Cyclobutanedicarboxylic Acid Imides, and Compositions for Their Use as Phytopathogenic Fungicides

The present invention relates to novel cyclobutanedicarboxylic acid imides, to processes for producing them, to fungicidal compositions containing such compounds as active substance, as well as to the use of these compounds for combating fungi.

It is known from the JA-Patent Publication (unexamined) 74/71 141 that 3,5-dihalogenophenylcyclobutanedicarboxylic acid imides which are unsubstituted on the cyclobutane ring have antimicrobial properties, inter alia also fungicidal properties, and are suitable for example for combating fungus diseases on rice plants. The spectrum of activity of these 3,5-dihalogenophenylcyclobutanedicarboxylic acid imides is however limited. Thus, for example, 3,5-dichlorophenylcyclobutanedicarboxylic acid imide has only a weak action against Botrytis.

It has been shown that the compounds of the formula I according to the invention have excellent fungicidal properties ##STR2## wherein one of R.sub.1 and R.sub.6 is hydrogen, methyl or ethyl, and the other is methyl or ethyl, R.sub.2 and R.sub.3 independently of one another are each hydrogen, fluorine or methyl, or R.sub.2 is acetoxy or chlorine whilst R.sub.3 is hydrogen, and wherein R.sub.4 is hydrogen, methyl or chlorine, and R.sub.5 is hydrogen or methyl, whereby R.sub.3 and R.sub.4 together can also form an additional bond in the four-membered ring.

Compounds of the formula I surprisingly have pronounced activity against Botrytis. Botrytis spp. (Botrytis cinerea, Botrytis allii) constitutes, with grey mould on grape vines, strawberries, apples, onions and other fruit and vegetable varieties, a considerable economic loss factor.

The compounds of the formula I have a very favourable spectrum of action for practical requirements for the protection of cultivated plants, without affecting the plants disadvantageously by causing undesirable secondary effects. Cultivated plants within the scope of the present invention are for example: cereals, maize, rice, vegetables, sugar beet, soya bean, groundnuts, fruit trees, ornamental plants, grape vines, hops, Cucurbitaceae (cucumbers, pumpkins and melons), Solanaceae, such as potatoes, tomatoes and tobacco, as well as banana, cocoa and natural rubber plants.

Fungi occurring on plants or on parts of plants (fruit, blossom, foliage, stalks, tubers or roots) of the said crops and of relative cultivated crops can be inibited or destroyed with the active substances of the formula I, and also parts of plants subsequently growing remain preserved from such fungi. The active substances are effective against phytopathogenic fungi belonging to the following classes: Ascomycetes (for example Erysiphaceae, Fusarium or Helminthosporium); Basidiomycetes, such as in particular rust fungi (for example Puccinia and Tilletia); Fungi imperfecti (for example Moniliales and others, Cercospora, Sclerotinia and also Botrytis and Piricularia); and against Oomycetes belonging to the Phycomycetes class, such as Phytophthora or Plasmopara. The said active substances can also be used as dressing agents for the treatment of seed (fruits, tubers and grain) and of plant cuttings to protect them against fungus infections, as well as against phytopathogenic fungi occurring in the soil.

A subgroup of active substances comprises those compounds of the formula I wherein R.sub.3 and R.sub.4 form an additional bond. They are therefore compounds of the formula I which contain a cyclobutene ring.

A further subgroup of important active substances is formed by those halogen free cyclobutane compounds of the formula I wherein one of R.sub.1 and R.sub.6 is hydrogen, methyl or ethyl, and the other is methyl or ethyl, and R.sub.2, R.sub.3, R.sub.4 and R.sub.5 independently of one another are each hydrogen or methyl. The particularly preferred halogen free cyclobutane compounds are Nos. 1, 7 and 15 mentioned hereinafter.

Preferred active substances of the formula I are halo cyclobutane compounds wherein R.sub.1 and R.sub.6 have the same meaning and are methyl or ethyl, R.sub.2 is fluorine or chlorine, R.sub.3 is hydrogen, R.sub.4 is hydrogen, chlorine or methyl and R.sub.5 is hydrogen or methyl.

Particularly preferred are compounds of the formula I wherein R.sub.1 and R.sub.6 are each methyl, R.sub.2 is fluorine, R.sub.3 is hydrogen, R.sub.4 and R.sub.5 independently of one another are hydrogen or methyl. The particularly preferred fluorine compounds are Nos. 2 and 9 mentioned hereinafter.

The compounds of the formula I can be produced in good yields, using a simple and economical process, by

(a) reaction of a compound of the formula II ##STR3## with a compound of the formula III ##STR4## by irradiation at a wavelength shorter than 5000 Angstrom units, in the manner of a photochemical [2+2] cycloaddition, or

(b) stepwise reaction of a compound of the formula III with a compound of the formula IV ##STR5## firstly by irradiation at a wavelength shorter than 5000 Angstrom units, thus effecting photochemical [2+2] cycloaddition, to form a compound of the formula V ##STR6## further reaction of this with 3,5-dichloroaniline to form an amidocarboxylic acid of the formula VI ##STR7## and subsequently cyclisation of VI by intramolecular removal of water, whereby R.sub.1 to R.sub.6 in the formulae II to VI have the meanings given for the formula I. The preferred method of production is that according to process variant (a). The preferred reactant III in either process (a) or (b) is alkenylfluoride and -chloride, preferably vinylfluoride.

The photochemical [2+2] cycloaddition reaction according to the invention of compounds of the formula III with compounds of the formula II or IV is favourable in particular also from the ecological viewpoint. The reaction proceeds surprisingly without dimers of maleic anhydrides or imides being formed, such as those always formed otherwise in comparable photochemical cycloaddition reactions [see for example Chem. Ber., 110, 2986-2995 (1977); Chem. Ber., 96, 498-508 (1962) and Chem. Ber., 98, 764-780 (1965); particularly Zhurnal Organischeskoi Khimii, Vol. 8, No. 2, pp. 377-382 (Feb. 1972)]. Special emphasis should be put on the fact that fluorinated and chlorinated representatives of the reactant III react in either process (a) and (b) without noteworthy side reactions.

The photochemical [2+2] cycloaddition reaction of the compounds of the formula III with compounds of the formula II or IV is advantageously performed in the presence of an inert organic solvent at temperatures of between about -80.degree. C. and +30.degree. C., preferably between about -78.degree. C. and -20 C.

Suitable inert organic solvents are for example: optionally chlorinated aliphatic or aromatic hydrocarbons, such as dichloromethane, 1,2-dichloroethane, 1,2,3-trichloropropane, 1,1,2,2-tetrachloroethane, benzene, chlorobenzene and dichlorobenzenes; aliphatic carboxylic acid esters, such as methyl acetate and ethyl acetate, dialkyl ethers having 2-6 C atoms in each of the alkyl parts, such as diethyl ether, di-n-propyl ether and di-isopropyl ether; cyclic ethers, such as dioxane and tetrahydrofuran; alkyl nitriles, particularly those having 2-5 C atoms, such as acetonitrile, proprionitrile and butyronitrile. Preferred solvents are chlorinated aliphatic hydrocarbons, especially dichloromethane. Also suitable is acetone or methyl ethyl ketone.

Compounds known per se can be used as sensitisers for the photochemical cycloaddition reactions mentioned above, preferably such compounds which have an E.sub.T (triplet energy) of .gtoreq.230 kJ/mol [see Paul S. Engel and Bruce M. Monroe "Advance in Photochemistry", Vol. 8, pp. 297-306, New York 1971]. Examples of sensitisers of this kind are benzophenone, acetophenone, m-methoxy-acetophenone, thioxanthone and biacetyl. The sensitiser preferably used is benzophenone. The sensitiser is in general used in an amount of about 0.5-10 percent by weight, relative to the starting compound of the formula II or IV.

For the photochemical reactions according to the invention, there can be used light sources which emit light at wavelengths of below 5000 A, for example optionally metal-atom-doped high-pressure mercury vapour lamps, xenon vapour lamps, mercury-xenon lamps, mercury low-pressure or medium-pressure lamps, halogen lamps or D.sub.2 lamps.

The photochemical reactions are advantageously carried out in a low-temperature irradiation apparatus. An approximately 2-20% solution of the compound of the formula II or IV together with the sensitiser is placed into the irradiation apparatus; the solution is then saturated, by way of a gas-inlet, with the desired compound of the formula III, and the reaction mixture is subsequently irradiated for about 2-10 hours depending on concentration, quantum yield and photon flux. The reaction product is processed for example by concentrating the reaction solution by evaporation, and recrystallising the crude product from suitable organic solvents, preferably from mixtures of dichloromethane and n-hexane. The resulting products of the formulae I and V, respectively, are analytically pure.

The reaction of the anhydrides of the formula V with 3,5-dichloroaniline is performed in a manner known per se, advantageously without solvent at temperatures of between about 80.degree. and 120.degree. C., or in an organic medium at temperatures of between about 20.degree. and 120.degree. C. Suitable organic solvents are for example: optionally chlorinated aliphatic or aromatic hydrocarbons, such as benzene, toluene, xylene, dichloromethane, chloroform, carbon tetrachloride and o-dichlorobenzene; aliphatic or cycloaliphatic ketones, such as acetone, methyl ethyl ketone, cyclopentanone and cyclohexanone; also dialkyl ethers having 2-6 C atoms in each of the akyl, parts, and cyclic ethers, such as tetrahydrofuran and dioxane.

Cyclisation of the amidocarboxylic acids of the formula VI with separation of water is performed thermally by customary methods, that is to say, by mere heating of the reaction mixture, or with the use of known dehydrating agents at temperatures between about 20.degree. and 120.degree. C. Suitable dehydrating agents are in particular anhydrides of aliphatic monocarboxylic acids which have 2-5 C atoms and which are unsubstituted or are subsituted by halogen atoms or alkyl groups, such as anhydrides of acetic acid, propionic acid, butyric acid and valeric acid, and anhydrides of trichloro-, trifluoro-, trimethyl-, triethyl- and tri-n-butylacetic acid. A preferred dehydrating agent is acetic acid anhydride.

The reaction of the anhydrides of the formula I with 3,5-dichloroaniline can be performed also without the addition of solvents, the formed amidocarboxylic acids being then advantageously thermally cyclised, that is to say, by dry heating.

The starting compounds of the formulae II, III and IV and 3,5-dichloroaniline are known, and can be produced by methods known per se. Compounds of the formula II can be obtained for example by reaction of anhydrides of the formula IV with 3,5-dichloroaniline.

The invention also relates to the novel intermediates of the formula VI as well as to the intermediates of the formula V, wherein one of the substitutents R.sub.1 and R.sub.6 is hydrogen, methyl or ethyl and the other is methyl or ethyl, R.sub.3 and R.sub.3 independently of one another are each hydrogen, fluorine or methyl, or R.sub.2 is acetoxy or chlorine whilst R.sub.3 is hydrogen, and wherein R.sub.4 is hydrogen, methyl or chlorine and R.sub.5 is hydrogen or methyl. The invention particularly relates to compounds of the formula V or VI, wherein R.sub.1 and R.sub.6 have the same meaning and are methyl or ethyl, R.sub.2 is fluorine or chlorine, R.sub.3 is hydrogen, R.sub.4 is hydrogen, chlorine or methyl and R.sub.5 is hydrogen or methyl. Said intermediates can be used for preparing valuable fungicides of the formula I.

In a low-temperature irradiation apparatus, provided with a 125 W high-pressure mercury vapour lamp in a cooled Pyrex immersion well, stirrer and gas-inlet tube, 10 g (0.037 mol) of 2,3-dimethylmaleic acid-(3,5-dichlorophenyl)-imide and 1.0 g (0.0055 mol) of benzophenone in 220 ml of dichloromethane are introduced, and are cooled, by means of an external cooling bath containing an acetone/dry-ice mixture, to -50.degree. to -55.degree. C. Vinyl fluoride is now passed through this solution for 2 hours, and the solution is subsequently irradiated for 6hours, during which time a weak flow of vinyl fluoride through the solution is maintained. The solvent is then evaporated off to leave 4.8 g of white crystals. Recrystallisation from dichloromethane/n-hexane yields 4.0 g (47% of theory) of 1,2-dimethyl-3-fluorocyclobutane-1,2-dicarboxylic acid-(3,5-dichlorophenyl)-imide in the form of white crystals; m.p. 122.degree.-123.degree. C. NMR spectrum (100 MHz, CDCl.sub.3, .delta. in ppm): 1.4 (m, 6H, 2CH.sub.3); 2.0-3.0 (m, 2H, --CH.sub.2 --); 4.6-5.4 (2m, --CHF--); 7.2-7.4 (m, 3H, aromat.). IR spectrum KBr, cm.sup.-1, vs=very strong, s=strong, m=medium, w=weak): 1700.sup.vs, 1590.sup.m, 1585.sup.s, 1450.sup.s, 1450.sup.s, 1360.sup.s, 1150.sup.s, 805.sup.s. Compound No. 2.

In a manner analogous to that described in Example 1, there are produced:

1,2-dimethyl-cyclobutane-1,2-dicarboxylic acid-(3,5-dichlorophenyl)-imide, m.p. 149.degree.-152.degree. C., starting with 2,3-dimethylmaleic acid-(3,5-dichlorophenyl)-imide and ethylene Compound No. 1;

1,2,3-trimethyl-cyclobutane-1,2-dicarboxylic acid-(3,5-dichlorophenyl)-imide, m.p. 88.degree.-89.degree. C., starting with 2,3-dimethylmaleic acid-(3,5-dichlorophenyl)-imide and 1-propene: Compound No. 3;

3,3-difluoro-1,2-dimethyl-cyclobutane-1,2-dicarboxylic acid-(3,5-dichlorophenyl)-imide, m.p. 135.degree.-140.degree. C., starting with 2,3-dimethylmaleic acid-(3,5-dichlorophenyl)-imide and ,1-difluoroethylene: Compound No. 4;

2-ethyl-1-methyl-cyclobutane-1,2-dicarboxylic acid-3,5-dichlorophenyl)-imide, m.p. 91.degree.-93.degree. C., starting with 2-ethyl-3-methylmaleic acid-(3,5-dichlorophenyl)-imide and ethylene: Compound No. 5); and

1,2,3,4-tetramethyl-cyclobutane-1,2-dicarboxylic acid-(3,5-dichlorophenyl)-imide, m.p. 81.degree.-83.degree. C., starting with 2,3-dimethylmaleic acid-(3,5-dichlorophenyl)-imide and trans-2-butene: Compound No. 6).

(a) In a low-temperature irradiation apparatus, provided with a 125 W high-pressure mercury vapour lamp in a cooled Pyrex immersion well, stirrer and gas-inlet tube, 15 g (0.12 mol) of dimethylmaleic acid anhydride and 1 g of benzophenne (0.0054 mol) are dissolved in 300 ml of dichloromethane, and the solution is cooled, by means of an external cooling bath containing an isopropanol/dry-ice mixture, to -60.degree. to -70.degree. C.; ethylene is passed through for 1 hour, and the solution is irradiated at this, temperature for 12 hours whilst a weak flow of ethylene passes through the solution. The solvent is then evaporated off, and the crude product is recrystallised from dichloromethane/n-hexane. The yield is 10 g of 1,2-dimethyl-cyclobutane-1,2-dicarboxylic acid anhydide (54% of theory) in the form of white crystals; m.p. 84.degree.86.degree. C. NMR Spectrum (100 MHz), .delta. in ppm: 1.4 (s, 6H, 2CH.sub.3); 2.0-2.5 (m, 4H, --CH.sub.2 CH.sub.2 --). IR Spectrum (KBr, cm.sup.-1, vs=very strong, s=strong, m=medium, w=weak): 2940.sup.m, 1850.sup.s, 1780.sup.vs, 1470.sup.m, 1445.sup.m, 1300.sup.s, 1280.sup.s, 1240.sup.s, 1170.sup.vs, 970.sup.vs, 950.sup.vs and 920.sup.vs.

(b) 15.4 g (0.1 mol) of 1,2-dimethyl-cyclobutane-1,2-dicarboxylic acid anhydride are dissolved in 100 ml of toluene, and 16.2 g (0.1 mol) of 3,5-dichloroaniline are added. After 16 hours' stirring at 25.degree. C., the colourless amidocarboxylic acid which has precipitated is separated. The yield is 27.8 g of 1-(3,5-dichlorophenylcarbamoyl)-1,2-dimethylcyclobutane-1-carboxylic acid (88% of theory), m.p. 164.degree. C. NMR Spectrum (50 MHz) .delta. in ppm: 1.34 (s, 3H, CH.sub.3); 1.45 (s, 3H, CH.sub.3); 1.6-3.0 (m, 4H, --CH.sub.2 CH.sub.2 --); 6.9 (m, 1H, aromat.); 7.6 (m, 2H, aromat.); 8.75 (s, 1H, --COOH, exchangeable with D.sub.2 O).

Elementary analysis for C.sub.14 H.sub.15 Cl.sub.2 NO.sub.3 (molecular weight 316.2): calculated: C 53.2% H 4.8% N 4.4% O 15.2% Cl 22.4%: found: C 53.2% H 4.8% N 4.7% O 15.2% Cl 22.5%.

(C.sub.1) 14.3 g of the above amidocarboxylic acid in 100 ml of cetic anhydride are refluxed for 6 hours. After cooling, the imide which has precipitated is filtered off. The yield is 10.3 g (77% of theory) of 1,2-dimethyl-cyclobutane-1,2-dicarboxylic acid-(3,5-dichlorophenyl)-imide, the properties of which correspond to those of the compound produced according to Example 1.

(c.sub.2) Cyclisation of the amidocarboxylic acid can also be performed by heating 3.2 g (0.01 mol) of 1-(3,5-dichlorophenylcarbamoyl)-1,2-dimethylcyclobutane-1-carboxylic acid for 2 hours at 160.degree. C. After cooling, the crude product is recrystallised from ethyl acetate. The yield is 1.3 g (44% of theory) of 1,2-dimethyl-cyclobutane-1,2-dicarboxylic acid-(3,5-dichlorophenyl)-imide.

1,2-Dimethyl-cyclobutane-1,2-dicarboxylic acid-(3,5-dichlorophenyl)-imide can also be produced as follows:

(c.sub.3) 7.7 g (0.05 mol) of 1,2-dimethylcyclobutane-1,2-dicarboxylic acid anhydride with 8.1 (0.05 mol) of 3,5-dichloroaniline are heated for 8 hours at 180.degree. C. After cooling, the crude product is recrystallised from ethyl acetate to obtain 5.1 g (34% of theory) of 1,2-dimethylcyclobutane-1,2-dicarboxylic acid-(3,5-dichlorophenyl)-imide, the properties of which are identical to those of the compound produced according to Example 1.

(c.sub.4) 7.7 g (0.05 mol) of 1,2-dimethylcyclobutan-1,2-dicarboxylic acid anhydride and 8.1 g (0.05 mol) of 3,5-dichloroaniline are dissolved in 100 ml of xylene, and the solution is refluxed for 8 hours with use of a water separator. The reaction solution is cooled, and the imide which has precipitated is filtered off. The yield is 11.6 g (78% of theory) of 1,2-dimethylcyclobutane-1,2-dicarboxylic acid-(3,5-dichlorophenyl)-imide.

(a) By a procedure analogous to that described in Example 7 (a), 1-methyl-cyclobutane-1,2-dicarboxylic acid anhydride (m.p. 59.degree.-60.degree. C.) is produced by reaction of citraconic anhydride with ethylene.

(b) 10 g (0.07 mol) of 1-methyl-cyclobutane-1,2-dicarboxylic acid anhydride are dissolved in 50 ml of toluene, and 11.6 g (0.07 mol) of 3,5-dichloroaniline are added. After 24 hours' stirring at room temperature, the amide acid (m.p. 106.degree.-108.degree. C.) which has precipitated is separated. This amidocarboxylic acid is suspended in 40 ml of acetic anhydride, and the suspension is stirred for 24 hours at room temperature, in the course of which everything goes into solution. The acetic anhydride is evaporated off in a water-jet vacuum, and the pulverulent residue is recrystallised from dichloromethane/n-hexane to yield 15 g (73% of theory) of 1-methyl-cyclobutane-1,2-dicarboxylic acid-(3,5-dichlorophenyl)-imide, m.p. 110.degree.-111.degree. C. NMR Spectrum (100 MHz) .delta. in ppm: 1.55 (s,3H, CH.sub.3), 2.0-3.2 (m, 5H, --CH.sub.2 CH.sub.2 --CH--), 7.2-7.5 (m, 3H, aromat.). Compound No. 7.

The following compounds of the formula I are produced in a manner analogous to that of Example 8: (R.sub.5 =H):

Production of ##STR8## 1,2-dimethyl-cyclobut-3-ene-1,2-dicarboxylic acid-(3,5-dichlorophenyl)-imide [Compound No. 15].

(a) In a manner according to that of Example 7 (a), acetylene is passed through 10 g (0.079 mol) of 2,3-dimethylmaleic acid anhydride and 1 g (0.0054 mol) of benzophenone in 250 ml of dichloromethane at -60.degree. C. for 1 hour, and the reaction mixture is subsequently irradiated for 6 hours whilst a weak flow of acetylene is maintained. After the solvent has been evaporated off and the crude product has been recrystallised from dichloromethane/hexane, the yield is 7.5 g (62% of theory) of 1,2-dimethylcyclobut-3-ene-1,2-dicarboxylic acid anhydride, m.p. 84.degree.-86.degree. C.

(b) 6.9 g (0.0454 mol) of the intermediate produced according to (a) in 50 ml of toluene with 7.4 g (0.0454 mol) of 3,5-dichloroaniline are stirred for 24 hours at room temperature. The white precipitate obtained is stirred in 50 ml of acetic anhydride for 48 hours at room temperature and for 8 hours at 40.degree. C. The oil obtained after concentration by evaporation is recrystallised from dichloromethane/hexane. The yield of final product is 3.6 g (27% of theory), m.p. 158.degree.-160.degree. C.

In a corresponding manner are obtained the following compounds of the formula I in which R.sub.3 and R.sub.4 form an additional bond in the four-membered ring:

Any of the compounds of the formula I can in fact be produed by photochemical reaction both with the desired imide and with the desired anhydride (and subsequent further reaction with 3,6-dichloroaniline), that is to say, by either of the process variants (a) or (b) outlined in the text and further illustrated in the Example 1 to 9.

The compounds of the formula I can be used on their own or together with suitable carriers and/or other additives. Suitable carriers and additives can be solid or liquid and they correspond to the substances common in formulation practice, such as natural or regenerated mineral substances, solvents, dispersing agents, wetting agents, adhesives, thickeners, binders and/or fertilisers. Active substances of the formula I can be used in admixture with other pesticidal preparations or with preparations for improving plant growth.

The content of active substance in commercial compositions is between 0.1 and 90%.

For application, the compounds of the formula I can be in the following forms (the weight-percentage figures in brackets signify advantageous amounts of active substance):

The active substances are intimately mixed in suitable mixers with the additives, and the mixture is then ground in the appropriate mills and rollers. There are obtained wettable powders which have excellent wetting and suspension properties, and which can be diluted with water to give suspensions of the desired concentration, and these suspensions are particularly suitable for leaf application.

Emulsifiable concentrate: The following substances are used to produce a 25% emulsifiable concentrate:

25 parts of active substance,

2.5 parts of epoxidised vegetable oil,

10 parts of an alkylarylsulfonate/fatty alcohol polyglycol ether mixture,

5 parts of dimethylformamide, and

57.5 parts of xylene.

Emulsions of the concentration required can be prepared from these concentrates by dilution with water, and they are particularly suitable for leaf application.

Bean plants about 10 cm in height were sprayed with a spray liquor produced from wettable powder of the active susgstance (0.006% and 0.002%, respectively, of active substance), and after 48 hours, the treated plants were infested with a conidiospore suspension of the fungus. After incubation of the infested plants for 2-3 days with 95-100% relative humidity at 21.degree. C., and assessment of the fungus infection was made. With an application concentration of 0.006%, all compounds of the formula I, namely compounds Nos. 1 to 18, effected complete prevention of infection (0-5% fungus infection). At a concentration of 0.002%, infection was completely prevented by compounds Nos. 1, 2, 5, 7, 9, 10, 15 and 16 (0-5% fungus infection), and was greatly reduced by the remainder of the 18 compounds listed (5-20% fungus infection).

Artificially damaged apples were infested with Sclerotinia fructigena by transferring by pipette to each site of damage one drop of a mycelium suspension. After drying of the inoculum drop, the apples were sprayed with a wettable-powder suspension of the active substance (0.02% of active substance). The treated apples were placed into plastics containers and stored at 20.degree.-22.degree. C. for 14 days. An evaluation was made on the basis of the number of damage sites which has begun to rot. With compounds Nos. 1, 5, 7, 9, 10, 15 and 18, infection had been prevented almost completely (below 10% infection). No infection at all occurred after treatment with Compound No. 2.

Barley plants about 8 cm high were sprayed with a spray liquid produced from wettable powder of the active substance (0.02% of active substance). After 3-4 hours, the treated plants were dusted with conidia of the fungus. The infested barley plants were left in a greenhouse at about 22.degree. C. and the level of fungus infection was assessed after 10 days. Fungus infection was completely prevented by, among others, Compounds Nos. 11, 12, 14 and 16.

A number of completely blossomed stone-fruit branches were sprayed with a spray liquor produced from an emulsion concentrate (containing 0.025% of active substance). A few hours later, the blossom clusters were cut off, placed with the stems into the moist sand contained in plastic dishes and inoculated with a spore suspension. The dishes were then loosely covered with transparent plastic sheet and were kept at room temperature for 2 days. The extent of infection was estimated on the basis of the number of infected blossoms, 40 blossoms being used per active substance. The compounds Nos. 1 to 18 effected a reduction of infection to below 20%. Some compounds prevented infection completely, for example Compounds Nos. 2 and 7.

The best mode of the invention is represented by 1,2-dimethyl-3-fluorocyclobutane-1,2-dicarboxylic acid-(3,5-dichlorophenyl)-imide, its process for manufacture and its use for preventing fungus infection.