GB2075344A - Slow release herbicide granules - Google Patents

Abstract

A novel slow-release thiolcarbamate herbicide composition comprising porous granules impregnated with a thiolcarbamate herbicide and coated with a coating material of cured glycerides of one or more unsaturated C10-C24 aliphatic acids and the mono- and polycyclopentadiene copolymers thereof. The composition is particularly useful for slow release in water or surroundings with a high moisture content.

Description

SPECIFICATION Slow release herbicide granules This invention relates to coated herbicide granules. In particular, this invention relates to por ous granules impregnated with a thiolcarbamate herbicide and coated with a material which permits diffusion ofthe herbicide into the surrounding medium at a controlled rate.

Chemical herbicides are widely used to protect crops from weeds and other vegetation which inhibit crop growth. The form in which such chemicals are applied at the field site varies widely depending on the chemical and physical nature of the active com pound, the type of crop to be protected, the weeds to be controlled, and the mode of action by which the herbicidal effect is achieved. Consequently, herbi cide formulations range from liquid systems such as solutions, emulsions, and suspensions, to solid systems such as dusts, powders, and granules.

In many cases, granules provide advantages over othertypes offormulations. Granules are porous inert solid particles typically of about 1 to 2 millimet ers in diameter impregnated with herbicidally active materials. Unlike most liquid formulations, granules require no dilution prior to field application, and by virtue oftheir mass, they can be distributed effectively by aircraft, resulting in application over a wide area in a short period of time. Granules are particu larly useful in application to flooded fields, where their mass will cause the granules to sink readily through the water down to the soil where the herbi cide effect is most needed. Granules also increase the versatility of liquid herbicides by permitting one to store, transport, and apply them as one would any solid material.Granules are particularly useful in thiolcarbamate formulations.

Like other types of formulations, however, granules are often unable to deliver their active ingredients at the point in time in the growth cycle or in the quantity which will have the maximum effect.

Some thiolcarbamates have relatively short half lives in terms of herbicidal potency, which makes it difficu It to match their potency curve to the growth cycle of the weed sought to be controlled. In addition, thiolcarbamates are sometimes subject to leaching and evaporation aswell as chemical degra dation when in contact with the soil. Due to the vol atility of thiolcarbamates, granules containing them 'must often be restricted to flooded field application and pre-plant soil incorporation rather than pre emergence soil surface application or post-plant soil incorporation, in order to avoid loss ofthe active compound to the atmosphere.The volatility also creates an odor problem in the storage of some thiolcarbamate granules, since the liquid in the granule pores has a very high concentration of thiol carbamate and is in direct contact with the atmos phere.

It is therefore an object of the present invention to provide a thiolcarbamate herbicide granule with the ability to control the release rate of the herbicide to the surrounding medium and to extend the herbicidal effectiveness over a longer period of time than conventional thiolcarbamate granules.

Another object of this invention is to provide a thiolcarbamate herbicide granule of reduced thiolcarbamate volatility and improved odor control.

A further object of this invention is to provide a method of controlling weeds with improved efficiency.

Other objects will be apparent from the following description.

The present invention resides in a novel slow release thiolcarbamate herbicide composition which comprises a porous granule impregnated with a herbicidally effective amount of a thiolcarbamate herbicide of the formula

in which R' is selected from the group consisting of C16 alkyl, C26 alkenyl, phenyl, and benzyl, all optionally substituted with one or more members selected from chlorine and C13 alkyl; and R2 and R3 either independently form C16 alkyl or Cs-C7 cycloalkyl, or conjointly form C57 alkylene; and coated with (a) a cured glyceride of one or more unsaturated C,0-C24 aliphatic acids or (b) a cured mono- or polycyclopentadiene copolymer of a glyceride of one or more unsaturated C,0-C24 aliphatic acids, the coating comprising from about 1%to about 30% by weight of the composition.

Preferred thiolcarbamates are those in which R' is C16 alkyl; and R2 and R3 either independently form C16 alkyl or C57 cycloalkyl, or conjointly form C57 alkylene.

More preferred thiolcarbamates are those in which R1 is C2-C4 alkyl; and R2 and R3 either independently form C24 alkyl or C7 cycloalkyl, or conjointly form C57 alkylene.

The terms "alkyl" and "alkenyl" are used herein to denote both straight-chain and branched-chain groups. Examples of alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, etc. Examples of alkenyl groups include vinyl, allyl, 2-butenyl, isobutenyl, etc. The term "alkylene" is used herein to denote multiples of the H2- group, optionally substituted with alkyl groups. Examples includeH2CH2CH2CH2CH2- (pentamethylene), -CH2CH2CH2CH2CH2CH2- (hexamethylene), WH2CH2CH2CH2CH2CH2CH2- (heptamethylene), WH2CH(CH3)CH2CH2CH2CH2- (2methylhexamethylene), etc.

The term "aliphatic acids" is used to denote compounds of the formula

in which R is an unsaturated hydrocarbon group.

Unsaturated groups include those with up to three multiple bonds, which may be double or triple bonds. Examples include palmitic, stearic, linoleic, linolenic, oleic, licanic, eleostearic, and tariric acids.

All carbon atom ranges are intended to be inclusive of their upper and lower limits.

This invention also resides in a method of control ling undesirable vegetation which comprises apply ing to the locus where control is desired a herbici dally effective amount of the above composition.

The term "herbicide" is used herein to denote a compound or composition which controls or mod ifies the growth of plants. The term "herbicidally effective amount" is used to indicate the quantity of such a compound or composition which is capable of producing a controlling or modifying effect. Controlling or modifying effects include all deviations from natural development, such as, killing, retardation, defoliation, desiccation, regulation, stunting, tillering, stimulating, leaf burn, dwarfing and the like.

The term "plants" is used to include germinating seeds, emerging seedlings, and established vegetation, including roots and above-ground portions.

For a further understanding of the invention, each of its various components will be discussed in both broad and preferred aspects.

The granular material to be used in the present invention can be any porous inert solid substance which is insoluble in either water or any of the liquid materials applied to the granule. This includes granules formed by extrusion, agglomeration, or prilling as well as naturally occurring materials. The latter can be useful in their naturally occurring form or they can be subjected to physical modification prior to use, such as drying, crushing, and screening, to achieve the desired size and moisture characteristics. In general, the granule size will range from under 1 millimeter to over 1 centimeter in diameter or length. Atypical granule size is about 1 to 2 millimeters in diameter. Examples of such carriers are vermiculite, sintered clay granules, kaolin, attapulgite clay, bentonite clay, talc, pyrophyllite, diatomite, and granular carbon.A common commercially available carrier material is "Trusorb," a naturally occurring material consisting of calcined clay sericilte granules, commonly of -24 + 48 mesh (Tyler) grain size, with atypical chemical analysis asfollows: Percent Silica (SiO) 85.40 Aluminium oxide (AlO) 4.48 Iron oxide (FeO) 0.88 Calcium oxide (CaO) 0.20 Magnesium oxide (MgO) 0.54 Sodium and potassium oxide (RD) 0.15 Loss on ignition (largely combined water) 8.35 100.00 Examples ofthiolcarbamates useful in the present invention are:: S - ethyl N - cyclohexyl N - ethyl thiolcarbamate (cycloate) S - ethyl hexahydro - 1 H - azepine -1 - carbothioate (molinate) S - 2, 3 - dichloroallyl diisopropylthiolcarbamate (di allate) S - 2, 3, 3 - trichloroallyl diisopropylthiolcarbamate (tri-allate) S - ethyl di - n - propylthiolcarbamate (EPTC) S - 4 - chlorobenzyl diethyithiolcarbamate (benthiocarb) S - ethyl diisobutylthiolcarbamate (butylate) S - benzyl di - sec - butylthiolcarbamate S - propyl dipropylthiolcarbamate (vernolate) S - propyl butylethylthiolcarbamate (pebulate) S - isopropyl hexahydro -1 H - azepine -1 - carbothioate The quantity of thiolcarbamate present in the granule pores in not critical to the invention and can vary over a wide range, determined primarily by the degree and type of control sought and the herbicidal potency of the particular thiolcarbamate used, within the limitations of the pore volume available in the granule. In general, the herbicide will comprise from about 1%to about 20% by weight of the total composition, preferably from about 5% to about 15%.

The coating materials to be used in the present invention are glycerides of one or more unsaturated fatty acids. Although the presence of unsaturated groups is essential to the curing of the glycerides, saturated groups can also be present without serious detriment to the utility of the glycerides. In fact, the available glycerides are generally mixtures of various acid groups, differing from one molecule to the next, including both saturated and unsaturated groups. These materials are plant and animal products commonly known as drying oils, since they can be cured by the use of heat, air contact, or certain metallicsaltsto form dry, hard, resinous films.

The general structure of these oils is as follows:

in which the acid portions may be the same or different and include those derived from the unsaturated aliphatic acids described above. Thus, R4, R5, and R6 are defined to include R in Formula II above as well as unsaturated analogs. Examples of such oils are castor oil, linseed oil, menhaden oil, oiticica oil, safflower oil, sardine oil, soybean oil, sunflower oil, tung oil, corn oil, cottonseed oil, perilla oil, poppyseed oil, rapeseed oil, and walnut oil. The acids which form the acid portions of these oils include saturated acids such as myristic, palmitic, stearic, arachidic, behenic, and lignoceric acids, and unsaturated acids such as myristoleic, palmitoleic, oleic, erucic, ricinoleic, linoleic, linolenic, licanic, and eleostearic acids.The oils contemplated for use in the present invention are those with acid groups (RCOO-) containing from 10 to 24, preferably from 15 to 20, carbon atoms each. The most preferred oil is linseed oil, the composition of which lies within the following ranges (weight percents): unsaturated acids: linolenic C,8H3002 35-65 oleic C18H3402 12-34 linoleic C18H3202 7-27 saturated acids: palmitic C16H3202 4-7 stearic C,8H3602 2-5 arachidic C20H4002 0.3-0.9 lignoceric C24H4802 trace-0.4 As coating materials, the oils may be applied in their naturally occurring form or as copolymers of mono- or po lycyclopentadienes, preferably d icyc lopentadiene.The cyclopentadiene content can range as high as 70% by weight, preferably less than 25% by weight, and serves to promote fast drying and to increase the water resistance of the coating.

Curing, or "drying" in common terminology, of the oils, is accomplished by either prolonged expos urn to air, the application of heat, or the use of drying catalysts. Drying catalysts are preferred, since the volatile thiolcarbamate herbicides tend to evaporate when heat is applied and a long period of time is required for air drying. Useful drying catalysts include metal salts of naphthenic or other aliphatic acids-for example: cobalt, lead, manganese, cerium, copper, chromium, iron, tin, vanadium, and zirconium salts of linoleic, resin, or naphthenic acids. Cobalt, lead, and manganese salts are prefer red, and cobalt naphthenate is most preferred. The quantity used relative to the quantity of drying oil is not critical, and can vary over a wide range depend ing on the thickness of the resulting coating and the drying time.A catalytic amount is sufficient, i.e., any quantity which will increase the curing rate. In gen eras, the quantity of catalyst will be from about 0.01% to about 20%, preferably from about 0.01% to about 5% by weight of catalyst, based on the coating mat erial. Catalysts can be used individually or in combi nation.

Drying can further be enhanced by using an oil which has been heat treated prior to being applied to the granule. Boiling the oil or blowing heated air 'through it are two common methods of pretreatment. The result in each case is a more viscous, faster-drying oil.

The thickness of the coating is not critical to the invention and can vary over a wide range, depend ing on the degree of control sought in the release of the thiolcarbamate. The desired degree of control will depend on the quantity of thiolcarbamate resid ing in the granule pores, the potency of the thiolcar bamate, and the particular crops and weeds to which the granule will be applied. Generally, however, the coating will range from about 1% to about 30% by weight of the entire composition, preferably from about 5% to about 20%.

In the preparation of the composition, the thiol carbamate is added to the granule first, followed by the glyceride coating. Once applied, the coating is allowed to cure. Application of each component is accomplished by any conventional technique. The most convenient technique is spraying, by which a fine mist of the liquid component is applied directly to the granule, which is sufficiently agitated to pro vide maximum and uniform exposure. When a dry ing catalyst is used, it is combined with the glyceride in a homogeneous liquid mixture which is applied in a single spray.

The temperature at which the liquid components are applied to the granule is not critical. It will be most convenient, however, to apply the components at approximately ambient temperature, i.e., about 1 50C to about 30"C, to minimize the loss of volatile components to the atmosphere.

The following examples are offered to further illus trate the utility of the present invention. These examples are offered for illustrative purposes only, and are intended neitherto limit nor define the invention in any manner. Such limitations are set forth in the appended claims.

EXAMPLE I Water Submersion Tests This example demonstrates the slow release properties ofthe coated granules of the present composition in an aqueous environment.

Trusorb granules obtained from Excel Mining Co., Santa Barbara, California, and kaolin granules obtained from Little Rock, Arkansas, were impre gnated with approximately 10 weight percent of the herbicide S-ethyl hexahydro - 1 H - azepine - 1 - car s bothioate (molinate), and then coated with a linseed oil/cobalt naphthenate mixture at various coating thicknesses. The granules were then placed in narrow-neck glass bottles containing 120 ml of water The quantity of granules used in each bottle was selected such that the total amount of active ingre dient (molinate) per bottle was 6.0 mg (or 50.0 mg/liter).

Each bottle was then agitated with a slow speed magnetic stirrer. A 5-ml sample of the water was taken immediately from the bottle for a zero-time analysis of the amount of molinate released from the granule. The analysis was performed by extracting the herbicide from the water with chloroform and analyzing the extract by gas chromatography. The contents of the bottle were then stirred for 24 hours and a second sample was taken for analysis. After 48 hours, a third sample was taken and analyzed. The results of these analyses are shown in Tables I and II, where coated granules are compared to uncoated granules and the quantity of released molinate is normalized to mg/l. Table I lists data pertaining to Trusorb granules, while Table II pertains to kaolin granules. In each case, the release rate of molinate from the granule into the surrounding water was substantially reduced. Table Ill lists the results of a similar test where 2 mm of mud was present in each bottle.

TABLEI WATER SUBMERSION TESTRESULTS Trusorb Granules Impregnated with Molinate Molinate Released rml/l) Composition Weight Percents Hours Submerged: Trusorb Molinate Oil Catalyst 0 24 48 Uncoated: 89.58 10.42 16.8 53.2 59.2 Coated: 74.67 8.67 15.83(a) 0.83(d) 1.2 29.2 37.6 74.67 8.67 15.83(b) 083(d) 1.6 27.2 32.4 74.67 8.67 15.83(c) 0.83(d) 3.2 39.2 35.2 64.00 7.43 27.14(a) 1.43(d) 0.6 12.4 18.0 (a) Oil:CPL-70, a copolymer of linseed soil and dicyclopentadiene, the latter constituting 20% byweight (b) Oil: blown linseed oil (c) Oil: boiled linseed oil (d) Catalyst: cobalt naphthenate (expressed as total weight of 6% solution) TABLE IT WATER SUBMERSION TEST RESULTS Kaolin Granules Impregnated with Molinate Molinate Released (mlll) Composition Weight Percents Hours Submerged: Koalin Molinate Oil Catalyst 0 24 48 Uncoated: 89.58 10.42 8.4 42.4 49.2 Coated: 74.67 8.67 15.83(a) 0.83(d) 0.8 13.2 28.4 74.67 8.67 15.83(b) 0.83(d) 0.8 16.4 26.8 74.67 8.67 15.83(c) 0.83d 1.2 19.2 26.0 (a) Oil: CPL-70 (b) Oil: blown linseed oil (c) Oil: boiled linseed oil (d) Catalyst: cobalt naphthenate (expressed as total weight of 6% solution) TABLEIII WA TER SUBMERSION TEST RESUL TS - IN PRESENCE OF MUD Koalin Granules Impregnated with Molinate, Submerged in Water Containing 2 mm of Mud Molinate Released (% of total) Composition Weight Percents Hours Submerged: Kaolin Molinate Oil(a) Catalyst(b) 1.5 24 48 Uncoated: 89.58 10.42 2.66 84.1 100.0 Coated: 82.98 9.64 7.00 0.37 0.44 39.0 55.6 80.16 9.32 10.00 0.52 0.76 25.3 49.5 (a) Oil: CPL-70 (b) Catalyst: cobalt naphthenate (expressed as total weight of 6% solu tion) EXAMPLE2 Delayed Soil lncorporation Tests This example demonstrates the herbicidal effectiveness of the present compositions when applied to wet soil surfaces and incorporated into the soil 24 hours later.

The granular compositions used in this example were prepared on Trusorb granules, obtained from Excel Mining Co., Santa Barbara, California. A liquid thiolcarbamate herbicide was sprayed on the granules using compressed air and a spray nozzle in a rotating drum. A dicyclopentadiene/linseed oil copolymer identified as "CPL-70", obtained from Cargill Co., Minneapolis, Minnesota, containing 20% d icyclopentadiene by weight, was then sprayed on as a mixture with cobalt naphthenate. The final product in each case contained 10.15% thiolcarbamate, 15.00% CPL-70, and 0.80% cobalt naphthenate, all on a weight basis, the granule itself constituting the balance. For comparison, further granules were prepared without the coating. Each contained 10.15% thiolcarbamate by weight, the granule constituting the balance.

Metal planting flats measuring 9.0 x 12.0 x 3.0 inches (23.0 x 30.5 x 7.6 cm) were filled with loamy sand soil and saturated with 500 ml of water. The granular herbicidal compositions were then distributed evenly over the soil surface at application rates corresponding to 0.75,1.0, 1.5, and 2.0 pounds of active ingredient (thiolcarbamate) per acre (0.84, 1.12,1.68, and 2.24 kilograms active ingredient per hectare). The flats were then placed in a greenhouse for 24 hours, after which time the soil from each flat was removed, placed in a rotary mixer where it was thoroughly mixed to incorporate the herbicide com positions, and then placed back in the flat.The flats were then seeded with barley (Hordeum sp. ), green foxtail Setaria viridis), watergrass (Echinochloa crusgalli), wild oat (Avena fatua), crabgrass (Digitaria sanguinalis), annual ryegrass (Lolium multiflorum), andjohnsongrass (Sorghum halepense) in individual rows. Ample seeds were planted to pro duce about 20 to 50 seedlings per row after emergence depending on the size of the plants.

Further flats containing untreated soil were also seeded for use as standards to measure the extent of weed control occurring in the treated flats. After seeding, all flats were placed in the greenhouse for three weeks, where they were watered regularly.

At the end of the three-week period, the treated flats were compared to the standard by a visual rating system in which the percent control was estimated ranging from 0% to 100%, with 0% representing the same degree of growth in the treated flat as the corresponding row in the standard flat, and 100% representing complete kill of all weeds in the row. All types of plant injury were taken into consideration.

The results are listed in Table IV, where four differ entthiolcarbamates are shown in both coated and uncoated granules. It is clear in each case that a substantial improvement in herbicidal activity is achieved by the use of the coating in each case.

TABLE IV HERBICIDA L ACTIVITY WITH DELA YED SOIL INCORPORATION Average Percent Weed Control (" Granule, Application Granule, 10% A.l., Herbicide Rate (IblA) 10%A.1.t2) 15% Coatin3 S-ethyl diisobutyl- 1.5 19 41 thiolcarbamate 2.0 9 35 S-ethyl di - n - propyl thiolcarbamate 1.0 16 48 S-ethyl N - cyclohexyl- 1.0 0 45 N - ethyl thiol carbamate 1.5 68 75 S - propyl di - n - propyl- 0.75 0 0 thiolcarbamate 1.0 26 67 ( Figures represent average control of seven weed species: barley, green fox tail, watergrass, wild oat, crabgrass, annual ryegrass, and johnsongrass (2) A.l.: Active ingredient (the thiolcarbamate) (3) Coating: CPL-70 EXAMPLE 3 Post-Flood Bioassay Tests This example demonstrates the herbicidal effectiveness of the present compositions when applied to watergrass, a weed frequently associated with rice crops, in post-flood, post-emergence application.

Three preparations of coated granules were used in these tests, all of which were Trusorb granules impregnated with approximately 10 weight percent of the herbicide S - ethyl hexahydro - 1 H - azepine - 1 - carbothioate (molinate), then coated with the dicyc lopentadiene/linseed oil copolymer CPL-70 and a small quantity of colbalt naphthenate at various coating thicknesses. An uncoated preparation with the same molinate content was also included in the test for comparison.

The test procedure was as follows: Plastic tubs measuring 10 x 7.5 x 5.75 inches (25.4 x 19.0 x 14.6 cm) were filled to a depth of 2 inches (5.1 cm) with 8 pounds (3.6 kg) of a loamy sand soil, containing 200 parts per million (ppm) of cis - N t (trichloromethyl) thiod - 4 - cyclohexene - 1, 2 - dicarboximide (a commercial fungicide known as "Cap tan ").Several rows 0.5 inch (1.27 cm) deep were impressed across the width of each tub and seeds of watergrass (Echinochloa crusgalli) were planted and covered by pinching together the soil on either side of the seeder rows. Six days later, when the grass was in the two-leaf stage, 1 to 2 inches (2.54to 5.1 cm) high, the soil was flooded with 2 inches (5.1 cm) of water.The prepared granules were then added to the flooded soil in such quantity as to achieve equivalent application rates of 0.75, 1.0, and 1.5 pounds active ingredient (molinate) per acre (1 b/A) (0.84, 1.12, and 1.68 kilograms/hectare). Atub nottreated with the herbicide was included as a standard for determination of the degree of control achieved in the treated tubs. Following the granule application, the tubs were allowed to stand in a greenhouse and water was added as needed to maintain the water level. At the end of nineteen days, the watergrass in each tub was rated visually in terms of percent con- trol ranging from Oto 100%, where 0% represents no injury and 100% represents complete kill when compared to the untreated standard.The percent control was based on the total injury to the watergrassdue to all factors.

The results in terms of percent control are listed in Table V, in which the first entry represents the uncoated granule. As in the previous examples, compari- son of the uncoated and coated granules shows a large and consistent improvement in herbicide effectiveness owing to the retention characteristics of the coating.

TABLE V WA TERGRASS CONTROL INPOSTFLOOD POST-EMERGENCE APPLICA TION Percent Control Application Composition Weight Percents Rate (Ib/A): Trusorb Molinate CPL-70 Catalystta) 0.75 1.0 1.5 Uncoated: 89.58 10.42 0 20 75 Coated: 82.82 5.65 10.00 0.53 20 40 85 74.68 8.66 15.83 0.83 40 75 80 64.01 7.42 27.14 1.43 60 85 85 (a) The drying catalyst was a 6% solution of cobalt naphthenate.

EXAMPLE4 Post-Flood Bioassay Tests This example demonstrates further the application of the present compositions to flooded fields, this time in the presence of rice species and several attendantweeds. Granular formulations similarto those of Example 3 were used, in comparison with an emulsifiable concentrate of the same herbicide.

The test procedure was as follows: Plastic tubs measuring 10 x 7.5 x 5.75 inches (25.4 x 19.0 x 14.6 cm) were filled to a depth of 2 inches (5.1 cm) with 8 pounds (3.6 kg) of a loamy sand soil, containing 50 ppm each of cis - N [(trichloromethyl) thio - 4 - cyclohexene -1,2 - dicarboximide and 18-18-18 fertilizer (containing 18% N, 18% P2Os, and 18% K2O on a weight basis). One pint (0.47 liter) of the soil was removed, the remaining soil was leveled and several rows were impressed across the width of the flat Yellow nutsedge tubers (Cyperus esculentus), and seeds of annual morning glory (Ipomoea purpurea ), curly dock (Rumex crispus), sesbania (Sesbania spy.) and Cay rose and Starbonnet rice (Oryza sativa) were planted in separate rows.The pint of soil was then used to place a 0.5 inch (1.27 cm) layer over the seeds and tubers. The planted soil was placed in a greenhouse, and irrigated by sprinkling as needed to keep the soil moist. Two days after the initial seeding another row was impressed 0.5 inches (1.27 cm) deep across the width of the flat and seeds of watergrass (Echinochloa crusgalli) were planted and covered by pinching together the soil on either side of the seeder row. Five days later, the soil was flooded with 2 inches (5.1 cm) of water. At flooding time the grass species were in the two leaf stage, 1 to 2 inches (2.54 to 5.1 cm) high, and the nutsedge was 1 inch (2. cm) high.

The prepared granules and emulsifiable concentrates were then added to the flooded soil in such quantity as to achieve an equivalent application rate of 0.75 pounds active ingredient (molinate) per abre (Ib/A) (0,84 kilogram/hectarn). A standard tub was used as in Example 3 to allow a determination of the degree of control achieved by the granules.

Afterthe granule application, the tubs were placed in the greenhouse and water was added as needed to maintain the water level. After 25 days, the species were rated visually for percent control as in Example 3. The results are listed in Table VI, where the first entry represents the emulsifiable concentrate. The morning glory and curly dock species fell victim to fungal infections and could not be rated.

The remaining species, however, showed a large improvement in herbicidal effectiveness obtained with the coated granules as compared to the emulsi fiable concentrate. In addition, neither rice species showed any injury at all.

TABLE VI WEED CONTROL IN SIMULA TED RICE PADDIES Percent Control at 0.75 IblA Water- Yellow grass Nutsedge Sesbania A. Standard Formulation: Emulsifiable Concentrate (6lbmolinatepergallon) 20 30 0 B. Coated Granules (weight %): Trusorb Molinate CPL-70 Catalyst 74.68 8.66 15.83 0.83 80 50 0 64.01 7.42 27.14 1.43 75 60 0 The herbicidal compositions of the present inven tion are useful in controlling undesirable vegetation by pre-emergence or post-emergence application to the locus where control is desired, including soil incorporation both prior to and subsequent to the planting of crops, soil surface application, applica tion to flooded fields, and application to fields through irrigation systems, in which the composi tions are added to irrigation water before the water is distributed to the field.The latter technique is applicable in all geographical areas regardless of rainfall, since it permits supplementation of the natural rainfall at critical stages of plant growth. In a typical application, the concentration of active herbi cide in the irrigation water will range from about 10 to about 150 parts per million by weight. The irriga tion water can then be applied bythe use of sprinkler systems, surface furrows, or flooding. Such applica tion is most effectively done before the weeds ger minate, either early in the spring prior to germina tion or within two days cultivation of the field. The compositions of this invention are particularly useful when applied to agricultural loci where the sur rounding medium is water itself, a water-containing material such as soil, or air-exposed surfaces in areas of frequent rainfall. The preferred use of these compositions is in the control of weeds in flooded rice paddies.

The amount of composition of the present inven tion which constitutes a herbicidally effective amount depends upon the nature of the seeds or plants to be controlled. The rate of application of active ingredient varies from about 0.01 to about 50 pounds per acre, preferably about 0.1 to about 25 pounds per acre, with the actual amount used depending on the overall cost and the desired results. It will be readily apparent to one skilled in the art that compositions exhibiting lower herbicidal activity will require a higher dosage rate than more active compounds for the same degree of control.

Claims (16)

1. An herbicidal composition comprising a por ous granule impregnated with a herbicidally effec tive amount of thiolcarbamate of the formula

in which R' is selected from the group consisting of C16 alkyl, C26 alkenyl, phenyl, and benzyl, all optionally substituted with one or more members selected from chlorine and C13 alkyl; and R2 and R3 either independently form C16 alkyl or Cs-C, cycloalkyl, or conjointly form Cs-C7 alkylene; said herbicide comprising from about 1%to about 20% by weight of the composition; and coated with a coating material selected from (a) a cured glyceride of one or more unsaturated C10-C24 aliphatic acids and (b) a cured mono- or polycyclopentadiene copolymer of a glyceride of one or more unsaturated C,0-C24 aliphatic acids, the coating comprising from about 1% to about 30% by weight of the composi tion.

2. A composition according to Claim 1 in which R1 is C2-C4 alkyl; and R2 and R3 either independently form C24 or C57 cycloalkyl, or conjointly form C57 alkylene.

3. A composition according to Claim 1 in which said thiolcarbamate herbicide is S-ethyl hexahydro 1 H - azepine - 1 - carbothioate.

4. A composition according to Claims 1, 2, or 3 in which the herbicide comprises from about 5% to about 15% by weight of the composition, and the coating material is selected from (a) a cured glyceride of one or more unsaturated Crs-C20 alipha tic acids and (b) a cured dicyclopentadiene copolymer of a glyceride of one or more unsaturated C,s-C20 aliphatic acids, and the coating material comprises from about 5% to about 20% by weight of ) the composition.

5. A composition according to Claims 1,2, or 3 in which the coating material is selected from cured linseed oil and a cured dicyclopentadiene/linseed oil copolymer.

5

6. A composition according to Claims 1,2, or 3 further comprising one or more drying catalysts selected from cobalt, lead, and manganese salts of linoleic, resin, and naphthenic acids, at a concentra tion from about 0.01 % to about 20% by weight, based on the coating material.

7. Acomposition according to Claims 1,2, or3 further comprising from about 0.01% to about 5% by weight of cobalt naphthenate, based on the coating material.

8. A method of controlling undesirable vegetation in rice cultivation which comprises applying to flooded rice paddies a herbicidally effective amount of a composition comprising porous granules impregnated with a herbicidally effective amount of a thiolcarbamate herbicide of the formula

in which R' is selected from the group consisting of C1C6 alkyl, C26 alkenyl, phenyl, and benzyl, all optionally substituted with one or more members selected from chlorine and C,-C3 alkyl; and R2 and R3 either independently form C1C6 alkyl or C > -C, cycloalkyl, or conjointly form Cs-C, alkylene; said herbicide comprising from about1%to about 20% by weight of the composition; and coated with a coating material selected from (a) a cured glyceride of one or more unsaturated C10C24 aliphatic acids and (b) a cured mono- or polycyclopentadiene copolymer of a glyceride of one or more unsaturated C10-C24 aliphatic acids, the coating comprising from about 1 % to about 30% by weight of the composition.

9. A method according to Claim 8 in which R' isC2-C4alkyl; and R2 and R3 either independently form C2-C4 alkyl or C7 cycloalkyl, or conjointly form C7 alkylene.

10. A method according to Claim 8 in which said thiolcarbamate herbicide is S - ethyl hexahydro - 1 H azepine - 1 - carbothioate.

11. A method according to Claims 8,9, or 10 in which the herbicide comprises from about 5% to about 15% by weight of the composition, and the coating material is selected from (a) a cured glyceride of one or more unsaturated C'rC20 aliphatic acids and (b) a cured dicyclopentadiene copolymer of a glyceride of one or more unsaturated C16rC20 aliphatic acids and the coating material comprises from about 5% to about 20% by weight of the composition.

12. A method according to Claims 8,9, or 10 in which the coating material is selected from cured linseed oil and a cured dicyclopentadiene/linseed oil copolymer.

13. A method according to Claims 8, 9, or 10 further comprising one or more drying catalysts selected from cobalt, lead, and manganese salts of linoleic, resin, and naphthenic acids, at a concentra tion from about 0.01 % to about 20% by weight, based on the coating material.

14. A method according to Claims 8, 9, or 10 further comprising from about 0.01% to about 5% by weight of cobalt naphthenate, based on the coating material.

15. Acomposition as claimed in claim 1 substantially as herein described with reference to the Examples.

16. A method of controlling undesirable vegetation substantially as herein described.