N-Phenylsulfonyl-N'-Triazinylureas

The present invention relates to novel N-phenylsulfonyl-N'-triazinylureas having herbicidal and plant growth-regulating properties, to the production thereof, to compositions containing them, and to the use thereof for controlling weeds, in particular selectively, in crops of useful plants, or for regulating and inhibiting plant growth.

The N-phenylsulfonyl-N'-triazinylureas of this invention have the general formula I ##STR2## wherein A is difluoromethyl or 1,1,2,2-tetrafluoroethyl,

X is oxygen, sulfur, a sulfinyl or sulfonyl bridge,

Z is oxygen or sulfur and

R.sub.3 and R.sub.4, each independently of the other, are hydrogen, C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy, C.sub.1 -C.sub.4 alkylthio, C.sub.1 -C.sub.4 haloalkyl, halogen or alkoxyalkyl of at most 4 carbon atoms.

Herbicidally active ureas, triazines and pyrimidines and are generally known in the art. Arylsulfamoyl-heterocyclylaminocarbamoyl compounds with herbicidal and plant-growth-regulating action have recently been described, for example in European patent publications 1514 and 1515, U.S. Pat. No. 4,127,405, German Offenlegungsschrift No. 2 715 786 or French patent specification No. 1 468 747.

In the above definitions, alkyl denotes straight-chain or branched alkyl, e.g. methyl, ethyl, n-propyl, isopropyl, the four isomers of butyl, n-amyl, isoamyl, 2-amyl, 3-amyl, n-hexyl or isohexyl.

Alkoxy denotes methoxy, ethoxy, n-propyloxy, isopropyloxy and the four butyloxy isomers, and is, in particular, methoxy, ethoxy or isopropyloxy.

Alkylthio is e.g. methylthio, ethylthio, n-propylthio, isopropylthio and n-butylthio, with methylthio and ethylthio being preferred.

Examples of alkenyl radicals are vinyl, allyl, isopropenyl, 1-propenyl, 1-butenyl, 2-butenyl, 3-butenyl, 1-isobutenyl, 2-isobutenyl, 1-pentenyl, 2-pentenyl, 3-pentenyl and 4-pentenyl, with vinyl, allyl and 4-pentenyl being preferred.

Alkylsulfinyl is e.g. methylsufinyl, ethylsulfinyl, n-propylsulfinyl and n-butylsulfinyl, with methylsulfinyl and ethylsulfinyl being preferred.

Alkylsulfonyl is e.g. methylsulfonyl, ethylsulfonyl, n-propylsulfonyl and n-butylsulfonyl, with methylsulfonyl and ethylsulfonyl being preferred.

Halogen in the definitions of R.sub.1 and R.sub.2 and in haloalkyl, haloalkoxy, haloalkylsulfinyl, haloalkylsulfonyl and haloalkylthio is fluorine, chlorine and bromine, with fluorine and chlorine being preferred.

A haloalkyl radical A is a radical which carries one or more halogen atoms. Preferably several hydrogen atoms, and optionally even all hydrogen atoms, of the alkyl radicals are replaced by halogen atoms.

The invention also comprises the salts which the compounds of formula I are able to form with amines, alkali metal and alkaline earth metal bases or quaternary ammonium bases.

Preferred salt-forming alkali metal and alkaline earth metal hydroxides are the hydroxides of lithium, sodium, potassium, magnesium or calcium, most preferably of sodium or potassium.

Examples of suitable salt-forming amines are primary, secondary and tertiary aliphatic and aromatic amines such as methylamine, ethylamine, propylamine, isopropylamine, the four isomeric butylamines, dimethylamine, diethylamine, diethanolamine, dipropylamine, diisopropylamine, di-n-butylamine, pyrrolidine, piperidine, morpholine, trimethylamine, triethylamine, tripropylamine, quinuclidine, pyridine, quinoline and isoquinoline. Preferred amines are ethylamine, propylamine, diethylamine or triethylamine, with isopropylamine and diethanolamine being most preferred.

Examples of quaternary ammonium bases are, in general, the cations of haloammonium salts, e.g. the tetramethylammonium cation, the trimethylbenzylammonium cation, the triethylbenzylammonium cation, the tetraethylammonium cation, the trimethylethylammonium cation, and also the ammonium cation.

Preferred compounds of the formula I are those in which

(a) Z is oxygen and

(b) R.sub.3 and R.sub.4 together contain not more than 4 carbon atoms.

A preferred group of compounds in group (a) comprises those compounds in which both radicals --X--A are in the 2 und 5-position to the sulfonyl group.

A further preference in connection with compounds of the above subgroup consists in the feature that the radicals R.sub.3 and R.sub.4 together contain at most 4 carbon atoms. Accordingly, a particularly preferred group of compounds of formula I is the group in which the two radicals --X--A are in the 2- and 5-position to the sulfonyl radicals, and R.sub.3 and R.sub.4 together contain not more than 4 carbon atoms.

Preferred compounds belonging to the group are those in which A is --CHF.sub.2.

A preferred individual compound is N-[2,5-bis-(difluoromethoxy)phenylsulfonyl]-N'-(4-methoxy-6-methyl-1,3,5-t riazin-2-yl)urea.

The process for obtaining the compounds of formula I is carried out in an inert organic solvent.

In a first process, the compounds of the formula I are ontained by reacting a phenylsulfonamide of the formula II ##STR3## wherein A and X are as defined for formula I, in the presence of a base, with a N-triazinyl-carbamate of the formula III ##STR4## wherein R.sub.3, R.sub.4 and Z are as defined for formula I.

In a second process, compounds of formula I are obtained by reacting a phenylsulfonylisocyanate or phenylsulfonylisothiocyanate of the formula IV ##STR5## wherein A, X and Z are as defined for formula I, optionally in the presence of a base, with an amine of the formula V ##STR6## wherein R.sub.3 and R.sub.4 are as defined for formula V.

In a further process, the compounds of formula I are obtained by reacting a sulfonamide of the formula II above, optionally in the presence of a base, with an isocyanate or isothiocyanate of the formula VI ##STR7## wherein R.sub.3, R.sub.4 and Z are as defined for formula I.

Finally, the compound of formula I can also be obtained by reacting a N-phenylsulfonylcarbamate of the formula VII ##STR8## wherein A and X are as defined for formula I, with an amine of the formula V above.

If desired, the ureas of formula I can be converted into salts with amines, alkali metal or alkaline earth metal hydroxides or quaternary ammonium bases. This conversion is carried out e.g. by reacting the compounds of formula I with the equimolar amount of a base and removing the solvent by evaporation.

Some of the starting materials of the formulae II, IV and VII are novel and can be prepared by the following methods.

The novel sulfonamides of formula II used as intermediates are obtained from the corresponding anilines by diazotisation and replacement of the diazo group, with sulfur dioxide, in the presence of a catalyst such as copper(I) chloride, in hydrochloric acid or acetic acid, and reacting the resultant phenylsulfonyl chloride with ammonium hydroxide solution.

The phenylsulfonylisocyanates of the formula IV can be obtained by reacting the sulfonamides of the formula II with phosgene, in the presence of butylisocyanate in a chlorinated hydrocarbon as solvent, at reflux temperature. Similar reactions are described in "Newer Methods of Preparative Organic Chemistry", Vol. VI, 223-241, Academic Press, New York and London.

The isothiocyanates of the formula IV are obtained by treating the sulfonamides of formula II with carbon disulfide and potassium hydroxide and by subsequent reaction of the dipotassium salt with phosgene. Such processes are described in Arch. Pharm. 299, 174 (1966).

The N-phenylsulfonylcarbamates of the formula VII are obtained by reacting the sulfonamides of the formula II with diphenyl carbonate in the presence of a base. Similar processes are described in Japanese patent specification 61 169.

The starting materials of the formulae III, V and VI are known or they can be prepared by known methods.

Isocyanates of the formula VI can be prepared by reacting amines of the formula V with oxalyl chloride in a chlorinated hydrocarbon as solvent. Amines of the formula V are known and some are commercially available, or they can be prepared by known methods, q.v. "The Chemistry of Heterocyclic Compounds", Vol. XIV, Interscience Publishers, New York, London.

It is expedient to carry out the reactions for obtaining compounds of formula I in aprotic, inert organic solvents such as methylene chloride, tetrahydrofurane, acetonitrile, dioxane or toluene.

The reaction temperatures are preferably in the range from -20.degree. and +120.degree. C. The reactions are normally slightly exothermic and can be carried out at room temperature. To shorten the reaction time or also to initiate the reaction it is expedient to heat the reaction mixture briefly to boiling point. The reaction times can also be shortened by addition of a few drops of a base or isocyanate as catalyst.

The final products can be isolated by concentrating the reaction mixture and/or removing the solvent by evaporation, and by recrystallisation or by triturating the solid residue in solvents in which it is poorly soluble, such as ether, aromatic hydrocarbons or chlorinated hydrocarbons.

The compounds of formula I are stable compounds, and no protective measures are required for handling them.

The compounds of formula I have pronounced plant growth-regulating, especially plant growth-inhibiting, properties. The growth of both monocots and dicots is inhibited. Thus, for example, the compounds of formula I selectively inhibit the growth of leguminosae which are frequently planted as cover crops in tropical regions, so that, while soil erosion between cultivated plants is prevented, the cover crops cannot compete with the cultivated plants.

Further, the compounds of formula I are suitable for preventing stored potatoes from seeding. During winter storage, potatoes often develop sprouts which result in shrinkage, weight loss, and rot.

When the compounds of formula I are applied in higher rates of application, all tested plants are so damaged in their development that they wither. When used in lower rates of application, the compounds of formula I have good selective growth-inhibiting and selective herbicidal properties which make them most suitable for use in crops of useful plants, especially in cereals, cotton, soybeans, maize and rice. In some cases damage is also caused to weeds which have up to now have only been controlled with total herbicides.

The mode of action of these compounds is unusual. Many are translocatable, i.e. they are absorbed by the plant and transported to other parts of it where they then deploy their action. The unusual feature of the compounds is that they do not only take the path through the vascular bundle in the ligneous part from the roots to the leaves, but can also be translocated through the sieve tubes in the bast part of the leaves back into the roots. Thus, for example, it is possible to damage perennial weeds to the very roots by surface treatment. Compared with other herbicides and growth regulators, the novel compounds of the formula I are effective even when used in very low rates of application.

The invention also relates to herbicidal and plant growth-regulating compositions which contain a novel compound of the formula I, and also to methods of controlling weeds pre- and postemergence and of inhibiting the growth of monocots and dicots, especially grasses, tropical cover crops and tobacco plant suckers.

The compounds of the formula I are used in unmodified form or preferably together with the adjuvants conventionally employed in the art of formulation, and are therefore formulated in known manner to emulsifiable concentrates, directly sprayable or dilutable solutions, dilute emulsions, wettable powders, soluble powders, dusts, granulates, and also encapsulations in e.g. polymer substances. The methods of application, such as spraying, atomising, dusting, scattering or pouring, are chosen in accordance with the intended objectives and the prevailing circumstances, just like the nature of the compositions.

The formulations, i.e. the compositions or preparations containing the compound (active ingredient) of the formula I and, where appropriate, a solid or liquid adjuvant, are prepared in known manner, e.g. by homogeneously mixing and/or grinding the active ingredients with extenders, e.g. solvents, solid carriers and, where appropriate, surface-active compounds (surfactants).

Suitable solvents are: aromatic hydrocarbons, preferably the fractions containing 8 to 12 carbon atoms, e.g. xylene mixtures or substituted naphthalenes, phthalates such as dibutyl phthalate or dioctyl phthalate, aliphatic hydrocarbons such as cyclohexane or paraffins, alcohols and glycols and their ethers and esters, such as ethanol, ethylene glycol, ethylene glycol monomethyl or monoethyl ether, ketones such as cyclohexanone, strongly polar solvents such as N-methyl-2-pyrrolidone, dimethyl sulfoxide or dimethyl formamide, as well as epoxidised vegetable oils such as epoxidised coconut oil or soybean oil; or water.

The solid carriers used e.g. for dusts and dispersible powders are normally natural mineral fillers such as calcite, talcum, kaolin, montmorillonite or attapulgite. In order to improve the physical properties it is also possible to add highly dispersed silicic acid or highly dispersed absorbent polymers. Suitable granulated adsorptive carriers are porous types, for example pumice, broken brick, sepiolite or bentonite; and suitable nonsorbent carriers are materials such as calcite or sand. In addition, a great number of pregranulated materials of inorganic or organic nature can be used, e.g. especially dolomite or pulverised plant residues.

Depending on the nature of the compound of formula I to be formulated, suitable surface-active compounds are nonionic, cationic and/or anionic surfactants having good emulsifying, dispersing and wetting properties. The term "surfactants" will also be understood as comprising mixtures of surfactants.

Suitable anionic surfactants can be both water-soluble soaps and water-soluble synthetic surface-active compounds.

Suitable soaps are the alkali, alkaline earth or unsubstituted or substituted ammonium salts of higher fatty acids (C.sub.10 -C.sub.22), e.g. the sodium or potassium salts of oleic or stearic acid, or of natural fatty acid mixtures which can be obtained e.g. from coconut oil or tallow oil. Mention may also be made of fatty acid methyltaurin salts.

More frequently, however, so-called synthetic surfactants are used, especially fatty sulfonates, fatty sulfates, sulfonated benzimidazole derivatives or alkylarylsulfonates.

The fatty sulfonates or sulfates are usually in the form of alkali, alkaline earth or unsubstituted or substituted ammonium salts and contain a C.sub.8 -C.sub.22 alkyl radical which also includes the alkyl moiety of acyl radicals, e.g. the sodium or calcium salt of lignosulfonic acid, of dodecylsulfate or of a mixture of fatty alcohol sulfates obtained from natural fatty acids. These compounds also comprise the salts of sulfuric acid esters and sulfonic acids of fatty alcohol/ethylene oxide adducts. The sulfonated benzimidazole derivatives preferably contain 2 sulfonic acid groups and one fatty acid radical containing 8 to 22 carbon atoms. Examples of alkylarylsulfonates are the sodium, calcium or triethanolamine salts of dodecylbenzenesulfonic acid, dibutylnaphthalenesulfonic acid, or of a naphthalenesulfonic acid/formaldehyde condensation product. Also suitable are corresponding phosphates, e.g. salts of the phosphoric acid ester of an adduct of p-nonylphenol with 4 to 14 moles of ethylene oxide.

Non-ionic surfactants are preferably polyglycol ether derivatives of aliphatic or cycloaliphatic alcohols, or saturated or unsaturated fatty acids and alkylphenols, said derivatives containing 3 to 30 glycol ether groups and 8 to 20 carbon atoms in the (aliphatic) hydrocarbon moiety and 6 to 18 carbon atoms in the alkyl moiety of the alkylphenols.

Further suitable non-ionic surfactants are the water-soluble adducts of polyethylene oxide with polypropylene glycol, ethylenediaminepolypropylene glycol and alkylpolypropylene glycol containing 1 to 10 carbon atoms in the alkyl chain, which adducts contain 20 to 250 ethylene glycol ether groups and 10 to 100 propylene glycol ether groups. These compounds usually contain 1 to 5 ethylene glycol units per propylene glycol unit.

Representative examples of non-ionic surfactants are nonylphenol-polyethoxyethanols, castor oil polyglycol ethers, polypropylene/polyethylene oxide adducts, tributylphenoxypolyethoxyethanol, polyethylene glycol and octylphenoxypolyethoxyethanol. Fatty acid esters of polyoxyethylene sorbitan and polyoxyethylene sorbitan trioleate are also suitable non-ionic surfactants.

Cationic surfactants are preferably quaternary ammonium salts which contain, as N-substituent, at least one polyglycol ether or C.sub.8 -C.sub.22 alkyl radical and, as further substituents, lower unsubstituted or halogenated alkyl, benzyl or lower hydroxyalkyl radicals. The salts are preferably in the form of halides, methylsulfates or ethylsulfates, e.g. stearyltrimethylammonium chloride or benzyldi(2-chloroethyl)ethylammonium bromide.

The surfactants customarily employed in the art of formulation are described e.g. in the following publications: "McCutcheon's Detergents and Emulsifiers Annual", MC Publishing Corp., Ridgewood, N.J., 1979; Sisley and Wood, "Encyclopedia of Surface Active Agents", Chemical Publishing Co. Inc., New York, 1964.

The pesticidal formulations usually contain 0.1 to 95%, preferably 0.1 to 80%, of a compound of the formula I, 1 to 99.9% of a solid or liquid adjuvant, and 0 to 25%, preferably 0.1 to 25%, of a surfactant.

Preferred formulations are composed in particular of the following constituents (%=percentage by weight):

Whereas commercial products will be preferably formulated as concentrates, the end user will normally employ dilute formulations. The formulations can be diluted to a concentration as low as 0.001%. The rates of application are normally 0.01 to 10 kg a.i./ha, preferably 0.025 to 5 kg a.i./ha.

The compositions can also contain further ingredients such as stabilisers, antifoams, viscosity regulators, binders, adhesives, as well as fertilisers or other active compounds, in order to attain special effects.

260 g of chloro-difluoromethane are introduced at a temperature of 70.degree.-75.degree. C. into a mixture of 110 g of hydroquinone, 600 ml of dioxane and 600 ml of 30% aqueous sodium hydroxide solution within 3 hours. The organic phase is separated and poured into 1500 ml of water. The mixture is extracted with ethyl acetate. The organic phases are collected, washed with water and 5% aqueous sodium hydroxide solution, dried over sodium sulfate and evaporated to dryness, yielding 74 g of 1.4-bis(difluoromethoxy)benzene in form of a yellow-brown oil.

10 ml of nitric acid (100%) are added dropwise at a temperature of -5.degree. to 0.degree. C. within 5 minutes to a solution of 13.9 g of 1.4-bis(difluoromethoxy)benzene in 33 ml of 1.2-dichloroethane. The reaction mixture is stirred for a further hour at a temperature of 5.degree. C. and allowed to warm to 15.degree. C. within 1/2 hour. The mixture is then poured into icewater. The organic phase is separated, washed with 10% aqueous sodium hydroxide solution, dried over sodium sulfate and evaporated to dreyness, yielding 12.6 g of crude 2.5-bis(difluoromethoxy)-nitrobenzene in form of a yellowish oil.

A mixture of 12.6 g of 2.5-bis(difluoromethoxy)nitrobenzene, 1.3 g of Raney-nickel catalyst and 130 ml of dioxane is agitated in a hydrogen atmosphere for 15 hours at a temperature of 20.degree.-25.degree. C. The hydrogen consumption is 3.34 liters. After removal of the catalyst the mixture is evaporated to dryness, yielding 11.0 g of crude 2.5-bis(difluoromethoxy) aniline in form of a yellow-brown oil.

While cooling at 0.degree. C., 21 ml of a 40% solution of sodium hydrogen sulfite are added dropwise to a solution of 3.0 g of copper sulfate pentahydrate in 90 ml of 32% hydrochloric acid. To the resultant solution is then made the simultaneous dropwise addition of 21 ml of a 40% solution of sodium hydrogen sulfite and a diazonium salt solution which has been cooled to -10.degree. C. and obtained by the dropwise addition, with cooling, of 6.9 g of sodium nitrite in 10 ml of water, to a suspension of 50 ml of water, 15 of 32% hydrochloric acid and 26.2 g of 2.5-bis(difluoromethoxy)aniline hydrochloride. During this addition the temperature of the reaction mixture rises to 25.degree. C., accompanied by the simultaneous evolution of gas. The reaction mixture is stirred for 2 hours, whereupon a brown oil precipitates. The organic phase is separated and the aqueous phase is extracted with methylene chloride. The organic phases are combined and evaporated to dryness, affording, as crude product, 12.7 g of 2.5-bis(difluoromethoxy)-phenyl sulfonyl chloride in the form of a brown oil.

To a mixture of 30 ml of methylene chloride, 30 ml of water and 50 ml of 30% ammonia solution is slowly added a solution of 12.7 g of crude 2.5-bis(difluoromethoxy)phenylsulfonyl chloride in 150 ml of methylene chloride. The reaction mixture is stirred for 5 hours at room temperature. The organic phase is washed with water, dried over sodium sulfate and evaporated to a volume of about 40 ml. From the residue crystallise 10.7 g of 2.5-bis(difluoromethoxy)phenyl-sulfonamide with a melting point of 73.degree.-74.degree. C.

The following novel intermediates, specially developed for the synthesis of compounds of formula I, are obtained in analogous manner.

14.5 g of 2.5-bis(difluoromethoxy)phenylsulfonamide are suspended in 50 ml of absolute methylene chloride. Then 3.5 g of methyl isocyanate are added and 6.3 g of triethylamine are subsequently added dropwise over 10 minutes to form a clear solution. The solution is stirred at room temperature for a further hour, evaporated to dryness, and the residue is dissolved in 5% sodium carbonate solution. N-[2,5-bis(difluoromethoxy)phenylsulfonyl]-N'-methylurea with a melting point of 162.degree.-165.degree. C., is precipitated from the solution by acidification with 10% hydrochloric acid. Yield: 15.0 g.

15.0 g of N-[2.5-bis(difuloromethoxy)phenylsulfonyl]-N'-methylurea are suspended in 170 ml of chlorobenzene and made absolute by distilling off about 20 ml of solvent as an azeotrope. Then 7.5 g of phosgene are introduced at 120.degree.-130.degree. C. over 45 minutes. The chlorobenzene is then completely distilled off, affording 12.8 g of 2.5-bis(difluoromethoxy)phenylsulfonyl isocyanate in the form of yellowish oil.

6.3 g of 2.5-bis(difuloromethoxy)phenylsulfonyl isocyanate and 2.8 g of 2-amino-4-methoxy-6-methyl-1,3,5-triazine are stirred in 60 ml of absolute dioxane for 3 hours at 80.degree.-90.degree. C. The solution is then cooled to 20.degree. C., filtered and concentrated to about 1/4 of its volume. After addition of an acetone ether mixture (1:4), 6.2 g of N-[2.5-bis(difluoromethoxy)phenylsulfonyl]-N'-(4-methoxy-6-methyl-1.3.5-tr iazin-2-yl)urea crystallise from the residue. Melting point: 113.degree. C.

The compounds of formula I listed in the following table are prepared in similar manner.

The active ingredient is thoroughly mixed with the adjuvants and the mixture is thoroughly ground in a suitable mill, affording wettable powders which can be diluted with water to give suspensions of the desired concentration.

Emulsions of any required concentration can be obtained from this concentrate by dilution with water.

Dusts which are ready for use are obtained by mixing the active ingredient with the carriers, and grinding the mixture in a suitable mill.

The active ingredient is mixed and ground with the adjuvants, and the mixture is subsequently moistened with water. The mixture is extruded and then dried in a stream of air.

The finely ground active ingredient is uniformly applied, in a mixer, to the kaolin moistened with polyethylene glycol. Non-dusty coated granulates are obtained in this manner.

The finely ground active ingredient is intimately mixed with the adjuvants, giving a suspension concentrate from which suspensions of any desired concentration can be obtained by dilution with water.

In a greenhouse, plant seeds are sown in flower pots of 12-15 cm diameter. Immediately after sowing, the surface of the soil is treated with an aqueous dispersion or solution of the compounds to be tested. Concentrations of 4 kg a.i./ha are employed. The pots are then kept in the greenhouse at 22.degree.-25.degree. C. and 50-70% relative humidity. The test is evaluated 3 weeks later in accordance with the following rating:

1=plants totally withered

2-3=very pronounced action

4-6=medium action

7-8=insignificant action

9=no action (as untreated controls)

A large number of plant seeds are treated with compounds to be tested at different rates of application in the same test procedure as described in Example 4. Evaluation is made in accordance with the same rating.

A number of weeds and cultivated plants in pots, both monocots and dicots, are sprayed postemergence, in the 4- to 6-leaf stage, with an aqueous active ingredient dispersion at a rate of application of 4 kg a.i./ha, and then kept at 24.degree.-26.degree. C. and 45-60% relative humidity. The test is evaluated 15 days after treatment and the action is assessed in accordance with the same rating as in Example 4.

Rate of application: 4 kg a.i./ha

A large number of plants are treated with the compounds to be tested at different rates of application in the same test procedure as described in Example 6. Evaluation is made using the same rating as in Example 4.

A number of commercially available potatoes of the "Urgenta" variety, without sprouts, are washed and dried. The potatoes are then immersed in emulsions of the compounds to be tested in different concentrations, placed on filter paper in plastic dishes, and kept in the dark at 14.degree. and 21.degree. C. and 50% relative humidity. Evaluation is made 34 days after application.

The percentage weight loss of the tubers and the weight of the sprouts compared with untreated controls are simultaneously determined.

In this test, a number of compound of the formula I inhibited sprouting completely. At the same time the weight loss of the potatoes was less than 10% of the weight loss of the controls.

The test plants (centrosema plumieri and centrosema pubescens) are reared until fully grown and then cut back to a height of 60 cm. The plants are sprayed 7 days later with an aqueous emulsion of the compound to be tested. The test plants are kept at 70% relative humidity and 6000 lux artificial light for 14 hours per day, at day temperatures of 27.degree. C. and night temperatures of 21.degree. C. The test is evaluated 4 weeks after application.

In this test, the new growth of plants treated with a number of compounds of the formula I is markedly reduced (less than 20%), without damage being caused to the test plants.