OA11764A - Fungicidal composition and method of controling fungus infestation. - Google Patents

Abstract

Fungicidal composition with improved biodegradation in the soil contain metalaxyl, furalaxyl or benalaxyl, of which more than 70 wt.% is the R-enantiomer, and a suitable carrier. The amt. of R-enantiomer in the active ingredient is above 85 (esp. above 97) wt.% and the active ingredient is free from S-enantiomer. Esp. compositions are highly conc. formulations and contain more than 30 wt.% metalaxyl.

Description

- 1- Ή 764

Fungicidal composition and method of controlling fungus infestation

The présent invention relates to a novel method of controlling and preventing Oomyceteinfection of plants by using metalaxyl, furalaxyl or benalaxyl, hercinbelow termed activeingrédient I, in each case with an R-enantiomer content of over 70 % by weight, and to 5 suitable fungicidal compositions for this purpose.

Metalaxyl was the first commercially available préparation from the sériés of the class of♦active ingrédients originally termed acylalanines, laterphenylamides, which areoutstandingly active against Oomycetes. The Oomycetes include ail downy mildews,which attack mainly potatoes, tomatoes, vines, hops, maize, sugar beet, tobacco, 10 vegetables, lettuce, but also bananas, rubber, as well as lawns and omamentals.

The prefened application of the acylalanine fungicides is foliar application, the foliageand the growing plant being treated with the active ingrédient Some of the activeingrédient is taken up by the plant but some remains on the plant and is washed off by therain or otherwise taken up by the soil due to leafdropor time of maturation. In the case of 15 soil application, the active ingrédient is incorporated into the soil directly by applying it in.liquid form, or, for example, by means of granules. A disadvantage in this context is the slow dégradation rate of the représentatives of thissubstance class in the soil, which dépends largely on whether the soils are humous soils,mixed sandy/loamy soils or strongly adsorptive soils (loam/clay). In the case of prolonged 20 treatment periods, on the one hand in perennial crops, such as grapevines, on the other intypical soil crops, such as potatoes, sugar beet or lawns, the soils may be subjected tocumulative loading with acylalanine fungicides, which, in tum, aie an enviionmentalhazard, but in particular a groundwater hazard.

Metalaxyl is N-(2,6-dimethylphenyl)-N-(methoxyacetyl)-DL-alanine methyl ester. 25 Benalaxyl is N-(2,6-dimethylphenyl)-N-(phenylacetyl)-DL-alanine methyl ester.

Furalaxyl is N-(2,6-dimethylphenyl)-N-(2-furanylcaibonyl)-DL-alanine methyl ester.

The compounds aie known from the literature. The dégradation data given vary. The référencé book “The Pesticide Manual", lOth Edition 1994, edited by the British Crop

Protection Council, gives the following information on the hydrolytic half-lives of these 30 products. (DT = disappearance time). ί7* -2-

Metalaxyl: DT-50 (20°C)

Benalaxyl: DT-50Furalaxyl: DT-50 (20°C) 5 pHl :>200dpH9 :115 dpH9.25 : 86dpHl :>200dpH9:>200d

These data show an undesirably high stabUity in the aqueous medium. ( Attempts were made to accelerate the dégradation behaviour by means of suitable formulations, for example by means of hydrophobie additives which prevent deeperpénétration of the active ingrédient into the soil and expose it on the surface to the 10 incidence of sunlight and to elevated températures. It was attempted to exploit a fortherdisadvantageous property of the acylalanine fongicides, namely their high volatility,which is a nuisance under the effect of sun and high températures. It would hâve beenexpected that the volatility of the active ingrédient on the soil surface would be equallyhigh, a fact which has not been observed in practice. 15 AU these attempts hâve not resulted in convincing solutions. Once the active ingrédient isadsorbed by the soil surface, even only within die uppermost 2 cm, dégradation is reduceddrasticaUy, which entails ail the adverse conséquences of sparingly degradable activeingrédients which die expert is familiar with.

Entirely surprisingly, it has now been found that the solution of this problem is found in 20 the acylalanine active ingrédient itself, in which the R-enantiomer is, unexpectedly, degraded more rapidly than the S-enantiomer or than the commercially available activeingrédients which are based on the racemates in question. Since 1975, which is when thissubstance class became known, one has been familiar with the fact that it is theR-enantiomer anyway which is the more fungicidaUy active ingrédient (cf. e.g. 25 GB-1 500581).

As a solution for practical use, the literature has never seriously proposed, in 19 years, theaUegedly adjacent solution of using, from the start, the respective R-enantiomer of anacylalanine fongicide. On the one hand, one must not underesdmate the technologicaldifficulties of preparing an R-enantiomer in pure form or an active substance enriched 30 with R-enantiomer (for example fractional ciystallization of the racemate or stereospecific synthesis), on the other hand there was no incentive and no technological necessity for the practitioner for acting in such a way. However, the décisive factor is this. It could not hâve 764 -3- been assumed that a réduction or complété élimination of the proportion of S-enantiomerin the racemate would solve the problem of die unduly long résidence time of the activeingrédient in the soil. As yet, no R-enantiomers, or R-enantiomer-enriched racemates, ofacylalanine fungicides hâve been put on die market With respect to the overall ecologicalsituation of the otherwise effective contiol of downy mildews (Oomycetes) withacylalanine fungicides, in particular with metalaxyl, the solution of the dégradationproblem proposed herein is of décisive technological importance in agricultural practiceworldwide. It is a standard demand in crop protection to achieve an optimal effect with anactive ingrédient at die lowest dosage rate requircd while simultaneously keeping thepollution of the environment as low as possible.

In the field of the acylalanine fungicides, in particular in the case of its main représentative, metalaxyl, this problem can be considered as solved. An evidently betterbiodegradability in the soil is achieved if the content of R-enantiomer in die activeingrédient is over 70 % by weight

The présent invention provides an ecologically désirable method of controlling andpreventing Oomycete infestation of plants by using an R-enantiomer of metalaxyl orbenalaxyl

R = OCH3 (R-metalaxyl) R = C6H5 (R-benalaxyl) or by using the R-enantiomer of furalaxyl

(R-furalaxyl) -4- Π 764 in each case at least 70 per cent by weight of the particular amount of total activeingrédient

Here and below, the racemates of the three active ingrédients metalaxyl, benalaxyl andfuralaxyl are termed active ingrédient I. With increasing contents of R-enantiomer in die 5 active ingrédient the dégradation properties in the soil are improved.

The invention preferably relates to a method of controlling Oomycetes in which the activeingrédient employed has an R-enantiomer content of over 85 % by weight, in particularover 92 %, and prcferably over 97 %, based on die total amount of active ingrédientParticularly preferrcd is die method in which the active ingrédient I is essentially 10 ~ composed of R-enantiomers and is essentially free of S-cnantiomers (< 1 %).

The présent invention furthermore relates to a composition for controlling Oomycetes inwhich the amount of R-enantiomers in active ingrédient I amounts to over 70 % byweight, prcferably 85 % by weight, and particularly prefered over 92 %, based on the totalamount of active ingrédient In particular, the invention relates to a composition wherein 15 the content of the R-enantiomer in the active ingrédient is more than 97 % by weight and especially to one wherein the active ingrédient is essentially free from S-enantiomer (< 1 % by weight). The indicated percentages do not take into account that technicallyproduced active ingrédient additionally contains traces of by-products and intennediates(ca. 3-5 % b.w.). 20 The composition and the method of the présent invention control, amongst the Oomycetes, in particular fungal pests from the group of the Peronosporales, in particular Plasmoparaviticola, furthermore Phytophthora spp., such as P. infestans, Pythium pathogens, Bremia,Pseudoperonospora and others.

The rates per application (spraying, dusting, incorporation into the soil and the like) are 25 60 g of active ingrédient per hectare (a.iTha) to 300g of a.i./ha based on the pure R-enantiomer.

The active ingrédient employed can be furalaxyl, benalaxyl, but prcferably metalaxyl.

Formulations of R-metalaxyl are prcferably highly concentrated (more than 30 % b.w. of active ingrédient). This results in savings in transport and storage capacity. 117 6 4 -5-

Furthermore, pathogens on live plants hâve ievealed that the activity displayed by theR-enantiomer of active ingrédient I is many times higher in comparison with the racemateand not just twice as high, as expected. The activity can be 20 to 30 times higher, undercertain conditions up to 100 times higher, than in the case of the racemate. 5 Conformation studies demonstrated tirât in the type of active ingrédient in question of the acylalanines of the formula above, the right-hand side half of the molécule (see above) isfixed in a virtually vertical position relative to tire 2,6-dimethylphenyl plane when in tire C crystalline State and that in solutions, when this barrier of rotation about the phenyl-N-axis can be overcome by energy, the methylene group tir which tire substituent R is attached 10 forms an angle towards this phenyl group, as shown above by tire formula (R. Nyfeler, P. Huxley, Monograph No. 31, British Crop Protection Conférence Publication, Croydon1985, p. 45 et seq.). This means that the iemaining substituents in the molécule can varytheir positions relative to the C atom of tire alanine methyl ester, which is responsible forthe absolute configuration. This also applies analogously to the compound furalaxyl, 15 which has attached tir it a 2-furanyl radical instead of tire substituent CH2-R, which is shown above.

In recent years, a plurality of biological investigations hâve confirmed, in principle, thefinding that the R-enantiomer has a better fungicidal activity than the S-enantiomer. In ς Phytophthora palmivora, DJ. Fisher and A.L. Hayes (Crop protection [1985] 4 (4) 20 PP» 501-510) found that the ED50 inhibitory values in the nucleic acid synthesis were approximately fifty times more unfavorable in the case of the S-enantiomer of metalaxylthan in the case of the R-enantiomer, while the conesponding ED50 values ofR-enantiomer and racemate were in a ratio of approximately 3.1:5.6. The skilled tnanwould thus expect that the activity of a given amount of R-enantiomer is approximately 25 équivalent to twice the amount of racemate, and readily conclude that the much loweractivity of the S-enantiomer in the racemate attributes, to this S-enantiomer, essentiallythe rôle of an inert material whose presence does not matter.

Resolution of the racemate of active ingrédient I and use of the R-enantiomer only wastherefore not an option for the practitioner, even if only because of the high level of action 30 of the racemates, and has therefore not been proposed in the literature of the last 19 years as a solution for practical use.

Thus, it has to be assumed that, in the ready-for-use State of the racemic active ingrédientI, the contribution of the R-enantiomer to the activity is reduced antagonistically by the -6- **764 S-enantiomer and by other conformations of the molécule. For example, it would beconceivable that a large number of biochemical receptors are temporaiily occupied by theineffective components of the racemate I, but not permanently blocked. Since,furthermore, the active ingrédients I, in particular metalaxyl and furalaxyl, became knownfor having a systemic and penetrating action, further négative efîects of these isomers,which hâve previously prevented the rapid pénétration capacity of die R-enantiomer intothe cell tissue of the plant and hâve resulted in elevated losses due to volatilization, mightalsoplay a rôle.

The R-enantiomers of the formula I can be obtained for example by fractionalcrystallization of a sait prcpared from N-(2,6-dimethylphenyl)-a-aminopropionic acid andan N-containing optically active base with subséquent libération of the optically activeantipode and estérification with methanol. An example of an optically active base isα-phenylethylamine (GB P.l 448 810).

Furthermore, the R-enantiomers of the active ingrédients can also be obtained by theactivation of the hydioxyl group as leaving group in the naturally occurring L(+) lacticacid, esters or salts, and its replacement by 2,6-dimethylaniline with reversai ofconfiguration. The use of the acid or its salts nécessitâtes subséquent estérification withmethanol. The use of an lactic ester other titan the methylester nécessitâtes subséquenttransestérification with methanol. The boiling point of pure R-metalaxyl is143-145°Ç/0.03 mbar.

The active ingrédient in question is formulated in a known manner to give pesticidalcompositions, as is described, for example, in GB P.l 500 581.

The formulations are prepared in a known manner, for example by intimately mixingand/or grinding the active ingrédients with extenders, such as, for example, with solvents,solid carriers and, if appropriate, surface-active compounds (surfactants).

Suitable carriers and additives can be solid or liquid and correspond to the substancesexpediently used in formulation technology, such as, for example, natural or regeneratedminerai substances, solvents, dispersants, wetting agents, tackifiers, thickeners, binders orfertilizers. A preferred method of applying the R-enantiomer is application to the aerial parts of the plant, especially the foliage (foliar application). Number and rate of application dépend on ”764 the biological and climatic enviionmental conditions for the pathogen. Altematively, theR-enantiomer can reach the plant via the soil through the root System (systemic action), bydienching the site of the plant with a liquid composition or by incorporating the substancesinto the soil in solid fonn, for example in the fonn of granules (soil application). 5 The compound is employed as pure active ingrédient or, preferably, together with theadjuvants conventionally used in the art of formulation and is thercfore processed in aknown manner to givc, for example, émulsion concentrâtes, spreadable pastes, diiectlysprayable or dilutable solutions, dilute émulsions, wettable powders, soluble powders,dusts, granules, or by encapsulation, for example in polymeric substances. The methods of 1Ό application, such as spraying, atomizing, dusting, scattering, brushing cm or pouring, as well as the type of the compositions, are selected to suit the intended aims and theprcvailing circumstances.

As a rule, the agrochemical compositions comprise 0.1 to 99 %, in particular 0.1 to 95 %,of active ingrédient 1,99.9 to 1 %, in particular 99.9 to 5 %, of a solid or liquid additive, 15 and Oto 25%, in particular 0.1 to 25%, of a surfactant

Wbile concentrated compositions aie more prcfened as commercially available goods, theend consumer uses, as a rule, dilute compositions. Such (agro)chemical compositions arepart of the présent invention.

The examples which follow aie intended to illustrate the invention, "active ingrédient F ? preferably being metalaxyl, but also furalaxyl or benalaxyl, with a preferably highR-enantiomer content (70-100 % by weight). Wettable powders a) b) c) d) Active ingrédient metalaxyl 25% 50% 75% 24% 25 (96 % R-enantiomer) Sodium lignosulfonate 5% 5% 5% Sodium lauryl sulfate 3% - 5% 4% Sodium diisobutylnaphthalene- - 6% 10% - sulfonate Octylphenol polyethylene glycol ether 2% 30 (7-8 mol of ethylene oxide) Highly-disperse silica 5% 10% 10% 5% Kaolin 62% 27% - 62% 764 -8-

The active ingrédient is mixed thoroughly with the additives and the mixture is groundthoroughly in a suitable mill. This gives wettable powders which can be diluted with waterto give suspensions of any desired concentration.

Emulsion concentrate 5 Active ingrédient metalaxyl 10% (96 % R-enantiomer)

Octylphenol polyethylene glycol ether 3% (4-5 mol of ethylene oxide)

Calcium dodecylbenzenesulfonate 3 % 10 Castor oil polyglycol ether 4% (35 mol of ethylene oxide)

Cyclohexanone 30 %

Xylene mixture 50 %

Emulsions of any desired dilution, which can be employed in crop protection, can be15 preparcd from this concentrate by diluting it with water.

Dusts

• Active ingrédient I (> 85 % R-enantiomer)Talc 20 Kaolin

Rock powder a) b) c)5% 6% 4% 95% 94% 96%

Ready-for-use dusts are obtained by mixing the active ingrédient with the carrier andgrinding the mixture in a suitable mill.

Extrader granules 25 Active ingrédient I 15 % (> 92 % R-enantiomer)

Sodium lignosulfonate 2 %

Carboxymethylcellulose 1 %

Kaolin 82 % 30 The active ingrédient is mixed with the additives, and the mixture is ground and moistened -9- with water. This mixture is extruded and subsequently dried in a stream of air.

Coated granules

Active ingrédient I 8 % (> 70 % R-enantiomer) 5 Polyethylene glycol (MW 200) 3 %

Kaolin 89 % (MW = molecular weight) €

In a mixer, the finely ground active ingrédient is applied uniformly to thekaolin which hasbeen moistened with polyethylene glycol. In this mariner, dust-frce coated granules axe 10 obtained.

Suspension concentrate

Active ingrédient I 40 % (> 92 % R-enantiomer)

Propylene glycol 10 % 15 Nonylphenol polyethylene glycol ether 6 % (15 mol of ethylene oxide)

Sodium lignosulfonate 10 %

Carboxymethylcellulose 1 %

Silicone oil 1 % 20 (in the form of a 75 % aqueous émulsion)

Water 32 %

The finely ground active ingrédient is mixed intimately with the additives. This gives asuspension concentrate fiom which suspensions of any desired dilution can be prepared bydiluting it with water. Such dilutions can be used for treating live plants and plant 25 propagation material by spraying, watering or immersing and for protecting them againstattack by microorganisms. -10- 11 ?64 I) Biological Examples

Test mcthod

Vine plantlets cv. "Gutedel" aie grown under grcenhouse conditions using one plant perpot (0 = 6 cm) and sprayed with a spray broth prepared from an émulsion concentrate, 5 either in the two-leaf stage or in the three-leaf stage. The following concentrations of active ingrédient aie used per batch of 4 plains: 200; 60; 20; 6; 2; 0.6; 0.2; 0.06 mg ofax/litre. This dilution saies is prepared in demineralized water immediately prior toapplication as a foliar spray. To exclude a gas-phase effect of the a.i. in the vicinity, ailplants aie sepaiated from each other on the side using translucent plastic foils and kept in 10 the dark for one day at 20-22°C and a relative humidity of approximately 100 %.

Then, the entire leaf surface area of the plants is uniformly sprayed to dxip point with afreshly prepared sporangia suspension (120 000/ml) of a metalaxyl-sensitive strain ofPlasmoyara viticola. The plants are then kept for 7 days under a 16 hour photoperiod withartificial daylight at 20-22°C and a relative humidity of approximately 100 %. This is 15 followed by évaluation of the infestation, separating three-leaf and two-leaf stage sprayings. The tables show in each case the average of 4 parallel sprayings. A) Sprayings in the two-leaf stage (PL viticola on vines)

Level of action of R-metalaxyl and racemic metalaxyl Active ingrédient Dose [mg of a.iyiitre] Foliar infestation [%] 200 0 60 0 20 0 R-metalaxyl 6 0 2 4 0.6 78 0.2 97 0.06 92 25 11 7 6 4 - 11- untreated control 96 200 0 60 0 20 38 racemic 6 76 metalaxyl 2 87 0.6 100 0.2 97 0.06 96 10 Whilc conventional racemic metalaxyl docs not resnlt in a clear-cut action against foliar infestation in a concentration range of below 60 mg of aôVlitre and is without effect for practical purposes at aconcentration of below 20 mg of aôVlitre, tbe activityof enantiomeric R-metalaxyl is up to 30times betterup to dilutions of 2mg of aôVlitre.

In tbe case of spraying in the three-leaf stage, the différences in activity are even clearer, as shown 15 byTableB). B) Sprayings in tbe three-leaf stage (PI. viticola on vines) JLevel of action of R-metalaxyl and racemic metalaxyl K Active ingrédient Dose [mg of aôVlitre] Foliar infestation [%] 20 200 0 60 0 20 0 R-metalaxyl 6 0 2 0 25 0.6 0 0.2 78 0.06 93 untreated control 92 1 7 6 4 - 12- 200 0 60 0 20 27 racemic 6 85 5 metalaxyl 2 80 0.6 96 0.2 90 0.06 92

Whilc convcntional racemic metalaxyl shows virtually no activity in a concentration range of 6 mg 10 of a.iyiitre (or less) and a more clear-cut activity isonly discemibleat 20 mg of ax/Iitre, the activity of enantiomeric R-metalaxyl is approximately 100 times better up to a concentration rangeof 0.6 mg of ax/litie. H) Dégradation of the active ingrédients in the soil

Example 1 15 Degradationbehaviour of racemic metalaxvl and R-metalaxyl in moderately heaw soil

Two groups of 8 samples each of biologically active soil (silt/loam; loam: 13.9 %;silù 54.3 %; sand: 31.8 %; organic carbon: 2.1 %; pH 7.3; biomass: 65.1 mg microbialcarbon per 100 g soil; origin: Les Evouettes, Valais, Switzeriand) are trcated in parallelwith racemic metalaxyl or R-metalaxyl, respectively, in each case in acetonic solution. 20 The rate of application is 0.5 mg/kg of soil sample, which corresponds to a rate of application of 0.5 kg/hectare. The iesults aie evaluated in duplicate after 0,7,14 and21 days. Results: -13-

Table 1: Rate of Dégradation of rac. Metalaxyl and R-Metalaxyl in fieldfresh Soil(Silt/Ioam) under laboratory Conditions

Time (days) racemic metalaxyl(% of applied) R-metalaxyl(% of applied) 5 mean mean 0 90.41 93.61 0 90.36 90.39 98.94 96.28 7 47.28 24.74 7 45.17 46.23 25.7 2523 10 14 35.88 9.07 14 35.54 35.71 10.62 9.85 21 29.34 7.57 21 29.06 29.20 7.82 7.69

The dégradation équations aie: 15 Metalaxyl racemate: Q = 86.66* e(-0.0644*t) DT-50 = ln2/0.0644; DT-90 = lnl0/0.0644R-metalaxyl: Ç = 95.9* e(-0.1776*t) DT-50 = 1π2Λ).Ο1776; DT-90 = lnl0/0.1776

The dégradation curves axe shown in Figure 1 (Appendix). 20 They allow the following dégradation times to be calculated: racemic R-metalaxyl metalaxyl DT-50:(50 % dégradation)DT-90:(90 % dégradation) 10.8 days35.7 days 3.9 days 13.0 days 11 7 6 4 - 14-

Example 2 Dégradation bchaviour of racemic metalaxyl and R-metalaxyl in sandy soil

Two groups of 16 samples each of biologically active soil (sandy soil; loam: 5.1 %;silt: 11.4 %; sand: 83.5 %; organic carbon: 1.6 %; pH4; biomass: 51 mg microbial 5 carbon/100 g soil; origin: Collombey, Valais, Switzexiand) aie treated in parallel with racemic metalaxylor R-metalaxyl, respectively, in each case in acetonic solution. The rate < of application is 0.5 mg/kg of soil sample, which corresponds to a rate of application of 0.5 kg/hcctare. The results are evaluated in duplicate after 0,1,3,7,9,15,21 and 29 days.Results: 10 Table 2: Rate of Dégradation of rac. Metalaxyl and R-Metalaxyl in fieldfresh Soil (Sand) under laboratory Conditions.

Time (days) racemic metalaxyl(% of applied) R-metalaxyl(% of applied) mean mean 0 98.00 100.32 0 97.56 97.78 99.72 100.02 1 87.75 89.16 1 87.88 87.82 90.13 89.64 3 80.32 76.96 3 79.69 80.01 74.01 75.48 7 65.41 52.59 7 64.60 65.01 52.59 52.59 9 55.84 47.22 9 56.68 56.26 46.45 46.84 15 43.49 24.77 15 41.58 42.54 29.89 27.33 21 30.77 17.12 21 33.21 31.99 17.05 17.09 29 28.70 8.82 29 28.28 28.49 8.62 8.72 Dégradation équations rac. Metalaxyl: Ct=93.67* β(-οθ5006η). DT.5o=in 2/0.05006; DT-90=ln 10/0.5006 R-Metalaxyl: Ct=98.53* β(-θ·θ8548*0; DT-50=ln 2/0.08548; DT-90=ln 10/0.08548 11 7 6 4 -15-

The dégradation curves are shown in Figure 2 (Appendix).

They allow the following dégradation times to be calculated:

.X racemic R-metalaxyl metalaxyl C 5 DT-50:(50 % dégradation') 13.9 days 8.1 days DT-90:(90 % dégradation) 46.0 days 26.9 days

Claims (16)

1. A fungicidal composition having improved dégradation in the soil, on the basis of anOomycetes controlling fiingicide selected from metalaxyl, furalaxyl and benalaxylwherein the content of the R-enantiomer in the active ingrédient is more than 70 % b.w., 5 together with a suitable carrier matériel therefor.

2. A composition according to daim 1, wherein the content of the R-enantiomer in theactive ingrédient is more than 85 % by weight

3. A composition according to claim 2, wherein the content of the R-enantiomer in dieactive ingrédient is more than 92 % by weight 10

4. A composition according to claim 3, wherein the content of the R-enantiomer in the active ingrédient is more than 97 % by weight.

5. A composition according to claim 4, wherein the active ingrédient is essentially ôeefrom S-enantiomer.

6. A composition according to claim 1, wherein the active ingrédient enriched with (15 R-enantiomer is metalaxyl.

7. A composition according to claim 1, wherein the active ingrédient enriched withR-enantiomer is furalaxyl.

8. A composition according to claim 1, wherein the active ingrédient enriched withR-enantiomer is benalaxyl. 20

9. A composition according to claim 6 comprising metalaxyl as highly concentrated formulation of more than 30 % b.w. active ingrédient in addition to carrier material.

10. In a process for controlling or preventing attack of Oomycetes by applying to plants, parts of plants or to a locus liable to be infected by Oomycetes, a fiingicide selected from metalaxyl, furalaxyl and benalaxyl the improvement that for better biodégradation in the 25 soil the fiingicide consists of more than 70 % b.w. of R-enantiomer. - 17-

11. In a process according to claim 10 wherein the fungicide consiste of more than 85 %b.w. of R-enantiomer.

11 7 6 4 - 16- What we claim is:

12. In a process according to claim 11 wherein the fungicide used is metalaxyl consistingof more than 92 % b.w. of R-enantiomer.

13. In a process according to claim 12 wherein thé metalaxyl used consiste of more than 97 % b.w. of R-enantiomer.

14. In a process according to claim 11 wherein the fungicide used is benalaxyl consistingof more than 92 % b.w. of R-enantiomer.

15. In a process according to daim 11 wherein the fungicide used is furalaxyl consisting 10 of more than 92 % b.w. of R-enantiomer.

16. In a process according to daim 10 wherein the rate of application corresponds to 60 ga.i. per hectare to 300 g ai. per hectare of essentially pure R-enantiomer.