GB2124198A - Plant growth regulating method - Google Patents

Abstract

A method of regulating the growth of plants, which comprises applying to the plants or their seeds, or to the locus surrounding the plant or seed, a compound of formula (I): <IMAGE> wherein R<1> is hydrogen, an optionally subsituted aliphatic radical, or an acyl radical; R<2> is an optionally substituted aliphatic radical; R<3> is an aliphatic radical; and n is 1, 2, 3, 4, or 5.

Description

SPECIFICATION Plant growth regulating method This invention relates to a method of regulating the growth of plants by application of certain 5 (methyl-substituted phenyl) cyclohexane- 1 , 3-dione derivatives thereto.

According to the present invention there is provided a method of regulating the growth of plants, which comprises applying to the plants, or to the seed of the plant, or to the locus surrounding the plant or seed, a compound of formula (I)

wherein R1 is hydrogen, an optionally substituted aliphatic radical, or an acyl radical; R2 is an optionally substituted aliphatic radical; R3 is an aliphatic radical; and n is 1, 2, 3, 4 or 5.

The term aliphatic radical is intended to include for example, alkyl, alkenyl and alkynyl radicals, for example C18 alkyl, C26 alkenyl and C26 alkynyl radicals. Optional substituents for R1 and R2 include halogen (ie. fluorine, chlorine, bromine or iodine), hydroxy, alkoxy (e.g. C16 alkoxy), alkylthio (e.g. C16 alkylthio), phenyl and phenyl substituted with 1 to 3 or more substituents, which may be for example fluorine, chlorine, bromine, iodine, nitro, cyano, C18 alkyl, CF3, C16 alkoxy and C16 alkylthio.

The term acyl is intended inter alia, to include radicals derived from carboxylic and sulphonic acids, for example alkanoyl of 2 to 6 carbon atoms, benzoyl, substituted benzoyl, alkanesulphonyl of 1 to 6 carbon atoms, benzenesulphonyl and substituted benzenesulphonyl. The substituents of the benzoyl and benzenesulphonyl radicals may include, for exampe, any of the substituents listed above for phenyl.

It may be noted that when R1 is hydrogen in formula (I), the compounds used in the invention may exist in any of the three tautomeric forms shown below:

A subclass of compounds of formula I for use in the method of the invention includes those compounds wherein: R1 is hydrogen, benzoyl or substituted benzoyl wherein the benzene ring is substituted with from one to three substituents chosen from halogen, nitro and cyano; R2 and R3 are independently methyl, ethyl, n-propyl, allyl and propargyl; and n is 2 or 3.

A further subclass of compounds for use in the invention comprises those compounds of formula I in which the benzene ring is substituted in the 2-, 4- and 6-positions with methyl groups. That is, compounds of formula Ill:

Specific examples of compounds for use in the method of the invention include those compounds detailed in Table 1 below.

TABLE 1

COMPOUND NO (CH3)n R1 R2 R3 1 2,3-(CH3)2 H C2H5 C2H5 2 2,4-(CH3)2 H C2H5 C2H 3 2,5-(CH3)2 H C2H5 C2H5 4 2,6-(CH3)2 H C2H5 C2H5 5 3,4-(CH3)2 H C2H5 C2H5 6 3,5-(CH3)2 H C2H5 C2H5 7 2,4,6-(CH3)3 H C2H5 C2H5 8 2,4,5-(CH3)3 H C2H5 C2H5 9 2,3,5,6-(CH3)4 H C2H5 C2H5 10 2,3,4,6-(CH3)4 COC6H5 C2H5 C2H5 11 3,4-(CH3)2 COCH3 C2H5 C2H5 12 3,4-(CH3)2 COC6H5 C2H5 C2H5 13 2,5-(CH3)2 COC6H5 C2H5 C2H5 14 2,3-(CH3)2 COC6H5 C2H C2H5 15 2,4,6-(CH3)3 COC6H5 C2H5 C2H5 16 2,4,6-(CH3)3 H CH2CH =CH2 n-C3H7 17 2,4,6-(CH3)3 H CH2CH = CH2 C2H5 18 2,4,6-(CH3)3 H C2H5 n-C3H7 19 4-CH3 H C2H8 C2H5 20 4-CH3 H C2H5 nC3H7 21 4-CH3 H CH2CH = CH2 C2H5 COMPOUND NO (CH3)n R1 R2 R3 22 3-CH3 H C2H5 C2H5 23 4-CH3 H CH3 C2H5 24 4-CH3 H nC3H7 C2H5 25 4-CH3 H CH3 nC3H7 26 4-CH3 H nC3H7 nC3H7 27 4-CH3 H C2H5 -CH2CH(CH3)2 28 3-CH3 H CH2CH = CH2 C2H5 29 3-CH3 H C2H5 nC3H7 30 3-CH3 H -CH2CH = CH2 nC3H7 31 4-CH3 H nC3H7 nC3H7 32 4-CH3 CH3CO C2H5 C2H5 33 4-CH3 H CH2C#CH C2H5 34 4-CH3 H -CH(CH3)2 nC3H7 35 4-CH3 H -CH(CH3)2 nC3H7 36 2,4,6-(CH3)3 H -CH2C#CH C2H5 37 2,4,6-(CH3)3 H -CH2C#CH nC3H7 38 2,4,6-(CH3)3 H C2H5 CH3 39 4-CH3 H -(CH2)4CH3 C2H5 40 4-CH3 H -(CH2)4CH3 nC3H7 41 (CH3)5 C2H5CO C2H5 C2H5 42 2,4,5,6-(CH3)4 H -CH2CH2F nC3H7 43 (CH3)5 H -CH2CH2F nC3H7 44 (CH3)5 H -CH2CH2F C2H5 45 (CH3)5 H CH3 nC3H7 46 (CH3)5 H nC3H7 nC3H7 47 (CH3)5 H CH3 C2H5 48 (CH3)5 H -CH2C(Cl)= CH2 nC3H7 49 (CH3)5 H -CH2CH = CHCH3 C2H7 50 4-CH3 H -CH2CH2F nC3H7 51 2,4,6-(CH3)3 H -CH2CH2OH nC3H7 The compounds used in the method of the invention and processes for preparing them, are described in published European Patent Application No 80301. For convenience in reference, however, a process for preparing the compounds is outlined in Scheme A below: Scheme A

According to Scheme A, a methyl-substituted benzaldehyde IV is condensed with acetone to give the unsaturated ketone (V).This is in turn condensed in step (b) with a malonic ester (R stands for an alkyl group of e.g. 1 to 6 carbon atoms in the malonic ester formula) to give the 5-(substituted phenyl) cyclohexane-1,3-dione derivative of formula (VI). This is then subjected to alkaline hydrolysis followed by acidification and decarboxylation to give the cyclohexane 1,3dione (VII). This is then reacted in step (d) with an acid anhydride (R3CO)20 in presence of a salt of the acid R3CO2M, to give the 2-acyl-5-(substituted phenyl) cyclohexane-dione of formula (VIII).This is then reacted in step (e) with an O-substituted hydroxylamine to give the compound (II). Compounds of formula I in which R1 is an optionally substituted aliphatic radical or an acyl radical may be prepared from compounds of formula II by reaction with the appropriate aliphatic halide or acyl halide as required.

The plant growth regulating effects of the compounds of formula (I) may be manifested in various ways. In general, the expression plant growth regulation is intended to include substantially non-damaging changes in the structure or physiological state or stage of development of a plant brought about by application of the compounds of formula (I).

The use of compounds of formula (I) as selective herbicides is described in the aforementioned European Patent Application No 80301; for a particular plant species, a higher level of application will in general be required to produce herbicidal effects than to produce plant growth regulating effects.

The plant growth regulating method of the invention may be applied to either monocotyledonous or dictyledonous plants. According to one aspect of the invention there is provided a method of regulating the growth of graminaceous crop plants, particularly wheat and barley.

More particularly, there is provided a method of inducing tiller formation in monocotyledonous plants, particularly wheat and barley, which comprises applying to the plant, to seed of the plant, or to the locus surrounding the plant or seed, a compound of the formula (I) as hereinbefore defined.

The induction of tiller formation by the method of the invention may have usefulness in a variety of crops. In cereal crops, the tillers may give rise to ripe grain-bearing ears at harvest. In grass swards, increase in tillering can lead to a denser sward; in forage grass, it may lead to increased yields and better quality (e.g. improved digestibility). In sugar cane, increased tillering can lead to an increased yield of sugar.

The rate at which the compounds are applied in the field to induce tillering will depend upon factors such as the particular plant species and variety to be treated, the compound chosen for application, the growth stage of the plant to which the compound is to be applied, and the climatic conditions prevailing at the time. However, as a general guide, application rates of from 0.1 to 0.5 kilograms per hectare are often suitable, although up to 4 kilograms or more may be desirable in some cases.

In a further aspect the invention provides a method of stunting or dwarfing the growth of monocotyledonous plants, particularly wheat and barley, which comprises applying to the plants, or to the locus surrounding the plant or seed, a compound of formula (I) as hereinbefore defined.

Such stunting or dwarfing may be useful where reduction in stem height, with or without further advantageous effects such as stem strengthening, thickening, internode shortening and more erect stem orientation may reduce the risk of lodging and may permit increased amounts of fertiliser to be applied. In the case of sugar cane, stunting or dwarfing may bring about an increase in the concentration and total yield of sugar.

Rates of application are dependent on a variety of factors such as those listed above in relation to the use of the compounds to induce tillering; howerver, application rates of from 0.1 to 0.5 kilograms per hectare are often suitable.

The compounds are preferably applied in the form of a composition, comprising the active ingredient in admixture with a carrier comprising a solid or liquid diluent. Preferably the composition also comprises a surface-active agent.

The solid compositions of the invention may be for example, in the form of dusting powders, or may take the form of granules. Suitable solid diluents include, for example, kaolin, bentonite, kieselguhr, dolomite, calcium carbonate, talc, powdered magnesia, and Fuller's earth.

Solid compositions may also be in the form of dispersible powders or grains comprising in addition to the active ingredient, a wetting agent to facilitate the dispersion of the powder or grains in liquids. Such powders or grains may include fillers, suspending agents and the like.

Liquid compositions include aqueous solutions, dispersions and emulsions containing the active ingredient preferably in the presence of one or more surface active agents. Water or organic liquids may be used to prepare solutions, dispersions, or emulsions of the active ingredient. The liquid compositions of the invention may also contain one or more corrosion inhibitors for example lauryl isoquinolinium bromide.

Surface active agents may be of the cationic, anionic or non-ionic type. Suitable agents of the cationic type include for example quaternary ammonium compounds, for example cetyltrimethyl ammonium bromide. Suitable agents of the anionic type include for example soaps, salts of aliphatic mono-esters of sulphuric acid, for example sodium lauryl sulphate; and salts of sulphonated aromatic compounds, for example dodecyl-benzenesulphonate, sodium, calcium and ammonium ligno-sulphonate, butylnaphthalene sulphonate, and a mixture of the sodium salts of diisopropyl- and triisopropyl-naphthalenesulphonic acid. Suitable agents of the non-ionic type include, for example, the condensation products of ethylene oxide with fatty alcohols such as oleyl alcohol and cetyl alcohol, or with alkyl phenols such as octylphenol, nonylphenol, and octylcresol.Other non-ionic agents are the partial esters derived from long chain fatty acids and hexitol anhydrides, for example sorbitol monolaurate; the condensation products of the said partial esters with ethylene oxide and the lecithins.

The compositions which are to be used in the form of aqueous solutions, dispersions or emulsions are generally supplied in the form of concentrate containing a high proportion of the active ingredient, the concentrate being diluted with water before use. These concentrates are usually required to withstand storage for prolonged periods and after such storage to be capable of dilution with water in order to form aqueous preparations which remain homogeneous for a sufficient time to enable them to be applied by conventional spray equipment.

The compositions used in the invention may contain, in addition to carriers and surface-active agents, various other constituents to increase their usefulness. They may contain, for example, buffering salts to maintain the pH of the composition within a desired range; antifreeze agents, for example urea or propylene glycol; adjuvants, for example, oils and humectants; and sequestrants, for example citric acid and ethylenediaminetetracetic acid, which help to prevent the formation of insoluble precipitates when the compositions are diluted with hard water.

Aqueous dispersions may contain anti-settling agents and anti-caking agents.

The compositions may in general contain a dye or pigment to impart a characteristic colour.

Agents for increasing viscosity may be added to reduce the formation of fine droplets during spraying, and thereby reduce spray drift. Other additives useful for particular purposes will be known to those skilled in the formulation art.

In general concentrates may conveniently contain from 10 to 85% and preferably from 25 to 60% by weight of active ingredient. Dilute preparations ready for use may contain varying amounts of the active ingredient, depending upon the purpose for which they are to be used; however, dilute preparations suitable for many uses contain between 0.01 % and 10% and preferably between 0. 1% and 1 % by weight of the active ingredient.

The invention is illustrated by the following Examples, in which all parts are by weight and all temperatures in degrees celsius unless otherwise specified.

EXAMPLE 1 2-[1-(EthoxviminoJpropyl]-3-hydroxy-5-mesitylcyclohex-2-en- 1-one (Compound No 7 in Table 1) (i) An aqueous solution of 1 % sodium hydroxide (29.5 ml) was added dropwise over a period of 5 minutes to a suspension of mesityladldehyde (10. g; 68 mmole) in acetone (50 ml) and water (50 ml). The mixture was stirred at a temperature of 65"C for a period of 1.5 hours and then extracted with dichloromethane (200 ml). The organic extract was washed several times with water, dried over anhydrous sodium sulphate, and the solvent was removed by evaporation under reduced pressure using a rotary evaporator. The product 1-(2,4,6-trimethylphenyl)but-1- en-3-one, a viscous oil, solidified on standing to give a white solid (11.5 g; 90%), m.p. 64"C.

Proton magnetic resonance spectrum (CDCI3; in ppm): 2,25 (12H,m); 6.30 (1H,d); 6.88 (2H,s); 7,64 (1 H,d).

(ii) Diethyl malonate (10.1 g; 60 mmole) was added to a solution of sodium metal (1.4 g; 60 mmole) in anhydrous absolute ethanol (50 ml) and the mixture was heated to reflux temperature. A mixture of 1-(2,4,6-trimethylphenyl)but-1-en-3-one (11.4 g; 61 mmole) in anhydrous absolute ethanol (50 ml) was added over a period of 2 minutes and the mixture was heated under reflux for a period of 2 hours. An aqueous solution of sodium hydroxide (7.3 g; 180 mmole in 100 ml of water) was added and the mixture was heated under, reflux for a further 4.5 hours. The solution was poured into water (200 ml) and the aqueous mixture was extracted twice with ethyl acetate (100 ml). The aqueous phase was acidified with concentrated hydrochloric acid and warmed gently until the evolution of carbon dioxide ceased.The aqueous mixture was extracted with ethyl acetate, dried over anhydrous sodium sulphate, and the solvent was removed by evaporation under reduced pressure using a rotary evaporator. The product, 3hydroxy-5-mesitylcyclohex-2-en-1-one, was obtained as a pale yellow solid (10.9 g; 77.4%), mp 165"C. Proton magnetic resonance spectrum (dimethylsulfoxide; in ppm): 2.0-4.1 (14H,m); 5.2 (1 H,s); 6.8 (2H,s); 11.2 (1 H,br.s).

(iii) Propionic anhydride (15.0 ml) was added cautiously to freshly prepared sodium methoxide (0.47 g; 9 mmole). On completion of the reaction 3-hydroxy-5-mesitylcyclohex-2-en-1 -one (5.0 g; 22 mmole) was added and the reaction mixture was heated under reflux at a temperature of 160"C for a period of 2 hours. The excess propionic anhydride was removed by evaporation under reduced pressure using a rotary evaporator. Aqueous 30% sodium hydroxide solution (50 ml) was added to the residue and the mixture was heated uner reflux for a period of 1 hour with vigorous stirring. After cooling the mixture was acidified with concentrated hydrochloric acid and the aqueous mixture was extracted with dichloromethane.The organic extracts were dried over anhydrous sodium sulphate and the solvent was removed by evaporation under reduced pressure using a rotary evaporator. The product, a brown oil was purified by chromatography over silica gel (eluant dichloromethane) to give 3-hydroxy-5-mesityl-2-propionylcyclohex-2-en-1 - one (3.17 g; 50.2%) as a pale yellow oil. Proton magnetic resonance spectrum (CDCI3; in ppm): 1.60 (3H,t,J = 8Hz); 2.24 (3H,s); 2.37 (6H,s); 2.64-5.26 (7H,m), 6.84 (2H,m); 18.26 (1 H,s).

(iv) Ethoxyamine hydrochloride (0.45 g) and then aqueous 1 % sodium hydroxide (18.4 ml) were added to a solution of 3-hydroxy-5-mesityl-2-propionylcyclohex-2-en-1-one (1.2 g; 4.2 mmole) in anhydrous absolute ethanol (200 ml). The mixture was stirred at room temperature for a period of 4 hours and then the ethanol was removed by evaporation under reduced pressure using a rotary evaporator. The residue was treated with dichloromethane and the organic phase was washed twice with dilute aqueous hydrochloric acid and twice with water.

The organic phase was dried over anhydrous sodium sulphate and the solvent was removed by evaporation under reduced pressure to give the product, 2-(1-(ethoxyimino)propylj-3-hydrnxy-5 mesitylcyclohex-2-en-1-one (1.25 9; 93%), as a pale yellow oil.

The product was characterised by proton nuclear magnetic resonance and carbon-13 nuclear magnetic resonance spectroscopy.

EXAMPLE 2 Compounds No 1, 2, 3, 4, 5, 6, 8, 9 and 10 (see Table 1) were prepared from the appropriate benzaldehyde derivative following essentially the same procedure as that described in Example 1 parts (i) to (iv). Each of the products was characterised by proton nuclear magnetic resonance and/or carbon-13 nuclear magnetic resonance spectroscopy.

EXAMPLE 3 3-Benzoyloxy-2-f 1 -(ethoxyimino)prnpyI-5-mesityI-cycIohex-2-en 1-one (Compound No 15 of Table 1) Aqueous 1 % sodium hydroxide solution (6 ml) was added to a solution of 2-1 -(ethoxyimino)- propyl]-3-hydroxy-5-mesitylcyclohex-2-en-1-one (0.42 91.28 mmole) in acetone (50 ml). The mixture was stirred at room temperature for a period of 5 minutes and then benzoyl chloride (0.2 g) was added dropwise. The mixture was stirred for a further period of 1 5 minutes and then the solvent was removed by evaporation under reduced pressure using a rotary evaporator.

The product was purified by chromatography over silica gel (eluant dichloromethane) to give 3 benzoyloxy-2-[ 1 -(ethoxyimino)propylj-5-mesitylcyclohex-2-en- 1-one (0.38 g; 68.6%) as a pale yellow oil.

The product was characterised by proton nuclear magnetic resonance spectroscopy.

EXAMPLE 4 Compounds No 11, 12, 1 3 and 14 (See Table 1) were prepared from the appropriate 2-[1 ethoxyamino)propylj-3-hydroxy-5-(substituted phenyl)cyclohex-2-ene-1-one derivative and the appropriate acid chloride following essentially the same procedure as that described in Example 3. Each of the products was characterised by proton nuclear magnetic resonance spectroscopy.

EXAMPLE 5 2-[1-(AllyloxysminoJbutyl7-3-hydroxy-5-mesitylcyclohex-2-en- 1-one (Compound No 16 of Table 1) (i) n-Butyryl chloride (2.3 g; 21.7 mmole) and then pyridine (1.7 g; 21.7 mmole) were added to a stirred mixture of 3-hydroxy-5-mesitylcyclohex-2-en-1-one (5.0 g; 21.7 mmole) and dichloromethane (50 ml) under a nitrogen atmosphere. The mixture was stirred at room temperature for a period of two hours and then poured into slightly acidic water. The organic phase was thoroughly extracted with dichloromethane. The combined organic phase and extracts were washed with water, dried over anhydrous magnesium sulphate and the solvent was removed by evaporation under reduced pressure using a rotary evaporator.The residue was dissolved in 1.2-dichloroethane (50 ml), stannic chloride (5.7 9; 22 mmole) was added and the mixture was heated under reflux for a period of 8 hours. The mixture was cooled and poured into water and the aqueous mixture was extracted several times with dichloromethane. The combined organic extracts were dried over anhydrous magnesium sulphate and the solvent was removed by evaporation under reduced pressure using a rotary evaporator. The residue was purified by chromatography over silica gel (eluant dichloromethane) to give 2-butyryl-3-hydroxy 5-mesitylcyclohex-2-en-1 -one (2.4 g). Proton nuclear magnetic resonance spectrum (CDCl3: in ppm): 1.01 (3H,t); 1.30-1.60 (2H,m); 2.23 (3H,s); 2.37 (6H,s); 2.40-3.45 (7H,m); 6.83 (2H,s); 18.24(1H,s).

(ii) Allyloxyamine hydrochloride (0.72 g) and then a solution of sodium hydroxide (0.25 g) in water (3 ml) were added to a stirred mixture of 2-butyryl-3-hydroxy-5-mesitylcyclohex-2-en-1 -one (1.78 g; 5.9 mmole) and 95% ethanol. The progress of the reaction was monitored using thin layer chromatography on silica gel (eluant dichloromethane). On completion of the reaction the ethanol was removed by evaporation using a rotary evaporator and the residue was extracted with dichloromethane. The organic extract was washed with aqueous 5% hydrochloric acid and then with water and dried over anhydrous magnesium sulphate. The solvent was removed by evaporation under reduced pressure using a rotary evaporator to give the product, 2[1 (allyloxyimino)butyl]-3-hydroxy-5-mesitylcyclohex-2-en-1-one (1.6 g) as an oil.

The product was characterised by proton nuclear magnetic resonance spectroscopy.

EXAMPLE 6 2-[1 -Ethoxymino)butyl]-3-h ydroxy-5-mesitylcyclohex-2-en-l-one (Compound No 1 8 of Table 1) Compound 19 (see Table 1) was prepared from 2-butyryl-3-hydroxy-5-mesitylcyclohex-2-en-1one (see Example 5 part (i)) and ethoxyamine hydrochloride following essentially the same procedure as that described in Example 1 part (iv). The product was characterised by proton nuclear magnetic resonance spectroscopy.

EXAMPLE 7 2-[2-(Allyloxvimino)propyl]-3-hydroxy-5-mesitylcyclohex-2-en- 1 -one (Compound No 17 of Table 1) Compound 1 7 (see Table 1) was prepared from 3-hydroxy-5-mesityl-2-propionylcyclohex-2-en- 1-one (see Example 1 parts (i) to (iii) and allyloxyamine hydrochloride following essentially the same procedure as that described in Example 5 part (ii). The product was characterised by proton nuclear magnetic resonance spectroscopy.

EXAMPLE 8 This Example illustrates the plant growth regulating effects of Compound No 7 of Table 1.

The compound was formulated for spraying by mixing it with a solution comprising Span 80 (21.8 grams per litre) and Tween 20 (78.2 g/litre) in methylcyclohexanone. Span 80 is a Trade Mark for a surface-active agent comprising sorbitan monolaurate, Tween 20 is a Trade Mark for a surface-active agent comprising a condensate of 20 molar proportions of ethylene oxide with sorbitan monolaurate. The mixture was diluted with water containing 1 gram per litre of Agral 90 to give an emulsion containing 5% by volume of the methylcyclohexanone solution. Agral 90 is a Trade Mark for a surface-active agent comprising a condensate of from 7 to 8 molar proportions of ethylene oxide with pnonylphenol.

The spray composition so prepared was applied to young pot plants (3 to 4 leaf stage) grown in John Innes Compost No 2. The plants were spring and winter barley and spring wheat. After four weeks the height of the plants and the numbers of tillers were measured. The results are given in the table below; each result is the mean of five replicates.

MAINSTEM APPLICATION HEIGHT NUMBER OF TEST PLANT RATE KG/HA (mm) TILLERS SPRING 0.1 331 3.9 BARLEY 0.2 82 4.3 UNTREATED 413 2.7 WINTER 0.1 223 2.7 BARLEY 0.2 76 3.4 UNTREATED 228 2.3 SPRING 0.1 289 2.5 WHEAT 0.2 184 3.3 UNTREATED 325 1.9 EXAMPLE 9 This Example illustrates the plant growth regulating effects of further compounds used in the method of the invention. The compounds were formulated and applied to test plants in a spray volume of 1000 litres per hectare as described in Example 8, and the effects asssessed by comparison with untreated control plants at the number of days after treatment given in Table 2 below. In the table, the numbers 1, 2, and 3 denote the degree of stunting or dwarfing caused by the compound, according to the following scale: Number Percentage retardation of growth 1 1-30 2 31-75 3 75 or more.

The symbol T used in the table means that the compound caused increased tillering, and G means that the colour of the plant leaves was darker green than that of the control. The symbol D means that the plant died; in such cases the rate of application of the compound was probably too high, and a lower rate could probably have brought about growth regulation without damage to the plant. A dash (-) in the table means that no test was carried out.

TABLE 2 Test plants Concentration Compound Days after of spray (parts Spring Spring No. treatment per million) wheat barley 2 18 4000 1T 1 3 18 4000 1T 2 4 18 4000 1T 2 5 18 4000 1T 2T 6 19 1000 1T T 10 18 4000 3 11 18 4000 T 2T 12 19 4000 1 15 19 1000 T T 20 18 4000 1T 3T 21 18 4000 3T 3 22 18 4000 2 2 23 18 4000 1T 1T 24 18 4000 1T 1T 25 18 4000 1T 1T 26 18 4000 1 27 18 3000 1 1 28 18 4000 2T 2 29 18 4000 iT 2 30 19 1000 1T 1T 31 19 1000 T T 32 19 1000 1T 1T 33 19 1000 T T 34 19 1000 T T 35 19 1000 T T 36 19 1000 T 38 19 1000 1T 1T 39 19 1000 T T 43 12 4000 3 D 44 12 4000 3 D 45 12 4000 3TG D 46 12 4000 1 2T 47 12 4000 3 48 12 4000 3TG 3TG 49 12 4000 3 D 50 12 4000 T 3TG In addition to the tests on barley and wheat summarised in Table 2, tests were also carried out on a variety of other plant species. The following compounds were found to increase tillering in soya bean plants: Compounds no 3, 7, 11, 22, 23, 27, 28, 29.

In tests on sugar-beet the following compounds induced stunting: Compounds no 30, 31, 33, 34, 35, 36, 38, 40, 41, 44, 51.

In tests on lettuce, the following compounds induced stunting: Compounds no 12, 39, 41, 51.

In tests on cotton, the following compounds induced stunting: Compounds no 10, 12, 42, 43, 44, 45, 47, and 49.

In tests on tomato, the following compounds induced stunting: Compounds no 23, 30, 38, 41 and 51.

Claims (5)

1. A method of regulating the growth of plants, which comprises applying to the plants, or to the seed of the plant, or to the locus surrounding the plant or seed, a compound of formula (I):

wherein R1 is hydrogen, an optionally substituted aliphatic radical, or an acyl radical; R2 is an optionally substituted aliphatic radical; R3 is an aliphatic radical; and n is 1,2, 3,4 or 5.

2. A method as claimed in claim 1 wherein the group R' is hydrogen, the group R2 is an optionally substituted C16 alkyl, C26 alkenyl, or C26 alkynyl radical, and the group R3 is an alkyl radical of 1 to 6 carbon atoms.

3. A method claimed in claim 1 wherein R' is hydrogen, benzoyl, or substituted benzoyl wherein the benzene ring is substituted with from one to three substituents chosen from halogen, nitro, and cyano; R2 and R3 are independently methyl, ethyl, n-propyl, allyl, and propargyl; and n is 2 or 3.

4. A method as claimed in any of claim 1 to 3 wherein a compound of formula (I) as defined therein is applied to wheat or barley plants or to the locus surrounding the plants or their seed, whereby tiller formation and/or stunting is induced in the plants.

5. A method as claimed in any af the preceding claims wherein the compound of formula (I) is applied in admixture with another plant-growth regulating agent not of formula (I).