DE2241665A1 - HERBICIDAL COMPOUNDS OR MEASURES AND THEIR USE - Google Patents

Description

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PATENTA NW OLD

Munich: Frankfurt / M .: Dlpl.-Chem. Dr. D. Thomien Dipl.-Ing. W. Wainkauff Dlpl.-Ing. H. Tiedtke (Fuchihohl 71)

Dipl.-Chem. G. Buehling Dipl.-Ing. R. Kinne Dipl.-Chem. Dr. U. Eggara

80 0 0 Munich 2

Kaiser-Ludwlg-Platzö August 24, 1972

Imperial Chemical Industries Limited
London / Great Britain

herbicidal compounds or compositions and their use

The invention relates to brominated and iodinated Fluoropyridine derivatives with herbicidal. Properties, methods of production and herbicidal compositions which the contain brominated and iodinated fluoropyridine derivatives.

According to the invention, a bromofluoro- or iodofluoro-4-hyaroxypyridine is used or a salt, ester or ether thereof is provided.

The 4-hydroxypyridine can only have a bromine and fluorine or contain an iodine and fluorine substituent or may additionally contain other substituents, for example chlorine. 309811/1173

The 4-hydroxypyridine preferably bears substituents in each of the 2,3,5- and 6-positions of the ring, but the invention also includes compounds with an unsubstituted ring position, i.e. a ring position occupied by a hydrogen atom. Preferred compounds according to the invention are those which have fluorine atoms in the 2- and / or 6-position of the pyridine ring. Particularly preferred compounds are those according to Table I below and salts, esters and Ether from this.

Table I.

Connection no. ^X l X ₂ ^X 3 ^X 4 Melting point ⁰ C 1 F. Br Br F. 118-119 2 F. Br Br Br 178 3 F. Br F. F. 118-120 4th F. Br Cl F. 102 5 F. Br Br Cl 162-163 6th F. I. I. F. 151 7th F. I. I. Cl ' 164 8th F. Br I. F. 119-121 9 F. Br, I Cl 154-155

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Compound no. 9 consists of a 1: 1 mixture of 3-bromo-2-chloro-6 * »fluoro-4-hydroxy-5-iodopyridine and 5-bromo-2-chloro-6-fluoro-4-hydroxy-3-iodopyridine.

Salts according to the invention are metal salts, for example Alkali metal salts, brodalkali metal salts and amine salts, for example salts consisting of primary, secondary and tertiary Alkylamines are formed in which the alkyl groups are preferred Have 1 to 4 carbon atoms »

Ethers according to the invention include compounds in which the hydrogen atom of the 4-hydroxyl group of 4-hydroxypyridine is replaced by an etherifying radical containing an unsubstituted or substituted hydrocarbon group. Preferred etherifying radicals are aliphatic radicals, in particular alkyl radicals with 1 to 4 carbon atoms, soft optionally by alkoxy radicals with 1 to 4 carbon atoms are substituted.

Esters according to the invention are compounds in which the hydrogen atom of the 4-hydroxy group of the 4-hydroxypyridine is replaced by an esterifying radical containing an acyl group. Preferred acyl groups are alkylcarbonyl and Alkylsulphonyl groups, especially those with 2 to 4 carbon atoms or with 1 to 4 carbon atoms.

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Bromofluoro- and iodofluoro-4-hydroxypyridines or their Sale · can expediently be prepared from the corresponding 4-fluorine derivatives by customary methods, for example by hydrolysis with an alkali metal hydroxide. It is however, it is preferred to prepare the bromofluoro and iodofluoro-4-hydroxy compounds of the invention by reacting the corresponding 4-fluoro derivatives with a metal carboxylate in a non-hydroxylic solvent prepared according to the general method described in British patent application 31,563 / 70.

The bromofluoro derivatives which are required as intermediates can conveniently be prepared by vapor phase bromination of the appropriate substituted fluoropyridine as described in the British patent applications 39.639 / 71 and 12.080 / 72 or by conventional methods. The iodofluoropyridine derivatives, which are required as intermediate products, can be prepared by iodination of the corresponding fluoropyridine in the presence of fuming nitric acid will. The methods used to prepare the compounds according to the invention usually give the compounds in the form of their metal salts. The free bromo-, fluoro- or iodofluoro-4-hydroxypyridines can be prepared from their metal salts, for example by hydrolysis of the metal salts with water, i. by dilution with a large excess of water, or by adding an aqueous solution of an acid. The free bromofluoro- or iodofluoro-4-hydroxy-

11/117 3

Pyridine can be converted into a salt by customary methods, such as neutralization with an alkali metal hydroxide, which can be the same as or different from the salt obtained as described above.

The compounds of the invention are useful as herbicides. Accordingly, the invention also extends to a method of inhibiting the growth of undesirable vegetation, which consists in applying a fluorofluorine or bromine fluoride to the place of the vegetation or the place of the seed Iodofluoro-4-hydroxypyridine or a salt, ester or ether thereof, as defined above, applies. The angry For example, the amount of bromofluoro- or iodofluoro-4-hydroxypyridine depends on the particular one selected for use 4-hydroxy compound and the identity of the vegetation to be treated away. Preferably, however, the compounds of the invention are applied at a rate of from 0.2 to 10 kg per hectare. A rate of 1 to 5 kg per hectare is particularly preferred.

The compounds of the invention are useful for inhibiting the growth of a wide variety of plants. In general the compounds have a greater herbicidal activity when applied to foliage for a given rate of application the plants are applied as if they are applied to the soil containing the seeds of the plants,

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whose germination and growth is to be inhibited. However, in some cases application to the floor may be preferred for example, when it is desired to take advantage of the selective herbicidal activity which the compounds in some plants. Compounds of the invention can be used selectively to inhibit weed growth in corn crops such as rice and cotton.

Preferably, the compounds of the invention are in Mixing applied with a carrier. According to a further embodiment, therefore, according to the invention is a herbicidal Mass provided, containing a bromofluoro- or iodofluoro-4-hydroxypyridine or a salt as the active ingredient Esters or ethers thereof, as defined above, in admixture with a carrier of a solid or liquid diluent.

The herbicidal composition preferably also contains a surface-active agent. Comprising masses according to the invention both masses which are ready for immediate use and concentrated masses which have to be diluted before use. The masses preferably contain 0.01 up to 90% by weight of the active ingredient. Diluted, for use finished masses preferably contain from 0.01 to 2% active ingredient, while concentrated masses contain from 5 to 90% active ingredient although 20 to 70% is normally preferred

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Solid masses can be in the form of a powder, in which the active ingredient with a solid diluent is mixed. Suitable solid diluents are, for example, Fuller's earth, powdered kaolin, plaster of paris, chalk and diatomaceous earth.

Liquid compositions can contain a solution or dispersion of an active ingredient in water, optionally including a surfactant, or they can be a solution or dispersion of an active ingredient in one contain organic diluents, which optionally contain a surface-active agent. Another form of one Liquid mass consists of a solution of an active ingredient in a water-immiscible solvent, which is called Droplet is dispersed in water.

Examples of surfactants which can be used in the compositions of the invention are. Products of the condensation of ethylene oxide with the following substances: alkyl-substituted phenols, for example p-octylphenol and p-nonylphenol: sorbitan monolaurate, oleyl alcohol and propylene oxide polymer. A particular example of such a surface-active agent is the condensate of p-nonylphenol with 7 to 8 molar proportions of ethylene oxide, available under the name "Lissapol" NX ("Lissapol ¹¹ is a trademark). Other surface-active agents are calcium dodecylbenzenesulphonate and calcium, Sodium and

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Aitunonium Lignosulphonate. The selection of a suitable surfactant is of course well within the knowledge of those skilled in the art of preparing agricultural chemicals.

The compositions of the invention are conveniently used as Concentrates transported and stored, i.e. masses which contain a high level of active ingredient and which must therefore be diluted, usually with water, before using come into use.

Line particularly preferred form of a concentrate consists of a salt of a bromofluoro- or iodofluoro-4-hydroxypyridine, which is dissolved in a surfactant-containing water. Preferably the salt is an alkali metal salt, for example the potassium salt.

Another form of concentrate consists of a "wettable powder", i.e. a mixture of finely divided active Ingredient with a solid surfactant, either with or without the addition of a solid diluent. When mixed with water, the surfactant helps disperse the finely divided active ingredient.

If desired, the compounds of the invention can in conjunction with other herbicidal agents, either in combination or sequentially. After a

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Another embodiment is therefore a according to the invention herbicidal mass provided, containing a bromofluoro- or iodofluoro-4-hydroxypyridih in admixture with a herbicide, which is a diazine, a triazine, a urea, a carbamate, an amide, a phenol, a nitrile, a benzoic acid, a Phenoxyalkanoic acid, a nitroaniline or a bipyridylium quarternary Salt is. Examples of such herbicides are the following: ..

Bromacil (5 Erom-B-methyl-3-s-butyluracil) , -

Pyrazone (5-amino-4-chloro-2-p.henyl-3-pyridazinone), Simazine (2-chloro-4,6-diethylamino-1,3,5-t'riazine), Anthrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazini, Monuron O-p-chlorophenyl-ljl-dimethylurea), Diuron 3 (3,4-dichlorophenyl-l, -dimethylurea), Chlortoluron 3 (3-chloro-4-m.ethylphenyl) -1-methoxy-l-roethylur-

substance, chlorpropham (isopropyl-N- (3-chlorophenyl) carbamate),

Propachlor (2-chloro-N-isopropyl-N-phenylacetamide), Dinoseb (2,4-dinitro-6 ~ s-b; utylphenol),

Dichlobenil J (2,6-dichlorobenzonitrile), bromoxynir "(3,5-ibromo-4-hydroxybenzonitrile), dicamba (3,6-dichloro-2-methoxybenzoic acid), MCPA (2-methyl-4-chlorophenoxyacetic acid), Trifluoroaline (2,6-i) .initro-N, N-dipropyl-4-trifluoromethylaniline), paraquat (l, l ^l -D.imethyl-4 _i 4 '-aipyridylium ion), oiquat (1, l'-ethylene- 2.2 ^l -dipyridylium ion).

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The compositions preferably also contain a diluent or a carrier.

The invention is illustrated in more detail by the following examples.

example 1

This example illustrates the preparation of 3,5-dibromo-2,6-difluoro-4-hydroxypyridine.

A mixture of 29.2 g of 3,5-dibromotrifluoropyridine, prepared by vapor phase bromination of 2,4,6-trifluoropyridine, 24 g of potassium acetate and 120 ml of acetone were refluxed with stirring for 2.5 hours. The solvent was distilled off, and the remaining solid was taken up in 25 ml of water and washed with 50 ml of methylene chloride. The mixture was acidified to pH 1 with dilute hydrochloric acid and extracted with chloroform. The chloroform extracts were evaporated and the remaining solid off Recrystallized chloroform, 21 g of 3,5-dibromo-2,6-difluoro-4-hydroxypyridine having a melting point of 118 to 119 ° C.

Example 2 ,

Following the procedure described in Example 1, compounds 2 to 9 of Table I were prepared. From-

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-. 11 -

gang material, the solvent used for recrystallization and the physical properties of the product are given in Table II below. The structure of the Products were confirmed by testing their mass spectra, their infrared spectra and their nuclear magnetic resonance spectra.

Table II

ndi mg starting material Recrystallization
solvent Enamel
point ⁰ C 2 2,4-fluoro
tr ib rompy r1d in Carbon tetrachloride
material 178 3 3-fcsrom-tetra-
fluoropyridine Methylene
dichloride 116-120 4th 3-bromo-5-chloro
trifluoropyriain chloroform 102 5 6-chloro-3,5-
dibromo-2,4-di-
fluoropyridine Tetrachlor
carbon 162-163 b 3.5 diiodine
trifluoropyridine chloroform 151 7th 2-chloro-4,6-
difluor-3,5-
diiodopyridine Tetrachlor
carbon 164 8th 3-bromo-5-iodine
trifluoropyridine Tetrachlor
carbon 119-121 9 2-chloro-4 _# 6-
üifluorbromoiodine-
pyridin.isoruere Tetrachlor
carbon 154-155

The starting materials for compounds 2, 3 and 4 were prepared by vapor phase bromination of 2,4-difluoropyridine;

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2 _# 4,5,6-tetrafluoro-3-dalorpyridine and 3,5-dichloro-2,4,6-trifluoropyridine, respectively, as described in British patent applications 39,639 / 71 and 12,080 / 72. The remaining starting materials were prepared manufactured as follows:

6-chloro-3,5-dibromo-2,4-difluoropyridinι

A mixture of 15 g of 6-chloro-2,4-difluoropyridine, 3 g of bromine and 45 ml of fuming nitric acid were added Heated to reflux for 24 hours. The mixture was in water poured and extracted with Methylenchloriu, and the extracts were washed with sodium hydroxide solution. Evaporation of the extracts and distillation of the residual oil gave 25.2 g 6-chloro-3,5-dibromo-2,4-aifluoropyridine with a melting point of 46 ° C after recrystallization from chloroform.

3,5-Diiodotrifluoropyridine:

A mixture of 20 g of 2,4,6-trifluoropyridine, 60 g of iodine and 90 ml of fuming nitric acid was heated under mild reflux for 12 hours. The mixture was poured into water and extracted with methylene chloride. The extracts were washed with aqueous potassium iodide solution and water. Evaporation of the solvent and recrystallization from petroleum ether (Boiling point 100 ° to 120 ° C.) yielded 32 g of 3,5-diiodotrifluoropyridine with a melting point of 79 ° to 80 ° C.

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2-chloro-4,6-difluoro-3,5-diiodopyridine:

A mixture of 15 g of 6-chloro-2,4-difluoropyridine, 35 g of iodine and 30 ml of fuming nitric acid was refluxed for 3 days. 30 ml of fresh nitric acid was added at 24 hour intervals. The mixture was poured into water and extracted with methylene chloride. The extracts were washed with aqueous potassium iodide and water. Evaporation of the solvent and crystallization from petroleum ether (boiling point 100 ° to 120 ° C) gave 2-chloro-4,6-difluoro-3 _r 5-diiodopyridine with a melting point of 96 ° to 97 ° C. The mother liquors from the recrystallization contained 2-chloro-4,6-difluoro-3-iodopyridine and 2-chloro-4,6-difluoro-5-iodopyridine.

3-bromo-5-iodotrifluoropyridine

A mixture of 35 g of 3-bromo-2,4-6-trifluoropyridine, prepared by vapor phase bromination of 2,4,6-trifluoropyridine as described in British patent applications 39,839 / 71 and 12,080 / 72, 22 g of iodine and 30 ml of fuming Nitric acid was refluxed for three days. 10 ml of fuming nitric acid was added at 24 hour intervals. The mixture was poured into water and extracted with methylene chloride, and the extracts were washed with aqueous potassium iodide and water. Evaporation of the solvent and recrystallization of the residue from petroleum ether (boiling point 100 ° to 120 ⁰ C) gave 3-bromo-5-jodtrifluorpyridin having a melting point of 57.5 ° C.

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2-chloro-6-fluoro-bromoiodopyridinej

A mixture of 12 g of 2-chloro-4,6-difluoro-3-iodopyridine and 2-chloro-4,6-difluoro-5-iodopyridine, prepared as follows from the description above of the preparation of 2-chloro-4,6-difluoro-3,5-diiodopyridine, 4 ml of bromine and 25 ml of fuming nitric acid were added Heated to reflux for 18 hours. The mixture was poured into water, extracted with methylene chloride and washed with sodium hydroxide solution. Evaporation of the solvent and recrystallization of the product from petroleum ether yielded a mixture of the two 2-chloro-4,6-difluorobromoiodopyridines, the mixture having a melting point of about 50 ° C.

Example 3

This example illustrates the herbicidal activity of the hydroxypyridines according to the invention. Every connection was made as its potassium salt dissolved in water / and 0.1% by weight of a surface-active agent, available under the designation "AGRAL" 90 was added. ("AGRAL" is a trademark for a surface-active agent containing a condensate of p-nonylphenol with 7 to 8 molar proportions of ethylene oxide).

The solutions were then tested for pre-emergence and post-emergence activity in the following ways:

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When testing for herbicidal pre-emergence activity, Flat fiber troughs were filled with compost. Then there were seeds sown on the compost, and the compost with the test masses at der.Rate of 1000 liters per hectare (5 kg hydroxypyridine per Hectares), sprayed. The seeds were then covered with fresh compost, and after 14 days the number of healthy seedlings, which had developed, with the increasing number in the compost which had not been sprayed with the test masses, compared.

In a test for herbicidal pre-emergence activity seeds were sown in flour pots and allowed to ripen into seedlings at the two-leaf stage. The seedlings were then sprayed with the test mass at a rate of 1000 liters per hectare (5 kg hydroxypyridine per hectare). After 14 days it was the damage to the plants was determined on a scale from 0 to 5, with 0 representing no effect and 5 representing complete killing.

The results of the tests are shown in Table Iia.

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- 16 table Ha

Connection no. Tent of up Sb K Test plants P. On 5 B. R. oat (see table I) bringing 5 4th C. 4th 4th 5 4th 2 4th 1 before 5 5 4th 4th 5 5 4th 2 5 after b 3- 5 4th O 3 1 O 2 2 before 5 5 4th 5 4th 5 4th 5 after 5 4th 5 5 - 4th 5 3 3 vp r 4th 4th 4th 4th - 2 2 4th after 5 3 4th 4th 3 3 2 4th 4th before 5 5 3 5 5 4th 3 5 after 4th 3 5 4th - 3 i 4th S. before 5 5 2 5 - 5 4th 5 after 3 2 5 3 3 O O 1 6th before 5 5 3 5 5 3 3 4th after 4th 1 5 1 2 O O 2 7th before 5 5 2 5 - 4th 3 4th after 5 4th 5 3 1 0 2 8th before 5 5 2 5 2 O 5 after 4th 1 5 1 1 - O 9 before 5 5 2 2 4th 1 4th after 5

The abbreviations for the names of the remaining plants have the following meanings:

Sb sugar beet K Cabbage C. carrot P. pea

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On onion B. barley R. rice

Oat oats

It can be seen that some of the compounds in the table above have relatively little deleterious activity Rice in comparison with its effects on other plant species have in the table.

Example 4

This example illustrates the selective herbicidal activity of some compounds of the invention. For comparison, the results of the tests with 3,5-dichloro-2,6-difluoro-4-hydroxypyridine, which are mentioned as a herbicide in British Patent 1,161,491, are also listed. This compound is named in Table III below by its general name HALOXYDINE. Ha of the traced pieces of soil were sown with seeds of the plant species listed in Table III below. On the day after sowing, the soil parts were sprayed with aqueous solutions of the potassium salt of the compounds listed in the table. The volume of the spray solution applied was 4000 l per hectare and the solution contained 0.1% by weight of "Agral" 90 as a wetting agent.

Five weeks after spraying, the condition became 309811/1173

Plants on the test areas were determined on a scale from 0 to 10, where 0 means no effect and 10 means complete kill. The results are shown in Table III.

Table III

link
No. Application rate
kg / ha W. B. Oat Pt SB R. C. P. Haloxydine 0.25 I. 3 O 8th 6th 2 4th 3 0.5 5 7th 9 9 9 8th 9 9 2 2.0 O O 7th 8th 7th 7th 9 8th 4.0 O 2 3 9 9 9 9 9 3 1.0 O O O 7th 6th 1 9 9 2.0 O O 9 7th 9 7th 9 9 4th 1.0 O O 8th 8th 6th 3 9 8th 2.0 O O 9 9 9 6th 9 9 5 1.0 O O 4th 6th 5 4th 9 5 2.0 O O % 7th 7th 5 9 8th 6th 2.0 O O 9 O 7th 7th 9 9 4.0 O O 9 4th 7th 9 9 9

The abbreviations for the plant names have the following meanings) '

W wheat

» B devices

Oat oats

Pt Poa trivialis (Riapengraa)

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SB sugar beet R. Haps C. carrot P. pea

From the above results it can be seen that compounds 2 to 6 inclusive against wheat and barley are more selective than Haloxydin. Furthermore, compounds 4 and 5 'gave good results besides regulating the broadleaf species Regulation of the other two annual grass species in this experiment (i.e. oats and iba trivialis).

Example 5

This example illustrates the selective herbicidal activity of 3-bromo-5-chloro-2 _r 6-difluoro-4-hydroxypyridine (Compound No. 4 of Table 1) against the grass species "common Quicke" (Agropyron repens) which grows between barley plants . For comparison, a test using 3,5-dichloro-2,6-difluoro-4-hydroxypyridine (Haloxydin) was also carried out. In the test, three individual species of common quicks and five barley seeds were sown 1 1/4 cm deep in separate 3 inch pots. The pots were then sprayed with Haloxydin and with compound no. 4 of Table I, both in the form of the aqueous solutions of their potassium salts / containing 0.1% "Agral" 90 as a wetting agent. After spraying

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was (0.5 cm thick) placed on the sprayed surface be a further layer of soil. The soil used was a compost consisting of 1 part of sterilized clay

1/2 part vermiculite

1/2 part of semolina with a small amount of added inorganic fertilizer,

The damage to the plants was determined 21 days after spraying on a scale from 0 to 100, where 0 means no effect and 100 means complete kill.

The results are given in Table IV below.

Table IV

link
No. Application
rate kg / ha barley Agropyron repens Haloxydine 0.0625 9 26th 0.125 5 42 0.250 75 99 4th 0.0625 6th 53 0.125 13th 97 0.250 59 91

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Example 6

This example illustrates the ability of 2-fluoro-4-hydroxytribromopyridine (Compound No. 2 of Table I) for causing considerable herbicidal damage Range of broad-leaved plant species at application rates, which cause essentially no herbicidal damage to cotton, for comparison was also 3.5- ■ Dichloro-2,6-difluoro-4-hydroxypyridine (Haloxydin) the same set of species tested.

Divided plots of land were planted with seeds from the plant species listed in Table V below, sown. After sowing, the pieces of land were washed with aqueous solutions of the potassium salts of the compounds listed in the table sprayed, the solutions 0.1% by weight "Agral" contained*

28 days after the spraying, the damage to the plants was determined on a scale from O to 9, where O no effect and 9 mean complete kill. The results are shown in Table V. .

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Table V

Application
rate kg / ha Co R. T Cbp So T On S. . 0.25 3 5 6th 7th 4th 9 9 3 0.5 9 7th 9 5 8th 9 9 6th 1.0 0 2 6th 6th 8th 9 9 5 2.0 0 2 8th 8th 8th 9 9 7th link
No. Haloxydln 2

The abbreviations for the plant names have the following meanings:

Co cotton R. Rapeseed T Turnips Cbp Capsella bursa pastoris So Soybean T tomato On onion S. Cereal grass

Le can be seen that Compound No. 2 of Table I. while haloxydin caused essentially no damage to cotton at application rates which seriously damaged or killed a number of other plant species was highly damaging to cotton even at low application rates.

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~ 23 -

Example 7

This example illustrates the herbicidal before ^ emergence and post-emergence activity of compounds according to the invention. The pre- and post-emergence tests were as described in Example 3 using that described in Example 5 Compost as a plant growth medium. The injury against the plants was 26 days after spraying on one Scale from 0 to 9 noted, with 0 no effect and 9 complete Mean killing. The results are in the following Table VI listed.

Table VI

link Application · * pre-emergence test R. Sb P. S. post-emergence test R. Sb P. S. haloxydine rate kg / ha 0.7 3.0 2.7 0.3 1.3 3.3 7.0 0.7 0.1 2.3 4.7 8.7 1.7 2.7 9 9 2.3 6th 0.2 0 0 0 0. 6.0 8.0 9 9 0.2 0 1.0 0 0.3 9 9 9 9 4th 0.4 0 0.3 1.3 1.3 2.3 4.3 6.0 7.3 0.2 1.7 3.0 5.3 4.0 9 9 9 9 7th 0.4 0 - - 0 2.3 - - 9 0.2 D. - - 0 9 - - 9 5 0.4 y 1.3 1.0 0 7.7 7.7 9 7.0 0.2 3 2.0 2.7 0 9 8.3 9 9 0.4

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!, * 'The abbreviations in Table VI have the following meaning

ff '■

tungent

R rape

Sb sugar beet P Polygonum persicarla S. Senecio vulgaris

From the results in Table VI it can be seen that the compounds of the invention are relatively more active in post-emergence use than in pre-emergence use, while the known herbicidal haloxydin is only slightly less active when it is applied as a pre-emergence spray compared to the Application to the foliage. Therefore, compared to Haloxydin, the compounds of the invention have the advantage that they as post-emergence sprays for weed control in orchards * or plantations.

3 0 9 R 1 1/1 1 7 3

Claims (8)

Claims 1. Herbicidal halogenated 4-hydroxypyridine compound or preparations containing them "characterized in that the compound at least one fluorine substituent and at least contains a bromine or iodine substituent or is present as a salt, ester or ether of the 4-hydroxypyridine compound. 2. Compound or preparation according to claim 1, characterized in that each of the 2,3,5- and 6-positions of the pyridine ring is substituted. 3. Compound or preparation according to claim 1 or 2, characterized in that the 2- or 6-position of the pyridine ring is substituted by a fluorine atom. 2-fluoro-4-hydroxy-3,5,6-tribromopyridine. 5. Preparation according to one of the preceding claims, characterized in that there is a compound according to claim 1 in admixture with a solid as active ingredient or carrier containing liquid diluent. 6. Preparation according to claim 5, characterized in that it further contains a surface-active agent. 309811/1173 7. Use of the compounds or preparations according to one of the preceding claims for inhibiting the growth of undesired vegetation by applying halogenated 4-hydroxypyridine or a preparation containing this compound to the area in which the vegetation or the seeds of which are present. 8. Use of the compounds or preparations according to one of the preceding claims for inhibiting the growth of weeds in corn plants by applying a halogenated 4-hydroxypyridine or a preparation containing it according to claim 1 to the plant area in an amount which, however, is sufficient to inhibit the growth of the weeds is insufficient to cause substantial damage to the plants. 309811/1173