GB2050334A - Promoting tiller formation in plants - Google Patents

Abstract

A method for promoting tillering in a plant e.g. cereals by applying first to the plant or locus of the plant a compound of formula <IMAGE> wherein R1 is optionally substituted benzyl; and R2 is alkyl; or a salts or metal complex thereof, and then a gibberellin.

Description

SPECIFICATION Tiller formation This invention relates to a method of promoting tiller formation in cereal plants whereby at least some of the tillers formed survive to give mature ear-bearing tillers.

Our British Patent Application No. 34590/76, which corresponds to Dutch Patent Application No. 7709197 (the disclosure of which Applications is incorporated herein by reference), discloses compounds of general formula (I):

wherein R1 is alkenyl, alkynyl or optionally substituted aralkyl, Y is = N- or =CH-, R2 is cycloalkyl, alkyl or haloalkyl, and R3 is hydrogen, methyl or alkenyl, or an ester, an ether, an acid addition salt or metal complex thereof. It is stated that the compounds can promote tillering in monocotyledonous plants (e.g. cereals).

We have found that when the above compounds are used to promote tillering, few if any of the tillers mature into ripe ear-bearing ears at the same time as the main ear bears grain. We have now found that the application of certain of the compounds of general formula (I) applied at a specific growth stage in the life of the cereal plant followed by an application of a gibberellin at another specific growth stage has the result that some of'the tillers formed by the application of the compounds of general formula (I) mature into ripe grain-bearing ears at substantially the same time as the main ear bears grain. Further, the application of the gibberellin can at least partially reverse the stunting effect caused by the application of the compound of general formula (I).

The invention therefore provides a method of promoting the formation of tillers in a cereal plant, the number of said tillers that mature into grain-bearing ears at substantially the same time as the main ear bears grain being increased, the method comprising applying to the cereal plant, during the tiller formation growth stage in (e.g. at the two to three leaf stage in the growth of) the plant, or to the locus surrounding the plant at said stage, a compound of general formula (I) wherein R1 is benzyl optionally ring substituted with one, two or three substituents selected from the class consisting of halogen, alkyl, alkoxy, nitro and trifluoromethyl and/or optionally substituted on its methylene moiety with one alkyl (e.g. methyl or ethyl), Y is = N- R2 is propyl (i.e. n-or i-propyl) or butyl (i.e. n-, sec-, i-ort-butyl) and F3 is hydrogen, or an acid addition salt or metal complex thereof, and then subjecting the plant to an application (e.g. more than one application) of a gibberellin.

Preferably the gibberellin application (or, when more than one gibberellin application is being employed, the first gibberellin application) is made after the end of the tiller formation growth stage and before the start of the stem elongation growth stage.

Taking temperate cereals (e.g. barley and wheat) as an example, an using the well-known Feekes' Scale, [see Large, Plant Pathology, 1954, 3 (4), 128-129, the disclosure of which document is incorporated herein by reference], the compound of general formula (I) or a salt or complex thereof as defined above is suitably applied at Feekes' Scale Stages 1 to 5 (e.g. 1 to 3) and the gibberellin is suitably applied at Feekes' Scale Stages 2 to 8 (e.g. 5 to 7).

Examples of suitable cereal plants are wheat, barley, rye, oats, triticale, rice, maize and sorghum.

It will be appreciated that the compounds of general formula (I) contain two chiral centres. This means that the compounds can exist in four optical isomeric forms. Two of these isomers are enantiomers (i.e. mirror images) of each other, as are the other two isomers. One pair of enantiomers are diastereoisomers of the other pair of enantiomers.

The alkyl groups which can be straight or branched chain, preferably have 1 to 5 carbon atoms; examples are methyl, ethyl propyl (n-or propyl) and butyl (n-, sec-, i- ort-butyl).

As indicated above, the benzyl can be substituted in its CH2 and/or phenyl moieties. Suitable substituents on its phenyl moiety are halogen, C14 alkyl [e.g. methyl, ethyl, propyl (n-or i-propyl) and butyl (n-, sec-, i- or t-butyl)j, trifluoromethyl, nitro and CiA alkoxy (e.g. methoxy, ethoxy, propoxy or butoxy).

Examples of suitable benzyl groups are benzyl itself, ct-methylbenzyl, a-methylchlorobenzyl (e.g.

a-methyl-p-chlorobenzyl), a-methyldichlorobenzyl (e.g. a-methyl-2,4-dichlorobenzyl), a-methylbromobenzyl (e.g. a-methyl-p-bromobenzyl), a-methylfluorobenzyl [e.g. a-methyl-p-fluorobenzyl], a-ethylchlorobenzyl (e.g. a-ethyl-p-chlorobenzyl), a-ethylfluorobenzyl (e.g. a-ethyl-p-fluorobenzyl), chlorobenzyl (for example o-, m- or p-chlorobenzyl), dichlorobenzyl (e.g. 3,4-, 2,4-, 3,5- or 2,6-dichlorobenzyl), trichlorobenzyl (e.g. 2,3,6- or 2,4,5-trichlorobenzyl), bromobenzyl (e.g. o-, m- or p-bromobenzyl), dibromobenzyl (e.g. 2,4-dibromobenzyl), fluorobenzyl (e.g. o-, m- or p-fluorobenzyl), difluorobenzyl (e.g. 2,4- or 3,4-difluorobenzyl), iodobenzyl (e.g.

o-iodobenzyl), methylbenzyl (e.g. o-, m- or p-methylbenzyl), dimethylbenzyl (e.g. 2,6- 2,5- or 3,4dimethylbenzyl), ethylbenzyl (e.g. p-ethylbenzyl), propylbenzyl (e.g. p-i-propylbenzyl), butylbenzyl (e.g.

p-t-butylbenzyl), nitrobenzyl (e.g. o-, m- or p-nitrobenzyl, dinitrobenzyl (e.g. 2,4-dinitrobenzyl), (trifluoromethyl) benzyl [e.g. o-, m- or p-(trifluoromethyl)-benzyl], methoxybenzyl (e.g. o-, m-or pmethoxybenzyl), dimethoxybenzyl (e.g. 2,4-, 3,4- or 3,5-dimethoxybenzyl), ethoxybenzyl (e.g. o-, m- or p-ethoxybenzyl), propoxybenzyl (e.g. p-i-propoxybenzyl or p-n-propoxybenzyl), butoxybenzyl (e.g. o-, m- or p-i-butoxybenzyl), chloronitrobenzyl (e.g. 3-nitro-4-chlorobenzyl), fluornitrobenzyl (e.g. 2-nitro-4fluorobenzyl), chlorofluorobenzyl (e.g. 2-fluoro-4-chlorobenzyi, 2-chloro-6-fluorobenzyl or 2-chloro-4fluorobenzyl), fluorobromobenzyl (e.g. 2-fluoro-4-bromobenzyl), methoxychlorobenzyl (e.g. 3-chloro-4methoxybenzyl), methoxybromobenzyl (e.g. 2-methoxy-5-bromobenzyl or 3-b romo4-meth oxybenzyl), methoxynitrobenzyl (e.g. 2-methoxy-5-nitrobenzyl or 4-methoxy-3-nitrobenzyl), ethoxynitrobenzyl (e.g.

4-ethoxy-3-nitrobenzyl), ethoxychlorobenzyl (e.g. 4-ethoxy-3-chlorobenzyl) and ethoxybromobenzyi (e.g.

4-ethoxy-3-bromobenzyl). In this paragraph, all the substituents except the a-methyl and a-ethyl substituents are ring substituents.

The halogen can be fluorine, chlorine, bromine or iodine.

The preferred compounds are those wherein R1 is benzyl, a-methylbenzyl, a-methyl-p-chlorobenzyl, a-methyl-2,4-dichlorobenzyl, a-methyl-p-bromobenzyl, a-methyl-p-fluorobenzyl, a-ethyl-p-chlorobenzyl, aethyl-p-fluorobenzyl. o-, m- or p-chlorobenzyl, 2,4- 3,4- or 2,6-dichlorobenzyl, 2,4,5- or 2,3,6-trichlorobenzyl, pentachlorobenzyl, o-, m- or p-bromobenzyl, 2,4-dibromobenzyl, o-, m- or p-fluorobenzyl, 2,4-difluorobenzyl, o-iodobenzylt o-, m- or p-methylbenzyl, 2,5- or 3,4-di-methylbenzyl, p-ethylbenzyl, p-i-propylbenzyl, p-t-butylbenzyl, o-, m- or p-nitrobenzyl, o-, m- or p-(trifluoromethyl)benzyl, o-, m- or p-methoxybenzyl, o-, mor p-ethoxybenzyl, 3-nitro-4-chlorobenzyl, 2-nitro-4-fluorobenzyl, 2-chloro-4-fluorobenzyl, 2-fiuoro-4- chlorobenzyl, 2-chloro-6-fluorobenzyl, 2-fluoro-4-bromobenzyl, 3-bromo-4-methoxybenzyl, 2-methoxy-5nitrobenzyl, Y is = N-, R2 is i-propyl, i-butyl ort-butyl, and B3 is hydrogen or methyl.

Suitable salts are salts with inorganic or organic acids, e.g. hydrochloric, nitric, sulphuric, toluenesulphonic, acetic or oxalic acid.

The metal complex is suitably one including copper, zinc, manganese or iron. It preferably has the general

wherein Y, R1, R2 and B3 are as defined above, M is a metal, A is an anion (e.g. a chloride, bromide, iodide, nitrate, sulphate or phosphate anion), n is 2 or 4, and Y is O or an integer of 1 to 12.

Table I gives specific examples of compounds of general formula (I).

TABLE I Melting (or No R1 R2 boiling) point 0C 1* p-CI-C6H4CH2- t-Bu 162-164 2 C6HscH2- t-Bu 91-93 3 p-F-C6H4CH2- t-Bu 137-142 4X p-CI-C6H4CH2 t-Bu 109-111" 5* p-CI-C6H4CH2- t-Bu 133-134" 6 p-CI-C6H4CH2- t-Bu 179-181" 7 p-NO2-C6H4CH2 t-Bu 157-159 8 3,4-diCI-C6H3CH2 t-Bu 186-188" 9 o-F-C6H4CH2 t-Bu 100-102" 10* 2,4-diCI-C6H3CH2 t-Bu 140-143" 11 m-CF3-C6H4CH2 t-Bu 71-73" TABLE I Continued...

Melting (or No. R1 R2 boiling) point 'C 12 3-NO2-4-CI-C6H3CH2 t-Bu 177-178 13 o-CI-C6H4CH2 t-Bu 100-102 14 p-Br-C6H4CH2 t-Bu 81-183 15 m-F-CsH4CH2 t-Bu 110-113 16 m-Br-C6H4CH2 t-Bu 133-136 17 2,4-diCI-C6H3CH2 i-Pr 127-130 18 p-CI-C6H4CH2 i-Pr 100-103 19+ p-CI-C6H4CH2 t-Bu 138-140 20 p-F-C6H4CH2 i-Pr 74-78 21 2,6-diCI-C6H3CH2 t-Bu 151-154 22 2-Ci-4-F-C6H3CH2 t-Bu 137-140 23 o-F-C6H4CH2 i-Pr 122-127 24 2,4,5-triCl-C5H2CH2 t-Bu 188-192 25 2,3,6-triCI-C6H2CH2 t-Bu 168-172 26 2-F-4-CI-C6H3CH2 t-Bu 150-153 27 2,4-diF-C6H3CH2 t-Bu 111-114 28 p-F-C6H4CH(Me)- t-Bu 197-201 29 2,4-diCI-C6H3CH(Me) t-Bu 145-147 30 p-Cl-C6H4CH(Me) t-Bu 182-185 31 2-F-4-Br-C6H3CH2 t-Bu 171-174 32 2,4-diBr-C6H3CH2 t-Bu 157-160 33 o-MeO-C6H4CH2 t-Bu 141-144 34 o-Me-C6H4CH2 t-Bu 123-125 35 p-Me-C6H4CH2 t-Bu 144-146 36 2,5-diMe-C6H3CH2 t-Bu 114-117 37 m-CI-C6H4CH2 t-Bu 127-129 38 p-MeO-C6H4CH2 t-Bu 116-118 39 2-MeO-5-Br-C6H3cH2 t-Bu 184-186 40 p-EtO-C6H4CH2 t-Bu 116-117 41 o-EtO-C6H4CH2 t-Bu 152-154 TABLE I Continued..

Melting (or No R1 R2 boiling) point 'C 42 2-NO2-4-F-C6H3CH2 t-Bu 43* 2,4-diCI-C6H3CH2 t-Bu 197-199 44 o-Br-C6H4CH2 t-Bu 113-114,5 45 3-Br-4-MeO-C6H3CH2 t-Bu 163 46 p-CI-C6H4CH2 i-Bu 45-50 47 2,4-diCI-C6H3CH2 i-Bu 119-123" 48 o-l-C6H4CH2 t-Bu 117-119" 49 m-NO2-C6H4CH2 t-Bu 170-172" 50 p-(t-Bu)-C6H4CH2 t-Bu 90 51 3-CI-4-MeO-C6H3CH2 t-Bu 148 52 2-CI-6-F-C6H3CH2 t-Bu 120-122 53 p-CF3-C6H4CH2 t-Bu 139-141 54 p-F-C6H4CH2 i-Bu 55 m-Me-C6H4CH2 t-Bu 124 56 p-Et-C6H4CH2 t-Bu 89 57 2-CI-4-F-C6H3CH2 i-Bu 94-97 58 C6H5CH2 i-Bu oil 59 o-CF3-C6H4CH2 t-Bu 105 60 m-EtO-C6H4CH2 t-Bu 106-108 61 3,4-diMe-C6H3CH2 t-Bu 141 62 p-(i-Pr)-C6H4CH2 t-Bu 63 p-Me-C6H4CH2 i-Bu 70-73 64 o-F-c6H4cH2 i-Bu 64-68 65x 2,4-diCl-C6H3CH2 t-Bu 126-128 *Compounds 1 and 5 are diastereoisomers of each other as are Compounds 10 and 43. Each of Compounds 1 and 10 is a racemic mixture of an enantiomer wherein the carbon carrying the triazole ring is in the R-configuration and the carbon carrying the hydroxy group is in the R-configuration and an enantiomer which is its mirror image. Each of Compounds 5 and 43 is a racemic mixture of an enantiomer wherein the carbon carrying thetriazole ring is in the R-configuration and the carbon carrying the hydroxy group is in the S-configuration and an enantiomer which is its mirror image.

+Compound 19 is in the form of a copper complex believed to have the structure

"Nuclear magnetic resonance studies have shown that Compounds 20, 22, 23 and 29 are each in the form of a mixture of diastereoisomers. The weight ratios of the two diastereoisomers in each case are as follows: Compound Weight ratio 20 9:1 22 7:1 23 4:1 29 1.5:1 Compound 4 is the acetate of Compound 1 and Compound 65 is the acetate of Compound 10.

The compounds of general formula (I), or a salt thereof, can be prepared by reducing, preferably at O to 100"C and for 1 to 12 hours, a compound of general formula (ill):

wherein Y, R1 and R2 are as defined above, or a salt thereof. Suitable reducing agents are sodium borohydride, lithium aluminium hydride or aluminium isopropoxide. If desired, catalytic hydrogenation using a suitable metal catalyst can be used. When the compound of general formula (II) is a sterically hindered ketone, a Grignard reagent, for example butylmagnesium halide (e.g. bromide or iodide) can be used as the reducing agent; when a reagent such as a butyl-magnesium halide is used, single diastereoisomers are often produced.

The reduction can be performed by dissolving the reactants in a solvent such as diethyl ether or tetrahydrofuran (for lithium aluminium hydride reduction) or hydroxylic solvents (for sodium borohydride reduction). The reaction temperature will depend on the reactants and solvent; but generally the reaction mixture is heated under reflux. After the reaction, the product can be isolated by extraction into a convenient solvent after acidification with dilute mineral acid. On removal of the solvent in vacuo, the product may be crystallised from a convenient solvent.

Details of the preparation of the compounds of general formula (II) can be found in British Patent Application No. 34590/76.

The salts and metal complexes of the compounds of general formula (I) can be prepared from the latter in known manner. For example, the complexes can be made by reacting the uncomplexed compound with a metal salt in a suitable solvent. The substituent on the ring of the benzyl groups in the compound of general formula (I) can often be changed by methods known in the art.

The gibberellins are a group of plant growth regulators derived from cultures of the fungus GiDberlla fujikuroi (for a description of these substances, see Grove, Quarterly Reviews, 1961, 1556-71). The gibberellins include, for example, gibberellin A3 (or gibberellic acid) disclosed in British Patent Specification No.783,611, gibberellin A4 and gibberellin A7 (the latter being disclosed in British Patent Specification No.

914,893), the disclosures of both these Specifications being incorporated herein by reference Gibberellin A, is obtained commercially as a mixture with a varying (e.g. an equal) proportion of gibberellin A4, in which form it is generally used for plant growth regulating purposes. Other suitable gibberellins are gibberellin GA1 and GAg.

The gibberellins can be employed in the form of a salt of the gibberellin with an amine having at least 8, for example 8 to 40, carbon atoms.

The amine can be a primary, secondary or tertiary amine in which the nitrogen atom may oe attached to an aliphatic, alicyclic, aromatic or heterocyclic residue and may itself form part of a heterocyclic ring. The amine can be an alkylamine or arylamine. Preferred amines have 16 to 36 carbon atoms; conveniently they are secondary or tertiary alkylamines, for example trinonylamine, disoyaamine, dicocoamine and dimethylcocoamine. Dicocoamine is a commercially available mixture of secondary alkylamines manufactured from the mixed fatty acids of coconut oil, the bulk of the mixed alkylamines having C12, C14 or C16 alkyl moieties.

These gibberellin salts make it possible to apply the gibberellins by the so-called ULV (ultra-low volume) application technique (i.e. as little as 1 to 50, e.g. 2 to 10, litres of the gibberellin composition are applied per hectare).

More details of these salts, their preparation, compositions containing them and their use are disclosed in British Patent Specification No. 1538502, the disclosure of which document is incorporated herein by reference.

In carrying out the method of the invention, the amounts of the compound of general formula (I) and of the gibberellin applied to promote tillering in the plants will depend upon a number of factors, for example the particular compound selected for use and the identity of the plant species. However, in general, an application rate of 0.05 to 5, preferably 0.1 to 2, kg of the compound of general formula (I) per hectare, and an application rate (or a total application rate when more than one gibberellin application is used) or 1 to 500g, preferably 1 to 2009 especially 1 to 1 00g of gibberellin per hectare, are employed. Routine tests may be necessary to determine the best rates of application for a specific compound of general formula (I) and of a specific gibberellin for any specific plant.

The compounds of general formula (I) and the gibberellin are conveniently formulated into compositions for use on the plants. These compositions comprise a compound of general formula (I) or a gibberellin, and a carrier or diluent.

The active ingredients can be applied directly to the foliage of a plant. They can be sprayed or dusted on the plants or they can be applied as a cream or paste formulation, or as a vapour, to the plants. Application can be to any part of the plant, for example to the foliage, stems, branches or roots. The compounds of general formula (I) can also be applied to the soil in which the plants are growing.

The compositions may be in the form of dusting powders or granules comprising the active ingredient and a solid diluent or carrier, for example fillers such as kaolin, bentonite, kieselguhr, dolomite, calcium carbonate, talc, powdered magnesia, Fuller's earth, gypsum, Hewitt's earth, diatomaceous earth and China clay. Such granules can be preformed granules suitable for application to the soil without further treatment.

These granules can be made either by impregnating pellets of filler with the active ingredient or by pelleting a mixture of the active ingredient and powdered filler. Compositions for dressing seed, for example, may comprise an agent (for example a mineral oil) for assisting the adhesion of the composition to the seed; alternatively the active ingredient can be formulated for seed dressing purposes using an organic solvent (for example N-methylpyrrolidone or dimethylformamide).

The compositions may also be in the form of dispersible powders, granules or grains comprising a wetting agent to facilitate the dispersion in liquids of the powder or grains which may contain also fillers and suspending agents.

The aqueous dispersions or emulsions may be prepared by dissolving the active ingredient(s) in an organic solvent optionally containing wetting, dispersing or emulsifying agent(s) and then adding the mixture to water which may also contain wetting, dispersing or emulsifying agent(s). Suitable organic solvents are ethylene dichloride, isopropyl alcohol, propylene glycol, diacetone alcohol, toluene, kerosene, methylnaphthalene, the xylenes, trichloroethylene, furfuryl alcohol, tetrahydrofurfuryl alcohol, and glycol ethers (e.g. 2-ethoxyethanol and 2-butoxyethanol).

The compositions to be used as sprays may also be in the form of aerosols wherein the formulation is held in a container under pressure in the presence of a propellant, e.g. fluorotrichloromethane or dichlorodifluoromethane.

The active ingredient can be mixed in the dry state with a pyrotechnic mixture to form a composition suitable for generating in enclosed spaces a smoke containing the compounds. Alternatively, the active ingredient may be used in a microencapsulated form.

By including suitable additives, for example additives for improving the distribution, adhesive power and resistance to rain on treated surfaces, the different compositions can be better adapted for various utilities.

The active ingredient can be used as mixtures with fertilisers (e.g. nitrogen-, potassium- or phosphoruscontaining fertilisers). Compositions comprising only granules of fertiliser incorporating, for example coated with, the active ingredient, are preferred. Such granules suitably contain up to 25% by weight of the active ingredient.

The compositions may also be in the form of liquid preparations for use as dips or sprays which are generally aqueous dispersions or emulsions containing the active ingredient in the presence of one or more surfactants e.g. wetting agent(s), dispersing agent(s), emulsifying agent(s) or suspending agent(s). These agents can be cationic, anionic or non-ionic agents. Suitable cationic agents are quaternaryammonium compounds, for example cetyltrimethylammonium bromide.

Suitable anionic agents are soaps, salts of aliphatic monoesters of sulphuric acid (for example sodium lauryi sulphate), and salts of sulphonated aromatic compounds (for example sodium dodecylbenzenesulphonate, sodium, calcium or ammonium lignosulphonate, butylnaphthalene sulphonate, and a mixture of sodium di-isopropyl- and triisopropyl-naphthalene sulphonates).

Suitable non-ionic agents are the condensation products of ethylene oxide with fatty alcohols such as oleyl or cetyl alcohol, or with alkyl phenols such as octyl- or nonyl-phenol and octylcresol. Other non-ionic agents are the partial esters derived from long chain fatty acids and hexitol anhydrides, the condensation products of the said partial esters with ethylene oxide, and the lecithins. Suitable suspending agents are hydrophilic colloids (for example polyvinylpyrrolidone and sodium carboxymethylcellulose), and the vegetable gums (for example gum acacia and gum tragacanth).

The compositions for use as aqueous dispersions or emulsions are generally supplied in the form of a concentrate containing a high proportion of the active ingredient(s), the concentrate to be diluted with water before use. These concentrates often should be able to withstand storage for prolonged periods and after such storage 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 concentrates may conveniently contain up to 95%, suitably 10-85%, for example 25-60%, by weight of the active ingredient(s).These concentrates suitably contain organic acids (e.g. alkaryl or aryl sulphonic acids such as xylenesulphonic acid or dodecylbenzensulphonic acid) since the presence of such acids can increase the solubility of the active ingredient(s) in the polar solvents often used in the concentrates. The concentrates suitably contain also a high proportion of surfactants so that sufficiently stable emulsions in water can be obtained. After dilution to form aqueous preparations, such preparations may contain varying amounts of the active ingredient(s) depending upon the intended purpose, but an aqueous preparation containing 0.0005% or 0.01% to 10% by weight of active ingredient(s) may be used.

The compositions can be applied to the plants using the so-called electrodynamic spraying technique. A suitable apparatus for this technique is disclosed in British Patent Application No. 29539/76, the disclosure of which Application is incorporated herein by reference. A suitable formulation for this technique and containing a compound of general formula (I) is disclosed in British Patent Application No.7916861, the disclosure of which Application is incorporated herein by reference.

The compositions can comprise also other compound(s) having biological activity, e.g. compounds having fungicidal, plant growth regulating, herbicidal or insecticidal activity.

The fungicidal compound can be for example one which is capable of combating ear diseases of cereals (e.g. wheat) such as Septoria, Gibberella and Helminthosporium spp., seed and soil borne diseases and downy and powdery mildews on grapes and powdery mildew and scab on apple etc. Examples of such fungicidal compounds are imazalil, benomyl, carbendazim (BCM), thiophanate-methyl, captafol, captan, sulphur, dithiocarbamates, carbathiins, copper oxychloride, triforine, dodemorph, tridemorph, dithianon, pyrazophos, binapacryl, quinomethionate, panoctine, furalaxyl, aluminium tris (ethylphosphonate), DPX3217, ethirimol, dimethirimol, bupirimate, chlorothalonil, Chevron RE20615, vinclozolin, procymidone, iprodione and metaxanine.

Suitable insecticides are pirimor, croneton, dimethoate, metasystox and formothion.

The other plant growth regulating compound can be one which controls weeds, improves the level or longevity of the plant growth regulating activity of the compounds of general formula (I), selectively controls the growth of the less desirable plants (e.g. grasses) or causes the compound of general formula (I) to act faster or slower as a plant growth regulating agent. Some of these other agents will be herbicides. Examples of suitable agents are the auxins (e.g. indoleacetic acid, indolebutyric acid, naphthoxyacetic acid or naphthylacetic acid), the cytokinins (e.g. kinetin, diphenylurea, benzimidazole, benzyladenine or BAP), phenoxyacetic acids (e.g. 2,4-D or MCPA), substituted benzoic acids (e.g. TIBA), morphactins (e.g.

chlorfluorecol), maleic hydrazide, glyphosate, glyphosine, long chain fatty alcohols and acids (e.g. Off Shoot O or Off Shoot T), dikegulac, Sustar, Embark, substituted quaternary ammonium and phosphonium compounds (e.g. CCC or Phosfon-D), Ethrel, carbetamide, Racuza, Alar, asulam, abscissic acid, isopyrimol, RH531, hydroxybenzonitriles (e.g. bromoxynil), Avenge, Suffix or Lontrel.

Tiller formation in cereal plants corresponds to the formation of side shoots in other plants. The invention may also be applicable to these other plants; examples of such plants are soya bean, oil seed rape and field beans.

The following Example illustrates the invention; the temperatures are given in degrees Centigrade (").

Example Seeds of wheat (cv Sappo) were grown four per four inch pot in a soil-less compost. The plants were grown in a greenhouse set under the following conditions: 18 C/12 C day/night, 14 hour day length with natural photoperiod extended by high pressure mercury illumination (type MBFR). The plants were top-watered.

The plants were treated with the combinations of Compound 1 and gibberellic acid shown in Table li.

TABLE II Rate Applied Treatment Number Compound 1 Gibberellic acid 500 ppm at T1 2 500 ppm at T1 10 ppm at T2 3 500 ppm at T, 25 ppm at T2 4 500 ppm at Tr 50 ppm at T2 5 500 ppm at T1 100 ppm at T2 6 500 ppm at T1 10 ppm T2 and T3 7 500 ppm at T1 25 ppm at T2 and T3 8 500 ppm at T, 50 ppm at T2 and T3 9 Untreated Control Compound 1 was applied at T1, i.e. when the plants had two fully extended leaves. Gibberellic acid was applied at T2 and in some cases T3; T2 corresponded to the cessation of tiller formation in the control plants (Feekes Scale Stages 5-6) and T3 was 7 days later than T2.

The active ingredients were formulated in 1 ml of a composition containing 95% cyclohexanone, 3.33% Synperonic NPE 1800 and 1.76% Tween 85 and the mixture was diluted to 20 ml with distilled water before use. Compound 1 was applied by root application at 500 ppm by pouring 20 ml of the formulation into the pot. Gibberellic acid was sprayed at varying rates (see Table II) at a volume equivalent to 1000 litres per hectare.

Sdme plants were treated with Compound 1 only, to serve as a treated control; others were left untreated.

There were five replicate pots per treatment.

After treatment, the plants were returned to their original environment and grown to maturity. The plants were then harvested and the following data recorded: (i) Number of ears per plant (ii) Total weight of tiller ears per plant (iii) Weight of main shoot ear per plant (iv) Total weight of all ears borne by the plant.

These data are shown in Table Ill.

TABLE III No. of ears Total weight of Weight of main Total weight of tiller Treatement per plant tiller ears (g) shoot ears (g) + main shoot ears (g) (% control) (% control) (% control) (% control) 1 3.90 (189) 3.12 (73) 1.42 (44) 4.54 (60) 2 3.30 (160) 6.28 (147) 3.23 (101) 9.50 (127) 3 2.70 (131) 7.98 (186) 3.07 (96) 11.05 (148) 4 2.80 (136) 4.69 (109) 3.13 (98) 7.82 (105) 5 2.80 (136) 7.68 (179) 3.46 (108) 11.14 (149) 6 2.90 (140) 6.38 (149) 2.95 (92) 9.33 (125) 7 2.50 (121) 5.66 (133) 3.76 (117) 9.43 (126) 8 2.50 (121) 4.65 (109) 2.79 (87) 7.44 (99) Control 2.06 4.27 3.20 7.47 Difference between treatment means Sig. Sig. Sig. Sig.

LSD P=5% 0.66 2.38 1.02 3.07 P=1% 0.89 3.18 1.37 4.12 Sig.=significance at P=5% LSD P=5%=the least significant difference between two treatment means at the 5% probability level.

The results show that: (i) Treatment with Compound 1 (Treatment 1) alone led to large and statistically significant increases in the number of ears borne by the plants. However, these ears were smaller and total yield was reduced compared with the controls. The reductions in yield were apparent in both main shoot and tiller ears.

(ii) Treatment with Compound 1 followed by gibberellic acid (Treatments 2-8) increased the numbers of ears borne by the plants and also increased the yield, in comparison with the untreated control and with compound 1 alone (Treatment 1). The increases in yield occurred in the tiller ears and to a lesser extent in the main shoot ears.

It may be concluded that application of Compound 1 followed by one or more applications of gibbereilic acid increased grain yields.

Claims (1)

1. A method of promoting the formation of tillers in a cereal plant, the number of said tillers that mature into grain-bearing ears at substantially the same time as the main ear bears grain being increased, the method comprising applying to the cereal plant, during the tiller formation growth stage (e.g. at the two or three leaf stage in the growth of) in the plant, or to the locus surrounding the plant at said stage, a compound of general formula (I)

   wherein R1 is benzyl optionally ring substituted with one, two or three substituents selected from the class consisting of halogen, alkyl, alkoxy, nitro and trifluoromethyl and/or optionally substituted on its methylene moiety with one alkyl (e.g. methyl or ethyl), and R2 is propyl (i.e. n- or i-propyl) or butyl (i.e. n-, sec, i- or t-butyl) or an acid addition salt or metal complex thereof, and then subjecting the plant to an application (e.g.

   more than one application) of a gibberellin.