GB2164257A - Controlled release fungicidal formulations - Google Patents

Abstract

A controlled release formulation containing tricyclazole and a polymer having a minimum film forming temperature of 100 DEG C or lower and a water absorbency ranging from about 5% to 500% is useful for protecting rice plants against rice blast by applying said formulation to the locus of the rice plants.

Description

SPECIFICATION Controlled Release Formulations and Their Use The present invention relates to a controlled release formulation and a use thereof and, more particularly, to a controlled release formulation of 5-methyl-l ,2,4-triazolo[3,4-b]benzoth iazole and a use thereof for controlling rice blast.

The control of rice blast is of great economic benefit in sustaining a rice crop. The rice blast reduces rice yields and harvest to a great effect. Although it was of practically great significance to prevent a rice crop from being affected by the rice blast, there had been no commercially available fungicide that may prevent the rice blast. In order to meet such a demand, 5-methyl-1 ,2,4-triazolo[3,4-bibenzothiazole (hereinafter referred to as "tricyclazole") had been developed. Tricyclazole is a systemic fungicide for the control of Piricularia oryzae, the causative organism of rice blast (U.S. Patent No.4,064,261) and it is commercially available in Japan and some other Asian countries.

Commercially available tricyclazole formulations in the form of aqueous suspension, granules, wettabie powders or in any other form release the tricyclazole rapidly when applied to the soil so that they do not-provide a protection overthe rice blast for the full length necessary to protect the rice plants through the leaf blast stage. Such commercially available formulations may also release the active ingredient in such a high concentration that it may be injurious to young rice seedlings. Accordingly, there has been a great demand to provide a tricyclazole formulation that will control the release of the tricyclazole for a period of time long enough to protect rice seedlings from rice blast.

The controlled release formulation according to the present invention contains tricyclazole as an active ingredient, a polymer as an additional ingredient, and an agriculturally acceptable carrier. The polymer to be employed for the formulations according to the present invention possesses a minimum film forming temperature of about 1000C or lower and a water absorbency (a water-absorption rate) ranging from about 5% to 500%.

The term "polymer", as used herein, refers to both a homopolymer and a copolymer. The polymer to be employed for the present invention may have an average molecular weight ranging generally from about 500 to 3,000,000 and, more preferably, from about 1,000 to 1,000,000.

The polymer to be employed therefor should have a minimum film forming temperature of 1 00 C or lower as has been described hereinabove. The minimum film forming temperature may be determined with a device that may be conventionally utilized for measuring minimum film forming temperatures of polymers. In instances where formulations have a poor film of the polymer, they may not reproduce the release of the active ingredient and the control over the release may be rendered inadequate. It is thus preferred to have a film formed under drying conditions. If the film is formed in a poor state under such drying conditions, it is desired to form a film at elevated temperatures that may exert no adverse effects on tricyclazole.

As has been described hereinabove, the polymer to be employed for the controlled release formulation according to the present invention should have a water absorbency ranging generally from about 5% to 500%. The water absorbency is that obtained when measured in 24 hours in accordance with JIS K7209 of the Japanese Standards Association. If the water absorbency does not reach the minimum limit, the release rate of the tricyclazole is too slow to provide a concentration necessary to make the tricyclazole effective for the control of rice blast and a large amount of the formulations may be required to release the active ingredient in a concentration effective enough to protect rice plants from attack by rice blast. Further, such formulations have the tendency to allow a majority of the tricyclazole not to be released and utilized effectively.If the water absorbency of a polymer used exceeds the maximum limit, the release of tricyclazole may become too quick to provide an adequate control over the release of tricyclazole. Thus it is not desired to use a polymer whose water absorbency cannot be measured on account of dissolution or re-dispersion in water.

In accordance with the present invention, the polymer to be used may be linear, cross-linked or cross linkable with a metallic ion as long as it meets the above-mentioned requirements. Although the polymer is not limited to any particular one, it may most preferably be one in the form of an aqueous emulsion or an aqueous solution because it is easy to handle in steps of preparing formulations.

Representative examples of the polymers in the form of an emulsion to be used for the present invention may include acrylic emulsions such as Acriset(R) EMN-10X, Acriset" EMN-20X and Acriset(R' EMN-30X (manufactured by Nippon Shoukubai Kagaku Kogyo Co., Ltd.); ethylenevinyl acetate copolymer emulsions such as Sumikaflex(R) 400 and 500 (manufactured by Sumitomo Chemical Co., Ltd.); vinylidene chloride emulsions such as Krehalon(R)DO and AO (manufactured by Kureha Chemical Industry Co., Ltd.); polyolefinic emulsions such as KemipallR) A-100 and S-100 (manufactured by Mitsui Petrochemical Industries, Ltd.); Styrene-maleic acid water-soluble resins such as 5MAR) 2625A and 17352 (manufactured by Alco Chemical K.K.); and so on.

The controlled release formulations according to the present invention may be prepared preferably by formulating tricyclazole and at least one of the polymers as illustrated immediately hereinabove with an agriculturally acceptable carrier. Such a carrier may be adsorptive or absorptive in nature. Typical examples of the carriers may include limestone, sand, gypsum, ground volcanic rock, clays such as montmorillonite, attapulgite, kaolin and ball clays, talc, a fertilizer and ground agricultural products such as soybean mill run, corncob grits, rice hulls and the like. Of these carriers, attapulgite clay and ground rice hulls are preferred. In instances where the formulations are granulated by extrusion, ball clays are preferred. Carriers are chosen with regard to their availability and cost.

The concentrations of tricyclazole and the polymer in the controlled release formulations according to the present invention are not critical so long as the polymer is present in the concentration effective enough to control the release of the tricyclazole. Generally speaking, the higher the concentration of the polymer in the formation, the slower the release rate of tricyclazole into the surrounding. Preferred concentrations of tricyclazole and the polymer may vary with the composition of the formulation, that is, whether the formulation consists merely of tricyclazole and the polymer or whether it contains an agriculturally acceptable carrier in addition.The formulations consisting merely of tricyclazole and the polymer without the presence of any carrier may contain tricyclazole in a concentration ranging from about 0.1 % to 75% by weight (these and subsequent figures being on a dry weight basis unless otherwise stated) and the polymer in a concentration ranging from about 25% to 99.9% by weight. Preferred concentrations are, respectively, from about 1% to 50% by weight and from about 50% to 99% by weight.

The controlled release formulations consisting of three or more components may generally contain tricyclazole in a concentration ranging from about 0.1% to 30% by weight and preferably from about 1% to 20% by weight, a polymer or polymers in a concentration ranging from about 10% to 60% by weight and preferably from about 20% to 60% by weight, and an agriculturally acceptable carrier or carriers in a concentration ranging from about 20% to 89.9% by weight and preferably from about 20% to 79% by weight.

The controlled release formulations according to the present invention may be prepared in the following manner. The active substance, preferably in a finely divided form, is added to an aqueous emulsion or an aqueous solution of a polymer or polymers as described hereinabove to form a slurry. The finely divided particles of the active substance may be prepared by milling the technical grade by any conventional milling procedures such as the milling technique in a fiuid energy mill. In the Examples which follow, tricyclazole is employed which has particle sizes such that 99.9% may pass a 326 mesh screen. The slurry may be prepared by adding the agriculturally acceptable carrier or carriers to a mixture of tricyclazole in an aqueous emulsion or an aqueous solution of the polymer or polymers and then mixing them to form a homogeneous mixture.The mixture may then be formulated to granules or other forms of preparations suitable for application to the locus of rice plants for control of rice blast. In order to provide the formulations which may release tricyclazole in a controlled manner, it is necessary to dry them usually at elevated temperature. In applying the heat to the formulations, it is desired to subject the drying treatment at temperatures higher then the minimum film forming temperature of the polymer used and it is more preferred to apply the temperatures higher by about 1 00C then the minimum film forming temperature.

In accordance with the present invention, a slurry of tricyclazole and a polymer or polymers may be preferably added with stirring to an agriculturally acceptable carrier or carriers with a conventional device in accordance with a well-known procedure. The carrier may also be added to a mixture of tricyclazole with a polymer or polymers. The mixing may be carried out usually at ambient temperatures. Representative types of mixers to be utilized for stirring may include a coating pan mixer, cement mixer, Hobart mixer, mini-tumbler mixer, ribbon blender or any similar rotary mixer.

Aftertricyclazole, a polymer or polymers and a carrier or carriers, as needed, are mixed to uniformity, it is preferred to have the mixture dried at elevated temperatures in order to form a continuous polymer film by accelerating coalescence of the polymer particles. The temperatures to be applicable may vary with the kind of the polymer used. It is desirable, however, that the temperatures are higher than the minimum film forming temperature of the polymer used and more preferred to use the temperature higher by about 10 C than it.The temperatures to be applicable may be generally in the range from about 5 to 180"C and more preferably in the range from about 30 to 125"C. It is of course possible to carry out the drying first at temperatures lower than the minimum film forming temperature of the polymer used and then higher by about 1 0"C than the minimum film forming temperature of the polymer used. In instances where the polymer to be used has a minimum film forming temperature lower than the ambient temperature, such a formulation as containing the polymer may be dried under ambient conditions.

The type of a drying apparatus is not critical and may be chosen from any device well known to those in the art. Typical driers may include a rotary type drier and an oven to be operated at either standard or reduced pressures.

Alternatively, a uniform mixture of tricyclazole, a polymer or polymers and an appropriate carrier or carriers may be extruded to pellets, granules or any other forms of formulations and then dried. Procedures and equipment to be utilized for extrusion are well known. In this embodiment of the present invention, it is important to use a type of clay suitable as a carrier for extrusion, and ball clays are generally preferred. The exact identity of the clay, however, is not critical and a choice of clays to be used may vary with local availabilty.

It is desirable to use a suitable surface active agent to aid dispersion of the formulated granule or other formulation in water when a carrier is employed in the formulation which is not readily dispersed throughout the aqueous medium. The choice of a surface active agent, and an amount thereof employed, is dictated by the nature of the composition ingredients, and by the ability of the surface active agentto facilitate the dispersing of the formulation in water. For instance, when using rice hulls as the carrier, a surface active agent is required to facilitate dispersion of the formulation in water. Suitable surface active agents are in the dry form and may be nonionic, anionic or cationic.Examples of anionic surface active agents may include alkyl or aryl sodium sulphonates or sulfonic acids, calcium alkylaryl sulphonates and alkyl alcohol esters are phosphoric acid. Examples of nonionic surface active agents may include ethoxylated alkyl phenols, ethers and alcohols, sorbitan esters and ethoxylated sorbitan esters and ethers.

Emulsifiers and adjuvants may be employed as surface active agents. Commercially significant emulsifiers are primarily anionic or nonionic agents. The surface active agent may be present in the formulation in a concentration ranging generally from about 0.01 % to 5% on a dry weight basis.

Although the precise mechanism of a controlled release of tricyclazole by the formulations according to the present invention is not yet known, it is considered that the tricyclazole would be diffused through a particular polymer matrix into the surrounding aqueous medium. It is to be noted, however, that the present invention is not limited to any mode of functions which may be performed by the formulations according to the present invention.

The controlled release formulations according to the present invention may be applied to the locus of rice plants in a conventional manner. The application may be carried out manually or by mechanical means.

As a mechanical equipment may be employed a metering applicator that may apply an accurately measured quantity of the granular formulation to the soil surface. An operator needs to handle an application equipment so as to apply the formulation at a desired application rate per unit area and a uniform quantity of the formulation to the locus of rice plants to be treated.

The controlled release formulations according to the present invention may be applied preferably to the soil of a standard transplant flat with rice seedlings, but they may be applied to a flooded rice paddy. To secure an optimal disease control when applying the formulation to the soil of the transplant flat, it is important to transplant the rice seedlings with a mechanical transplanter. If the mechanical transplanting is not feasible, the transplanting should be done so as to have the soil around the roots of the rice seedlings transplanted together with the seedlings. This procedure may allowtricyclazole present in the soil around the roots of the rice seedlings in the transplant flat to be utilized for a continuous control over rice blast throughout the full length of vegetative growth stage.

The controlled release formulations according to the present invention release tricyclazole in a controlled quantity over a long period of time without causing the tricyclazole concentration to become too high at the initial stage of application to rice seedlings. Accordingly, the present formulations have the great advantage over conventional tricyclazole formulations in reducing or preventing phytotoxity to rice seedlings. Another advantage the controlled release formulations of the present invention offer is that rice breeding farmers may save a lot of time and money because the present formulations, if applied to rice seedlings, do not require to be applied at the leaf blast stage so often as conventional agents which have been employed to cure the leaf rice blast.

The following Examples are provided in an effort to more fully illustrate specific aspects of the present invention. The Examples are not intended to limit the present invention in any respect and should not be so construed.

Example 1 To a mixed slurry of 40 g of air milled tricyclazole and 425 g of ACRISET(R) EMN-20X (acrylic emulsion manufactured by Nippon Shokubai Kagaku Kogyo Co., Ltd.) was added 760 g of Foundry Hill Creme Clay (ball clay supplied by Spinks Clay Co.; hereinafter referred to as "FHC Clay"), and the mixture was mixed well in a mixer. After 10 minutes of mixing, the mixture was formulated into granules having a diameter of 2 mm and a length of 3-7 mm by extruding it through experimental pellet mills equipped with a dice mold having a thickness of 5 mm. The granules were allowed to dry at 40"C for 24 hours.

The minimum film-forming temperature and water absorbency of ACRISET(R) EMN-20X used here were found to 17.5"C and 53%, respectively.

Examples 2-9 and Comparative Examples 1-3 The granules were formed in the same manner as in Example 1 above with the exception that, by using the polymer as listed in Table 1 below, the composition was formulated as shown in Table 2 below. In Examples 4 and 8, the granules were dried at 100'C for2 hours.

TABLE 1 Ex. Concentration Water** Nos. Polymer (%) MFT*) ( C) Absorbency (%) 2 ACRISET(R) 50 < 0 134 EMN-30X 3 SUMIKA-FLEX R) 55 0 11 400 4 KEMIPAL(R) 27 90 6.5 S-100 5 KREHALON(R) 50--52 14 19 DOA 6 ACRISET(R) 47 17.5 53 EM N-20X 7 SUMIKA-FLEX(R) 55 0 11 400 8 KEMlPAL(R) 27 90 6.5 S-100 9 SMA(R) 2625A 20 0 66 (Ammonium salt) Comp. FINETEXzR) 30 6.5 Dissolved Ex. 1 650 Comp. KURARAY 20 0 Dissolved Ex. 2 POVAL 205 Comp. Carboxylmethyl 1 0 Dissolved Ex. 3 cellulose (Na salt) Note: MFT (Minimum Film-forming Temperature): The MFTwas measured with a MFT measuring device sold by Nippon Rigaku Kogyo K.K.

Water Absorbency: Measured according to JIS K7209.

Preparation of Test Specimens: An aqueous emulsion or aqueous solution of the polymer to be tested was coated on a Teflon plate so as to form a film having a dry film thickness of 1 mm, and the film was dried at room temperature for 2 days and then at 50"C for 24 hours in a thermostat. The Kemipal S-100 film was allowed to stand at room temperature for 1 day and dried at 100 C for 2 hours in a thermostat.

Measurement for Water Absorbency: A 50 mmx50 mm test specimen was immersed in distilled water of 25 C for 24 hours, and the water of absorbency was calculated from the following equation: W2-W3 Water Absorbency (%)= # x100 W1 W1=Weight of Test Specimen before Immersion W2=Weight of Test Specimen after Immersion W3=Weight of Dry Test Specimen after Immersion.

TABLE 2 Ex. Amount of Amount of Nos. Carriers TCA (%) Polymer (%) 2 FHC clay 4 20 3 -do- 4 20 4 -do- 4 20 5 -do- 4 10 6 Ground Rice Hulls 8 30 7 -do- 8 30 8 -do- 8 30 9 FHC clay 4 20 Comp. -do- 4 20 Ex. 1 Comp. -do- 4 20 Ex. 2 Comp. -do- 4 1 Ex. 3 Experiment 1 One-third sections of a 28x58x3 cm. flat containing 18 day old rice plants were surface applied with slow-release granules of tricyclazole. The granules contained the active ingredient at concentrations of either approximately 4% and 8%. Treatments were made at 1.5,3.0 and 6.0 grams of active ingredient for each flat as a whole. Twenty-four hours after treatment the sections were transplanted into flooded, one-quart 4 inch diameter plastic pots without drainage holes filled with nonsterile soil. Injury ratings were made 14 and 23 days after transplanting from the flats to the flooded containers.Twenty-three days after transplanting the plants were inoculated with a rice blast (Piricularia oryzae) spore suspension and incubated in a moist chamber at 70"F. (21"C) for 48 hours. Seven days after inoculation the percent of rice blast disease incidence on the rice plants was recorded. Formulated slow-release granules not containing tricyclazole (blank granules) and water controls were run as well. Tricyclazole formulated as a 75 WP (wettable powder containing 75% of the active agent by weight) was also tested for comparison. Crop injury rating, as compared to untreated controls, was made from S10 according to the following scale: 0=no injury 13=slight injury 46=moderate injury 7-9=severe injury 10=death to the plant.

The results of this test appear below in Table 3 as the average of three replications.

TABLE 3 Example No. Rate Crop Injury Rating Percent of Formulation Grams of Days After Transplanting Disease Tested TricyclazolelFlat 14 23 Incidence 1 6.0 4.3 3.7 0 3.0 2.3 1.7 0 1.5 0.3 0.3 0.7 2 6.0 4.7 4.3 0 3.0 2.7 2.0 0 1.5 1.3 0.7 0.03 3 6.0 5.7 4.7 0 3.0 2.7 2.3 0 1.5 1.7 0.7 0.7 4 6.0 4.7 3.3 0.7 3.0 3.0 0.7 2.3 1.5 1.0 0 8.7 5 6.0 6.0 4.7 0 3.0 4.3 3.0 0 1.5 2.3 1.7 0.03 6 6.0 4.0 2.7 0 3.0 2.7 1.3 0.03 1.5 0.7 0.3 0.7 Tricyclazole WP 6.0 8.3 7.7 0 3.0 6.7 6.0 0 1.5 3.3 3.0 1.7 Comparative Ex. 1 6.0 7.7 7.3 0 3.0 6.3 6.0 0 1.5 3.7 3.3 0.7 Comparative Ex. 2 6.0 7.0 6.7 0 3.0 5.7 6.0 0.03 1.5 3.0 2.7 1.3 As is apparent from the above experiments, representative controlled release formulations of this invention effectively control rice blast with a lesser degree of injury to the plant than noted with current commercial formulations.

A study was also conducted in an effort to demonstrate the sustained release properties of the present formulation. The following procedure was used to illustrate these properties: A beaker was filled with three liters of deionized water at room temperature. The exemplary sustained release granules totaling 60 mg of active agent were added to the water to provide a concentration of 20 ppm when all of the tricyclazole was released from the granule. At various time intervals after addition, 1 ml samples of water were taken from the beaker and analyzed to determine the concentration of active agent therein. For some of the formulations evaluated in this study, after the concentration of active agent in water began to stabilize, the water was removed by decanting and the residues on the bottom was allowed to dry.This residue was then analyzed to determine the concentration of active agent remaining. A 75% wettable powder formulation was also studied for comparison. The results of this study appear below in Table 4 as parts per million. TABLE 4 Concentration (ppm) of TCA Released after Time of Addition (Hours) Experiment Nos. 2 5 10 24 48 72 96 120 144 168 192 240 288 1 1.2 2.8 3.4 4.9 8.5 10.5 11.0 11.7 12.5 12.8 14.0 14.6 15.0 2 2.4 3.4 6.9 10.5 14.3 16.7 18.2 19.0 19.1 19.6 19.7 19.7 3 1.9 2.6 5.7 6.4 10.1 11.2 13.6 15.7 16.4 16.5 19.0 20.1 4 1.0 0.8 1.6 2.4 3.9 4.8 5.7 6.3 7.2 7.2 7.5 8.1 8.6 5 1.7 3.2 6.5 8.7 13.6 17.0 19.6 20.9 21.8 21.9 22.7 22.6 6 0.8 2.1 2.6 3.7 6.5 8.3 10.3 11.0 11.8 12.5 13.0 13.9 14.4 7 1.9 2.5 3.6 6.3 8.4 9.8 11.1 14.0 15.6 17.3 18.3 19.5 19.8 8 0.6 0.8 1.0 2.0 2.5 3.5 4.8 5.6 6.2 6.8 7.3 7.4 7.7 9 1.8 2.3 2.7 4.3 7.5 9.9 14.9 15.6 17.6 17.9 17.6 18.0 19.8 Comparative Ex. 1 14.2 18.4 19.1 19.1 19.8 19.4 19.6 19.9 19.8 19.6 19.8 19.8 Comparative Ex. 2 7.2 15.9 18.4 20.0 20.8 20.6 20.9 21.4 21.3 21.3 21.0 21.0 Comparative Ex. 3 11.0 16.6 18.3 19.7 20.0 17.9 19.8 20.1 19.9 20.1 20.1 20.3 Tricyclazole 75 WP 19.5 19.3 19.3 19.4 - - - - - - - - - This study effectively demonstrates that the present controlled formulation does control the release rate of the active agent over an extended period of time, particularly when compared to the tricyclazole wettable powder formulation, wherein the active agent is released almost instantly (within one hour).

Claims (10)

1. A controlled release formulation containing tricyclazole and a polymer having a minimum film forming temperature of 100"C or lower and a water absorbency ranging from about 5% to 500%.

2. The formulation according to Claim 1 wherein tricyclazole and the polymer are formulated together with an agriculturally acceptable carrier.

3. The formulation according to any of Claims 1 and 2 wherein the polymer is in the form of an aqueous emulsion.

4. The formulation according to any of Claims 1 to 3 wherein it is dried at temperatures higher than the minimum film forming temperature of the polymer.

5. The formulation according to Claim 2 wherein the carrier is clay.

6. The formulation according to Claim 2 wherein the carrier is rice hulls.

7. The formulation according to Claim 2 wherein the carrier is limestone.

8. A method for protecting rice plants against rice blast by applying to the locus of the rice plants a controlled release formulation as claimed in any one of Claims 1 to 7.

9. A controlled release formulation as claimed in Claim 1 substantially as herein described, with particular reference to Example 1-9.

10. A method for protecting rice plants according to Claim 8, substantially as described herein.