GB2051578A - Herbicidal agent - Google Patents

Abstract

The invention relates to a new synergistic herbicidal composition comprising one or more active compounds of the formula <IMAGE> in which Z is chlorine or bromine, R is straight-chain or branched alkyl group with 1 to 18 carbon atoms or phenyl, X is oxygen or sulphur and Y is sulphur and if X is sulphur, Y also may be oxygen, and of one or more compounds of the formula <IMAGE> in which Z' is bromine or iodine and R' is alkyl with 4 to 10 carbon atoms, the combination having a high selective and synergistic action when used for combating weeds, especially in grain cultures and maize cultures, and to a process for combating weeds by treatment with the said composition.

Description

SPECIFICATION Herbicidal agent This invention relates to a herbicidal composition comprising a synergistic mixture of a known phenylpyridazine derivative, and a known 3,5-dihalo-4-hydroxynitrile derivative. The novel combination of the active compounds possesses a particularly high selective and synergistic activity in combating weeds. The invention also relates to a process for combating weeds, especially weeds which are difficult to combat in grain crops and maize crops, by treatment with the said composition.

It is known from Austrian Patent Specification 326,409 that phenylpyridazines of the general formula

in which Z is a chlorine or bromine atom, R is a straight-chain or branched alkyl group having 1 to 1 8 carbon atoms or the phenyl group, X is an oxygen or sulphur atom and Y is a sulphur atom and, where X is a sulphur atom, Y also may be oxygen, exhibit herbicidal properties and are distinguished by good toleration by many crop plants, inter alia grain cultures.

In particular, the compound 0-(3-phenyl-6-chloropyridazin-4-yl)-S-(n.octyl)-thiocarbonate ("Pyridate") has proved of value as an agent for combating weeds in grain cultures and maize cultures (Diskus et al., Proc. 9th British Weed Control Conf. 1976, Vol. 2, 717), and is active against a broad spectrum of weeds.

However, on practical use in the open it has been found that some types of weeds, such as, for example, Stellaria media (chickweed) and Polygonum convolvulus (black bindweed) can be combated only with relatively high doses of the active substance or, as in the case of, for example, Palaver rhoeas (corn poppy), are substantially unsuppressable. This is particularly the case where the weeds are in an advanced state of development.

It is also known that 3,5-dihalo-4-hydroxybenzonitriles exhibit good properties as contact herbicides (Nature, London, 1963, Vol. 200, page 28). In particular, the octyl esters of the compound 4-hydroxy-3,5-diiodobenzonitrile ("loxynil-octanoate") and of the compound 4 hydroxy-3,5-dibromobenzonitrile ("Bromoxynil-octanoate") are used for the post-emergence treatment of annual broad-leaved weeds (H. Martin and Ch. R Worthing "Pesticide Manual" 5th edition 1977, pages 293 and 54). Moreover, a number of weeds become more resistant with increasing age, so that relatively large amounts of the active compound must be used for combating them.These weeds include inter alia, Galium aparine (cleavers) and Galeopsis tetrahit (hemp nettle) (Kurth, H.: "Chemische Unkrautbekmpfung" ("Chemical Combating of Weeds"), Fischer Verlag Jena, 1975, page 170).

We have now found that mixtures of active substances from the phenylpyridazines of general Formula (I), especially the compound 0-(3-phenyl-6-chloro-pyridazin-4-yl)-S-(n-octyl)-thiocarbo- nate ("Pyridate") with active substances from the 3,5-dihalo-4-hydroxybenzonitriles, especially the compounds 4-hydroxy-3, 5-diiodobenzonitrile octanoate (loxynil-octanoate") and 4-hydroxy3,5-dibromobenzo-nitrile octanoate ("8romoxynil-octanoate") exhibit a herbicidal activity which is substantially higher than the activity to be expected from a merely additive action of both components. Accordingly, what is involved is a genuine synergistic effect, the degree of which in no way foreseeable and must be regarded as distinctly surprising.

Accordingly, the present invention provides a herbicidal composition comprising, as the active component, a mixture of one or more compounds of the general formula

in which Z is a chlorine or bromine atom, R is a straight-chain or branched alkyl group with 1 to 1 8 carbon atoms or the phenyl group, X is an oxygen or sulphur atom and Y is a sulphur atom, and, when X is a sulphur atom, Y also may be oxygen, with one or more compounds of the general formula

in which Z' is a bromine or iodine atom and R' is an alkyl group with 4 to 10 carbon atoms.

The increased herbicidai activity of the said mixtures of active compounds, which exceeds a purely additive action, results in substantial technical advantages since it is thereby possible substantially to reduce the amounts of the individual components used per unit treated area.

Among the compounds having Formula (I), the compounds 0-(-3-phenyl-6-chloro-pyridazin-4yl)-S-( propyl)-thiocarbonate, 0-(3-phenyl-6-chloro-pyridazin-4-yl)-S-( rrbutyl)-thiocarbonate 0-(3 phenyl-6-bromopyridazin-4-yl)-S-( > butyl)-thiocarbonate and O-(3-phenyl-6-chioro-pyridazin-4-yl)- S-( > dodecyl)-thiocarbonate produce substantial increases in activity in combination with compounds of Formula (II).

Amoung the compound of Formula (I), the compound 0-(3-phenyl-6-chloro-pyridazin-4-yl)-S- ( > octyl)-thiocarbonate ("Pyridate") is particularly active, whilst among the compounds of Formula (II) good results are achieved especially with 4-hydroxy-3,5-diiodobenzonitrile octanoate ("loxynil-octanoate") and/or 4-hydroxy-3,5-dibromobenzonitrilate octanoate ("Bromoxynil-octa noate").

The compositions according to the invention may be administered as customary formulations, such as solutions, emulsions, dispersions, powders, pastes or granules. These are prepared in a known manner, for example by mixing the active compounds with extenders, that is to say liquid solvents and/or solid carriers, optionally together with surface-active agents, that is to say emulsifiers and/or dispersants. Examples of suitable solid carriers are: natural rock powders, such as kaolins, alumina, talc and chalk, and synthetic rock powders, such as highly disperse silica and silicates.Examples of suitable emulsifiers are non-ionic and anionic emulsifiers, such as polyoxyethylene fatty acid esters, polyoxyethylene fatty alcohol ethers, alkylsulphonates, arylsulphonates and alkylarylsulphonates; and examples of suitable wetting agents and dispersants are lignin-sulphite waste liquors, methylcellulose and sodium olely-methyltauride.

In the compositions according to the invention the ratios of the amounts of the compound of Formula (I) to the compounds of Formula (II) (phenol equivalents) may vary within a certain range, for example from a ratio of 1:1.6 to 1:0.1. Mixtures in which the proportion of compounds of Formula (I) predominates are particularly preferred.

The active compound combination according to the invention may be formulated for example, as a wettable powder or as an emulsion concentrate, in accordance with the following proportions: active compound of Formula (I) 14 to 50% by weight active compound of Formula (Il) 3 to 20% by weight (based on phenol equivalents) wetting agent or dispersant 5 to 15% by weight inert fillers or carriers balance up to 100% by weight For use, the above formulation may be suspended or emulsified in water. It also may contain other known active substances, such as herbicides, fungicides or growth regulators.A combination with active substances selected from phenoxycarboxylic acids, such as, for example, MCPA, CM PP, 2,4-DP and 2,4-D, or with the salts or esters thereof, is particularly advantageous, since, with these, even perennial weeds can be combated in a single application.

The compositions according to the invention are employed for post-emergence treatment.

The amounts of the composition used also may be varied within a certain range. The amount depends upon the proportion of each active compound in the composition and on the nature of the weeds. Usually, the active compound of general Formula (I) is employed in an amount of 0.25 to 1.0 kg/ha and the active compound of general formula (II) in an amount of 0.1 to 0.4 kg/ha.

The use of the compositions according to the invention in grain cultures and maize cultures is particularly preferred, in which case the active compound of Formula (I) is employed in an amount of from 0.5 to 1.0 kg/ha and the active compound of Formula II in an amount of from 0.2 to 0.4 kg/ha.

The ascertain whether a mixture gives additive or synergistic effects, the following equation is usually employed as the basis: X.Y E=X+Y- 100 (according to Limpel, L.E., P.H. Schuldt, D. Lamont, 1962, Weed control by dimethyltetrachloroterephthalate alone and in certain combinations, Proc. NEWCC 16:48-53, based on Gowing, D.P., 1960, Comments of tests of herbicide mixtures, Weeds 8:379-391); wherein E is the herbicidal activity (% weed destruction) to be expected (from an additive action) after the use of A + B in an amount of p + q kg/ha.

X is the activity (%) when using active substance A at p kg/ha.

Y is the activity (%) when using active substance B at q kg/ha.

If the experimentally found value of E is above that calculated according to the above equation, a synergistic effect exists, whilst if the value is below, an antagonistic effect exists.

It emerges clearly from the results of Tables 1 to 5 that in almost all cases the herbicidal activity (% destruction) when using a combination of the active compounds / + II or / + III is substantially greater than the (calculated) values to be expected from a purely additive action.

The practical usefulness of a synergistic effect, of the degree indicated here, is extremely great. As is known, the E.W.R.C. rating scheme for herbicidal activity is based upon an approximately exponential function between the activity (% destruction) and the particular figure of merit (or rating), so that in the range encountered in practice, namely between 85 and 100% destruction, the rating gives substantially greater differentiation than in the economically uninteresting range of between 0 and 85% destruction (see E.W.R.C. rating scheme).

Increasing the activity in the upper range is therefore substantially more important than in the lower range. For example, increasing the activity from, for example, 95% to 100% (+ 5%) is equivalent to an improvement by two rating marks, whilst, for example, increasing the activity from 70% to 80% (+ 10%) corresponds to only one mark and is furthermore of little practical importance (both 70% and 80% destruction are regarded as still being inadequate).

As may be seen from the Example, it is however particularly in the range between 85% and 100% destruction that synergistic increases in activity, to an economically important extent, are to be found in every case.

The Example further shows that even when using only 0.25 kg/ha of compound I (pyridate) and 0.1 kg/ha of compound II (loxynil-octanoate) the herbicidal activity, in the case of all the weeds tested, is substantially greater than the sum of the actions of the individual components.

The synergistic effect is in this case particularly clear; for example, in the case of the weeds Galeopsis tetrahit (hemp nettle), Lamium purpureum (red deadnettle) and Veronica hederifolia (speed-well) it is respectively + 26, + 27 and + 29%.

In the case of the combination of 0.25 kg/ha of Compound I with 0.2 kg/ha of Compound II what is of great practical importance is the increase in activity against Galium aparine (cleavers), which is every difficult to combat, to 98% destruction, which is sufficiently high to correspond to a very good action according to E.W.R.C. scheme. In the case of the combination of 0.5 kg/ha of Compound Iwith 0.2 kg/ha of Compound II, all weeds, in particular also Galium aparine (cleavers), with only the exception of Polygonum convolvulus (black bindweed) are 100% destroyed.

Compound III (Bromoxynil-octanoate) is very similar, in its chemical, physical and biocidal properties, to Compound II (loxynil-octanoate). Accordingly, the synergistic effects may also manifest themselves in an entirely similar manner, as may be seen from Tables 4 and 5.

The following Example and Tables illustrate the effectiveness of the compositions according to the invention.

EXAMPLE The experimental units employed were rectangular plastic boxes (35 X 38 X 7 cm) which were planted with the particular weeds. The following field weeds, all of which are economically important, were used for the experiments: Chenopodium album white goosefoot = A Galeopsis tetrahit hemp nettle = B Galium aparine cleavers = C Lamium purpureum red deadnettle = D Lapsana communis nipplewort = E Lithospermum arvense corn gromwell = F Matricaria chamomilla wild camomile = G Palaver rhoeas corn poppy = H Polygonum convolvulus black bindweed = I Stellaria media chickweed = K Veronica hederifolia speedwell After the weeds had reached the state of development at which they are usually treated, in grain cultures, with post-emergence herbicides (for example Galium aparine branched with 3 to 6 whorls/side shoot, Lapsana communis in the 6- to 8-leaf stage, Matricaria chamomilla in the 8- to 1 0-leaf stage, Stellaria media already branched, with 4 to 6 pairs of leaves per side shoot, Galeopsis tetrahit with 2 to 3 pairs of leaves developed), the active compounds or active compound combinations were sprayed, in the stated dosages, on to the weeds. The amount of spray liquor was in every case 500 1 /ha.

Four weeks after spraying, the herbicidal activity was ascertained. The residual weed infestation which remained was harvested, separately for each type of weed, and its green weight was determined. The same procedure was used with the weeds in the comparison boxes which had remained untreated.

The residual weed infestation was compared to the weed infestation in the untreated boxes and the herbicidal activity (% destruction) was ascertained in this way in each case. In the case of the product mixtures, these values were then examined, for possible synergistic effects, by means of the Limpei formula.

The compound "Pyridate" was employed in the following formulation: 70.0% of the active compound 7.5% of an alkylarylsulphonate/polyoxyethylene emulsifier mixture 22.5% of solvent The compounds loxynil-octanoate and Bromoxynil-octanoate were employed in the following formulation: Mixture of Active aromatic Compound Emulsifier hydrocarbons loxynil-octanoate (corresponding to 400 g/l of phenol to make up to equivalent 47.02% 4.38% 100% Bromoxynil-octanoate (corresponding to 400 g/l of phenol to make up to equivalent) 51.08% 4.38% 100% The data on kg. of active compound/ha in the tables relate, in the case of loxynil-octanoate and Bromoxynil-octanoate, to the relevant equivalents of free phenol.

Dose of active substance Destruction of the weeds in % in kg/ha A B C D E F G H I K L 0-(3-Phenyl-6-chloro- 0.25 75 53 60 45 65 82 50 10 60 52 45 pyridazin-4-yl)-S- 0.5 89 72 75 66 76 85 62 35 65 70 70 (n-octyl)-thiocarbonate 1.0 100 100 98 100 100 100 95 55 75 85 82 (Pyridate)= I 4-Hydroxy-3,5-diidobenzonitrile-octanoate 0.1 55 40 33 50 78 25 70 87 32 70 52 0.2 72 65 67 90 52 75 92 76 75 70 0.4 100 100 88 78 98 75 100 100 89 90 90 (loxynil-octanoate)=II 4-Hydroxy-3,5-dibromo-0.1 42 50 30 44 67 22 80 73 22 65 45 0.2 68 60 58 70 84 55 92 87 45 73 72 0.4 100 100 77 80 95 68 100 100 75 89 95 (Bromoxynil-octanoate)=III Table 2 Dose of Active substances kg/ha Destruction of the weeds in % I + II A B C D E F G H I K L 0.25 + 0.1 calculated 100 98 87 100 98 95 100 98 92 100 85 found 89 72 79 73 93 87 85 88 73 86 56 difference + 11 + 26 + 8 + 27 + 5 + 8 + 15 + 15 + 19 + 14 + 29 + 0.2 calculated 100 100 98 100 100 97 100 100 95 100 92 found 93 94 87 81 97 92 88 93 91 88 84 difference + 7 + 6 + 11 + 19 + 3 + 5 + 12 + 7 + 4 + 12 + 8 + 0.4 calculated 100 100 100 100 100 100 100 100 100 100 100 found 100 100 96 88 100 96 100 100 96 96 95 difference - - + 4 + 12 - + 4 - - + 4 + 4 + 5 0.5 + 0.1 calculated 100 100 90 100 100 98 100 100 96 100 90 found 95 84 84 83 95 89 89 92 77 91 86 difference + 5 + 16 + 6 + 17 + 5 + 9 + 11 + 8 + 19 + 9 + 4 + 0.2 calculated 100 100 100 100 100 100 100 100 95 100 100 found 97 91 92 88 98 93 91 95 92 93 91 difference + 3 + 9 + 8 + 12 + 2 + 7 + 9 + 5 + 3 + 7 + 9 + 0.4 calculated 100 100 100 100 100 100 100 100 100 100 100 found 100 100 97 93 100 97 100 100 91 97 97 difference - - + 3 + 7 - + 3 - - + 9 + 3 + 3 Table 3 Dose of active substances kg/ha Destruction of the weeds in % I + II A B C D E F H I K L 1.0 + 0.1 calculated 100 100 100 100 100 100 100 100 95 100 100 found 100 100 99 100 100 100 99 95 83 96 92 difference - - + 1 - - - + 1 + 5 + 12 + 4 + 8 + 0.2 calculated 100 100 100 100 100 100 100 100 100 100 100 found 100 100 100 100 100 100 99 97 94 95 difference - - - - - - + 1 + 3 + 6 + 3 + 5 + 0.4 calculated 100 100 100 100 100 100 100 100 100 100 100 found 100 100 100 100 100 100 100 100 98 99 99 difference - - - - - - - - + 2 + 1 + 1 Table 4 Dose of active substances kg/ha Destruction of the weeds in % I + II A B C D E F H I K L 0.25 + 0.1 calculated 98 95 80 95 100 92 100 85 78 94 88 found 86 77 72 70 89 86 90 76 69 84 70 difference + 12 + 18 + 8 + 25 + 11 + 6 + 10 + 9 + 9 + 10 + 18 + 0.2 calculated 100 100 94 100 100 95 100 100 95 100 82 found 92 82 84 84 95 92 96 89 88 88 85 difference + 8 + 18 + 10 + 16 + 5 + 3 + 4 + 11 + 7 + 12 - 3 + 0.4 calculated 100 100 100 100 100 100 100 100 100 100 100 found 100 100 91 89 99 95 100 100 90 95 98 difference - - + 9 + 11 + 1 + 5 - - + 10 + 5 + 2 0.5 + 0.1 calculated 95 05 92 91 100 97 100 88 85 95 93 found 94 86 83 81 93 89 93 83 73 90 84 difference + 1 + 9 + 9 + 10 + 7 + 8 + 7 + 5 + 12 + 5 + 9 + 0.2 calculated 100 100 98 100 100 100 100 100 100 90 98 found 97 89 90 90 97 94 97 92 81 92 92 difference + 3 + 11 + 8 + 10 + 3 + 6 + 3 + 8 + 19 - 2 + 6 + 0.4 calculated 100 100 100 100 100 100 100 100 100 100 100 found 100 100 94 93 99 95 100 100 91 97 98 difference - - + 6 + 7 + 1 + 5 - - + 9 + 3 + 2 Table 5 Dose of active substance kg/ha Destruction of the weeds in % I + II A B C D E F G H I K L 1.0 + 0.1 calculated 100 100 98 100 100 100 100 95 92 92 97 found 100 100 99 100 100 99 88 80 95 90 difference - - - 1 - - - + 1 + 7 + 12 - 3 + 7 + 0.2 calculated 100 100 100 100 100 100 100 100 100 100 100 found 100 100 99 100 100 100 100 94 86 96 95 difference - - + 1 - - - - + 6 + 14 + 4 + 5 + 0.4 calculated 100 100 100 100 100 100 100 100 100 100 100 found 100 100 100 100 100 100 100 100 94 98 99 difference - - - - - - - - + 6 + 2 + 1 E.W.R.C. ratings scheme: Figure of Destruction of Effect of merit weeds formulation 1 1 00% excellent 2 97.5% very good 3 95% good 4 90% satisfactory 5 85% still adequate 6 75% inadequate 7 65% slight 8 32.5% very slight 9 0 none

Claims (7)

1. A herbicidal composition comprising, as the active component, a mixture of one or more compounds of the general formula

in which Z is a chlorine or bromine atom, R is a straight-chain or branched alkyl group with 1 to 1 8 carbon atoms or the phenyl group, X is an oxygen or sulphur atom and Y is a sulphur atom, and, when X is a sulphur atom, Y also may be oxygen, with one or more compounds of the general formula

in which Z' is a bromine or iodine atom and R' is an alkyl group with 4 to 10 carbon atoms.

2. A composition according to claim 1, in which the active component is a mixture of 0-(3 phenyl-6-chloro-pyridazin-4-yl)-S-(n-octyl)4hiocarbonate and 4-hydroxy-3, 5-diiodobenzonitrile-oc- tanoate and/or 4-hydroxy-3, 5-dibromobenzonitrile-octanoate.

3. A composition according to claim 1 or 2, in which the ratio of the compound of Formula (I) to the compound of Formula (II) is from 1:1.6 to 1:0.1, the amount of the compound of Formula (II) being expressed in phenol equivalents.

4. A composition according to any one of claims 1 to 3, in which there is also included a wetting agent or dispersant and in inert filler or carrier.

5. A composition according to claim 4, in which the proportions by weight of the ingredients are 14 to 50% of the active compound of Formula 1, 3 to 20% of the active compound of Formula II, 5 to 15% of wetting agent or dispersant and the balance inert filler or carrier.

6. A herbicidal composition according to claim 1, and substantially as hereinbefore described with reference to the Example.

7. A process for combating weeds which comprises treating the plants with a herbicidal composition according to any one of the preceding claims, the active compound of Formula (I) being applied in an aount of 0.25 to 1 kg/ha and the active compound of Formula (II) being applied in an amount of 0.1 to 0.4 kg/ha.