GB2113549A - Insecticidal and acaricidal compositions based on and a pyrethroid, and method for the treatment of plants to combat arthropoda by means of these compositions - Google Patents

Abstract

The invention relates to insecticidal and acaricidal compositions having a synergistic effect and containing, as the active ingredient, a combination of ethion with a pyrethroid of the general formula:- <IMAGE> wherein R represents a hydrogen atom or the cyano radical and R1 represents the 2,2-dimethyl-3-(2,2-dichlorovinyl)- cycloprop-1-yl radical, the 2,2- dimethyl-3-(2,2-dibromovinyl)- cycloprop-1-yl radical, the 2,2- dimethyl-3-(2-methylprop-1-enyl)- cycloprop-1-yl radical or the 1-(4- chlorophenyl)-isobut-1-yl radical, such as cypermethrin decamethrin, fenvalerate and permethrin and a method for the treatment of plants to combat crop-destroying arthropoda which comprises applying such compositions to the plants. The compositions and method are more particularly intended for combating plant-eating mites which have become resistant to organo-phosphorus pesticides.

Description

SPECIFICATION Insecticidal and acaricidal compositions based on ethion and a pyrethroid, and method for the treatment of plants to combat arthropoda by means of these compositions The present invention relates to insecticidal and acaricidal compositions having a synergistic effect, which are intended for combating crop-destroying arthropoda. It furthermore relates to a process for the treatment of plants to comact crop-destroying arthropoda, more particularly to combat plant-eating mites.

It is known to use organophosphorus pesticides in agriculture to combat crop-destroying arthropoda.

Amongst these compounds, ethion has been used successfully for a long time to combat plant-eating mites.

It is recalled that ethion is the active ingredient of the formula:

the chemical name of which isS,S'-methylene-bis - (0,0 -diethyl dithiophosphate). It has been described in U.S. Patent No. 2,873,228. This compound is also known by the common name diethion. In the present test, it will be systematically denoted by the common name "ethion".

For a long time, organophosphorus pesticides have been used successfully as insecticides and acaricides in agriculture. For some years, the appearance and development of strains of plant-eating mites which have become resistant to organophosphorus pesticides have been observed. Combating these mites resistant to organophosphorus pesticides led agriculturists to increase the treatment doses and hence the cost of these treatments; in spite of this, the results were frequently disappointing and there was an increase in the residues on the plants treated.

It is furthermore known to use, as insecticides andloracaricides in agriculture, a class of compounds denoted by the generic term pyrethroids, which are described especially in U.S. Patents Nos.

3,835,178 and 3,996,244. These compounds have in general an excellent insecticidal activity, but their acaricidal activity is generally considered inadequate.

It has now been found that the combination of certain pyrethroids with ethion makes it possible very considerably to improve the acaricidal activity thereof, in particular towards strains of plant-eating mites which have become resistant to organophosphorus pesticides; it is this finding which forms the subject of the present invention. This improvement is all the more surprising because, when they are used by themselves, pyrethroids have virtually no acaricidal activity, at the doses used, on these same strains of mites. This synergistic effect will be explained more clearly hereinafter with reference to the examples 8 to 11 illustrating the present patent application.

The present invention accordingly provides insecticidal and acaricidal compositions for use in combating crop-destroying arthropoda, which compositions comprise, as the active ingredient, a synergistic combination of ethion with a pyrethroid corresponding to the general formula:

wherein R represents a hydrogen atom or the cyano radical and R1 represents the 2,2 - dimethyl - 3 - (2,2 dichlorovinyl) - cycloprop - 1 - yl radical, the 2,2 dimethyl - 3 - (2,2, - dibromovinyl) - cycloprop -1 - yl radical, the 2,2 - dimethyl - 3 - (2 - methylprop -1 enyl) - cycloprop - 1 - yl radical or the 1 - (4 chlorophenyl) - isobut -1 - yl radical in association with an inert carrier or diluent acceptable in agriculture and/or a surface active agent which is acceptable in agriculture.

The pyrethroids according to the formula (II) frequently exist in different optical or geometric isomericforms, if appropriate mixed with one another.

In terms of the present text, the expression "pyrethroids according to the formula (II)" includes the different isomericforms of these compounds and also mixtures thereof.

The following compounds may be mentioned as examples of pyrethroids corresponding to the formula (all): - (RS) - alpha - cyano - 3 - phenoxybenzyl (1 RS) cis,trans - 3 - (2,2 - dichlorovinyl) - 2,2 - dimethylcyclopropanecarboxylate, the common name of which is cypermethrin, - 3 - phenoxybenzyl (1 RS) - cis,trans - 3 - (2,2 - dichlorovinyl) - 2,2 - dimethylcyclopropanecarboxylate, the common name of which is permethrin, - (S) - alpha - cyano - 3 - phenoxybenzyl (1 R) - cis - 3 (2,2 - dibromovinyl) - 2,2 - dimethylcyclopropanecarboxylate, the common name of which is de camethrin and which is also called deltamethrin, and - (RS) - alpha - cyano - 3 - phenoxybenzyl (RS) - 2 - (4 - chlorophenyl) - 3 - methylbutyrate, the common name of which is fenvalerate.

As used in the present specification, the word "composition" denotes not only compositions which are ready for use, if necessary after dilution (e.g. those prepared beforehand and intended for use after dilution), but also mixtures of the two active ingredients prepared for immediate use (i.e.

mixtures prepared just before application to the crops in question).

The present invention relates more particularly to the compositions comprising from 0.01 to 100 parts by weight of pyrethroid (II) per 100 parts byweightof ethion, and preferably from 0.01 to 10 parts by weight of pyrethroid per 100 parts by weight of ethion.

Cypermethrin is preferably used as the pyrethroid (II).

In addition to the synergistic combination consist ing of ethion and the pyrethroid according to the formula (II), the composition according to the inven tion generally comprise a solid or liquid inert carrier or diluentwhich is acceptable in agriculture and/or a surface active agent which is acceptable in agricul ture.

If necessary, these compositions may additionally contain other additives which are also acceptable in agriculture, e.g. protective colloids, adhesives, thickeners, thixotropic agents, penetrating agents, stabilisers, sequestering agents and the like, together, if necessary, with other known active ingredients having pesticidal properties (in particular insecticidal, acaricidal orfungicidal properties) or properties which promote plant growth.

In general, the compositions according to the invention comprises from 0.001 to 95% by weight of the combination of active ingredients, i.e. of the combination ethion + pyrethroid.

In the present account, the term "carrier or diluent" denotes any organic or inorganic, natural or synthetic material with which the combination of active ingredients is itself combined in order to facilitate its application to the crops or to the soil, or to facilitate its storage or handling. This carrier is generally inert and acceptable in agriculture, in particular to the crop treated.

The carrier or diluent can be solid or a liquid.

Solid carrier which may be mentioned in particular are clays, natural or synthetic silicates, natural silicas such as e.g. diatomaceuous earth, magnesium silicates such as talc, aluminium magnesium silicates such as e.g. attapulgites and vermiculites, aluminium silicates such as e.g. kaolinites, montomorillonites and micas, calcium carbonate, calcium sulphate, synthetic calcium or aluminium silicates, natural or synthetic resins such as e.g. polyvinyl chloride, styrene polymers and copolymers and solid polychlorophenols, waxes such as e.g. beeswax and paraffin, solid fertilisers such as superphosphates, and the like.

Liquid carriers which may be mentioned in particular are water, alcohols such as e.g. isopropanol and glycols, ketones such as e.g. acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, ethers, aromatic or paraffinic hydrocarbons such as e.g. benzene, toluene, xylenes, petroleum fractions fractions or cuts and kerosine, mineral oils, halogenohydrocarbons such as e.g. carbon tetrachloride, perchloroethylene or trichloroethane, of, if appropriate, liquefied gases. Mixtures oftheseva- rious liquid carriers are frequently used.

The surface-active agent can be an emulsifying, dispersing or wetting agent of ionic or non-ionic type. Examples which may be mentioned are salts of polyacrylic acids, salts of lignosulphonic acid, salts of phenolsulphonic or naphthalenesulphonic acids, polycondensates of ethylene oxide with fatty alcohols, fatty acids or fatty amines, substituted phenols (in particular alkylphenols or arylphenols), salts of sulphosuccinic acid esters, taurine derivatives (in particular alkyl-taurates) and phosphoric acid esters of condensates of ethylene oxide with alcohols or phenols. The presence of at least one surface-active agent is generally essential if the inert carrier is not soluble in water and if the vehicle of application is water.

The compositions according to the invention can be in a fairly wide variety of solid or liquid forms.

As forms of solid compositions, there may be mentioned dusting powders or sprinkling powders (with an active ingredient content which can range upto 90%).

As forms of liquid compositions or compositions which are to be made up into liquid compositions on application, there may be mentioned solutions, in particular water-soluble concentrates, emulsifiable concentrates, emulsions, suspension concentrates, aerosois, wettable powders (or spraying powders) and pastes.

The emulsifiable or soluble concentrates most frequently comprise 10 to 80% by weight of the combination of active ingredients, and the emulsions or solutions which are ready for application, also called spraying mixtures, contain 0.001 to 20% by weight of the combination of active ingredients.

In addition to the solvent and where necessary, the emulsifiable concentrations can contain 2 to 20% by weight of suitable additives such as stabilisers, surface-active agents, penetrating agents, corrosion inhibitors, dyestuffs and adhesives. The compositions of a few concentrates are now given as examples. Hereafter, A represents ethion and B cypermethrin.

EXAMPLE 1 - combination of the active ingredients (A/B = 2.4) 150 litre - calciumalkylarylsulphonate 3ngIlitre - 10:1 ethylene oxide/alkylphenol condensate 50 goitre - aromatic solvent (petroleum cut) q.s. 1 litre The composition of another emulsifiable concentrate according to the invention is now given as an example: EXAMPLE 2 - Combination of the active ingredients (A/B = 4.5) 500 goitre - calcium alkylarylsulphonate 40 goitre - 10:1 ethylene oxide/alkylphenol condensate 60 goitre - cyclohexanone 100g/litre - aromatic solvent (petroleum cut) q.s. 1 litre Starting from these concentrates, emulsions of any desired concentration, which are particularly suitable for application to the crops, can be obtained by dilution with water.

The wettable powders (or spraying powders) are usually prepared so as to contain 20 to 95% by weight of active ingredient, and they usually contain, in addition to the solid carrier, from 0 to 5% by weightofawetting agent, from 3to 10% by weight of a dispersing agent and, where necessary, from 0 to 10% by weight of one or more stabilisers and/or other additives such as penetrating agents, adhe sives, anti-caking agents, dyestuffs or the like.

Various compositions of wettable powers are now given as examples: EXAMPLE 3 - combination of active ingredients (A/B) = 10) 30% - calcium lignosulphonate (deflocculant) 5% - calcium alkylarylsulphonate (anionic wetting agent 1% - anti-caking silica 30% - kaolin (filled) 34% Another composition of a spraying powder, this time of 40% strength, uses the following constituents: EXAMPLE 4 - combination of active ingredients (A/B = 100) 400g - sodium dibutylnaphthylsulphonate 50 g - 3:2:1 naphthalenesulphonic acid/phenol sulphonic acid/formaldehyde condensate 30 g - kaolin 1209 - anti-caking silica 400 g Another composition of a spraying powder, this time of 25% strength, uses the following constituents:: EXAMPLE 5 - combination of active ingredients (A/B = 6.66) 250 g - calcium lignosulphonate 45 g - mixture of equal parts by weight of champagne chalk and hydroxyethyl cellulose 19g - sodium dibutylnaphthalenesulphonate 15 9 - silica 250 g - kaolin 4219 Another composition of a spraying powder, this time of 10% strength, uses the following constituents: EXAMPLE 6 - combination of active ingredients (A/B = 200) 100g - mixture of sodium salts of saturated fatty acid sulphates 30 g - naphthalenesulphonic acid/formaldehyde condensate 50 g - silica 1009 - kaolin 720g To obtain these spraying powders or wettable powders, the active ingredients are intimately mixed with the additional substances in suitable mixers, and the mixture is ground in mills or other suitable grinders.This gives spraying powders of advantageous wettability and suspendability; they can be suspended in water at any desired concentration, and this suspension can be used very advantageously, in particular for application to the leaves of the plants.

As already stated, the aqueous dispersions and aqueous emulsions, e.g. compositions obtained by diluting, with water, a wettable powder or an emulsifiable concentrate according to the invention, are included in the general scope of the compositions which can be used in the present invention.

The emulsions can be of the water-in-oil or oil-in-water type and they can have a thick consistency such as that of a "mayonnaise".

For so-called ultra-low volume (ULV) application, entailing spraying as very fine droplets, solutions of the two active ingredients in suitable solvents are prepared and a mixture of these solutions is supplied at a rate of about 1 to 5 litres/hectare. The composition of a ULV solution according to the invention is now given as an example: EXAMPLE 7 - combination of active ingredients (A/B) = 10) 200g/litre - aromatic solvent (petroleum cut) q.s. 1 litre The invention also provides a method for the treatment of plants to combat crop-destroying arthropoda, and more particularly to combat planteating mites such as spider mites, which comprises applying to these plants an effective amount of a composition containing, as the active ingredient, a combination of ethion with a pyrethroid corresponding to the formula (II) as hereinbefore described.The term "effective amount" is understood as meaning an amount sufficient to enable the arthropoda present on these plants, or in their immediate vicinity, to be controlled and destroyed. For the method according to the invention, it is preferred to use aqueous dispersions or aqueous emulsions. e.g.

compositions obtained by diluting, with water, a wettable powder or an emulsifiable concentrate described above. The method can also be carried out using an ultra-low volume (ULV) solution such as described above.

Advantageously, the method according to the invention is carried out using a composition, the formulation and the application dose of which are such that the ethion is applied at a rate of 100 g/ha to 5,000 g/ha and the pyrethroid (II) at a rate of 0.1 g/ha to about 500 g/ha. As indicated above, the compositions advantageously comprise from 0.01 to 100 parts by weight of pyrethroid (preferably cypermethrin) per 100 parts by weight of ethion.

The compositions and the method according to the invention can be used to protect various types of perennial or annual crops against arthropoda, such as, in particular: - major annual crops grown in a temperate climate or tropical climate (cereals, potatoes, beet, tobac co, cotton, soya, sugar cane and the like), - market-garden or tropical crops, - orchards and - crops grown for flowers and ornamental pur poses, this list not implying a limitation.

The composition and the method according to the invention can be used mainly for combating planteating mites, towards which they have a synergistic effect as shown by the examples described below.

They can also be used advantageously to combat different classes of plant-eating insects e.g. homoptera, coleoptera, lepidoptera and diptera.

The examples which follow further illustrate the invention without, however, limiting it.

Example 8: Greenhouse experiments on mites (Tet ran ych us urticae) Aqueous dispersions of ethion, cypermethrin and the combination ethion + cypermethrin are prepared. These dispersions are then diluted with distilled water so as to give the desired concentrations.

Bean plants of the "Roides Belges" variety, at the "2 trifoliate leaf" stage, are contaminated with strains of "Tetranychus urticae" mites considered to be resistant to organophosphorus pesticides and cypermethrin.

48 hours after contamination, each of the bean plants is sprayed with an aqueous dispersion containing the active ingredient or the combination of active ingredients at the dose in question (4 experiments/dose). A control plant is treated with distilled water not containing active ingredient.

Just before the treatment, one foliole is removed from each bean plant. Using a brush, the mites present on each foliole are knocked onto a white piece of paper. The mites are then crushed on the paper in order to permit a visual assessment of the number of mites present on each foliole before the treatment. The treated plants and the control plant are kept in a greenhouse under the usual conditions of temperature, lighting and humidity.

21 days after the treatment, one foliole is removed from each bean plant. Using a brush, the mites present on each foliole are knocked onto a white piece of paper and crushed on the paper. The number of mites present on each foliole is assessed in this way. The percentage mortality, relative to the control plant treated with distilled water not containing active ingredient, is thus determined. The results are as follows: Experiment cypermethrin ethion No. g/hl g/hl mortality 1 15 0 0% 2 0 12.5 0% 3 0 25 0% 4 0 50 95% 5 5 12.5 100% 6 5 25 100% 7 10 12.5 100% 8 10 25 100% These results show the very distinct synergism resulting from the combination of cypermetrhin with ethion.It will be observed, in particular, that the combination of 5 g/hl of cypermethrin with 12.5 g/hl of ethion results in a mortality of 100%, while cypermethrin used by itself at a rate of 15 g/hl causes no mortality, the same applying to ethion used by itself at a dose of 25 g/hl.

Example 9: Open-air experiment on mites {Panony- chus ulmi) with repeated treatments.

The experiment is carried out on an orchard of apple trees of the Starking variety, which is are about twenty years old and are arranged in different plots.

The cypermethrin is used in the form of an aqueous emulsion containing 2 g/hl of cypermethrin, obtained by diluting, with water, an emulsifiable concentrate having the following composition: - cypermethrin 100g - ethylene oxide/alkylphenol condensate 50 g - calcium alkylarylsulphonate 30 g - petroleum cut (aromatic solvent) q.s. 1,000 ml The ethion is used in the form of an aqueous emulsion containing 75 g/hl of ethion, obtained by diluting, with water, the emulsifiable concentrate marketed under the trademark Rhodocide and having the following composition:: - ethion 5009 - mixture of anionic and non-ionic surface active agents 80 g - ethylene oxide/castor oil condensate 30 g - diisopropylbenzene q.s. 1,000 ml By mixing the two emulsifiable concentrates described above and by diluting the resulting mixture with water, an emulsion was prepared which contained the combination of the two active ingredients in amounts of 2 g/hl of cypermethrin and 75 g/hl of ethion.

Using these emulsions, seven successive treatments are carried out on the following days: 8th April (T1), 24th April (T2), 7th May (T3), 21st May (T4), 5th June (T5), 16th June (T6) and 8th July (T7), by spraying at a rate of about 1,000 litres/ha, the treatment being repeated four times for each dose.

Fifteen days after the first treatment (day T1 + 15), 25 leaves are taken from each plot corresponding to one dose of an active ingredient; the number of living mites present is counted and the average number of mites per leaf is calculated.

The same measurement is made six days after each of the treatments T2, T3, T4, T5 and T6, and 19 days after treatment T7. The results are reported in the table below.

NUMBER OF LIVING MITES PER LEAF

Cypereethrin Day of the Untreated Cypermethrin Ethion (2 glhal) + ecasurelent control (2 g/hL) (75 glhl) ethion (75 glhL) T1 + 15 10.6 16 16 9.4 Tz + 6 8.7 7.4 3.2 3.4 T3 + 6 15.2 16.4 4.3 3.5 T4 + 6 26.4 35.1 7.5 4.9 T5 + 6 68.5 86.7 21.8 T6 + 6 52.8 9e.6 30.1 6.5 T7 + 19 622 1,357 1,098 284 It is observed that cypermethrin used by itself at a dose of 2 g/hl has no acaricidal activity in this experiment, and even that the number of mites present in the experiments involving treatment with cypermeth rln is frequently very much greater than the number on the untreated control. This phenomenon is probably due to the action of cypermethrin on the insects which compete with and/or prey on the mites, which indirectly favours the proliferation of the latter.It is also observed that ethion used by itself at a rate of 75 g/hl has only a slight acaricidal activity, and that, according to the last of the measurements (day T7 + 19), it also seems indirectly to favour the proliferation of the mites (number of mites greater than that on the control).

Finally, it is observed that the combination cypermethrin + ethion has an excellent acaricidal activity in all cases.

Example 10: Open-air experiment on various parasites, with repeated treatments.

This experiment is carried out in the same apple orchard and in accordance with the same method as in Example 9, the same compositions being used and the treatments being carried out on the days indicated in Example No. 9. The insecticidal activity towards the following parasites is then evaluated: a) Operophthera brumata (leaf-eating caterpillars) Fifteen days after treatment T1, the number of living caterpillars on the buds is counted and the number of living caterpillars per 100 buds is calculated. The results are as follows: untreated control : 10.3 cypermethrin (2 g/hl) : 1.6 ethion (75 g/hl) : 5 cypermethrin + ethion (2 + 75 g/hl) 0.3 b) Dysaphis plantaginea (aphides) Ten daysaftertreatmentT5,the number of branches attacked by this parasite is counted in each plot and the average number of branches attacked in one plot is thus determined.

The results are as follows: untreated control 82.6 cypermethrin (2 g/hl) 2.3 ethion (75 g/hl) 0 cypermethrin + ethion (2+75g/hl) 0 c) Eriosoma lanigerum (woolly aphis) Twenty days after treatment T7, the number of branches attacked and the number of branches not attacked are counted and the % of branches attacked is thus evaluated. The results are as follows: untreated control 24.7% cypermethrin (2 g/hl) : 81.7% ethion (75 g/hl) 4.7% cypermethrin + ethion 1.7% Example 11: Open-air experiment on mites (Panonychus ulmi) with a single treatment This experiment is carried out on an orchard of apple trees of the Golden variety, which are about 20 years old.

Starting from the emulsifiable concentrates described in Example 9, aqueous emulsions are prepared which contain, respectively, cypermethrin by itself (3 g/hl), or ethion by itself (75 g/hl), or the combination ethion + cypermethrin (75 g/hl - 3 g/hl).

The commercial acaricide tetrasul is used as the comparison product, and an aqueous suspension containing 40 g/hl ofthis product is prepared by diluting, with water, a wettable powder containing 20% of tetrasol.

Using these emulsions or dispersions, a treatment is carried out on 15th May (day T-0) by spraying at a rate of 1,500 litres/ha.

Immediately before the treatment, the number of living mites present on 25 leaves in each plot is determined and the average per leaf is calculated.

The same measurement is made respectively 3 days, 7 days and 17 days after treatment T (days T+3, T+7 and T+17). The results are reported in the table below: CHANGE IN THE NUMBER OF MITES (Average/leaf)

Day of Cypermethri the Untreated Tetrasul Cypermethrin Ethion (3 g/hl) + measure- controL 40 g/hL 3 g/hl 75 g/hl ethion ment (75 gill) T - 0 8.5 8.4 8.6 7.3 7.7 T + 3 6.3 2.2 0.3 0.3 0.1 T + 7 18.3 7.6 9 8.5 1.0 T + 17 36 24.5 34 32.5 10.8

Claims (26)

1. Insecticidal and acaricidal compositions for use in combatting crop-destroying arthropoda which comprise a syneryistic combination of ethion with a pyrethroid of the general formula

wherein R represents a hydrogen atom or the cyano radical and R1 represents the 2,2 - dimethyl - 3 - (2,2 dichlorovinyl) - cycloprop - 1 - yl radical, the 2,2 dimethyl - 3 - (2,2, - dibromovinyl) - cycloprop - 2 - yl radical, the 2,2 - methyl - 3 - (2 - methylprop 1 - enyl) - cycloprop - 1 - yl radical or the 1 - (4 - chlorophenyl) - isobut -1 - yl - radical, in association with an inert carrier or diluent acceptable in agriculture and/or a surface active agent which is acceptable in agncul- ture.

2. Composition according to claim 1 wherein the combination of ethion with a pyrethroid comprises from 0.01 to 100 parts by weight of pyrethroid of general formula II, wherein R and R1 are as defined in claim 1 per 100 parts by weight of ethion.

3. Composition according to claim 1 or 2 wherein the combination of ethion with a pyrethroid comprises from 0.1 to 10 parts by weight of pyrethroid of general formula II, wherein Rand R1 are as defined in claim 1, per 100 parts by weight of ethion.

4. Composition according to claim 1,2 or 3, wherein the pyrethroid is chosen from cypermethrin, permethrin, decamethrin and fenvalerate.

5. Composition according to claim 1,2,3 or 5 wherein the pyrethroid is cypermethrin.

6. Composition according to any one of claims 1 to 5 which comprise from 0.001 to 95% by weight of the combination of ethion with a pyrethroid.

7. Compositions according to any one of claims 1 to 6 which comprise a solid or liquid inert carrier or diluent.

8. Compositions according to any one of claims 1 to 7 which comprise a surface active agent.

9. Compositions according to any one of the preceding claims in the form of dusting powders or sprinkling powders, solutions, liquid water-soluble concentrates, emulsifiable concentrates, emulsions, suspension concentrates, aerosols, wettable pow ders, spraying powder or pastes.

10. Compositions according to any one of claims 1 to 7 in the form of emulsifiabie or soluble concentrates comprising from lotto 80% byweight of the combination of ethion with a pyrethroid.

11. Compositions according to claim 10 in the form of emulsifiable concentrates which comprise from 2 to 20% by weight of one or more suitable additives chosen from stabilisers, surface active agents, penetrating agents, corrosion inhibitors, dyestuffs and adhesives.

12. Compositions according to any one of claims 1 to 7 in the form of emulsions or solutions comprising from 0.001 to 20% by weight of the combination ofethionwith a pyrethroid.

13. Compositions according to any one of claims 1 1 to 7 in the form of wettable powders or spraying powders comprising from 20 to 95% by weight of the combination of ethion with a pyrethroid, from 0 to 5% by weight of a wetting agent, from 3 to 10% by weight of a dispersing agent and, optionally, from 0 to 10% by weight of one or more stabilisers and/or other additives.

14. Compositions according to any one of claims 1 to 7 in which the diluent or carrier comprises water.

15. insecticidal and acaricidal compositions for combatting crop-destroying arthopoda comprising a synergistic combination of ethion with a pyrethroid of general formula Il wherein Rand RI are as defined in claim 1, substantially as hereinbefore described.

16. Insecticidal and acaricidal compositions for combatting crop-destroying arthopoda comprising a synergistic combination of ethion with a pyrethroid of general formula II wherein R and R1 are as defined in claim 1 substantially as hereinbefore described in any one of Examples 1 to 11.

17. A method for the treatment of plants to combat crop-destroying arthropoda, which comprises applying to the plants an effective amount of a composition according to any one of claims 1 to 16.

18. A method according to claim 17, wherein the crop-destroying arthropoda are plant-eating mites.

19. A method according to claim 17 wherein the crop-destroying arthropoda are plant-eating insects.

20. A method according to claim 19 wherein the insects are homoptera, coleoptera, lepidoptera or diptera.

21. A method according to any one of claims 17 to 20 wherein the plants are cereals, potatoes, beet, tobacco, cotton, soya, sugar cane, market-garden or tropical crops, orchard or crops grown for flowers or ornamental purposes.

22. A method according to any one of claims 17 to 21 wherein the ethion is applied at a rate of 100 to 5,000 g/ha and the pyrethroid is applied at a rate of 0.1 to 500 g/ha.

23. A method according to any one of claims 17 to 22 wherein from 0.01 to 100 parts by weight of pyrethroid per 100 parts by weight of ethion is applied to the plants.

24. A method according to claim 22 wherein the pyrethroid is cypermethrin.

25. A method for the treatment of plants to combat crop-destroying arth ropoda substantially as hereinbefore described.

26. A method for the treatment of plants to combat crop-destroying arthropoda substantially as hereinbefore described in any one of Examples 8 to 11.