Garden lettuce is taxonomically part of the Compositae family. Many authorities categorize most garden lettuce varieties into four groups: head (crisphead, iceberg, cabbage lettuce), semi-heading (butterhead, boston, bibb), looseleaf (leaf) and cos (romaine). Garden lettuce varieties intermediate in form have also been developed, such as summer crisp (French crisp, Batavian), which is intermediate between crisphead and looseleaf. Celtuce (celery lettuce, stem lettuce) is variously recognized as fifth garden lettuce group or even as a distinct subspecies, i. e. Lactuca sativa var. asparagina Bailey. Celtuce is grown for its edible, enlarged stem, which is used in many Chinese dishes. For sake of brevity, garden lettuce is referred to hereafter as simply"lettuce", by which is specifically meant Lactuca sativa, including all subspecies, varieties and cultivars.

As lettuce plants can be adversely affected by weed competition, weed control is important for growing lettuce crops. While weed populations can be suppressed by rotational cropping and by tillage and non-selective herbicide treatments prior to planting lettuce seeds or transplants, this may not provide sufficient weed control. Particularly as lettuce is relatively shallow-rooted, it is vulnerable to injury from subsequent tillage. Hand weeding and cultivation is expensive, but for many growers this is the principal means of weed control. Herbicides can be useful for controlling weeds in lettuce crops, but few herbicides have been found and developed for weed control in lettuce crops, and even fewer can be applied after emergence or transplantation of the lettuce plants. These do not include all modes of herbicide action nor provide a full-spectrum of weed control. Therefore additional herbicides are needed for selective weed control in lettuce crops.

Since the discovery of sulfonylurea herbicides over twenty years ago, more than two dozen sulfonylureas have been commercially developed for weed control in major crops, but none for lettuce. As the mode of action of sulfonylurea herbicides is inhibition of the enzyme acetolactate synthase (ALS) found in plants but not animals, sulfonylurea herbicides provide a valued combination of excellent efficacy against plants and very low toxicity to animals, but finding sulfonylureas with sufficient safety to crop plants is challenging.

One approach for using sulfonylurea herbicides to control weeds in lettuce crops is described by C. Mallory-Smith, D. C. Thill and M. J. Dial (HortScience 1993,28 (1), 63- 64). This approach involves transfer of a sulfonylurea resistance gene found in a resistant

biotype of the weed prickly lettuce (Lactuca serriola L.) to garden lettuce (Lactuca sativa L.) by conventional hybridization followed by repeated backcrossing and artificial selection of resistance by treatment with sulfonylurea herbicides. Extensive backcrossing is required to remove the undesirable traits from L. serriola and restore the desirable traits of the L. sativa variety. Such breeding is complicated by the self-pollination of Lactuca species. A method for sulfonylurea herbicide weed control in existing, unmodified lettuce varieties would be more broadly applicable.

Ethametsulfuron-methyl is a sulfonylurea herbicide described in U. S. Patent 4,548,638 that has been developed for selective weed control in rapeseed and condiment mustards, and shows potential in cole crops. Rapeseed is comprised of two species: Brassica rapa L. and Brassica napus L. Cultivated mustards include brown and oriental mustards (Brassica juncea Coss.) Cole crops such as cabbage, cauliflower and broccoli belong to the single species Brassica oleracea L. These Brassica species are members of the Cruciferae (mustard) family. However, the tolerance to ethametsulfuron-methyl is not pervasive across Cruciferae, and indeed it is useful for controlling wild mustard (charlock) (Sinapis arvensis L.), flixweed (pinnate tansy mustard) (Descurainia sophia (L.) Webb ex Prantl) and stinkweed (field pennycress, fanweed, Frenchweed) (Thlaspi arvense L.), also members of Cruciferae.

It has now been surprisingly discovered that ethametsulfuron-methyl can be used to selectively control weeds in crops of lettuce (Lactuca sativa L., botanical family Compositae).

SUMMARY OF THE INVENTION This invention provides a method for controlling undesired vegetation in a lettuce crop by applying to the locus of the crop an effective amount of ethametsulfuron-methyl (methyl 2- [ [ [ [ [4-ethoxy-6- (methylamino)-1, 3,5-triazin-2-yl] amino] carbonyl] amino] sulfonyl]- benzoate, Formula I) or an agriculturally suitable salt thereof. This invention also relates to a method for controlling undesired vegetation in a lettuce crop by applying to the locus of the crop a composition comprising an effective amount of ethametsulfuron-methyl or an agriculturally suitable salt thereof and at least one of a surfactant, a solid diluent or a liquid diluent. Said composition may further comprise another crop protection chemical, such as a herbicide.

DETAILED DESCRIPTION OF THE INVENTION Ethametsulfuron-methyl (Formula I) can be prepared as described in U. S. Patent 4,548,638. The synthesis involves the reaction of the sulfonyl isocyanate of Formula 1 with the heterocyclic amine of Formula 2.

For the method of the present invention the sulfonylurea of Formula I (ethametsulfuron-methyl) can be in the form of an agriculturally suitable salt. Salts of the sulfonylurea of Formula I can be prepared in a number of ways known in the art. For example, metal salts can be made by contacting the sulfonylurea of Formula I with a solution of an alkali or alkaline earth metal salt having a sufficiently basic anion (e. g., hydroxide, alkoxide, carbonate or hydride). Quaternary amine salts can be made by similar techniques.

Salts of the sulfonylurea of Formula I can also be prepared by exchange of one cation for another. Cationic exchange can be effected by direct contact of an aqueous solution of a salt of the sulfonylurea of Formula I (e. g., alkali or quaternary amine salt) with a solution containing the cation to be exchanged. This method is most effective when the desired salt containing the exchanged cation is insoluble in water and can be separated by filtration.

Exchange may also be effected by passing an aqueous solution of a salt of the sulfonylurea of Formula I (e. g., an alkali metal or quaternary amine salt) through a column packed with a cation-exchange resin containing the cation to be exchanged for that of the original salt, and the desired product is eluted from the column. This method is particularly useful when the desired salt is water soluble (e. g., a potassium, sodium or calcium salt).

Formulation/Utility The Formula I compound 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 ingredients, 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 (includingEmulsifiable 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 of Insecticide 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 sulfonate formaldehyde condensates, polycarboxylates, and polyoxy- ethylene/polyoxypropylene block copolymers. Solid diluents include, for example, clays such as bentonite, montmorillinite, 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, NN-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, isophoron and 4-hydroxy-4-methyl-2-pentanone, and alcohols such as methanol, cyclohexanol, decanol, benzyl and tetrahydrofurfuryl alcohol.

Solutions, including emulsifiable concentrates, can be prepared by simply mixing the ingredients. Chemically stabilized aqueous sulfonylurea or agriculturally suitable sulfonylurea salt dispersions are taught in U. S. 4,936,900. Solution formulations of sulfonylureas with improved chemical stability are taught in U. S. 4,599,412. 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.

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. 4,172,714.

Water-dispersible and water-soluble granules can be prepared as taught in U. S. 4,144,050, U. S. 3,920,442 and DE 3,246,493. Tablets can be prepared as taught in U. S. 5,180,587, U. S.

5,232,701 and U. S. 5, 208,030. Films can be prepared as taught in GB 2,095,558 and U. S.

3,299,566.

For further information regarding the art of formulation, see T. S. Woods,"The Formulator's Toolbox-Product Forms for Modern Agriculture"in Pesticide Chemistry and Bioscience, The Food-Environment Challenge, T. Brooks and T. R. Roberts, Eds., Proceedings of the 9th International Congress on Pesticide Chemistry, The Royal Society of Chemistry, Cambridge, 1999, pp. 120-133. See also U. S. 3,235,361, Col. 6, line 16 through Col. 7, line 19 and Examples 10-41; U. S. 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. 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 ethametsulfuron-methyl 98.5% silica aerogel 0.5% synthetic amorphous fine silica 1.0%.

Example B Wettable Powder ethametsulfuron-methyl 65.0% dodecylphenol polyethylene glycol ether 2.0% sodium ligninsulfonate 4.0% sodium silicoaluminate 6.0% montmorillonite (calcined) 23.0%.

Example C Granule ethametsulfuron-methyl 10.0% attapulgite granules (low volatile matter, 0.71/0.30 mm; U. S. S. No. 25-50 sieves) 90.0%.

Example D Aqueous Solution Suspension ethametsulfuron-methyl 25.0% hydrated attapulgite 3.0% crude calcium ligninsulfonate 10.0% sodium dihydrogen phosphate 0. 5% water 61.5%.

Example Extruded Pellet ethametsulfuron-methyl 25.0% anhydrous sodium sulfate 10.0% crude calcium ligninsulfonate 5.0% sodium alkylnaphthalenesulfonate 1.0% calcium/magnesium bentonite 59.0%.

Example F High Strength Concentrate ethametsulfuron-methyl, sodium salt 98.5% silica aerogel 0.5% synthetic amorphous fine silica 1.0%.

Utility Test results indicate that the Formula I compound controls a variety of agronomically important weeds with safety to lettuce crops. It is especially valuable for controlling broadleaved weeds, particularly as most existing herbicides with excellent safety to lettuce are efficacious mainly against grasses. The Formula I compound can be used in preemergence or preplant incorporated application before the lettuce seedlings have emerged or been transplanted, but it is most advantageously applied postemergence after the lettuce

plants have emerged or been transplanted. The Formula I compound can be applied to the weeds instead of the lettuce plants as a directed postemergent treatment, but the surprising safety of the Formula I compound to lettuce plants allows spray onto the lettuce plants without excessive injury except possibly at the highest application rates, or in combination with strong adjuvants or other herbicides with less safety to lettuce.

In the method of this invention, undesired vegetation in a lettuce crop is controlled, by killing or injuring the undesired vegetation or reducing its growth, by applying or contacting a herbicidally effective amount of the Formula I compound to the locus of the lettuce crop, such as the foliage of the undesired vegetation or the soil containing seed or other propagules of the undesired vegetation or in which the undesired vegetation is growing. Typically the Formula I compound is applied in formulation as a composition comprising a herbicidally effective amount of the Formula I compound and at least one of a surfactant, a solid diluent or a liquid diluent.

A herbicidally effective amount of the compound of Formula I will vary depending on environmental conditions, formulation, method of application, amount and type of vegetation present, etc. In general, the Formula I compound is applied at a rate from about 4 to about 140 g a. i./ha and preferably at a rate from about 8 to about 70 g a. i./ha when applied postemergence to weeds and about 16 to about 140 g a. i./ha when applied preemergence or preplant incorporated. (The abbreviation"a. i." means"active ingredient".) For the method of this invention the Formula I compound can be applied in combination with one or more other crop protection chemicals including herbicides, insecticides or fungicides. Combination with another herbicide is particularly useful to broaden spectrum of weed control. The mixtures can be formulated in a number of ways: (a) the Formula I compound and other active ingredients 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 compound and other active ingredients can be formulated together in the proper weight ratio.

A mixture of one or more additional herbicides with the Formula I compound, or a composition comprising a herbicidally effective amount of said mixture and at least one of a surfactant, a solid diluent or a liquid diluent, may be particularly useful for weed control. In certain instances, combinations with other herbicides having similar spectrum of control but a different mode of action will be particularly advantageous for resistance management.

Examples of other herbicides as mixture partners for preemergence or preplant application to lettuce crops are: benfluralin (at 1200-1800 g a. i./ha), bensulide (at 4500-6750 g a. i./ha), chlorthal and its esters including chlorthal-dimethyl (at 4500-11200 g a. i./ha), glyphosate and its salts (at 800-7000 g acid equivalent/ha), oxyfluorfen (at 300-600 g a. i./ha), paraquat salts (at 500-1000 g a. i./ha), prometryn (at 700-3500 g a. i./ha), propyzamide (at 1000-2500

g a. i./ha), thiobencarb (at 4000-7000 g a. i./ha) and trifluralin (at 500-1100 g a. i./ha), where typical use rates are shown in parentheses. Examples of other herbicides as mixture partners for postemergent application to lettuce crops are: chlorthal and its esters including chlorthal- dimethyl (at 4500-11200 g a. i./ha), diclofop and diclofop-P acid and esters including diclofop-methyl (at 420-1400 g a. i./ha), fenoxaprop and fenoxaprop-P acid and esters including fenoxaprop-P-ethyl (at 55-280 g a. i./ha), fluazifop and fluazifop-P acid and esters including fluazifop-P-butyl (at 70-420 g a. i./ha), haloxyfop and haloxyfop-P acid and esters including haloxyfop-etoyl, haloxyfop-methyl and haloxyfop-P-methyl (at 30-560 g a. i./ha), oxyfluorfen (at 300-600 g a. i./ha), prometryn (at 700-3500 g a. i./ha), propyzamide (at 1000- 2500 g a. i./ha), quizalofop and quizalofop-P acid and esters including quizalofop-ethyl, quizalofop-P-ethyl and quizalofop-P-tefuryl (at 25-280 g a. i./ha), sethoxydim (at 150-700 g a. i./ha) and thiobencarb (at 4000-7000 g a. i./ha), where typical use rates are shown in parentheses.

Useful mixtures include the following specific examples, where the part amounts refer to weights of active ingredients: 1 part ethametsulfuron-methyl to 43 parts benfluralin, 1 part ethametsulfuron-methyl to 160 parts bensulide, 1 part ethametsulfuron-methyl to 224 parts chlorthal-dimethyl, 1 part ethametsulfuron-methyl to 26 parts diclofop-methyl, 1 part ethametsulfuron-methyl to 100 parts glyphosate-isopropylammonium, 1 part ethametsulfuron-methyl to 3 parts fenoxyprop-P-ethyl, 1 part ethametsulfuron-methyl to 4 parts fluazifop-P-butyl, 1 part ethametsulfuron-methyl to 90 parts glyphosate-trimesium, 1 part ethametsulfuron-methyl to 4 parts haloxyfop-P-methyl, 1 part ethametsulfuron-methyl to 13 parts oxyflurofen, 1 part ethametsulfuron-methyl to 21 parts paraquat dichloride, 1 part ethametsulfuron-methyl to 50 parts prometryn, 1 part ethametsulfuron-methyl to 50 parts propyzamide, 1 part ethametsulfuron-methyl to 2 parts quizalofop-P-ethyl, 1 part ethametsulfuron-methyl to 12 parts sethoxydim, and 1 part ethametsulfuron-methyl to 150 parts thiobencarb. Useful compositions include compositions comprising herbicidally amount of the herbicides in the aforesaid useful mixtures and at least one of a surfactant, a solid diluent or a liquid diluent.

The tests below measured the effect of the Formula I compound ethametsulfuron- methyl for selectively controlling weeds agronomically important in lettuce crops. Test A also included for comparison chlorthal-dimethyl, which is a herbicide used for preemergence control of annual grasses and some annual broad-leaved weeds in lettuce crops. Test E also included for comparison propyzamide, which is a herbicide used for preemergence and early postemergence control of many annual and perennial grasses, and some broad-leaved weeds in lettuce crops. These tests demonstrate the surprising utility of ethametsulfuron-methyl for selectively controlling weed species in lettuce crops. The weed control afforded by ethametsulfuron-methyl is not limited, however, to these species.

Test A Field plots (3.05 m x 1.37 m; 2% organic matter in mixture of 97% sand, 1% silt, 2% clay, pH 6.9) were tilled to remove weed cover and then planted in rows with head lettuce (Lactuca sativa capitata) variety"Montello"seedling transplants. The following weed species were observed to emerge uniformly in the plots at sufficient density to allow evaluation in all plots: Amaranthus blitoides S. Wats., Chenopodium album L., Eleusine indica (L.) Gaertn., Oenothera laciniata Hill., and Cyperus spp. After 18 days after transplanting, at which time the weeds had reached the 5 to 8 leaf stage, herbicide treatments were applied to the plots according to a complete randomized block design, with each herbicide treatment triply replicated. The herbicides were sprayed using standard flat fan nozzles moved perpendicular to the rows using water spray volumes of about 374 L/ha.

Ethametsulfuron-methyl was applied at 4.4 g a. i./ha, 17.5 g a. i./ha and 35.1 g a. i./ha.

Chlorthal-dimethyl formulated as"Dacthal@ herbicide"was applied at 673 g a. i./ha. For the ethametsulfuron-methyl treatments with surfactant, 0.25% by volume of Ortho X-77 ethoxylated fatty alcohol adjuvant was added to the spray mixtures.

Assessments of crop injury and weed control were made by visual inspection 15 days after herbicide treatment (15 DAT) and for some species also 22 days after herbicide treatment (22 DAT). A visual rating system was used based on a percentage scale from 0 to 100% compared to an adjacent untreated control plot. On this scale 0 represents no visual differences relative to an untreated control and 100 represents complete control of the given weed species. Results are listed in Table A.

TABLE A Evaluation of Ethametsulfuron-methyl for Weed Control in Head Lettuce Ethametsulfuron-Ethametsulfuron-Chlorthal- Rating methyl (g a. i./ha) methyl (g a. i./ha) + dimethyl Species Time Surfactant (g a. i./ha) Untreated 4.4 17. 5 35.1 4.4 17.5 35.1 673 Head Lettuce 15 DAT 2 0 0 3 0 3 3 7 15 DAT 0 78 100 67 89 100 44 0 Chenopodium album 22 DAT 0 82 91 55 73 100 45 0 Amaranthus blitoides 15 DAT 33 95 100 75 95 100 0 0 22 DAT 0 78 95 60 85 100 0 0 15 DAT 5 38 53 28 60 82 0 0 Eleucine indica 22 DAT 0 35 63 27 55 82 0 0 Cyperus spp. 15 DAT 0 0 0 0 0 0 0 0 Oenothera laciniata 15 DAT 17 67 62 43 78 87 0 0

As can be seen from the results of Table A, ethametsulfuron-methyl provided good to excellent control of Chenopodium album, Amaranthus blitoides, Elucine indica and Oenothera laciniata while causing essentially no injury to lettuce. The untreated check resulted in slight reduction of lettuce crop vigor, presumably as result of weed competition.

Ethametsulfuron-methyl gave much better control of the weeds studied compared to chlorthal-dimethyl at a much greater application rate.

Test B Field plots (3.05 m x 1.37 m; 2% organic matter in mixture of 97% sand, 1% silt, 2% clay, pH 6.9) were tilled to remove weed cover and then planted in rows with leaf lettuce (Lactuca sativa) variety"bibb"seedling transplants. The following weed species were observed to emerge uniformly in the plots at sufficient density to allow evaluation in all plots: Amaranthus blitoides S. Wats., Chenopodium album L., Digitaria spp., and Richardia scabra L. After 17 days after transplanting, at which time the weeds had reached at least the 3 to 4 leaf stage, herbicide treatments were applied to the plots according to a complete randomized block design, with each herbicide treatment triply replicated. The herbicides were sprayed using standard flat fan nozzles moved perpendicular to the rows using water spray volumes of about 374 L/ha. Ethametsulfuron-methyl was applied at 17.5 g a. i./ha, 35.1 g a. i./ha and 70.1 g a. i./ha; 0.25% by volume ofOrtho X-77@ ethoxylated fatty alcohol surfactant adjuvant was added to the spray mixtures. Weather conditions were unseasonably warm, causing lettuce to have the tendency to bolt prematurely and not develop the desired vegetative growth, thereby accentuating phytotoxicity. Lettuce is commercially produced under cool growing conditions.

Assessments of crop injury and weed control were made by visual inspection 8 days (8 DAT) and 23 days (23 DAT) after herbicide treatment. A visual rating system was used based on a percentage scale from 0 to 100% compared to an adjacent untreated control plot.

On this scale 0 represents no visual differences relative to an untreated control and 100 represents complete control of the given weed species. Results are listed in Table B.

TABLE B Evaluation of Ethametsulfuron-methyl for Weed Control in Leaf Lettuce Rating Effimetsulfuron-methyl Species Time (g a. i./ha) + Surfactant Untreated 17.5 35.1 70.1- Leaf Lettuce 8 DAT 3 7 10 O 23 DAT 5 10 18 3 Chenopodium album 8 DAT 100 100 100 0 23 DAT 97 100 100 0 Amaranthus blitoides 8 DAT 85 92 87 0 23 DAT 92 92 98 0 Digitaria spp. 8 DAT 87 83 93 0 23 DAT 82 83 85 0 Richardia scabra 8 DAT 70 78 80 0 23 DAT 62 70 88 0

As can be seen from the results in Table B, ethametsulfuron-methyl applied with the ethoxylated fatty alcohol surfactant adjuvant caused only slight early injury to lettuce in the test, with the injury becoming more noticeable at 23 days after treatement due to the unseasonably warm growing conditions causing premature bolting. The untreated check resulted in slight reduction in lettuce crop vigor, presumably as result of weed competition.

Particularly at higher application rates, the ethametsulfuron-methyl combination with surfactant gave good to excellent control of Chenopodium album, Amaranthus blitoides, Digitaria spp. and Richardia scabra.

Test C Field plots (3.05 m x 1.37 m; 2% organic matter in mixture of 97% sand, 1% silt, 2% clay, pH 6.9) were tilled to remove weed cover and then planted in rows with head lettuce (Lactuca sativa) and romaine lettuce (Lactuca sativa) seedling transplants. The following weed species were observed to emerge uniformly in the plots at sufficient density to allow evaluation in all plots: Amaranthus blitoides S. Wats., Chenopodium album L., Digitaria spp., and Richardia scabra L. After 17 days after transplanting, at which time the weeds had reached at least the 3 to 4 leaf stage, herbicide treatments were applied to the plots according to a complete randomized block design, with each herbicide treatment triply replicated. The herbicides were sprayed using standard flat fan nozzles moved perpendicular to the rows using water spray volumes of about 374 L/ha. Ethametsulfuron-methyl was applied at 17.5 g a. i./ha, 35.1 g a. i./ha and 70.1 g a. i./ha ; 0.25% by volume ofOrtho X-77@ ethoxylated fatty alcohol surfactant adjuvant was added to the spray mixtures. Weather conditions were

unseasonably warm, causing lettuce to have the tendency to bolt prematurely and not develop the desired vegetative growth, thereby accentuating phytotoxicity.

Assessments of crop injury and weed control were made by visual inspection 9 days (9 DAT) and 26 days (26 DAT) after herbicide treatment. A visual rating system was used based on a percentage scale from 0 to 100% compared to an adjacent untreated control plot.

On this scale 0 represents no visual differences relative to an untreated control and 100 represents complete control of the given weed species. Results are listed in Table C.

TABLE C Evaluation of Ethametsulfuron-methyl for Weed Control in Head and Romaine Lettuce Rating Ethametsulfuron-methyl Species Time (g a. i./ha) + Surfactant Untreated 17.5 35.1 70.1- Head Lettuce 9 DAT 3 7 8 0 26 DAT 7 3 2 2 9 DAT 7 10 12 0 Romaine Lettuce 26 DAT 0 5 8 0 9 DAT 88 100 100 0 Chenopodium album 26DAT 97 95 100 0 Amaranthus blitoides 9 DAT 82 88 93 0 26DAT 83 95 100 0 Digitaria spp. 9 DAT 83 87 98 0 26DAT 70 80 97 0 Richardia scabra 9 DAT 70 80 87 0 26DAT 47 65 90 0 As can be seen from the results in Table C, ethametsulfuron-methyl applied with the ethoxylated fatty alcohol surfactant adjuvant caused only slight injury to either head and romaine lettuce in the test, with the injury tending to lessen with time. The untreated check resulted in slight reduction in lettuce crop vigor, presumably as result of weed competition.

Particularly at higher application rates, the ethametsulfuron-methyl combination with surfactant gave good to excellent control of Chenopodium album, Amaranthus blitoides, Digitaria spp. and Richardia scabra.

Test D Field plots (3.05 m x 1.37 m ; 2% organic matter in mixture of 97% sand, 1% silt, 2% clay, pH 6.9) were tilled to remove weed cover and then planted in rows with romaine lettuce (Lactuca sativa) and bibb lettuce (Lactuca sativa) seedling transplants. The following weed species were observed to emerge uniformly in the plots at sufficient density to allow

evaluation in all plots: Amaranthus blitoides S. Wats., Chenopodium album L., Digitaria spp., and Eleusine indica (L.) Gaertn. After 17 days after transplanting, at which time the weeds had reached at least the 3 to 4 leaf stage, herbicide treatments were applied to the plots according to a complete randomized block design, with each herbicide treatment triply replicated. The herbicides were sprayed using standard flat fan nozzles moved perpendicular to the rows using water spray volumes of about 374 L/ha. Ethametsulfuron-methyl was applied at 8.8 g a. i./ha, 17.5 g a. i./ha and 35.1 g a. i./ha; where surfactant addition is indicated, 0.25% by volume of Ortho X-77@ ethoxylated fatty alcohol adjuvant was added to the spray mixtures.

Assessments of crop injury and weed control were made by visual inspection 35 days after herbicide treatment. A visual rating system was used based on a percentage scale from 0 to 100% compared to an adjacent untreated control plot. On this scale 0 represents no visual differences relative to an untreated control and 100 represents complete control of the given weed species. Results are listed in Table D.

TABLE D Evaluation of Ethametsulfuron-methyl for Weed Control in Romaine and Bibb Lettuce Ethametsulfuron-Ethametsulfuron-methyl Species methyl (g a. i./ha) (g a. i./ha) + Surfactant Untreated 17.5 35.1 8.8 17.5 35.1- Romaine Lettuce 350 0 3 0 Bibb Lettuce 0 0 0 0 0 0 Chenopodium album 10 51 35 76 81 0 Amaranthus blitoides 100 100 100 100 100 0 Digitaria spp. 35 75 25 71 98 0 Elucine indica 13 40 0 43 61 0 As can be seen from the results in Table D, ethametsulfuron-methyl caused little injury to either romaine or bibb lettuce when used alone or applied with the ethoxylated fatty alcohol surfactant adjuvant in this test. The surfactant significantly increased activity in controlling Chenopodium album, Digitaria spp. and Elucine indica. Even without the surfactant, ethametsulfuron-methyl gave excellent control of Amaranthus blitoides.

Test E Field plots (2.01 m x 2.74 m; 1.2% organic matter in mixture of 35% sand, 45% silt, 20% clay, pH 7.6) were tilled to remove weed cover and then planted in rows with leaf lettuce (Lactuca sativa) variety"Black Seeded Simpson"by direct seeding. The following weed species were observed to emerge uniformly in the plots at sufficient density to allow evaluation in all plots: Amsinckia intermedia Fisch. E, Brassica nigra (L.) Koch, Calandrina

ciliata, Sisymbrium irio L., and Stellaria media (L.) Vill./Cyr. After 39 days after seeding, at which time the weeds had reached at least 1-2 inches tall, herbicide treatments were applied to the plots according to a complete randomized block design, with each herbicide treatment triply replicated. The herbicides were sprayed using standard flat fan nozzles moved perpendicular to the rows using water spray volumes of about 374 L/ha. Ethametsulfuron- methyl was applied at 35.1 g a. i./ha and 70.1 g a. i./ha; propyzamide formulated as"Kerb 50W herbicide"was applied at 1680 g a. i./ha.

Assessments of weed control were made by visual inspection 77 days after herbicide treatment, and assessment of crop injury was made 16 days (16 DAT), 77 days (77 DAT) and 98 days (98 DAT) after herbicide treatment. A visual rating system was used based on a percentage scale from 0 to 100% compared to an adjacent untreated control plot. On this scale 0 represents no visual differences relative to an untreated control and 100 represents complete control of the given weed species. Results are listed in Table E.

TABLE E Evaluation of Ethametsulfuron-methyl for Weed Control in Leaf Lettuce Rating Ethametsulfuron-Propyzamide Species Time methyl (g a. i./ha) (g a. i./ha) Untreated 35.1 70.1 1680- Leaf Lettuce 16 DAT 0 0 40 0 77 DAT 0 0 0 0 98 DAT 0 0 0 0 Amsinckia intermedia 77 DAT 100 100 90 0 Brassica nigra 77 DAT 80 100 100 0 Calandrinia cilata 77 DAT 50 80 100 0 Sisymbrium irio 77 DAT 90 100 0 0 Stellaria media 77 DAT 100 100 0 0 As can be seen from the results in Table E, ethametsulfuron-methyl caused no injury to leaf lettuce in this test while propyzamide, which is used in lettuce, caused significant temporary injury. Even at 1680 g/ha, propyzamide had no effect on Sisymbrium irio and Stellaria media, while ethametsulfuron-methyl gave very good to excellent control at 35.1 to 70.1 g/ha. Ethametsulfuron-methyl also gave good to excellent control of Amsinckia intermedia and Brassica nigra, and had significant effect on Calandrinia cilata. The excellent activity of ethametsulfuron-methyl on Brassica nigra and Sisymbrium irio is remarkable, as both weed species are in the Cruciferae family, as are rapeseed and cole crops, which are tolerant to ethametsulfuron-methyl.

Test F Field plots (1.83 m x 4.57 m; 99% organic matter, pH 6.9) were tilled to remove weed cover and then planted in rows with head lettuce (Lactuca sativa) variety"Iceberg"by direct seeding. The following weed species were observed to emerge uniformly in the plots at sufficient density to allow evaluation in all plots: Amaranthus spp., Chenopodium album L., and Portulaca oleraceae L. After 24 days after seeding, at which time the weeds had reached at least the 3-5 leaf stage, herbicide treatments were applied to the plots according to a complete randomized block design, with each herbicide treatment triply replicated. The herbicides were sprayed using standard flat fan nozzles moved perpendicular to the rows using water spray volumes of about 374 L/ha. Ethametsulfuron-methyl was applied at 8.8 g a. i./ha, 17.5 g a. i./ha and 35.1 g a. i./ha ; where surfactant addition is indicated, 0.25% by volume of Ortho X-770 ethoxylated fatty alcohol adjuvant was added to the spray mixtures.

Assessments of crop injury and weed control were made by visual inspection 21 days after herbicide treatment. A visual rating system was used based on a percentage scale from 0 to 100% compared to an adjacent untreated control plot. On this scale 0 represents no visual differences relative to an untreated control and 100 represents complete control of the given weed species. Results are listed in Table F.

TABLE F Evaluation of Ethametsulfuron-methyl for Weed Control in Head Lettuce Ethametsulfuron-methyl Ethametsulfuron-methyl Species (g a. i./ha) (g a. i./ha) + Surfactant Untreated 8.8 17. 5 35. 1 8.8 17.5 35. 1 Head Lettuce 0 0 1 8 S 4 0 Chenopodium album 28 36 28 38 90 94 0 Portulaca oleracea 0 0 0 0 0 0 0 Amaranthus spp 85 96 98 98 99 100 0 As can be seen from the results in Table F, ethametsulfuron-methyl caused essentially no injury to leaf lettuce when used alone and only slight injury when applied with the ethoxylated fatty alcohol surfactant adjuvant in this test. The surfactant significantly increased efficacy on Chenopodium album and Amaranthus spp., but was not needed to provide very good to excellent control of the latter weed species.