EP3432716A1

EP3432716A1 - Method to control septoria leaf blotch caused by resistant zymoseptoria tritici strains

Info

Publication number: EP3432716A1
Application number: EP17710582.2A
Authority: EP
Inventors: Andreas MEHL; Jochen KLEEMANN
Original assignee: Bayer CropScience AG
Current assignee: Bayer CropScience AG
Priority date: 2016-03-24
Filing date: 2017-03-20
Publication date: 2019-01-30
Also published as: WO2017162567A1

Abstract

The present invention relates to a method for controlling septoria leaf blotch on cereal plants caused by Zymoseptoria tritici containing the V136A and/or I381V mutation and optionally the G143A mutation, comprising treating cereal plants, their seed or the soil with a composition comprising (a) prothioconazole as compound I and (b) difenoconazole or tebuconazole as compound II and (c) at least one strobilurine fungicide as compound III. The present invention also relates to the use of a composition comprising (a) prothioconazole as compound I and (b) difenoconazole or tebuconazole as compound II and (c) at least one strobilurine fungicide as compound III for controlling septoria leaf blotch on cereal plants caused by the pathogen Zymoseptoria tritici containing the V136A and/or I381V mutation and optionally the G143A mutation by treating cereal plants, their seed or the soil with the composition.

Description

Method to septoria leaf blotch caused by resistant Zymoseptoria tritici strains

The present invention relates to a method for controlling septoria leaf blotch on cereal plants caused by Zymoseptoria tritici containing the V136A and/or 138 IV mutation and optionally the G143A mutation, comprising treating cereal plants, their seed or the soil with a composition comprising (a) prothioconazole as compound I and (b) difenoconazole or tebuconazole as compound II and (c) at least one strobilurine fungicide as compound III. The present invention also relates to the use of a composition comprising (a) prothioconazole as compound I and (b) difenoconazole or tebuconazole as compound II and (c) at least one strobilurine fungicide as compound III for controlling septoria leaf blotch on cereal plants caused by the pathogen Zymoseptoria tritici containing the V136A and/or 138 IV mutation and optionally the G143A mutation by treating cereal plants, their seed or the soil with the composition.

Zymoseptoria tritici is a species of filamentous fungus, an ascomycete in the family Mycosphaerellaceae. It is a plant pathogen causing septoria leaf blotch, which is currently the most dominant cereal disease in Western Europe and is among the top two or three most economically damaging diseases of cereals in the United States. Control of Septoria leaf blotch is becoming more and more difficult for farmers. Reason is the capability of the fungi to develop resistance to widely used powerful fungicidal agents.

One task farmers are faced with in relation to the use of fungicides is that the repeated and exclusive application of an individual fungicidal compound leads in many cases to a rapid selection of harmful fungi, which have developed natural or adapted resistance against the active compound or at least an sensitivity shift to reduced control of the disease by using the active ingredient. Therefore there is a need for fungicidal products that help prevent or overcome resistance or a significant sensitivity shift. The application of fungicides in particular to control resistant or less sensitive fungi commonly bears the problem of unfavorable environmental or toxicological effects due to high dosage rates which are needed to effectively control the disease.

Fungicides containing azole and srobilurine mixtures have been widely and successfully used in recent years for Zymoseptoria tritici control. Due to particular mutations detected in the cytochrome b gene of some plant pathogenes, including Zymoseptoria tritici, a sensitivity shift against particular fungicides, including strobilurines and azole fungicides, has been observed during the last years but not all of these fungicides are affected to the same extent. Strobilurins lost their activity due to the development of the so called G143A resistance which is meanwhile widespread in most cereal growing regions in Europe (Fraaije B. A. , Brunett F. J., Clark W. S., Motteram J., Lucas J. A. (2005). Resistance development to Qol inhibitors in populations of Mycosphaerella graminicola in the UK. Modern fungicides and antifungal compounds II, eds Lyr H. , Russell P. E., Dehne H-W. Gisi U. Kuck K-H, 14th International Reinhardsbrunn Symposium, BCPC, Alton, UK, pp 63-71). The so called G143A resistance occurs for Zymoseptoria tritici strains with a change from glycine to alanine at position 143 in the cytochrome b gene - the G143A mutation. A change from valine to alanin at position 136 in the cyp51 gene - the V136A mutation - or a change from isoleucine to valine at position 381 in the cyp51 gene - the 138 IV mutation - govern a sensitivity shift or resistance to some azoles but not all azoles are affected to the same extent. Additionally, cross-resistances of azoles have been observed. Such cross resistances even more increase the difficulties in controlling septoria leaf blotch caused by such resistant strains.

Azoles are fungicides well known as sterol biosynthesis inhibitors, see FRAC classification (FRAC website http://www/frac.info/), in particular subgroup Gl. It is in particular known that azole fungicides are inhibitors of fungal sterol C14 demethylase cyp51 (demethylation inhibitor (DMI) fungicides), which is a cytochrome

P450 monooxygenase. Therefore, occurrence of a cross resistance of two azole fungicides having the same mode of action is not a surprise.

Thus, even though the fungicidal synergistic action of strobilurines and azoles is common knowledge (see for example for trifloxystrobin/prothioconazole mixtures WO-A 03/072852), reduced activity from the strobilurine fungicides against Zymoseptoria tritici containing the G143A mutation as well as decreased activity from the azole part due to sensitivity shift against Zymoseptoria tritici containing the V136A and/or 138 IV mutation would be expected.

Due to the decreasing susceptibility of strobilurines and some triazoles as well as the occurrence of cross- resistances against Zymoseptoria tritici appropriate resistance management measures are crucial to control this important disease caused by mutant strains.

Surprisingly, it has been found that a combination of (a) prothioconazole and (b) difenoconazole or tebuconazole and (c) at least one strobilurine fungicide show an unexpected fungicidal action towards Zymoseptoria tritici being at least partially resistant against strobilurines and showing a decreased susceptibility to solo azole applications. Thus, the present invention comprises a method for controlling septoria leaf blotch on cereal plants caused by

Zymoseptoria tritici containing the V136A and/or 138 IV mutation and optionally the G143A mutation, comprising treating cereal plants, their seed or the soil with a composition comprising

(a) prothioconazole as compound I; and

(b) difenoconazole or tebuconazole as compound II; and (c) at least one strobilurine fungicide as compound III.

Preferably, the present invention comprises a method for controlling septoria leaf blotch on cereal plants caused by Zymoseptoria tritici containing the V136A and 138 IV mutation and optionally the G143A mutation, comprising treating cereal plants, their seed or the soil with a composition comprising

(a) prothioconazole as compound I; and (b) difenoconazole or tebuconazole as compound II; and

(c) at least one strobilurine fungicide as compound III. Also preferably, the present invention comprises a method for controlling septoria leaf blotch on cereal plants caused by Zymoseptoria tritici containing the G143A and V136A or the G143A and the 138 IV mutation, preferably containing the G143A and V136A and 138 IV mutation, comprising treating cereal plants, their seed or the soil with a composition comprising (a) prothioconazole as compound I; and

(b) difenoconazole or tebuconazole as compound II; and

(c) at least one strobilurine fungicide as compound III.

Surprisingly, despite the expectation of decreased susceptibility of Zymoseptoria tritici containing the V136A and/or 138 IV mutation to azole applications the compositions according to the present invention comprising the particular combinations of (a) prothioconazole as compound I and (b) difenoconazole or tebuconazole as compound II and (c) at least one strobiluriene fungicide as compound III excellently control septoria leaf blotch caused by those Zymoseptoria tritici mutants. The use of such compositions comprising (a) prothioconazole as compound I and (b) difenoconazole or tebuconazole as compound II and (c) at least one strobilurine fungicide as compound III to control Zymoseptoria tritici containing the V136A and/or 138 IV mutation is important for appropriate resistance management, since Zymoseptoria tritici showing a sensitivity shift to azole applications can be successfully controlled without increasing the dosage rates.

It has been found that presence of the V136A mutation increases the sensitivity of Septoria leaf blotch populations against difenoconazole or tebuconazole whereas prothioconazole shows stronger intrinsic activity on strains carrying the 138 IV mutation but not the V136A mutation. Additionally, application of prothioconazole creates a selection pressure enriching the V136A mutation in the Zymoseptoria tritici population and on the other hand application of difenoconazole or tebuconazole creates a selection pressure enriching the 138 IV mutation in the Zymoseptoria tritici population. Therefore, the compositions according to the present invention comprising the particular combinations of (a) prothioconazole as compound I and (b) difenoconazole or tebuconazole as compound II and (c) at least one strobilurine fungicide as compound III can perfectly be used for controlling Zymoseptoria tritici containing the V136A and/or the 138 IV mutation, preferably for controlling Zymoseptoria tritici containing both, the V136A and the 138 IV mutation. Containing both, the V136A and the 138 IV mutation means that both mutations are present in the cyp51 gene.

Moreover, the efficacy of the additional strobilurine is not significantly affected by any of the V136A and 138 IV mutations and the presence of the G143A mutation does not significantly affect the sensitivity of the septoria populations against prothioconazole, tebuconazole or difenoconazole. Therefore, the compositions according to the present invention comprising the particular combinations of (a) prothioconazole as compound I and (b) difenoconazole or tebuconazole as compound II and (c) at least one strobilurine fungicide as compound III can perfectly be used for decreasing the selection pressure towards one of the mutations as well as for controlling Zymoseptoria tritici containing the G143A or the V136A or the 138 IV mutation, even preferably for controlling Zymoseptoria tritici containing the G143A and V136A or the G143A and the 138 IV mutation or even more preferably for controlling Zymoseptoria tritici containing the G143A and V136A and the 138 IV mutation. Additionally, the presence of at least one strobilurine can also have a further advantageous yield increase effect. Containing both, G143A and V136A or the G143A and the 138 IV mutation means that both mutations are present in the pathogen population, preferably that both mutations are present in the same genome. Containing the G143A and V136A and the 138 IV mutation means that all three mutations are present in the pathogen population, preferably that all three mutations are present in the same genome.

Moreover, it is particularly surprising that there is incomplete cross resistance of prothioconazole and any of the two azoles tebuconazole and difenoconazole although these azoles all have the same mode of action.

Thus, the present invention also comprises the use of a composition comprising

(a) prothioconazole as compound I; and

(b) difenoconazole or tebuconazole as compound II; and

(c) at least one strobilurine fungicide as compound III. for controlling septoria leaf blotch on cereal plants caused by the pathogen Zymoseptoria tritici containing the G143A and/or V136A and/or 138 IV mutation by treating cereal plants, their seed or the soil with the composition.

Preferably, the present invention also comprises the use of a composition comprising (a) prothioconazole as compound I; and (b) difenoconazole or tebuconazole as compound II; and

(c) at least one strobilurine fungicide as compound III. for controlling septoria leaf blotch on cereal plants caused by the pathogen Zymoseptoria tritici containing the V136A and 138 IV mutation and optionally the G143A mutation by treating cereal plants, their seed or the soil with the composition. Also preferably, the present invention also comprises the use of a composition comprising

(a) prothioconazole as compound I; and

(b) difenoconazole or tebuconazole as compound II; and

(c) at least one strobilurine fungicide as compound III. for controlling septoria leaf blotch on cereal plants caused by the pathogen Zymoseptoria tritici containing the G143A and V136A or the G143A and the 138 IV mutation, more preferably containing the G143A and V136A and 138 IV mutation by treating cereal plants, their seed or the soil with the composition.

The use according to the invention is an important use for resistance management by controlling Zymoseptoria tritici being less susceptible to azoles and/or strobilurines.

In preferred embodiments of the present invention the composition comprises prothioconazole as compound I and tebuconazole as compound II and at least one strobilurine fungicide as compound III.

In other preferred embodiments of the present invention the composition comprises prothioconazole as compound I and difenoconazole as compound II and at least one strobilurine fungicide as compound III. Preferred strobilurine fungicides are selected from the group consisting of trifloxystrobin, picoxystrobin, pyraclostrobin, fluoxastrobin, azoxystrobin, dimoxystrobin and metominostrobin.

Therefore, in further preferred embodiments of the present invention the composition comprises one of the combinations according to Table 1.

The most preferred strobilurine fungicide is trifloxystrobin.

Therefore, in preferred embodiments of the present invention the composition comprises prothioconazole compound I and tebuconazole as compound II and trifloxystrobin as compound III. In other preferred embodiments of the present invention the composition comprises prothioconazole as compound I and difenoconazole as compound II and trifloxystrobin as compound III.

Also part of the present invention are novel compositions comprising

(a) prothioconazole as compound I; and (b) difenoconazole as compound II, and

(c) at least one strobilurine fungicide as compound III.

In preferred embodiments of the present invention such novel compositions comprise prothioconazole as compound I and difenoconazole as compound II and at least one strobilurine selected from the group consisting of trifloxystrobin, picoxystrobin, pyraclostrobin, fluoxastrobin, azoxystrobin, dimoxystrobin and metominostrobin as compound III.

In more preferred embodiments of the present invention such novel compositions comprise prothioconazole as compound I and difenoconazole as compound II and trifloxystrobin as compound III.

According to the present invention the weight ratio of the compound I to compound II in the composition is from 10:1 to 1:10, preferably from 5:1 to 1:5, more preferably from 4:1 to 1:4, most preferably from 3:1 to 1:3.

According to the present invention the weight ratio of the compound I to compound III in the composition is from 10:1 to 1:10, preferably from 5:1 to 1:5, more preferably from 4:1 to 1:4, most preferably from 3:1 to 1:3.

According to the present invention the weight ratio of the compound II to compound III in the composition is from 10:1 to 1:10, preferably from 5:1 to 1:5, more preferably from 4:1 to 1:4, most preferably from 3:1 to

1:3.

According to the present invention the weight ratio of the compound I to compound II in the composition is from 10:1 to 1:10, preferably from 5:1 to 1:5, more preferably from 4:1 to 1:4, most preferably from 3:1 to 1:3; and the weight ratio of the compound I to compound III in the composition is from 10:1 to 1:10, preferably from 5:1 to 1:5, more preferably from 4:1 to 1:4, most preferably from 3:1 to 1:3; and the weight ratio of the compound II to compound III in the composition is from 10:1 to 1:10, preferably from 5:1 to 1:5, more preferably from 4:1 to 1:4, most preferably from 3:1 to 1:3.

According to the present invention the weight ratio of the compound I to compound II in the composition is from 10:1 to 1:10 and the weight ratio of the compound I to compound III in the composition is from 10:1 to 1:10 and the weight ratio of the compound II to compound III in the composition is from 10: 1 to 1:10. According to the present invention the weight ratio of the compound I to compound II in the composition is from 5: 1 to 1 :5 and the weight ratio of the compound I to compound III in the composition is from 5: 1 to 1 :5 and the weight ratio of the compound II to compound III in the composition is from 5: 1 to 1 :5.

According to the present invention the weight ratio of the compound I to compound II in the composition is from 4: 1 to 1 :4 and the weight ratio of the compound I to compound III in the composition is from 4: 1 to 1 :4 and the weight ratio of the compound II to compound III in the composition is from 4: 1 to 1 :4.

According to the present invention the weight ratio of the compound I to compound II in the composition is from 3: 1 to 1 :3 and the weight ratio of the compound I to compound III in the composition is from 3: 1 to 1 :3 and the weight ratio of the compound II to compound III in the composition is from 3 : 1 to 1 :3. The compositions according to the present invention can also be combined with known bactericides, acaricides, nematicides or insecticides, in order thus to broaden, for example, the activity spectrum or to further prevent development of resistance.

A combination with other known active ingredients, such as herbicides, or with fertilizers and growth regulators, safeners and/or semiochemicals, is also possible. According to the present invention the cereal plants, their seed or the soil in which the plant is growing or in which it is desired to grow can be treated. Treatment of plants according to the inventions also includes treatment of plant parts. The compositions used according to the invention can be used to curatively or preventively control the disease. Preferably the cereal plants or plant parts are treated with the compositions according to the present invention. Cereals according to the present invention include wheat and triticale.

Where a compound I or a compound II or a compound III can be present in tautomeric form, such a compound is understood hereinabove and hereinbelow also to include, where applicable, corresponding tautomeric forms, even when these are not specifically mentioned in each case.

Compounds I or compounds II or compounds III having at least one basic centre are capable of forming, for example, acid addition salts, e.g. with strong inorganic acids, such as mineral acids, e.g. perchloric acid, sulfuric acid, nitric acid, nitrous acid, a phosphoric acid, a hydrohalic acid, such as hydrogen fluoride, hydrogen chloride, hydrogen bromide and hydrogen iodide, or acidic salts, such as NaHSC^ and KHSO4, with strong organic acids, formic acid, carbonic acid and alkanoic acids, such as acetic acid, trifluoroacetic acid, trichloroacetic acid and propionic acid, and also glycolic acid, thiocyanic acid, lactic acid, succinic acid, citric acid, benzoic acid, cinnamic acid, maleic acid, fumaric acid, tartaric acid, sorbic acid oxalic acid, alkylsulphonic acids (sulphonic acids having straight-chain or branched alkyl radicals of 1 to 20 carbon atoms), arylsulphonic acids or aryldisulphonic acids (aromatic radicals, such as phenyl and naphthyl, which carry one or two sulphonic acid groups), alkylphosphonic acids (phosphonic acids having straight-chain or branched alkyl radicals of 1 to 20 carbon atoms), arylphosphonic acids or aryldiphosphonic acids (aromatic radicals, such as phenyl and naphthyl, which carry one or two phosphonic acid radicals), where the alkyl and aryl radicals may carry further substituents, for example p-toluenesulphonic acid, 1,5-naphthalenedisulphonic acid, salicylic acid, p-aminosalicylic acid, 2-phenoxybenzoic acid, 2-acetoxybenzoic acid, etc.. Compounds I or compounds II or compounds III having at least one acid group are capable of forming, for example, salts with bases, e.g. metal salts, such as alkali metal or alkaline earth metal salts, e.g. sodium, potassium or magnesium salts, or salts with ammonia or an organic amine, such as morpholine, piperidine, pyrrolidine, a mono-, di- or tri-lower alkylamine, e.g. ethyl-, diethyl-, triethyl- or dimethyl-propyl-amine, or a mono-, di- or tri-hydroxy-lower alkylamine, e.g. mono-, di- or tri-ethanolamine. In addition, corresponding internal salts may optionally be formed. In the context of the invention, preference is given to agro chemically advantageous salts. In view of the close relationship between the compounds I or the compounds II or compounds III in free form and in the form of their salts, hereinabove and herein below any reference to the free compounds I or free compounds II or free compounds III or to their salts should be understood as including also the corresponding salts or the free compounds I or free compounds II or free compounds III, respectively, where appropriate and expedient. The same also applies to tautomers of compounds I or compounds II or compounds III and to their salts.

The composition used according to the invention may also comprise an agriculturally acceptable support, carrier or filler.

According to the invention, the term "support" denotes a natural or synthetic, organic or inorganic compound with which the active compound I and II and optionally III is combined or associated to make it easier to apply, notably to the parts of the plant. This support is thus generally inert and should be agriculturally acceptable. The support may be a solid or a liquid. Examples of suitable supports include clays, natural or synthetic silicates, silica, resins, waxes, solid fertilisers, water, alcohols, in particular butanol, organic solvents, mineral and plant oils and derivatives thereof. Mixtures of such supports may also be used.

The composition may also comprise additional components. In particular, the composition may further comprise a surfactant. The surfactant can be an emulsifrer, a dispersing agent or a wetting agent of ionic or non-ionic type or a mixture of such surfactants. Mention may be made, for example, of polyacrylic acid salts, lignosulphonic acid salts, phenolsulphonic or naphthalenesulphonic acid salts, polycondensates of ethylene oxide with fatty alcohols or with fatty acids or with fatty amines, substituted phenols (in particular alkylphenols or arylphenols), salts of sulphosuccinic acid esters, taurine derivatives (in particular alkyl taurates), phosphoric esters of polyoxyethylated alcohols or phenols, fatty acid esters of polyols, and derivatives of the present compounds containing sulphate, sulphonate and phosphate functions. The presence of at least one surfactant is generally essential when the active compound and / or the inert support are water-insoluble and when the vector agent for the application is water. Preferably, surfactant content may be comprised from 5% to 40% by weight of the composition. Colouring agents such as inorganic pigments, for example iron oxide, titanium oxide, ferrocyanblue, and organic pigments such as alizarin, azo and metallophthalocyanine dyes, and trace elements such as iron, manganese, boron, copper, cobalt, molybdenum and zinc salts can be used. Optionally, other additional components may also be included, e.g. protective colloids, adhesives, thickeners, thixotropic agents, penetration agents, stabilisers, sequestering agents. More generally, the active compounds can be combined with any solid or liquid additive, which complies with the usual formulation techniques.

In general, the composition according to the invention may contain from 0.05 to 99% by weight of active compounds, preferably from 10 to 70% by weight.

The combination or composition according to the invention can be used as such, in form of their formulations or as the use forms prepared therefrom, such as aerosol dispenser, capsule suspension, cold fogging concentrate, dustable powder, emulsifiable concentrate, emulsion oil in water, emulsion water in oil, encapsulated granule, fine granule, flowable concentrate for seed treatment, gas (under pressure), gas generating product, granule, hot fogging concentrate, macrogranule, microgranule, oil dispersible powder, oil miscible flowable concentrate, oil miscible liquid, paste, plant rodlet, powder for dry seed treatment, seed coated with a pesticide, soluble concentrate, soluble powder, solution for seed treatment, suspension concentrate (flowable concentrate), ultra low volume (ULV) liquid, ultra low volume (ULV) suspension, water dispersible granules or tablets, water dispersible powder for slurry treatment, water soluble granules or tablets, water soluble powder for seed treatment and wettable powder.

The treatment of plants and plant parts with the composition according to the invention is carried out directly or by action on their environment, habitat or storage area by means of the normal treatment methods, for example by watering (drenching), drip irrigation, spraying, atomizing, broadcasting, dusting, foaming, spreading-on, and as a powder for dry seed treatment, a solution for seed treatment, a water-soluble powder for seed treatment, a water-soluble powder for slurry treatment, or by encrusting.

The compositions used according to the invention include not only compositions which are ready to be applied to the plant, seed or soil to be treated by means of a suitable device, such as a spraying or dusting device, but also concentrated commercial compositions which must be diluted before application to the plant, seed or soil. When using active ingredients as fungicides, the application rates can be varied within a relatively wide range, depending on the kind of application. The application rate of the active ingredients used according to the invention is generally and advantageously

• in the case of treatment of plants or plant parts, for example leaves: from 0.1 to 10 000 g/ha, preferably from 10 to 1000 g/ha, more preferably from 10 to 800 g/ha, even more preferably from 25 to 300 g/ha (in the case of application by watering or dripping, it is even possible to reduce the application rate, especially when inert substrates such as rockwool or perlite are used);

• in the case of seed treatment: from 2 to 200 g per 100 kg of seed, preferably from 3 to 150 g per 100 kg of seed, more preferably from 2.5 to 25 g per 100 kg of seed, even more preferably from 2.5 to 12.5 g per 100 kg of seed; • in the case of soil treatment: from 0.1 to 10 000 g/ha, preferably from 1 to 5000 g/ha.

In case of treatment of plants or plant parts the application rate of the active ingredients used according to the invention is preferably

• from 25 to 250 g/ha prothioconazole (Compound I), more preferably from 50 to 200 g/ha prothioconazole;

• from 25 to 250 g/ha tebuconazole (Compound II), more preferably from 50 to 200 g/ha tebuconazole;

• from 25 to 300 g/ha difenoconazole (Compound II), more preferably from 50 to 250 g/ha difenoconazole;

• from 25 to 300 g/ha strobilurine (Compound III), more preferably from 50 to 250 g/ha strobilurine.

Treatment of seeds

The compositions of the invention are particularly suitable for the treatment of seeds.

The invention comprises a procedure in which the seed is treated at the same time with a compound I and a compound II and optionally a compound III. It further comprises a method in which the seed is treated with compound I and compound II and optionally compound III sequentially or separately, i.e. at different times. If the single active ingredients are applied in a sequential / separate manner, i.e. at different times, they are applied one after the other within a reasonably short period, such as a few hours or days. Preferably the order of applying the compounds I and II and optionally III is not essential for working the present invention.

A large part of the damage to crop plants caused by harmful organisms is triggered by the infection of the seed during storage or after sowing, and also during and after germination of the plant. This phase is particularly critical since the roots and shoots of the growing plant are particularly sensitive, and even minor damage may result in the death of the plant. There is therefore a great interest in protecting the seed and the germinating plant by using appropriate compositions.

The control of phytopathogenic fungi by treating the seed of plants has been known for a long time and is the subject of constant improvements. However, the treatment of seed entails a series of problems which cannot always be solved in a satisfactory manner. For instance, it is desirable to develop methods for protecting the seed and the germinating plant, which dispense with, or at least significantly reduce, the additional deployment of crop protection compositions after planting or after emergence of the plants. It is also desirable to optimize the amount of the active ingredient used so as to provide the best possible protection for the seed and the germinating plant from attack by phytopathogenic fungi, but without damaging the plant itself by the active ingredient employed. In particular, methods for the treatment of seed should also take account of the intrinsic fungicidal properties of transgenic plants in order to achieve optimal protection of the seed and the germinating plant with a minimum expenditure of crop protection compositions. The control of phytopathogenic fungi which damage plants post-emergence is effected primarily by treating the soil and the above-ground parts of plants with crop protection compositions. Owing to the concerns regarding a possible influence of the crop protection compositions on the environment and the health of humans and animals, there are efforts to reduce the amount of active ingredients deployed. One of the advantages of the present invention is that the particular systemic properties of the active ingredients and compositions mean that treatment of the seed with these active ingredients and compositions not only protects the seed itself, but also the resulting plants after emergence, from phytopathogenic fungi. In this way, the immediate treatment of the crop at the time of sowing or shortly thereafter can be dispensed with. It is likewise considered to be advantageous that the active ingredients or compositions can especially also be used with transgenic seed, in which case the plant growing from this seed is capable of expressing a protein which acts against pests. By virtue of the treatment of such seed with the active ingredients or compositions, merely the expression of the protein, for example an insecticidal protein, can control certain pests. Surprisingly, a further synergistic effect can be observed in this case, which additionally increases the effectiveness for protection against attack by pests.

As also described below, the treatment of transgenic seed with the active ingredients or compositions is of particular significance. This relates to the seed of plants containing at least one heterologous gene.

In the context of the present invention, the composition is applied to the seed alone or in a suitable formulation. Preferably, the seed is treated in a state in which it is sufficiently stable for no damage to occur in the course of treatment. In general, the seed can be treated at any time between harvest and sowing. It is customary to use seed which has been separated from the plant and freed from cobs, shells, stalks, coats, hairs or the flesh of the fruits. For example, it is possible to use seed which has been harvested, cleaned and dried down to a moisture content of less than 15 % by weight. Alternatively, it is also possible to use seed which, after drying, for example, has been treated with water and then dried again. When treating the seed, care must generally be taken that the amount of the composition applied to the seed and/or the amount of further additives is selected such that the germination of the seed is not impaired, or that the resulting plant is not damaged. This has to be borne in mind in particular in the case of active ingredients which can have phyto toxic effects at certain application rates.

The compositions can be applied directly, i.e. without containing any other components and without having been diluted. In general, it is preferable to apply the compositions to the seed in the form of a suitable formulation. Suitable formulations and methods for seed treatment are known to those skilled in the art and are described, for example, in the following documents: US 4,272,417, US 4,245,432, US 4,808,430, US 5,876,739, US 2003/0176428 Al, WO 2002/080675, WO 2002/028186. The active ingredients usable in accordance with the invention can be converted to the customary seed dressing formulations, such as solutions, emulsions, suspensions, powders, foams, slurries or other coating compositions for seed, and also ULV formulations.

These formulations are prepared in a known manner, by mixing the active ingredients with customary additives, for example customary extenders and also solvents or diluents, dyes, wetting agents, dispersants, emulsifiers, antifoams, preservatives, secondary thickeners, adhesives, gibberellins and also water.

Useful dyes which may be present in the seed dressing formulations usable in accordance with the invention are all dyes which are customary for such purposes. It is possible to use either pigments, which are sparingly soluble in water, or dyes, which are soluble in water. Examples include the dyes known by the names Rhodamine B, C.I. Pigment Red 112 and C.I. Solvent Red 1.

Useful wetting agents which may be present in the seed dressing formulations usable in accordance with the invention are all substances which promote wetting and which are conventionally used for the formulation of active agrochemical ingredients. Preference is given to using alkyl naphthalenesulphonates, such as diisopropyl or diisobutyl naphthalenesulphonates. Useful dispersants and/or emulsifiers which may be present in the seed dressing formulations usable in accordance with the invention are all nonionic, anionic and cationic dispersants conventionally used for the formulation of active agrochemical ingredients. Usable with preference are nonionic or anionic dispersants or mixtures of nonionic or anionic dispersants. Suitable nonionic dispersants include especially ethylene oxide/propylene oxide block polymers, alkylphenol polyglycol ethers and tristryrylphenol polyglycol ether, and the phosphated or sulphated derivatives thereof. Suitable anionic dispersants are especially lignosulphonates, polyacrylic acid salts and arylsulphonate/formaldehyde condensates.

Antifoams which may be present in the seed dressing formulations usable in accordance with the invention are all foam-inhibiting substances conventionally used for the formulation of active agrochemical ingredients. Silicone antifoams and magnesium stearate can be used with preference. Preservatives which may be present in the seed dressing formulations usable in accordance with the invention are all substances usable for such purposes in agrochemical compositions. Examples include dichlorophene and benzyl alcohol hemiformal.

Secondary thickeners which may be present in the seed dressing formulations usable in accordance with the invention are all substances usable for such purposes in agrochemical compositions. Preferred examples include cellulose derivatives, acrylic acid derivatives, xanthan, modified clays and finely divided silica.

Adhesives which may be present in the seed dressing formulations usable in accordance with the invention are all customary binders usable in seed dressing products. Preferred examples include polyvinylpyrrolidone, polyvinyl acetate, polyvinyl alcohol and tylose. The gibberellins which may be present in the seed dressing formulations usable in accordance with the invention may preferably be gibberellins Al, A3 (= gibberellic acid), A4 and A7; particular preference is given to using gibberellic acid. The gibberellins are known (cf. R. Wegler "Chemie der Pflanzenschutz- und Schadlingsbekampfungsmittel" [Chemistry of the Crop Protection Compositions and Pesticides], vol. 2, Springer Verlag, 1970, p. 401-412).

The seed dressing formulations usable in accordance with the invention can be used, either directly or after previously having been diluted with water, for the treatment of a wide range of different seed, including the seed of transgenic plants. In this case, additional synergistic effects may also occur in interaction with the substances formed by expression. For treatment of seed with the seed dressing formulations usable in accordance with the invention, or the preparations prepared therefrom by adding water, all mixing units usable customarily for the seed dressing are useful. Specifically, the procedure in the seed dressing is to place the seed into a mixer, to add the particular desired amount of seed dressing formulations, either as such or after prior dilution with water, and to mix everything until the formulation is distributed homogeneously on the seed. If appropriate, this is followed by a drying process.

According to another aspect of the present invention, in the composition used according to the invention, the compound ratio I/II, I/III or I/II/III may be advantageously chosen so as to produce a synergistic effect. A synergistic effect of fungicides is always present when the fungicidal activity of the active compound combinations exceeds the total of the activities of the active compounds when applied individually. The expected activity for a given combination of two or three active compounds can be calculated as follows (cf.

Colby, S.R., "Calculating Synergistic and Antagonistic Responses of Herbicide Combinations", Weeds 1967, 15, 20-22).

The latter article mentions the formula for combinations of 2 active compounds:

X^■ Y

and the formula for a combination of 3 active compounds

X Y- X Z-Y Z χ - γ . ζ

E₀ = X + Y + Z - +

100 10000 wherein

X denotes the efficacy when using active compound A at an application rate of m ppm (or g/ha),

Y denotes the efficacy when using active compound B (or C) at an application rate of n ppm (or g/ha), Z denotes the efficacy when using active compound C at an application rate of r ppm (or g/ha),

Ei denotes the efficacy when using active compounds A and B at application rates of m and n ppm (or g/ha), and

E2 denotes the efficacy when using active compounds A and B and C at application rates of m and n and r ppm (or g/ha),

The term "synergistic effect" also means the effect defined by application of the Tammes method, "Isoboles, a graphic representation of synergism in pesticides", Netherlands Journal of Plant Pathology, 70(1964), pages 73-80.

Here, the efficacy is determined in %. 0 % means an efficacy which corresponds to that of the control, whereas an efficacy of 100 % means that no infection is observed.

If the actual fungicidal action exceeds the calculated value, the action of the combination is superadditive, i.e. a synergistic effect is present. In this case, the actually observed efficacy must exceed the value calculated using the above formula for the expected efficacy (Ei or E2).

The invention is illustrated by the following examples. However the invention is not limited to the examples.

Example

The following fungal strains were used in the experiments:

Zymoseptoria tritici field strains carrying cyp51 mutation 138 IV

Zymoseptoria tritici field strains carrying cyp51 mutation V136A Spore inoculum was produced by growing fungal isolates on Czapek-Dox agar medium, supplemented with

20 % (v/v) vegetable juice and 0.3 % (w/v) calcium carbonate, for one week at 20 °C. Spores were harvested by gentle scraping the agar surface and re-suspending the obtained spore material in glucose-peptone medium. The spore suspension was adjusted to lxlO⁶ spores/mL. All fungal isolates were tested with the following final test compound concentrations: 0; 0.0064; 0.032; 0.16; 0.8; 4; 20 and 100 μg active ingredient per mL. Microtiter plates were prepared as follows: Ten μΐ. of compound dilution (prepared in 80 % methanol), containing the amount of compound required for each concentration, was added to the cavities. After complete evaporation of the solvent, compounds were dissolved by adding 140 μΐ, glucose-peptone medium per cavity, followed by overnight incubation on a rotatory shaker at 150 rpm. After adding 60 μΐ, spore suspension into each cavity, plates were incubated at 20 °C and 90 % relative humidity for seven days on a rotatory shaker at 150 rpm. Fungal growth was determined photometrically at 620 nm. EC50 values

(concentration at which the pathogen growth is reduced by 50 %) were calculated from the resulting dose- response for each strain and active ingredient, according to the extinction values. To determine the level of cross-resistance between pairs of the tested fungicides, the correlation of their EC50 values was evaluated by calculation of Pearson's correlation coefficient for each pair. A lower correlation coefficient between the active ingredients indicates a lower level of cross-resistance between them.

Tab. 1 : Levels of cross-resistance between the indicated active ingredients determined by

correlation coefficients between sensitivities of Zymoseptoria tritici field strains

Correlation coefficients

Tebuconazole Prothioconazole Difenoconazole

Field strains carrying mutation V136A

Tebuconazole 1 0,68 0,63

Prothioconazole - 1 0,29

Difenoconazole - - 1

Field strains carrying mutation 138 IV

Tebuconazole 1 0,48 0,87

Prothioconazole - 1 0,48

Difenoconazole - - 1

These results clearly show that there is incomplete cross-resistance of prothioconazole and tebuconazole as well as of prothioconazole and difenoconazole in controlling the two different mutants. Such incomplete cross-resistance means that prothioconazole allows better control of mutant strains which show lower sensitivity against tebuconazole or difenoconazole, and vice versa.

Claims

1. Method for controlling septoria leaf blotch on cereal plants caused by the pathogen Zymoseptoria tritici containing the V136A and/or 138 IV mutation and optionally the G 143A mutation, comprising treating cereal plants, their seed or the soil with a composition comprising

(a) prothioconazole as compound I; and

(b) difenoconazole or tebuconazole as compound II; and

(c) at least one strobilurine fungicide as compound III.

2. Method for controlling septoria leaf blotch on cereal plants according to claim 1, characterized in that the pathogen Zymoseptoria tritici contains the V136A and the 138 IV mutation.

3. Method for controlling septoria leaf blotch on cereal plants according to claim 1, characterized in that the pathogen Zymoseptoria tritici contains the G143A and the V136A mutation or the G143A and the 138 IV mutation, preferably the G 143A and V136A and 138 IV mutation.

4. Method for controlling septoria leaf blotch on cereal plants according to any of claims 1 to 3, characterized in that the composition comprises prothioconazole as compound I and tebuconazole as compound II.

5. Method for controlling septoria leaf blotch on cereal plants according to any of claims 1 to 3, characterized in that the composition comprises prothioconazole as compound I and difenoconazole as compound II.

6. Method for controlling septoria leaf blotch on cereal plants according to any of claims 1 to 5, characterized in that the composition comprises at least one strobilurine fungicide selected from the group consisting of trifloxystrobin, picoxystrobin, pyraclostrobin, fluoxastrobin, azoxystrobin, dimoxystrobin and metominostrobin as compound III, preferably characterized in that the composition comprises trifloxystrobin as compound III.

7. Method for controlling septoria leaf blotch on cereal plants according to any of claims 1 to 6, characterized in that the weight ratio of the compound I to compound II and the weight ratio of compound I to compound III and the weight ratio of compound II to compound III is from 10: 1 to 1 : 10, preferably from 5: 1 to 1 :5, more preferably from 4: 1 to 1 :4, most preferably from 3: 1 to 1:3.

8. Use of a composition comprising

(a) prothioconazole as compound I; and

(b) difenoconazole or tebuconazole as compound II; and (c) at least one strobilurine fungicide as compound III; for controlling septoria leaf blotch on cereal plants caused by the pathogen Zymoseptoria tritici containing the V136A and/or 138 IV mutation and optionally the G 143A mutation by treating cereal plants, their seed or the soil with the composition.

9. Use according to claim 8, characterized in that the pathogen Zymoseptoria tritici contains the V136A and the 138 IV mutation.

10. Use according to claim 8, characterized in that the pathogen Zymoseptoria tritici contains the G143A and the V136A mutation or the G143A and the 138 IV mutation, preferably the G 143A and V136A and 138 IV mutation.

11. Use according to any of claims 8 to 10, characterized in that the composition comprises prothioconazole as compound I and tebuconazole as compound II.

12. Use according to any of claims 8 or 10, characterized in that the composition comprises prothioconazole as compound I and difenoconazole as compound II.

13. Use according to any of claims 8 to 12, characterized in that the composition comprises at least one strobilurine fungicide selected from the group consisting of trifloxystrobin, picoxystrobin, pyraclostrobin, fluoxastrobin, azoxystrobin, dimoxystrobin and metominostrobin as compound III, preferably characterized in that the composition comprises trifloxystrobin as compound III.

14. Use according to any of claims 8 to 13, characterized in that the weight ratio of the compound I to compound II and the weight ratio of compound I to compound III and the weight ratio of compound II to compound III is from 10: 1 to 1 : 10, preferably from 5: 1 to 1 :5, more preferably from 4: 1 to 1 :4, most preferably from 3: 1 to 1 :3.

15. Compositions comprising

(a) prothioconazole as compound I; and

(b) difenoconazole as compound II, and

(c) at least one strobilurine fungicide as compound III.

16. Compositions according to claim 15 comprising prothioconazole as compound I and difenoconazole as compound II and at least one strobilurine selected from the group consisting of trifloxystrobin, picoxystrobin, pyraclostrobin, fluoxastrobin, azoxystrobin, dimoxystrobin and metominostrobin as compound III, preferably comprising prothioconazole as compound I and difenoconazole as compound II and trifloxystrobin as compound III.