Mono-5-Substituted-Thio-3-Chloro-4h-1,2,6-Thiadiazin-4-One Antifungal Agents

The present invention relates to a method for controlling fungal disease in plants, to novel antifungal compositions, and to compounds useful for controlling fungi which attack agricultural and garden plants and seeds. More particularly, the invention relates to the use of a selected mono-5-substituted-3-chloro-4H-1,2,6-thiadiazin-4-one as an antifungal agent for controlling fungal disease in plants.

Geevers and Trompen disclosed the preparation 3,5-dichloro-4H-1,2,6-thiadiazin-4-one and its use as an intermediate to prepare various other 5-substituted-3-chloro-4H-1,2,6-thiadiazin-4-ones including the 5-phenylthio and 5-methylthio derivative. J. Geevers and W. P. Trompen, Rec. Trav. Chim., 93, 270 (1974). The 5-phenoxy derivatives are disclosed in U.S. Patent Application Ser. No. 728,860 filed of even date herewith.

While the 5-phenylthio and 5-methylthio derivatives and the method for preparing them have been disclosed, the reference provides no indication of any biological activity. More particularly, there is no suggestion that the compounds of this invention have antifungal activity.

It has now been found that selected mono-5-substituted 3-chloro-4H-1,2,6-thiadiazin-4-ones, which are hereinafter described, exhibit excellent antifungal activity and are useful in providing control of fungal disease in agricultural crops by foliar, seed, and soil application.

The present invention thus provides (1) a method for controlling fungal disease in plants which comprises applying a selected mono-5-substituted-3-chloro-4H-1,2,6-thiadiazin-4-one, as defined below, to the locus where control is desired, (2) antifungal compositions for control of fungal disease in plants, and (3) certain novel compounds which are useful for control of fungi.

In accordance with a first aspect of the present invention, there is provided a method for controlling fungal disease in agricultural crops and other plants which comprises applying to the locus where control is desired an effective fungistatic or fungicidal amount of a mono-5-substituted-3-chloro-4H-1,2,6-thiadiazin-4-one of the formula ##STR2## in which X is alkylthio, phenylthio, phenyl(lower)alkylthio, cycloalkylthio having 5 to 7 ring carbon atoms or substituted phenylthio of the formula ##STR3## in which each R is independently selected from lower alkyl, lower alkoxyl, lower acylamino, lower alkoxycarbonyl, nitro, cyano or halogen and n is an integer having a value of 1-3. However, when R is lower alkyl or halogen n may have a value of 1 to 5 inclusive.

Unless it is otherwise indicated, the term "lower" means having 1 to 6 carbon atoms, straight or branched chain, preferably 1 to 4 carbon atoms, the term alkyl means having 1 to 8 carbon atoms, and the term "halogen" means bromine, chlorine and fluorine or iodine, advantageously bromine, chlorine or fluorine, preferably chlorine or bromine.

In the method of this invention an effective fungistatic or fungicidal amount of active ingredient is applied to foliage or seeds of agricultural plants or to the soil in which the plants are growing or are to be planted, i.e., the locus where control is desired. When so applied, the compounds prevent fungal infection or inhibit further development of a preexisting fungal disease.

In the method of this invention the selected antifungal agent may be applied as the technical material or as a formulated product. Typical formulations include the antifungal agent in combination with an agriculturally acceptable carrier, preferably with a surface active agent, and optionally with other active ingredients. Suitable formulations include granules, powders, or liquids, the choice varying with the fungus and environmental factors present at the particular locus of infestation. Thus the compounds may be formulated as granules of various sizes, as dusts, as wettable powders, as emulsifiable concentrates, as solutions, as dispersions, as controlled release compositions, and the like.

A typical formulation may vary widely in concentration of the active ingredient depending on the particular agent used, the additives and carriers used, other active ingredients, and the desired mode of application. With due consideration of these factors, the active ingredient of a typical formulation may, for example, be suitably present at a concentration of about 0.5% up to about 99.5% by weight of the formulation. Additives and carriers may comprise about 99.5% by weight to as low as about 0.5% by weight of the formulation. Surface active agents, if employed in the formulation, may be present at various concentrations, suitably in the range of 1% to 30% by weight.

The formulation may be used as such or diluted to a desired use dilution with a suitable diluent or carrier. The concentration of the active ingredient in use dilution is normally in the range of about 0.001% to about 4% by weight. Many variations of spraying, dusting, soil-incorporated, and controlled or slow release compositions in the art may be used by substituting or adding a compound of this invention into compositions known or apparent to the art.

The antifungal agents of this invention may be formulated and applied with other compatible active ingredients, including nematicides, insecticides, acaricides, other fungicides, plant regulators, herbicides, fertilizers, etc.

In applying the foregoing chemicals, whether alone or with other agricultural chemicals, an effective inhibitory or fungicidal amount of the active ingredient must be applied. While the application rate will vary widely depending on the choice of compound, the formulation and mode of application, the plant species being protected, and the planting density, a suitable use rate may be in the range of 0.05 to 5 kg/hectare, preferably 0.5 to about 4 kg/hectare.

The antifungal composition of this invention comprises a compound of formula I as defined above in admixture with an agriculturally acceptable carrier, preferably containing a compatible surface active agent.

The novel compounds of this invention are those of Formula I in which X is other than methylthio or phenylthio; that is, the compounds of formula I in which X is alkylthio of 2 to 8 carbon atoms, phenyl(lower)alkylthio, cycloalkylthio having 5-7 ring carbon atoms or substituted phenylthio of the Formula II in which R is lower alkyl, lower alkoxyl, lower acylamino, lower alkoxycarbonyl, nitro, cyano or halogen and n in an integer having a value of 1 to 3 inclusive, with the proviso that when R is lower alkyl or halogen n may have a value of 1 to 5 inclusive.

The compounds of this invention are prepared according to the teaching of Geevers and Trompen, supra; that is, by reaction 3,5-dichloro-4H-1,2,6-thiadiazin-4-one with thiolate ions, for example, sodium phenothiolate. The following examples are typical of the preparation of the compounds.

A 50 ml flask was charged with 20 ml formic acid. The flask was purged with a stream of dry nitrogen. The nitrogen purge was continued while 6.3 g 3,4,4,5-tetra-chloro-4H-1,2,6-thiadiazinone was added dropwise over 0.5 hour during which the temperature of the reaction mixture was maintained at 10.+-.1.degree. C. Following addition the reaction mixture was stirred at 10.degree. C for 2 hours then at room temperature for 64 hours, then poured into 60 ml. ice-water with stirring. The resulting mixture was filtered and the filter cake washed with water and dried to yield 2.2 g of pale yellow 3,5-dichloro-4H-1,2,6-thiadiazin-4-one, mp 81.degree.-82.degree. C.

In one portion 2.5 g of trimethylamine was added to a solution of 4.6 g of 3,5-dichloro-4H-1,2,6-thiadiazin-4-one in 75 ml of ethyl ether in a 250 ml flask. A solution of 2.8 g of thiophenol in 25 ml of ethyl ether was then added dropwise to the flask during a 15 minute period. The reaction was allowed to stir for 3 hrs. after which it was filtered. The filter cake was washed with ether, and the filter cake was discarded. Successively, the ether solution was washed twice with 50 ml of water and once with 50 ml of saturated sodium chloride solution. The ether solution was then dried over anhydrous sodium sulfate. The ether was evaporated, leaving a solid residue which was recrystallized from 75 ml of cyclohexane. The yellow-orange 3-chloro-5-phenylthio-4H-1,2,6-thiadiazin-4-one weighed 3.6 g, mp 99.5.degree.-101.5.degree. C. (Lit. mp 102.5.degree.-103.5.degree. C, J. Geevers and W. P. Trompen, supra.). The ir spectrum was consistent with the assigned structure.

Analyses calc'd for C.sub.9 H.sub.5 ClN.sub.2 OS.sub.2 : C 42.11; H 1.96; N 10.91. Found: C 42.39; H 2.07; N 10.94.

The compounds of this invention which are set forth below have been synthesized in accordance with the typical preparatory method set forth in Examples I and II. An identifying number is provided for each compound. This compound number is used below in reporting biological data realting to the compound.

The following examples demonstrate the practice of the present invention. The test organisms used in these examples, together with an identifying codes which are in the tables to identify each organism, are as follows:

As = alternaria solani

Bc = botrytis cinerea

Cc = cladosporium cucumerinum

Ep = erysiphe polygoni

Fs = fusarium solani

Ho = helminthosporium oryzae

Po = pyricularia oryzae

Pu = pythium ultimum

Rs = rhizoctonia solani

Sf = sclerotinia fructicola

Up = uromyces phaseoli

Pi = phytophthora infestans

Vi = venturia inaequalis

The test chemical was dissolved or suspended in acetone in an amount such that 0.8 ml of the resulting suspension or solution, mixed with 40 ml water agar produced a water agar solution containing 40, 10, 2.5 and 1 ppm of test chemical. The resulting agar solution, at 50.degree. C, was then divided equally between two sterile petri dishes, each having four separated quadrants, and allowed to solidify. Three quadrants of each dish were flooded with 0.1 ml of a spore suspension in sterile water. Spores of two pathogens, Erysiphe polygoni and Uromyes phaseoli, from infected plant leaves, were brushed on the remaining two quadrants. The tests were then incubated 48 hours, at 24.degree. C.

Readings were then taken and the percentage of germinated spores calculated. From this percentage, a spore germination rating was assigned as follows:

Table I reports the inhibitory effect of these test compounds on spore germination and demonstrates improvement over benomyl which was used as a standard for comparison. In Table I, the lower the numeral used as a rating, the more effective the compound.

Aliquots of previously prepared solutions of active ingredient in acetone were added to tubes containing 20 ml of sterile, melted potato dextrose agar that had been cooled to 50.degree. C to provide mixtures of 40, 20, 10, 5 and 2.5 ppm. The tubes were shaken to ensure thorough mixing of the chemical with the agar, and the mixture poured into petri dishes having 4 quadrants to solidify. Each quadrant was inoculated with a 4 mm diameter disc of agar containing mycelium of the test fungi and incubated at 25.degree. C for 72-144 hours during which the samples were alternately exposed to light for 12 hours and to darkness for 12 hours. Growth was measured at the end of the incubation period by measuring the diameter of each fungus colony. Two measurements of the diameter, perpendicular to each other, were taken and the values averaged. Data are reported as percent inhibition (%I) by the following formula: ##EQU1## Captan and chlorothalonil were used as standards for comparison. The results reported in Table II indicate that the test compounds were generally more active than the standards.

The compounds of this invention were tested for corp disease control to determine the basic types of antifungal activity they exhibit.

The foliage of a tomato plant in the four leaf stage and a pinto bean in the primary leaf stage was sprayed with the test chemicals at a concentration of 150 ppm on a weight/volume basis, and the plant allowed to dry overnight.

Sporangia of Phytophthora infestans (late blight fungus) were harvested from cultures grown on lima bean agar for 10 to 14 days. A water suspension of sporangia (2 .times. 10.sup.5 sporangia/ml) was incubated at 12.degree. C for two hours in order to provide a zoospore suspension. Spores of Uromyces phaseoli (bean rust fungus) were collected from diseased plants and a 2% spore powder mixture prepared using ABB Pyrax talc as a diluent.

The tomato plants were inoculated in a spray hood with the zoospore suspension, then immediately incubated in a humidity chamber at 100% relative humidity at 18-20.degree. C for four to five days. The bean plants were inoculated by dusting the spore powder onto the leaves. This was accomplished by placing the spore powder in a cheesecloth bag and shaking the bag over the leaves. The inoculated plants were placed in the humidity chamber at 100% relative humidity and 21.degree. C for 24 hours and then placed in the greenhouse for four to six days until disease symptoms developed.

The percent disease control was then determined by comparing the disease incidence in treated plants and untreated check plants. Results reported in Table III demonstrate the efficacy of the compounds tested in preventing tomato late blight and bean rust when applied to foliage of uninfected plants at 150 ppm prior to disease infestation.

In the curative tests the plants were inoculated with the appropriate pathogen 24 hours before chemical treatment. The following host-parasite combinations were used:

Spores of bean rust and bean powdery mildew were obtained from diseased plants. Spores of Cercospora beticola and Pyricularia oryzae were harvested from petri dish cultures. C. beticola was grown on potato dextrose agar and P. oryzae on a glucose yeast extract medium. The cultures were grown at 25.degree. C for 10 days.

Beans (c. v. `Pinto`) were inoculated with rust as described in Example IV-A. Beans (c. v. `Bountiful`) at primary leaf stage were inoculated with powdery mildew by shaking diseased leaves over the test plants, thereby creating a spore deposit on leaves of the tests plants. Sugar beets and rice were inoculated by spraying a water suspension of spores of the appropriate pathogen on the foliage.

All of the plants except those inoculated with bean powdery mildew were incubated in the moisture chamber (21.degree. C) for 24 hours. The bean powdery mildew inoculated plants were incubated in the greenhouse.

The test chemical was sprayed on the foliage of the plants at 150 ppm 24 hours after inoculation. The bean and rice plants were removed from the moisture chamber and allowed to dry before chemical treatment. After treatment the plants were incubated in the greenhouse for 6-10 days. The sugar beets were sprayed while still wet, after which they were immediately returned to the moisture chamber for two days and then to the greenhouse for 10-14 days.

The results tabulated in Table III demonstrate curative activity when the compounds were applied after infection of the plant.

Containers having a volume of about 0.25 l. were 2/3 filled with topsoil and 25 cucumber c.v. Straight Eight seeds deposited on the soil surface of each pot. A suspension containing 150 ppm of the test chemical was poured over the seeds and into the soil in sufficient quantity to provide 3.75 to 3.8 mg active ingredient per pot.

Fungi used in this test were Pythium ultimum and Rhizoctonia solani. These fungi were each grown on potato dextrose agar for three to six days. The agar plus mycelium was then minced in a blender with water and 10 ml of the resulting slurry of minced mycelium poured over the seeds.

Following inoculation approximately 15 mm of topsoil was spread over the seeds, the container capped and incubated at 4.degree. C in darkness for three days, then transferred to a greenhouse (27.degree. C) for 10-14 days, at which time stand counts were made. Captan was used as a standard for comparison. Based on stand counts an Efficacy Index was calculated for each test chemical as follows: ##EQU2##

The results, set forth in Table III, show that several of the compounds tested were considerably more effective than captan while others were less effective for cucumber damping-off complex.

In a similar manner the soil around a bean seedling was drenched with a sufficient amount of 150 ppm suspension of test chemical to provide 3.8 mg active per pot. Twenty-four hours later the soil was inoculated with a suspension of minced mycelium of Fusarium solani. The inoculated plants were then placed in a greenhouse, evaluated after fourteen days, and percent control of root rot damage calculated. The results, reported in Table III, indicate that only a few of the compounds were effective under the test conditions in treating bean root rot, but these provided a high degree of control.