GB2223662A - Coated seeds - Google Patents

Abstract

Crop seeds are protected against soil-borne fungi or other pests by providing them with a coating comprising a polymer in which an organic biocide such as a root-absorbed systemic fungicide is chemically bound to the polymer by a hydrolytically unstable bond, optionally together with a water-soluble or water-swellable polymer to aid disintegration of its coating in soil, and a mineral filler.

Description

Coated Products This invention is concerned with the protection of seeds, seedlings and growing plants from biocides, especially soil borne fungi, for a prolonged period of time.

The value of crop losses from soil borne fungi has been estimated at 20,000,000,000 per annum worldwide, frequently by rotting of the seed or "damping off" at the seedling stage.

Conventionally, some protection is given to the seed in storage and immediately after planting by dusting with a protective biocide. This suffers from the defect that only small amounts of biocide can be adhered to the seed.

For the purpose of mechanised handling and planting seeds are frequently pelletised into roughly spherical shape.

Small seeds, elongated seeds, flat and rough seeds are especially difficult to handle and benefit from this surface treatment. The seeds are mixed with a coating material which is a mixture. of a mineral filler and a water-soluble or water-swellable adhesive polymer. The seeds can for example be rolled in or tumbled with the coating material. Fungicides are frequently added to the coating material. The simple addition of the fungicide by admixture is not a particularly efficient process since the coating material has to be designed to swell and dissolve and disintegrate in wet soil.

As soon as this happens the biocide is rapidly lost by diffusion from proximity with the root.

British Patent Specification 1,058,701 describes a method of protecting materials against the growth of pestiferous organisms by treating the material with a polymer of a compound of the formula: R3SnOOCR' in which R is a lower alkyl or phenyl radical and R' is a polymerisabic vinyl or alpha-methyl vinyl group.

Coated seeds according to the invention are characterised in that the seed coating comprises a polymer in which an organic biocide is chemically bound to the polymer by a hydrolytically unstable bond.

The seed coatings of the invention have the advantage that the polymer gradually hydrolyses giving controlled release of the organic biocide. One advantage of this is that biocides which would be too water-soluble for use as seed coatings may be incorporated. Another advantage of the controlled release biocide polymer is that biocides which would otherwise reach phytotoxic concentrations around the seed or seedling are controlled so that such concentrations are not reached.

The polymers of this invention are particularly useful for the long term deployment of root-absorbed systemic fungicides. This means that systemic fungicide can be delivered to the roots at a sufficient rate throughout the growing season, thus avoiding the need for repeated and frequent applications.

The controlled release biocide polymer is preferably an addition polymer of the formula:

where R', R2 and R3 can in general be selected from monovalent hydrocarbon groups such as alkyl, aryl or aralkyl, any of which can be substituted, halogen, nitro or cyano groups; X is a hydrolysable linkage; Z is a radical of a biocidal, preferably fungicidal, con-,pound; B represents at least one comonomer; n is a positive integer and m is 0 or a positive integer, and the sum of n and m is such that the polymer has a molecular weight of at least 500, preferably 1000 to 100000.

In one form of the Invention the seed coating comprises water-soluble or water-swellable polymer in addition to the controlled release biocide polymer defined above. This has the advantage that the seed coating rapidly dissolves or disintegrates in wet soil so that the seed can germinate, leaving particles of the controlled release biocide polymer in close proximity to the seed and subsequent seedling and growing plant.

Examples of preferred water-soluble or water-swellable polymers are gum arabic, gum tragacanth, polyvinyl alcohol or partially hydrolysed polyvinyl acetate, or a carboxylated latex such as a carboxylic acid functional acrylic emulsion polymer. When the controlled release biocide polymer is substantially water-insoluble before hydrolysis, the proportions of controlled release biocide polymer to water-soluble or water-swellable polymer in the seed coating are preferably 5:95 to 80:20 by weight, most preferably 10:90 to 60:40.

In another form of the invention the comonomer or comonomers B are such that the controlled release biocide, is itself water-soluble. For example the comonomers may include sufficient of an olefinically unsaturated carboxylic acid or anhydride such as acrylic acid, methacrylic acid or maleic anhydride to form a water-soluble polymer.

The seed coating preferably contains a mineral filler as well as the controlled release biocide polymer and a water-soluble or water-swellable polymer (which may be the same as the controlled release biocide polymer). Examples of mineral fillers are china clay, talc and calcium carbonate.

The mineral filler preferably forms 10 to 90 per cent by weight of the seed coating.

Examples of known biocides, mainly fungicides, which can be used to provide the radical Z of the controlled release biocide polymer are shown in the following Table 1.

TABLE 1 FUNCTIONAL FUNGICIDES FOR CONTROLLED RELEASE AS SEED DRESSING Name 1. Benazolin 3813-05-6 (C.A.S. registry number)

2. Benodanil 15310-01-7

3. Benomyl 17804-35-2

4. Bitertanol 55179-31-2

Diclobutrazol 75736-33-3

5. Carbendazim 10605-21-7

6. Carboxin 5234-68-4

7. Oxycarboxin 5259-88-1

8. Cycloheximide 66-81-9

9. Cymoxanil 57966-95-7

10. Dichlorophen 97-23-4

11. Dichloran 99-30-9

12. Dicofol 115-32-2

13. Dimethirimol 5221-53-4

14. Diniconazol 76714-88-0

15. DNOC 534-52-1

16. Dodemorph 31717-87-0

17. Dodine 2439-10-3

18. Ethirimol 23947-60-6

19. Fenaminosulf 140-56-7

20. Fenarimol 60168-88-9

21. Fenfuram 24691-80-3

22. Fluroprimidol 56425-91-3

23. Flutolanil 66332-96-5

24. Flutriafol 76674-21-0

25. Fuberidazole 3878-19-1

26. Guazatine Acetates [Iminooctamethylene Diamines] 39202-40-9

27. Hexaconazole 79983-71-4

28. 8-Hydroxy Quinoline 134-31-6

29. Hymexazol 10004-41-1

30. Mepronil 55814-41-0

31. Metalaxyl 57837-19-1

32. Nuarimol 63284-71-9

33. Paclobutrazol

34. Pencycuron 66063-05-6

35. 2-Phenyl-Phenol 90-43-7

36. Thiabendazol 148-79-8

37. Thiocyclam hydrogen oxalate

38.

Thiophanate 23564-06-9 Thiophanate-methyl 23564-05-8 39. Triadimenol 55219-65-3

40. Triforine 26644-46-2

41. Isothiazole salts

42. Iprodione

where Me = methyl, Et = ethyl, Bu = butyl The biocides shown in Table 1 all contain functional groups through which they may be attached to a polymer by a hydrolytically unstable linkage. Those biocides containing a free hydroxyl group, namely those numbered 4, 8, 10, 12, 13, 14, 15, 18, 20, 22, 24, 27, 28, 29, 32, 33, 35 and 39 in Table 1, can be attached to a polymer through a hydrolysable ester linkage. The biocide can for example be reacted with a polymer of an olefinically unsaturated carboxylic acid or anhydride or can be reacted with a polymerisable olefinically unsaturated carboxylic acid or anhydride and subsequently polymerised, preferably with at least one comonomer.

The olefinically unsaturated carboxylic acid or anhydride, and hence the groups R', R2 and R3 in the controlled release biocide polymer, can be selected so that the ester linkage X is hydrolysable. Mainly biocides have activated hydroxyl groups, for example those biocidal compounds having at least one aryl group in the alpha-position with respect to the hydroxyl group, such as biocides 8, 12, 20, 22, 24, 27 and 32 of Table 1, and those compounds having hydroxyl groups attached to a heterocyclic ring system, for example 8-hydroxy quinoline and hymexazol (28 and 29 in Table 1). For these biocides the ester linkage X will generally be 2 3 hydrolysable whatever the nature of the groups R', R2 and R3.

In this case the group R' is preferably hydrogen or methyl, R2 3.

is preferably hydrogen and R3 is preferably hydrogen or -COOR4, R4 being hydrogen or the biocide radical Z; that is, the polymers are derived from acrylic acid, methacrylic acid or maleic acid or anhydride.

Where the hydroxyl group of the biocide is not such an activated group, for example the biocides numbered 4, 10, 13, 14, 15, 18, 33 or 39 in Table 1, the group R' is preferably an electron-withdrawing group such as a halogen, preferably chlorine, cyano or nitro group so that the ester linkage X is hydrolysable.

The comonomer units B can be units of one or more acrylic ester, for example methyl, ethyl, butyl or hexyl acrylate or the corresponding methacrylates, a vinyl ester such as vinyl acetate, acrylonitrile or methacrylonitrile, styrene or a styrene derivative, or vinyl chloride. If the controlled release biocide polymer is itself designed to be water-soluble or water-swellable the comonomer units B preferably include acetic monomer units such as acrylic acid, methacrylic acid, maleic acid br anhydride or 2-acrylamido-2methyl-propane sulphonic acid units or a high proportion of vinyl alcohol units.

A biocidal compound containing a carboxyl functional group, for example that numbered 1 in Table 1, can be reacted with a hydroxyl functional polymer such as polyvinyl alcohol, a partially hydrolysed polyvinyl acetate or a polymer of a hydroxy alkyl acrylate or methacrylate to form ester linkages.

The nature of the biocidal compound, for example the presence of the heterocyclic ring system in benazolin, may render the ester linkages hydrolytically unstable.

Where the biocidal compound is an ionisable base, for example the compounds numbers 16, 17, 26, 37 and 41 in Table 1, the biocidal compound can be reacted with an acid functional polymer, for example a carboxylic acid functional polymer such as a polymer of acrylic acid, methacrylic acid or maleic acid to form hydrolysable ionic linkages. Where the biocidal compound is an anionic salt, for example that numbered 19 in Table 1, or a free carboxylic acid, for example that numbered 1 in Table 1, it can be reacted with a polybasic polymer such as polyethylene imine or polyvinyl pyridine or a quaternised polymer such as quaternised polyethylene imine to form a hydrolysable ionic linkage. Such polymers containing hydrolysable ionic linkages are generally more likely to form controlled release biocide polymers which are water-soluble in themselves.

Where the biocidal compound contains a -NH or -NH2 group, that is a primary or secondary amine group or a corresponding amide group, it can be reacted with an olefinicially unsaturated acyl chloride such as acryloyl chloride or methacryloyl chloride to form an unsaturated monomer which can subsequently be polymerised, preferably with a comonomer. The biocidal compounds numbered 2, 3, 5, 6, 7, 9, 11, 17, 21, 23, 25, 30, 34, 36, 38, 40 and 42 in Table 1 contain such amine or amide groups. The biocidal compounds 11, 17, 25 and 36 in Table 1 will react with an acyl chloride to form amide groups. The compounds 2, 5, 6, 7, 21, 23, 30, 38 and 40 in Table 1 will react with an acyl chloride to form imide groups. The Compounds numbered 3, 9, 34 and 42 in Table 1 will react with an acyl chloride to form ureide linkages.

Biocidal compounds containing a primary or second amine or amide group can alternative be reacted with an olefinically unsaturated sulphonyl chloride such as 2-acrylamido-2-methylpropane sulphonyl chloride to produce a hydrolysable sulphonamide group. Alternatively they can be reacted with a polymer containing anhydride groups, for example a styrene maleic anhydride copolymer, to produce amide, imide or ureide groups.

Claims (6)

1. Coated seeds, characterised in that the seed coating comprises a polymer in which an organic biocide is chemically bound to the polymer by a hydrolytically unstable bond.

2. Coated seeds according to claim 1 characterised in that the organic biocide is a root-absorbed systemic fungicide.

3. Coated seeds according to claim 1 or claim 2 characterised in that the biocide-containing polymer is an addition polymer of the formula

where R1, R2 and R3 are each hydrogen, a monovalent hydrocarbon group, a substituted monovalent hydrocarbon group, halogen, nitro or cyano; X is a hydrolysable linkage; Z is a radical of the biocide; B represents at least one comonomer; n is a positive integer and m is 0 or a positive integer and the sum of n and m is such that the polymer has a molecular weight of at least 500.

4. Coated seeds according to claim 4 characterised in that the biocide-containing polymer is substantially water-insoluble before the hydrolytically unstable bond is hydrolysed and the comonomer or comonomers B are an acrylic ester, a vinyl ester, acrylonitrile or methacrylonitrile, styrene, a styrene derivative or vinyl chloride.

5. Coated seeds according to any of claims 1 to 4 characterised in that the seed coating comprises a water-soluble or water-swellable polymer in addition to the biocide-containing polymer.

6. Coated seeds according to claim 3 in which the comonomer or comonomers B include sufficient of an olefinically unsaturated carboxylic acid or sulphonic acid that the biocide-containing polymer is water soluble before the hydrolytically unstable bond is hydrolysed.