GB1574430A - Plant growth regulating 3-phenyl-1,2,4-thiadiazol derivate - Google Patents

Description

(54) PLANT GROWTH REGULATING 3-PHENYL-1,2,4-THIADIAZOL DERIVATIVES (71) We, FISONS LIMITED, a British Company of Fison House, 9 Grosvenor Street, London W1X OAH do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to new esters which are plant growth regulant compounds.

UK patent specification 1328964 discloses that certain oxa- and thia-diazole derivatives are biocides and plant growth regulants. Among them is specified (3-phenyl-1,2,4- thiadiazol-5-ylthio)acetic acid. The specification states that functional derivatives of such acids may be employed and refers to esters e.g. lower alkyl, such as ethyl, esters. The only ester of this acid which is specified is the ethyl ester. We have now discovered that certain new esters of this acid are surprisingly advantageous plant growth regulant compounds.

Accordingly, the invention provides as a new compound the alkyl ester of (3-phenyl 1,2,4-thiadiazol-5-ylthio)acetic acid in which the alkyl group is methyl, n-propyl, n-butyl, n-hexyl an alkyl group of at least 7 carbon atoms or a branched chain alkyl group.

The invention provides also a method of regulating the growth of a plant, which method comprises applying to the plant or to the locus at which it is growing or is to grow a plant growth regulant amount of the compound.

The invention also provides a plant growth regulant composition containing the compound. particularly such a composition comprising the compound together with at least one material selected from carriers, surface active agents, other pesticides and other plant growth regulants e.g. such a composition which is solid and comprises the compound together with a solid carrier or such a composition which is liquid and comprises the compound together with a liquid carrier which Is a hydrocarbon whose boiling point is within the range 130-270"C.

The invention provides in addition a process for preparing the compound, which process comprises reacting 3-phenyl-1,24-thiadiazole-5-thiol with a haloacetate of the formula XCH2COOR in which X represents a halogen atom such as chlorine or bromine and R represents the alkyl group.

In addition the invention provides a process for preparing the compound, which process comprises reacting a 3-phenyl-5-halo-1.2,4-thiodiazole, especially one in which the halogen atom is chlorine or bromine. with a mercaptan of formula HSCH2COOR in which R is as defined above.

The invention provides in addition a process for preparing the compound, which process comprises esterifying (3-phenyl-1 2 ,4-thiadiazol-5-ylthio) acetic acid with an alkanol of formula ROH where R is as defined above.

The compounds are outstandingly useful as plant growth regulants. They possess a surprisingly good combination of safety and activity, hence for instance enabling a smaller amount of material to be applied to achieve a given effect on the plant or enabling a given effect to be obtained on the plant with a greater margin of safety to the plant. The high plant growth regulant activity of the alkyl esters in which the alkyl group contains at least 7 carbon atoms is particularly surprising since one would have expected that their larger molecules would find it more difficult to penetrate a plant and be absorbed than would a simpler ester such as the ethyl ester. The branched chain esters are similar. The present alkyl esters. and particularly those in which the alkyl group contains at least 4 carbon atoms, are surprisingly safe to plants compared with the safety of the known ethyl ester to plants.

The present compounds are preferably prepared by the reaction of the 3-phenyl-1,2,4thiadiazole-5-thiol with the halide of formula XCH2COOR. X usually represents a chlorine atom. The reaction is preferably carried out in the presence of an acid binding agent, for example potassium carbonate. The reaction may be carried out in an inert solvent, e.g. water, acetone or 2-butanone. The temperature is usually within the range 50-100 C.

The reaction of the 3-phenyl-5-halo-1,2,4-thiadiazole with the mercaptan of formula HSCH2COOR may be carried out in the presence of an inert solvent. The temperature is usually within the range 40-120"C.

The esterification of the (3-phenyl-1,2,4-thiadiazol-5-ylthio)acetic acid with the alkanol of formula ROH may be carried out under the usual esterification conditions. An inert solvent is usually employed, as is an acid catalyst. The temperature is usually within the range 50-150"C.

The plant physiologically active compositions can be prepared by admixing the ingredients. Usually the compositions are initially produced in the form of concentrates, e.g. containing 0.5-80%, for example 10-50%, of the present compound, and these are diluted with water or hydrocarbon, usually water, for application by spraying, generally such that the concentration of the compound is 0.005-5% e.g. 0.05-5%. Percentages, ratios and parts in this specification are by weight unless otherwise indicated.

The compositions normally contain a surface active agent and/or a carrier.

The carrier may be a liquid, e.g. water (e.g. water used to dilute a concentrate for application). If water is employed as carrier in a concentrate, an organic solvent may also be present as carrier, though this is not usually employed. A surface active agent may advantageously be present.

The carrier may be a liquid other than water, for example an organic solvent, usually a water-immiscible solvent, e.g. a hydrocarbon which boils within the range 130-270"C, in which the compound is dissolved or suspended. A concentrate containing an organic solvent suitably also contains a surface active agent so that the concentrate acts as a self-emulsifiable oil on admixture with water.

The carrier may be a solid, which may be finely divided. Examples of suitable solids are limestone, clays, sand, mica, chalk, attapulgite, diatomite, perlite, sepiolite, silicas, silicates. lignosulphonates and solid fertilizers. The carrier can be of natural or synthetic origin or can be a modified natural material.

Wettable powders soluble or dispersable in water may be formed by admixing the compound in particulate form with a particulate carrier or spraying molten compound on to the particulate carrier. admixing a wetting agent and a dispersing agent, and finely grinding the whole powder mixture.

An aerosol composition may be formed by admixing the compound with a propellant, e.g. a polyhalogenated alkane such as dichlorodifluoromethane, and suitably also with a solvent.

A flowable suspension concentrate may be formed by grinding the compound with water, a wetting agent and a suspending agent.

Thus the present composition can for example be solid (e.g. dust or granules) and contain a solid carrier or liquid (e.g. an emulsifiable concentrate) and contain a liquid carrier which is a hydrocarbon which boils within the range 130-270"C.

The term 'surface active agent' is used in the broad sense to include materials variously called emulsifying agents, dispersing agents and wetting agents. Such agents are well known in the art.

The surface active agents used may comprise anionic surface active agents, for example soaps, fatty sulphate esters such as dodecyl sodium sulphate, octadecvl sodium sulphate and cetyl sodium sulphate. fatty aromatic sulphonates such as alkyl-benzene sulphonates or butyl-naphthalene sulphonates, more complex fatty sulphonates such as the amide condensation product of oleic acid and N-methyl taurine or the sodium sulphonate of dioctvl succinate.

The surface active agents may also comprise non-ionic agents, for example condensation products of fatty acids. fatty alcohols or fatty substituted phenols with ethylene oxide, or fatty esters and ethers of sugars or polyhydric alcohols, or the products obtained from the latter by condensation with ethylene oxide. or the products known as block copolymers of ethylene oxide and propylene oxide.

The surface active agents may also comprise cationic agents. for example cetyl trimethvlammonium bromide.

Preferred surface active agents include fatty alkyl sulphates, alkyl aryl sulphonates, fatty alkyl ethoxylates. sulphonated fatty alkyl ethoxylates, dialkyl sulphosuccinate esters, lignin sulphonate salts. sulphonated naphthalene-formaldehyde condensates and sulphonated urea-formaldehvde condensates.

The present compounds can be applied in conventional ways, e.g. by spraying. The spray applied may for instance contain 100-4000, e.g. 500-2000, parts of surface active agent per million of spray.

The present active compound may be used in admixture or sequence with another pesticide, e.g. herbicide, insecticide or fungicide, or with another plant growth regulant or with a fertilizer. The sequence is usually carried out within the same crop season. The compound may be used in admixture or sequence with other plant growth regulants, such as 1-carboxyethyl, 3-chlorocarbanilate potassium salt; N,N-dimethylamino succinamic acid; maleic hydrazide; tributyl-2,4-dichlorobenzyl phosphonium chloride; 2,3,5-triiodobenzoic acid; or (2-chloroethyl)phosphonic acid; pesticides, such as carbaryl or dimethoate; herbicides, such as 2,4-dichlorophenoxyacetic acid, 2-methyl-4-chlorophenoxyacetic acid, or substituted triazines (e.g. 2-chloro-4,6-bis[ethylamino]-s-triazine) or ureas; or fungicides, such as copper compounds or dithiocarbamates. Of particular interest are mixtures or sequences with other plant growth regulants or herbicides. In general, the ratio of present compound, e.g. the 2-methylpropyl ester, to other pesticide or plant growth regulant lies in the range 1000:1 to 1:15 e.g. 1:0.1 to 1:15.

The present compounds may be in admixture with non-phytoxic oils, e.g. Agri-Oil Plus or Sun Oil 11E.

In the use of the compounds as plant growth regulants, low rates of application are usually required for instance 0.01-4 such as 0.1-4, e.g. 0.5-1, kg per hectare. For instance, to encourage branching, a preferred rate is 0.1-1 kg/ha while to increase fruit set a preferred ratio is 0.03-0.4 kg/ha.

For use as plant growth regulants, the compounds are applied to modify the growth of a plant without themselves killing it, though they may be used to increase the sensitivity of undesired plants (weeds) to herbicides. Usually, however, the compounds are applied to regulate the growth of a desired plant. They may be applied pre- or post-planting, or pre- or post-emergence, of the plant. Preferably they are applied post-emergence of the plant.

They may be employed on the farm or in the greenhouse, orchard or nursery. The growth regulation may take various forms. The compounds can be employed to reduce the overall height to which a plant will grow. They may be used on seeds or tubers to stimulate germination or root. stem or bud development. They may be used on cuttings and transplants to stimulate root formation. They may be used on blossoms to induce parthenogenesis, to retard blossoming, to stimulate the growth of abscission cells to produce premature dropping of blossom and set fruit, or to modify the growth of abscission cells to prevent drop of mature fruit. They may be used to increase the sugar content of sugarbeet. They may be employed to increase the number of flowers per branch. They may be employed to thin fruit.

The main type of growth regulant activity of the compounds seems to lie in their ability to break the apical dominance of a plant either permanently or temporarily, hence inducing greater branching. Greater branching can produce more flowers (e.g. on chrysanthemums) or more fruit (e.g. on apple trees or soya beans).

The plant growth regulant effect of the present compounds can be brought about on fruit, vegetable, plantation and ornamental plants, e.g. apple, pear or plum trees, chrysanthemums. soya bean plants or cotton plants. Particularly advantageous is use to increase the yield of soya beans or cotton. To increase the yield of soya beans, rates of 0.2-4, e.g. 0.2-2, especially 0.3-1.2, particularly 0.5-1.2. kg/hectare of the compounds are preferred. To increase the yield of cotton. rates of 0.03-4, especially 0.1-1.2, kg/hectare are preferred.

Particular compounds among the present new esters are specified in the following Examples. The esters in which the alkyl group contains at least 7 carbon atoms usually contain 7-16 e.g. 7-12 carbon atoms in their alkyl groups. The branched chain alkyl esters usually contain 3-16 e.g. 3-12 carbon atoms in their alkyl groups. Preferred among the present esters are the 1-methylheptyl, n-nonyl and 2-methylpropyl esters (e.g. for use on soya beans. apple trees or cotton plants) and the n-heptyl ester (e.g. for use on soya beans, chrysanthemums or cotton plants).

The invention is illustrated by the following Examples.

EXAMPLE 1 Preparation of the l-methvlheptyl ester of (3-phenyl-1,2, 4-thiadiazol-5-ylthio)acetic acid 3-Phenyl-1.2.4-thiadiazole-5-thiol and the 1-methylheptyl ester of chloroacetic acid were prepared by known methods. 3-Phenyl-1.2.4-thiadiazole-5-thiol (97 parts) was added to potassium carbonate (35 parts) in 2-butanone (MEK) (1600 parts) and refluxed for 30 minutes. 1-Methvlheptyl ester of chloroacetic acid (103 parts) was added while stirring and refluxing the solution. The mixture was refluxed for a further 5 hours. The solution was cooled and the solid filtered off. The filtrate was evaporated to dryness yielding an oil.

Excess petroleum ether of boiling point 60-80"C was added to the oil which was then boiled with charcoal. The charcoal was filtered off, the solvent removed under vacuum and the product obtained as a yellow oil (50 parts 33% yield) biling point 175 190 C at 0.15 mm Hg pressure.

Analysis C H N Found (%) 59.65 6.55 7.55 Calc for C18H24N202S2 (%) 59.31 6.64 7.69 Reaction:

EXAMPLES 2-16 Preparation of other compounds (C)

Prepared by analogous methods to Example 1 were the compounds indicated in the table.

Example Group R Ester M.p.

2 CH3 methyl 48-9 3 C3H7-n propyl 50-2 4 CH(CH)2 1-methylethyl 45-7 5 C4H9-n butyl 51-4 6 CH2CH( CH3)2 2-methylpropyl 60-2 7 C(CH3)3 1,1-dimethylethyl 74-6 8 C6H13-n hexyl 27-8 9 C7Hl5-n heptyl oil 10 CH(C3H7-n)2 1-propylbutyl 40-2 11 C8H17-n octyl oil 12 C9H19-n nonyl 28-9 13 CH(CH2CH(CH3)2)2 l-(2-methylpropyl)-3-methylbutyl oil 14 C10H21-n decyl oil 15 C11H23-n undecyl oil 16 C12H25-n dodecyl oil EXAMPLES 17-21 Growth regulant activity on apple seedlings Apple seedlings, Malus pumila, were grown in John Innes I potting compost in a controlled environment room (20"C; 65-85% R.H.; 14 hours per day artificial illumination at 13,000 lux) until the plants were between 90 and 140 mm tall. The plants were sprayed with doses of the present compounds, and also with doses of (3-phenyl-1,2,4-thiadiazol-5ylthio)acetic acid, at a rate equivalent to 900 I/ha. Each compound was sprayed at two dose rates, 0.7 and 2.8 kg/ha. Each dose rate was applied to 3 separate plants for each compound.

The compounds were formulated in one of two ways: (a) Suspension in water containing 0.1% of wetting agent (nonyl-phenol/ethylene oxide condensation product).

(b) Solution in 75% acetone : 25% water, by volume.

The formulation used for each is indicated in the table.

After spraying, the plants were returned to the controlled environment room. Three weeks later they were compared with untreated controls and with the plants sprayed with (3-phenyl-1 ,2,4-thiadiazol-5-ylthio)acetic acid (A) to assess growth regulant and phytotoxic effects.

The results are summarized in the table. Each result is the average of the 3 plants treated at each dose.

Growth regulant effects on apple seedlings Key: > : slightly more than compound (A) = : similar to compound (A) Sl : slight damage Phytoto % Height Mean number of xicity Reduction of axillary shoots of (A) control longer than 15mm Necrosis Dose kg/ha a.i. 2.8 0.7 2.8 0.7 2.8 0.7 Compound Formulation of example 4 (a) 45 35 8 6 = > of example 5 (a) 60 20 7 5 = > of example 6 (a) 35 30 5 5 = nil of example 9 (b) 30 30 6 6 > > of example 12 (b) 40 15 6 5 = nil (A) (a) 25 15 4 4 Sl nil Control - - - 0 0 nil nil In these tests. the present compounds inhibit the dominance and development of the apical bud but do not kill it. They thus cause height reduction and promote axillary shoot formation. They do not produce undesirable phytototoxic effects such as necrosis at an application rate of 0.7 kg/ha. They are an improvement on compound (A).

EXAMPLES 22-29 Growth regulant activitv on chrysanthemums Rooted cuttings of chrysanthemums var. Golden Princess Anne were planted in John Innes I potting compost and allowed to establish themselves for one week by which time they were 70-110 mm tall. The cuttings were grown in a controlled environment room (20"C; 65-85% R.H.; 14 hours per day artificial illumination at 13000 lux). The plants were then sprayed with doses of the present compounds and with doses of (3-phenyl-1,2,4thiadiazol-5-ylthio)acetic acid at a rate equivalent to 900 1/aha. Each compound was sprayed at two dose rates, 0.7 and 2.8 kg/ha. Each dose rate was applied to two separate plants for each compound.

The compounds were formulated in one of two ways: (a) suspension in water containing 0.1% of wetting agent (nonyl-phenoVethylene oxide condensation product).

(b) solution in 75% acetone : 25% water, by volume.

The formulation used for each compound is indicated in the table.

After being sprayed, the plants were returned to the controlled environment room.

Three weeks later they were compared with untreated controls and with plants sprayed with (3-phenyl-1 ,2,4-thiadiazol-5-ylthio)acetic acid (A) to assess growth regulant effects.

The results are summarised in the table. Each result is the average of the two plants treated.

Growth regulant effects on chrysanthemums % Height Mean number of Reduction axillary shoots of control longer than 30 mm Dose kg/ha a.i. 2.8 0.7 2.8 0.7 Compound Formulation of example 2 (a) 25 20 6X 7X of example 3 (a) 30 20 6X 5X of example 4 (a) 35 25 6X 7X of example 5 (a) 30 20 9X 6X of example 6 (a) 35 10 8X 6 of example 8 (b) 30 30 6X 7X of example 9 (b) 25 30 7X 7X of example 11 (b) 30 10 6X 5 (A) (a) 30 15 7 3 Control - - - 1 1 Key: X : better shaped plants than control with longer axillary shoots.

The results show the present compounds (C) have improved growth regulating ability compared to compound (A), especially at the lower dose.

EXAMPLES 30-35 Growth regulant activity on french beans French beans, var. Canadian Wonder, were grown in John Innes I potting compost in a controlled environment room (20"C; 65-85% R.H.; 14 hours per day artificial illumination at 13000 lux). After one week, when the first pair of leaves on each plant was expanding, the plants were sprayed with doses of the present compounds and with (3-phenyl-1,2,4thiadiazol-5-ylthio)-acetic acid at a rate equivalent to 900 I/ha. Each compound was sprayed at two dose rates, 0.7 and 2.8 kg/ha. The 0.7 kg/ha doses were applied to two separate plants per compound and the 2.8 kg/ha doses were applied to 3 separate plants.

The compounds were formulated in one of two ways: (a) suspension in water containing 0.1% of wetting agent (nonyl-phenol/ethylene oxide condensation product).

(b) solution in 75% acetone : 25% water, by volume.

The formulation used is indicated in the table.

After being sprayed, the plants were returned to the controlled environment room.

Three weeks later they were compared with untreated controls to assess growth regulant and phytotoxic effects. The results are summarised in the table. Each result is the average of the 2 or 3 plants treated.

Growth regulant effects on french beans % Height Axillary Phytotoxicity of (A) Reduction of Development Control Scale 0-5 Shoot deformity Necrosis Dose kg/ha a.i. 2.8 0.7 2.8 0.7 2.8 0.7 2.8 0.7 Compound Formulation of example 4 (a) 40 40 4 2 = = nil nil of example 5 (a) 20 25 4 1 = = nil nil of example 7 (a) 25 20 3 2 < < nil nil of example 9 (b) 40 15 4 2 > = > nil of example 11 (b) 30 25 4 2 > > nil nil of example 15 (b) 25 10 5 2 > = > nil (A) (a) 40 10 4 2 Mod Sl nil nil Control - - - 1 1 nil nil nil nil Key: < : slightly less than compound (A) > : slightly more than compound (A) = : similar to compound (A) Sl : slight damage Mod moderate damage French beans are sensitive and so are useful monitors of phytotoxicity. The results show that the present compounds (C) do not have undue phytotoxicity.

EXAMPLES 36-52 Phytotoxicity as indicated by mustard Mustard (sinapis alba) seeds were sown in aluminium pans 200 mm long x 100 mm wide x 50 mm deep containing John Innes No 1 potting compost. They were then watered and placed in a controlled environment room temperature 22"C, relative humidity 65-85%, artificial illumination 13000 metre-candles for 14 hours per day). Fourteen days after sowing, the seedlings were sprayed with (a) aqueous suspensions containing 0.1% of wetting agent (nonylphenol/ethylene oxide condensation product) or (b) aqueous acetone solutions (depending on the physical properties of the compounds), of the compounds listed in the table below, including (B) ethyl (3-phenyl-1,2,4-thiadiazol-5-ylthio)acetate. The formulation used for each compound is shown in the table. Each compound was sprayed at a rate of 2.8 kg of the compound in 900 litres per hectare. After seven days growth in the controlled environment room, the plants were visually assessed for scorch on a 0 to 9 scale in which 0 signifies no scorch and 9 signifies that most plants were dead or dying. R refers to the formula in Examples 2-16.

Example Compound Formulation R Scorch 36 of Example 2 (a) CH3 4 37 (B) (b) C2H5 7 38 of Example 3 (a) C3H7-n 3 39 " " 4 (a) CH(CH3)2 2 40 " " 5 (a) C4H9-n 2 41 " " 6 (a) CH2CH(CH3)2 1 42 1l 1l 7 (a) C(CH3)3 1 43 " " 8 (b) C6Hl3-n 4 44 " " 9 (b) C7H15-n 2 45 " " 10 (a) CH(C3H7-n)2 0 46 " " 11 (b) C8Hl7-n 1 47 " " 1 (b) CH(CH3)(CH2)5CH3 1 48 " " 12 (b) CgH19-n 1 49 " " 13 (b) CH(CH2CH(CH3)2)2 O 50 " " 14 (b) C1OH2l-n 0 51 " " 15 (b) C11H23-n O 52 " " 16 (b) C12H25-n 0 It can be seen that the present esters are surprisingly less phytotoxic than the known ethyl ester, and that the phytotoxicity of the known ester is uniquely high.

Claims (30)

WHAT WE CLAIM IS:

1. The alkyl ester of (3-phenyl-1,2,4-thiadiazol-5-ylthio)acetic acid whose alkyl group is methyl, n-propyl. n-butyl, n-hexyl, an alkyl group of at least 7 carbon atoms or a branched chain alkyl group.

2. The ester according to claim 1 whose alkyl group is methyl, n-propyl, n-butyl, n-hexyl, an alkyl group containing 7-16 carbon atoms or a branched chain alkyl group containing 3-16 carbon atoms.

3. The ester according to claim 2 whose alkyl group contains 7-12 carbon atoms.

4. The ester according to claim 2 whose alkyl group is a branched chain alkyl group containing 3-12 carbon atoms.

5. An ester according to claim 1 which is specified herein.

6. The 1-methylheptyl ester of (3-phenyl-1,2,44hia'diazd-5-yfthio)acetic acid.

7. The n-nonyl ester of (3-phenyl-1 ,2,4-thiadiazol-5-ylthio)acetic acid.

8. The 2-methylpropyl ester of (3-phenyl-1,2,4-thiadiazol-5-ylthio)acetic acid.

9. The n-heptyl ester of (3-phenyl-1,2,4-thiadiazol-5-ylthio)acetic acid.

10. A process for preparing the alkyl ester claimed in any one of the preceding claims, which process comprises reacting 3-phenyl-1,2,4-thiadiazole-5-thiol with a haloacetate of the formula XCH2COOR in which X represents a halogen atom and R represents the alkyl group.

11. A process for preparing the alkyl ester claimed in any one of claims 1-9, which process comprises reacting 3-phenyl-5-halo-1,2,4-thiadiazole with a mercaptan of formula HSCH2COOR in which R represents the alkyl group.

12. A process for preparing the alkyl ester claimed in any one of claims 1-9, which process comprises esterifying (3-phenyl-1 ,2,4-thiadiazol-5-ylthio)acetic acid with an alkanol of formula ROH in which R represents the alkyl group.

13. A process for preparing an alkyl ester, which process is performed substantially as hereinbefore described.

14. A process for preparing an alkyl ester, which process is performed substantially as hereinbefore described in any one of Examples 1-16.

15. An alkyl ester prepared by a process claimed in any one of claims 10-14.

16. A plant growth regulant composition comprising the ester claimed in any one of claims 1-9 and 15 together with at least one material selected from carriers, surface active agents, other pesticides and other plant growth regulants.

17. A composition according to claim 16 which is solid and comprises the ester together with a solid carrier.

18. A composition according to claim 16 which is liquid and comprises the ester together with a liquid carrier which is a hydrocarbon whose boiling point is within the range 130-2700C.

19. A composition according to claim 16 which contains a surface active agent.

20. A composition according to claim 16 which contains another pesticide or plant growth regulant.

21. A composition according to claim 16 substantially as hereinbefore described.

22. A composition according to claim 16 substantially as hereinbefore described in any one of Examples 17-52.

23. A process for preparing a composition claimed in any one of claims 16-22, which process comprises admixing the ingredients.

24. A composition prepared by a process claimed in claim 23.

25. A method of regulating the growth of a plant, which method comprises applying to the plant or to the locus at which it is growing or is to grow a plant growth regulant amount of an ester claimed in any one of claims 1-9 and 15.

26. A method according to claim 25 wherein the ester is applied in the form of a composition claimed in any one of claims 16-22 and 24.

27. A method according to claim 25 or 26 wherein the ester is applied to the locus at which the plant is growing.

28. A method according to any one of claims 25-27 wherein the ester is applied at a rate of 0.01-4 kg per hectare.

29. A method according to claim 25, which method is performed substantially as hereinbefore described.

30. A method according to claim 25, which method is performed substantially as hereinbefore described in any one of the Examples 17-52.