in noncrop areas is also important. The need for finding products that achieve such results continues to be commercially important.

Combinations of herbicides are typically used to broaden the spectrum of plant control or enhance the level of control of any given species through additive effect. Certain rare combinations surprisingly give a greater-than-additive or synergistic effect. Such valuable combinations have now been discovered.

U. S. Patent No. 5,362,704 and German Patent No. 1,039,779 disclose individual compounds used in the mixtures of this invention, but none of these references disclose the mixtures or their surprising synergistic utility.

SUMMARY OF THE INVENTION This invention relates to the mixture of 4- (2-chlorophenyl)-N-cyclohexyl-N-ethyl-4,5- dihydro-5-oxo-lH-tetrazole-1-carboxamide (Formula I)

with N- (3,4-dichlorophenyl) propanamide (propanil, Formula II) which has now been discovered to synergistically control weeds. This invention also relates to a herbicidal composition comprising herbicidally effective amounts of the aforesaid mixture and at least one of the following: surfactant, solid or liquid diluent. This invention also relates to a method of controlling undesired vegetation comprising applying to the locus of the vegetation herbicidally effective amounts of the aforesaid mixture.

For reason of weed control spectrum and/or crop selectivity, the preferred application of the mixture of this invention is in rice crops, especially in paddy rice cultivation.

DETAILS OF THE INVENTION The Formula I compound can be prepared as described in U. S. Patent No. 5,362,704.

The synthesis involves the coupling of the tetrazolinone of Formula 1 with the carbamyl chloride of Formula 2.

The Formula II compound can be prepared as described in German Patent 1,039,779.

The synthesis involves coupling of the aniline of Formula 3 with the activated acyl group of Formula 4.

LG is a leaving group such as halogen

Formulation The mixture of the Formula I and Formula II compounds can be formulated in a number of ways: (a) the Formula I and Formula II compounds can be formulated separately and applied separately or applied simultaneously in an appropriate weight ratio, e. g., as a tank mix; or (b) the Formula I and Formula II compounds can be formulated together in the proper weight ratio.

The mixture of the Formula I and Formula II compounds will generally be used in formulation with an agriculturally suitable carrier comprising a liquid or solid diluent and/or a surfactant wherein the formulation is consistent with the physical properties of the active ingredients, mode of application and environmental factors such as soil type, moisture and temperature. Useful formulations include liquids such as solutions (including emulsifiable concentrates), suspensions, emulsions (including microemulsions and/or suspoemulsions) and the like which optionally can be thickened into gels. Useful formulations further include solids such as dusts, powders, granules, pellets, tablets, films, and the like which can be water-dispersible ("wettable") or water-soluble. Active ingredients can be (micro) encapsulated and further formed into a suspension or solid formulation; alternatively the entire formulation of active ingredient can be encapsulated (or"overcoated").

Encapsulation can control or delay release of the active ingredients. Sprayable formulations can be extended in suitable media and used at spray volumes from about one to several hundred liters per hectare. High-strength compositions are primarily used as intermediates for further formulation.

The formulations will typically contain effective amounts of active ingredient, diluent and surfactant within the following approximate ranges which add up to 100 percent by weight.

Weight Percent Active Ingredient Diluent Surfactant Water-Dispersible and Water-soluble 5-90 0-94 1-15 Granules, Tablets and Powders.

Suspensions, Emulsions, Solutions 5-50 40-95 0-15 (including Emulsifiable Concentrates) Dusts 1-25 70-99 0-5 Granules and Pellets 0.01-99 5-99.99 0-15 High Strength Compositions 90-99 0-10 0-2 Typical solid diluents are described in Watkins, et al., Handbook oflnsecticide Dust Diluents and Carriers, 2nd Ed., Dorland Books, Caldwell, New Jersey. Typical liquid

diluents are described in Marsden, Solvents Guide, 2nd Ed., Interscience, New York, 1950.

McCutcheon's Detergents and Emulsifiers Annual, Allured Publ. Corp., Ridgewood, New Jersey, as well as Sisely and Wood, Encyclopedia of Surface Active Agents, Chemical Publ.

Co., Inc., New York, 1964, list surfactants and recommended uses. All formulations can contain minor amounts of additives to reduce foam, caking, corrosion, microbiological growth and the like, or thickeners to increase viscosity.

Surfactants include, for example, polyethoxylated alcohols, polyethoxylated alkylphenols, polyethoxylated sorbitan fatty acid esters, dialkyl sulfosuccinates, alkyl sulfates, alkylbenzene sulfonates, organosilicones, N, N-dialkyltaurates, lignin sulfonates, naphthalene sulfate formaldehyde condensates, polycarboxylates, and polyoxyethylene/polyoxypropylene block copolymers. Solid diluents include, for example, clays such as bentonite, montmorillonite, attapulgite and kaolin, starch, sugar, silica, talc, diatomaceous earth, urea, calcium carbonate, sodium carbonate and bicarbonate, and sodium sulfate. Liquid diluents include, for example, water, N, N-dimethylformamide, dimethyl sulfoxide, N-alkylpyrrolidone, ethylene glycol, polypropylene glycol, paraffins, alkylbenzenes, alkylnaphthalenes, oils of olive, castor, linseed, tung, sesame, corn, peanut, cotton-seed, soybean, rape-seed and coconut, fatty acid esters, ketones such as cyclohexanone, 2-heptanone, isophorone and 4-hydroxy-4-methyl-2-pentanone, and alcohols such as methanol, cyclohexanol, decanol and tetrahydrofurfuryl alcohol.

Solutions, including emulsifiable concentrates, can be prepared by simply mixing the ingredients. Dusts and powders can be prepared by blending and, usually, grinding as in a hammer mill or fluid-energy mill. Suspensions are usually prepared by wet-milling; see, for example, U. S. Patent No. 3,060,084. Granules and pellets can be prepared by spraying the active material upon preformed granular carriers or by agglomeration techniques. See Browning,"Agglomeration", Chemical Engineering, December 4,1967, pp 147-48, Perry's Chemical Engineer's Handbook, 4th Ed., McGraw-Hill, New York, 1963, pages 8-57 and following, and WO 91/13546. Pellets can be prepared as described in U. S. Patent No.

4,172,714. Water-dispersible and water-soluble granules can be prepared as taught in U. S.

Patent Nos. 4,144,050 and 3,920,442 and DE Patent No. 3,246,493. Tablets can be prepared as taught in U. S. Patent Nos. 5,180,587; 5,232,701; and 5,208,030. Films can be prepared as taught in GB Patent No. 2,095,558 and U. S. Patent No. 3,299,566.

For further information regarding the art of formulation, see U. S. Patent No.

3,235, 361, Col. 6, line 16 through Col. 7, line 19 and Examples 10-41; U. S. Patent No.

3,309,192, Col. 5, line 43 through Col. 7, line 62 and Examples 8,12,15,39,41,52,53,58, 132,138-140,162-164,166,167 and 169-182; U. S. Patent No. 2,891,855, Col. 3, line 66 through Col. 5, line 17 and Examples 1-4; Klingman, Weed Control as a Science, John Wiley and Sons, Inc., New York, 1961, pp 81-96; and Hance et al., Weed Control Handbook, 8th Ed., Blackwell Scientific Publications, Oxford, 1989.

In the following Examples, all percentages are by weight and all formulations are prepared in conventional ways.

Example A High Strength Concentrate 4-(2-chlorophenyl)-N-cyclohexyl-N-ethyl-4,(2-chlorophenyl)-N -cyclohexyl-N-ethyl-4, 5-dihydro- 5-oxo-lH-tetrazole-1-carboxamide 4.7% propanil 93.8% silica aerogel 0.5% synthetic amorphous fine silica 1.0%.

Example B Wettable Powder 4-(2-chlorophenyl)-N-cyclohexyl-N-ethyl-4,(2-chlorophenyl)-N -cyclohexyl-N-ethyl-4, 5-dihydro- 5-oxo-lH-tetrazole-1-carboxamide 3.1% propanil 61.9% dodecylphenol polyethylene glycol ether 2.0% sodium ligninsulfonate 4.0% sodium silicoaluminate 6.0% montmorillonite (calcined) 23.0%.

Example C Granule 4-(2-chlorophenyl)-N-cyclohexyl-N-ethyl-4,(2-chlorophenyl)-N -cyclohexyl-N-ethyl-4, 5-dihydro- 5-oxo-1H-tetrazole-1-carboxamide 0.5% propanil 9.5% attapulgite granules (low volatile matter, 0.71/0.30 mm; U. S. S. No. 25-50 sieves) 90.0%.

Example D Extruded Pellet 4-(2-chlorophenyl)-N-cyclohexyl-N-ethyl-4,(2-chlorophenyl)-N -cyclohexyl-N-ethyl-4, 5-dihydro- 5-oxo-lH-tetrazole-1-carboxamide 1.2%. propanil 23.8% anhydrous sodium sulfate 10.0% crude calcium ligninsulfonate 5.0% sodium alkylnaphthalenesulfonate 1.0% calcium/magnesium bentonite 59.0%.

Utility The mixture of the herbicidal compounds of Formula I and Formula II are now discovered to provide unexpected synergistic control of selected weeds while retaining selective safety to certain annual monocot plant species such as rice. The mixture of the

invention is effective in selectively controlling the growth of undesirable upland and aquatic grass, broadleaf, and sedge weed species while having little or no effect upon transplanted or direct seeded japonica or indica rice. The synergism this mixture provides in controlling barnyardgrass without injury to rice is both very valuable and remarkable, as both barnyardgrass and rice are grasses. Barnyardgrass is one of the most troublesome weeds in rice fields. By applying the mixture of this invention to dry or flooded soil infested with weed seed, or application to the foliage of weed plants, or application to water covering foliage, seeds or plant parts, weeds are killed or sufficiently injured to provide the rice crop a competitive advantage. Application to direct seeded rice at the preemergence to 5-leaf stage, application to transplanted rice at the 1.0-5.0-leaf stage and application to weeds at the preemergence to 4-leaf stage is preferable. Application can be made to unflooded or flooded rice fields. Of note is application to rice crops which are grown in a flooded or intermittently flooded paddy.

Herbicidally effective amounts of the compounds of Formula I and Formula II (propanil) will vary depending on environmental conditions, formulation, method of application, amount and type of vegetation present, etc. The use rate weight ratios of Formula I to Formula II are typically 1: 2 to 1: 100, with ratios of 1: 5 to 1: 40 preferred for most uses. Typically, the Formula I compound is applied at a rate from 100 to 400 g ai/ha and the Formula II compound is applied at a rate from 1000 to 6000 g ai/ha. Preferably, the Formula I compound is applied at a rate from 200 to 300 g ai/ha, and the Formula II compound is applied at a rate from 2000 to 4000 g ai/ha.

One skilled in the art can readily determine application rates and ratios of the herbicide of Formula I to the herbicide of Formula II as well as timing necessary for the desired level of weed control and crop safety.

For practical use as herbicide treatments, the mixtures of the invention may be employed in further admixture with other known herbicides and agricultural crop protection chemicals to provide additional spectrum of activity against additional weed species.

Herbicides which may be mixed include, but are not limited to, cyhalofop-butyl, cafenstrole, dimepiperate, epoprodan, etobenzanid, indanofan, pretilachlor, oxaziclomefone, thiobencarb, pyributicarb, pyrazolate, benxofenap, bromobutid, mefenacet, anilofos and benfuresate.

Particularly useful herbicide mixture partners are the sulfonylurea herbicides azimsulfuron, bensulfuron methyl, metsulfuron methyl, chlorimuron ethyl, pyrazosulfuron ethyl, imazosulfuron, cinosulfuron and cyclosulfamuron.

Additionally, the mixtures of the invention may be combined with agriculturally acceptable additives such as surfactants, safeners, spreaders, emulsifiers or fertilizers, to improve performance. The mixtures of the invention will generally be used as formulated compositions.

The following Tests demonstrate the control efficacy of the compounds of this invention against specific weeds. The weed control afforded by the compounds is not limited, however, to these species. In these tests, Compound 1 is the Formula I compound <BR> <BR> 4-(2-chlorophenyl)-N-cyclohexyl-N-ethyl-4, 5-dihydro-5-oxo-lH-tetrazole-1-carboxamide and Compound 2 is the Formula II compound propanil.

BIOLOGICAL EXAMPLES OF THE INVENTION Test A Protocol Individual containers of barnyardgrass (Echinochloa crus-galli) were seeded and allowed to grow until the 3-to 3.5-leaf stage of development. A Tama silt loam soil was used for the propagation. Rice (Oryza sativa, cv. IR64) was seeded at 1 cm soil depth and allowed to grow to the 4-leaf stage of development. Compounds 1 and 2 were formulated in a non-phytotoxic solvent mixture and applied to the leaf surfaces as a foliar spray. The soil surface was flooded to a 3 cm depth 48 hours after the plants were treated.

Treated plants and untreated controls were maintained under greenhouse conditions for 14 days at which time treated plants were compared to untreated controls and visually evaluated. Plant response ratings, summarized in Table A, are based upon a 0 to 100 scale where 0 is no effect and 100 is complete control.

Colby's equation was used to calculate the expected additive herbicidal effect of the mixtures of Compound 1 with Compound 2. Colby's equation (Colby, S. R."Calculating Synergistic and Antagonistic Responses of Herbicide Combinations,"Weeds, 15 (1), pp 20- 22 (1967)) calculates the expected additive effect of herbicidal mixtures, and for two active ingredients is of the form: Pa+b=Pa+Pb- (PaPb/100) wherein Pa+b is the percentage effect of the mixture expected from additive contribution of the individual components, Pa is the observed percentage effect of the first active ingredient at the same use rate as in the mixture, and Pb is the observed percentage effect of the second active ingredient at the same use rate as in the mixture.

Combinations of Compound 1 with Compound 2 are surprisingly found to provide better control of certain weeds than expected by calculation from Colby's equation, thus demonstrating synergism. Table A lists visual assessments of control of a specific weed with Compound 1 and Compound 2 applied alone as single active ingredients, applied as a mixture of the two active ingredients of Compound 1 and Compound 2, and the expected additive effect of the herbicidal mixture of Compound 1 and Compound 2 (Colby's equation). Different ratios of Compound 1 to Compound 2, and different formulation types, also provide useful weed control from the combination of the two herbicides.

TABLE A* Effect of Compound 1 and Compound 2 as Active Ingredients Alone and in Mixture Cmpd Cmpd Rice Barnyard Barnyard grass 1 a grass 2b 1 2 Observed Expectedt Observed Expected Observed Expected Alone 100 0 0-7-0- 200 0 0-27-40- 300 0 14-72-67- 0 1000 3-30-0- 0 2000 0-53-0- 0 4000 7-62-27- Mixtures 100 1000 10 3 73 35 53 0 100 2000 7 0 88 56 53 0 100 4000 7 7 97 65 47 27 200 1000 7 3 95 49 72 40 200 2000 7 0 98 66 75 40 200 4000 10 7 100 72 85 56 300 1 1000 37 17 95 80 80 300 2000 33 14 98 87 82 67 300 4000 34 20 100 89 85 76 * Application rates are expressed in g ai/ha for both Compound 1 and Compound 2. Data are reported as percent control. t Expected from the Colby Equation. a Normal barnyardgrass (Echinochloa crus-galli) b Propanil resistant barnyardgrass (Echinochloa crus-galli) As can be seen from this test, combinations of 4- (2-chlorophenyl)-N-cyclohexyl-N- ethyl-4,5-dihydro-5-oxo-1H-tetrazole-1-carboxamide (Compound 1) with propanil (Compound 2) surprisingly increased barnyardgrass control over that expected. In the case of 200 g of Compound 1 + 1000 g of propanil, control was increased from poor (49%) to excellent (95%). In the case of 100 g Compound 1 + 2000 g propanil, control went from the expected no control to 53% (moderate) on propanil resistant barnyardgrass. In the case of 200 g Compound 1 + 4000 g propanil, control went from the expected 56% (moderate) to

85% (good) on propanil resistant barnyardgrass. This synergism allows the mixtures of the invention to be used at substantially lower application rates than would be needed based on purely additive effects. These greenhouse results show little or no crop injury at mixture application rates as high as 200 g/ha of 4- (2-chlorophenyl)-N-cyclohexyl-N-ethyl-4,5- dihydro-5-oxo-lH-tetrazole-1-carboxamide (Compound 1) and 4000 g/ha of propanil (Compound 2). Rice is generally known to be more susceptible to injury from herbicides when grown under greenhouse conditions than under field conditions.