CN111387195B

CN111387195B - Method for preventing and treating plant powdery mildew

Info

Publication number: CN111387195B
Application number: CN202010319328.5A
Authority: CN
Inventors: 吴文君; 张继文
Original assignee: Individual
Current assignee: Individual
Priority date: 2020-04-21
Filing date: 2020-04-21
Publication date: 2021-05-28
Anticipated expiration: 2040-04-21
Also published as: CN111387195A

Abstract

The present invention provides a method of controlling powdery mildew in plants, said method comprising applying to said plants an effective amount of L-azetidine-2-carboxylic acid, or an agriculturally pharmaceutically acceptable salt thereof. Surprisingly, the L-azetidine-2-carboxylic acid compound provided by the invention has an excellent control effect on plant powdery mildew, particularly melon powdery mildew.

Description

Method for preventing and treating plant powdery mildew

Technical Field

The invention belongs to the field of plant disease control, and particularly relates to a method for controlling plant powdery mildew, in particular to application of L-azetidine-2-carboxylic acid or agriculturally and pharmaceutically acceptable salts thereof to control plant powdery mildew.

Background

Plant powdery mildew is a plant disease widely existing in plants worldwide, such as wheat, melon, strawberry, grape and flowers, such as Chinese rose, and at present, a common disease particularly in Cucurbitaceae (Cucurbitaceae) vegetables causes serious loss to cucumbers, melons and the like. It is shown by the relevant data that infection of plants with powdery mildew during flowering and fruiting may lead to substantial yield loss.

Powdery mildew mainly damages leaves and can also infect stems and petioles. At the early stage of the disease, the accumulation of white powder consisting of hyphae and conidia on the leaf surface, petiole and caulicle was visually observed. Under appropriate environmental conditions, pathogenic fungi can spread over the entire leaf surface as the disease progresses. Powdery mildew pathogenic bacteria absorb the nutrition of the plant, reduce its photosynthesis, cause the leaves to become chlorosis and even withered, and in severe cases even cause the death of the whole plant. Although the fruits of the plants are rarely directly attacked by the pathogenic bacteria of powdery mildew, the fruits develop malformation and spot formation due to the limited growth caused by the premature senility of the leaves of the infected plants, and finally the yield and the quality are reduced.

The main control measures at present include biological control and chemical control, for example, by selecting disease-resistant varieties and strengthening field management, or spraying chemical pesticides after removing severely infected leaves at the early stage of disease onset. However, the powdery mildew has high reproduction rate and repeated infection, and most systemic bactericides have single action site, so that the germs are easy to generate drug resistance, the dosage is increased by times, the problems of environmental pollution and food safety are caused, and the harm is caused to non-target organisms. The long-term use of chemical pesticides has caused powdery mildew to be p-benzimidazolesOrganic phosphorus, hydroxyl pyrimidine, methoxy acrylic ester, triazole, phenoxy quinoline and the like almost simultaneously generate drug resistance^[1]。

L-azetidine-2-carboxylic acid is a highly bioactive substance present in a variety of natural products, and due to its structure similarity to L-proline, L-azetidine-2-carboxylic acid is currently used for modification of polypeptide structures and preparation of many inhibitors, such as: hepatic fibrosis inhibitors, algae growth inhibitors, and the like. For example, prior art Biological activity of L-2-azetidinecarboxylic acid, isolated from Polygonatum odor var. pluralism, and The prior art of The effect of a chemical hybridization agent on The immunological and chemical composition of inorganic sexual grass, disclose that L-azetidine-2 carboxylic acid has activity in inhibiting algae; WL84811 discloses that azetidinecarboxylic acid WL84811 is useful as a chemical sterilant for annual ryegrass, wheat, and the like. However, at present, no application of L-azetidine-2-carboxylic acid for preventing and treating plant diseases is reported, and the application of L-azetidine-2-carboxylic acid for preventing and treating powdery mildew is not involved. Unexpectedly, the applicant finds that the L-azetidine-2-carboxylic acid compounds have excellent control effects on plant powdery mildew, and particularly have excellent control effects on melon powdery mildew.

Disclosure of Invention

The invention aims to overcome the problem that powdery mildew almost has drug resistance to a large number of chemical pesticides, such as benzimidazoles, organophosphates, hydroxypyrimidines, methoxy acrylates, triazoles, phenoxyquinolines and the like in the prior art, and provides a method for more effectively preventing and treating powdery mildew of plants. The present invention has been completed based on the surprising finding that L-azetidine-2-carboxylic acid-based compounds are effective in controlling powdery mildew in plants.

In one aspect, the present invention provides a method of controlling powdery mildew in plants, comprising applying to said plants an effective amount of L-azetidine-2-carboxylic acid, or an agriculturally pharmaceutically acceptable salt thereof.

In one embodiment, the agriculturally acceptable salts include inorganic and organic salts.

In one embodiment, the inorganic salt comprises at least one of ammonium, lithium, sodium, potassium, cesium, calcium, magnesium, copper, aluminum, zinc, barium, and quaternary ammonium salts.

In one embodiment, the organic salt comprises at least one of arginine, t-butylamine, dimethylamine, diethanolamine, ethanolamine, ethylenediamine, imidazole, lysine, methylamine, pyridine, picolinate, piperazine, triethylamine, triethanolamine, trimethylamine, and urea salts.

In one embodiment, the plant is a barley, wheat, strawberry, grape, rose, apple, rubber or melon plant. Further, the plant is preferably a melon plant.

In one embodiment, the melon plant is cucumber, melon, balsam pear, wax gourd, pumpkin, luffa, hami melon or cucurbita pepo.

In one embodiment, the L-azetidine-2-carboxylic acid, or an agriculturally pharmaceutically acceptable salt thereof, is formulated as a pesticide formulation.

In one embodiment, the pesticide formulation is at least one of an aqueous agent, a dust, a granule, a wettable powder, and a soluble powder.

In one embodiment, the pesticide formulation is configured as a spray for use, and the L-azetidine-2-carboxylic acid, or an agriculturally pharmaceutically acceptable salt thereof, is present in the spray in an amount of 20-2000 μ g/mL. In a preferred embodiment, the L-azetidine-2-carboxylic acid, or an agriculturally pharmaceutically acceptable salt thereof, is present in the spray in an amount of 50-200 μ g/mL.

In another aspect, the invention also provides the use of L-azetidine-2-carboxylic acid, or an agriculturally pharmaceutically acceptable salt thereof, for controlling powdery mildew in plants.

After research, the L-azetidine-2-carboxylic acid compounds provided by the invention have excellent control effects on various plant powdery mildews, such as wheat powdery mildew, barley powdery mildew, strawberry powdery mildew, grape powdery mildew, Chinese rose powdery mildew, apple powdery mildew, rubber powdery mildew and melon powdery mildews, wherein the control effects on the melon powdery mildews are particularly excellent. In particular, according to the experimental results in the examples, it can be surprisingly found that the L-azetidine-2-carboxylic acid-based compound provided by the present invention can achieve a significantly higher control effect at a lower concentration than tebuconazole, which is a positive control of a broad spectrum bactericidal pesticide.

Detailed Description

The following describes in detail specific embodiments of the present invention. It should be understood that the detailed description and specific examples, while indicating the present invention, are given by way of illustration and explanation only, not limitation.

The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.

Before describing the present invention in detail, it is to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to limit the scope of the present invention which will be limited only by the appended claims. For a more complete understanding of the invention described herein, the following terms are used, and their definitions are set forth below. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

The term "agriculturally acceptable" as used herein refers to a substance that does not affect the biological activity or properties of the compounds of the present invention and is relatively non-toxic, i.e., the substance may be administered to an individual without causing an undesirable biological response or interacting in an undesirable manner with any of the components included in the composition. In the present invention, the "agriculturally and pharmaceutically acceptable salt" may include inorganic salts and organic salts, wherein the organic salt may include, but is not limited to, ammonium, lithium, sodium, potassium, cesium, calcium, magnesium, copper, aluminum, zinc, barium, or quaternary ammonium salt, and the inorganic salt may include, but is not limited to, arginine, tert-butylamine, dimethylamine, diethanolamine, ethanolamine, ethylenediamine, imidazole, lysine, methylamine, pyridine, picolinate, piperazine, triethylamine, triethanolamine, trimethylamine, or urea salt.

The term "effective amount" as used herein refers to the amount of a controlling agent that confers a controlling effect on a plant to be controlled at a reasonable benefit/risk ratio applicable to the control of any agent. In some embodiments, an "effective amount" refers to an amount of a therapeutic agent or composition that is effective to treat, ameliorate or prevent (e.g., delay onset of) an associated disease or condition and/or exhibit a detectable therapeutic or prophylactic effect, such as by ameliorating symptoms associated with the disease, preventing or delaying the onset of the disease, and/or also reducing the severity or frequency of symptoms of the disease.

The L-azetidine-2-carboxylic acids referred to in the present invention are also known as (S) -azetidine-2-carboxylic acids, abbreviated as L-Aze. In 1955, Fowden isolated this compound from a 70% ethanol extract of fresh leaves and seeds of the plant, Convallaria majalis, the first natural amino acid with an azetidine structure to be shown to be present in plants^[2]。

According to what is known at present, L-azetidine-2-carboxylic acids are present in the Liliaceae (Liliaceae), Leguminosae (Leguminosae) Phoenix (Delonix regia) and Pimenta peltata (Peltophorum pterocarpum), Red algae and sugar beet (Beta vulgaris)^[2,3]。

In recent years, chemists have conducted extensive research on the method for the large-scale preparation of L-azetidine-2-carboxylic acid, mainly having the following synthetic route: (1) gamma-butyrolactone is used as a raw material; (2) taking L-N-methylsulfonyl-methionine as a raw material; (3) 4-amino-2-hydroxy methyl butyrate is used as a raw material; (4) alpha-methylaniline is used as a raw material; and (5) taking L-aspartic acid as a raw material.

In 2009, Bouazaoui et al also protected L-aspartic acidThe original L-2-amino-4-tert-butyl hydroxybutyrate 2 is taken as a raw material, and the L-azetidine-2-carboxylic acid is cyclized and synthesized by two methods^[4]. The method has simple steps, is green and safe, has high efficiency and high yield, and is an effective method for synthesizing the natural product L-azetidine-2-carboxylic acid.

In 2012, Jin and Zhang used 1, 3-dibromo compound and benzhydrylamine as raw materials, and passed through SN₂The intermolecular nucleophilic substitution reaction synthesizes the optically pure (S) -azetidine-2-carboxylic acid 1⁵]. The gamma-butyrolactone 6 is used as a raw material, 1, 3-dibromobutyrate 7 is obtained through bromination and esterification, an intermediate 8 is obtained through cyclization under the conditions of an acetonitrile solvent and potassium carbonate, and a target product 1 with gram-scale can be obtained through two steps of hydrogenolysis and tartaric acid resolution. The method is a new method for synthesizing an optically pure natural product L-azetidine-2-carboxylic acid, has certain potential for industrial application, but the price of the benzhydrylamine is slightly expensive.

L-azetidine-2-carboxylic acid is a very biologically active substance found in many natural products. The special amino acid structure of the four-membered ring is similar to the structure of L-proline which forms natural protein. The activity of L-azetidine-2-carboxylic acid in organisms is due to the structural similarity that two substances compete with each other in the process of forming protein chains, thereby interfering with the normal metabolism of L-proline and causing a series of changes in the organisms.

Since the structure of L-azetidine-2-carboxylic acid is similar to that of L-proline, L-azetidine-2-carboxylic acid is often used for modification of polypeptide structure and preparation of many inhibitors, such as hepatic fibrosis inhibitors, algae growth inhibitors, etc. In addition, due to the rigid structure of the four-membered ring, the L-azetidine-2-carboxylic acid is commonly used for constructing an organic chiral catalyst and is widely applied to a plurality of fields in asymmetric synthesis such as asymmetric addition reaction of ketone and alkyne, asymmetric Michael addition reaction, asymmetric cyclopropanation reaction, asymmetric Diels-Alder reaction and the like. However, at present, the application of the L-azetidine-2-carboxylic acid compounds to control plant powdery mildew is not reported.

According to the present invention, the agriculturally pharmaceutically acceptable salt may be any agriculturally pharmaceutically acceptable salt commonly found in the art. For example, in one embodiment, the agriculturally pharmaceutically acceptable salts may include inorganic and organic salts. More specifically, the inorganic salt may include at least one of ammonium, lithium, sodium, potassium, cesium, calcium, magnesium, copper, aluminum, zinc, barium, and quaternary ammonium salts, and the organic salt may include at least one of arginine, tert-butylamine, dimethylamine, diethanolamine, ethanolamine, ethylenediamine, imidazole, lysine, methylamine, pyridine, picolinate, piperazine, triethylamine, triethanolamine, trimethylamine, and urea salts, but is not limited thereto. That is, the agriculturally acceptable salt in the present invention may specifically be any of the above agriculturally acceptable salts alone, or any combination thereof.

In addition, the relevant data show that the powdery mildew is particularly serious in plants suffering from powdery mildew, and the melon plants infected with the powdery mildew at the flowering and fruiting stages can cause yield reduction by 20-40%. Thus, in an embodiment, the plant may in particular be a barley, wheat, strawberry, grape, rose, apple, rubber or melon plant, more in particular the melon plant may more in particular be cucumber, melon, balsam pear, wax gourd, pumpkin, luffa, hami melon or pumpkin, etc.

According to the present invention, the form of the administered L-azetidine-2-carboxylic acid, or an agriculturally pharmaceutically acceptable salt thereof, may take a wide range of forms, such as various common dosage forms in the art. In one embodiment, the L-azetidine-2-carboxylic acid, or an agriculturally pharmaceutically acceptable salt thereof, may be formulated into a corresponding pesticidal formulation, such as an aqueous agent, a powder, a granule, a wettable powder, or a soluble powder, as needed, and may be further configured as a spray at the time of use, so as to be applied to plants to be controlled in a spreading or spraying manner. Preferably, the L-azetidine-2-carboxylic acid, or an agriculturally pharmaceutically acceptable salt thereof, may be present in the spray in an amount of 20-2000 μ g/mL, such as 80 μ g/mL, 100 μ g/mL, 120 μ g/mL, 300 μ g/mL, 500 μ g/mL, 1000 μ g/mL, 1800 μ g/mL, or the like, more preferably, it may be present in an amount of 50-200 μ g/mL.

Additionally, one skilled in the art will recognize that the effective amount of L-azetidine-2-carboxylic acid, or an agriculturally pharmaceutically acceptable salt thereof, to be administered will vary according to: the nature and severity of the plant and disease, the control regimen (e.g., whether to coordinate its control strategy), and the chosen route of application, etc., and the appropriate dosage can be readily determined by one skilled in the art. In addition, the dosage can be repeated as many times as necessary, and if side effects are present, the amount and/or frequency of dosage can be varied or reduced according to normal clinical practice. Furthermore, the L-azetidine-2-carboxylic acid, or an agriculturally acceptable salt thereof, of the present invention may also be applied to the plant separately, sequentially or simultaneously with other anti-powdery mildew agents to prevent powdery mildew, which may for example be benzimidazoles, organophosphates, hydroxypyrimidines, methoxypropenoates, triazoles and phenoxyquinolines, and more specifically may for example be tebuconazole.

In another aspect, the invention also provides the use of L-azetidine-2-carboxylic acid, or an agriculturally pharmaceutically acceptable salt thereof, for controlling powdery mildew in plants. The usage mode of the application can be carried out by referring to the method for preventing and treating the powdery mildew of the plants, and the specific scheme can be the same as that of the method, and is not repeated herein.

After research, the L-azetidine-2-carboxylic acid compounds provided by the invention have excellent control effects on various plant powdery mildews, such as wheat powdery mildew, barley powdery mildew, strawberry powdery mildew, grape powdery mildew, Chinese rose powdery mildew, apple powdery mildew, rubber powdery mildew and melon powdery mildews, and particularly have excellent control effects on melon powdery mildews. In particular, according to the experimental results in the examples, it can be surprisingly found that the L-azetidine-2-carboxylic acid-based compound provided by the present invention can achieve a significantly higher control effect at a lower concentration than tebuconazole, which is a positive control of a broad spectrum bactericidal pesticide.

Hereinafter, the effect of the L-azetidine-2-carboxylic acid of the present invention on controlling powdery mildew of plants will be described in detail by examples.

Examples

In the examples, the plant seeds used were purchased from Shao agricultural development Co., Ltd, and the control effect of L-azetidine-2-carboxylic acid compounds on powdery mildew of plants was measured by the following method:

adding seedling raising matrix into a plastic flowerpot, sowing three plant seeds in each pot, placing the pot in a greenhouse at the temperature of about 25 ℃ for culturing after watering thoroughly, and performing a development test when the cotyledon is fully developed and the 1 st true leaf is just exposed (about 10 days). When the cotyledons of the plant seedlings are fully unfolded, uniformly brushing powdery mildew conidia on the diseased plant leaves by using a writing brush on healthy plant seedlings, culturing in a greenhouse at about 25 ℃, and periodically preserving and propagating strains on new plants for later use. Then, the compounds to be tested were prepared to the required concentration with 0.05% tween-20 aqueous solution, and sprayed onto the prepared plants, wherein tebuconazole was used as the positive control group, 0.05% tween-20 aqueous solution was used as the blank control group, each group contained 9 plants, and the average value was calculated. And (5) after culturing for 7-8 d, investigating the damage level and the number of the cotyledons of each treated plant according to the following standards, and calculating the disease index and the prevention and treatment effect.

Reference to classification methods^[6]。

Level 0: no disease spots;

level 1: the lesion area accounts for less than 5% of the whole leaf area;

and 3, level: the lesion area accounts for 6 to 10 percent of the whole leaf area;

and 5, stage: the lesion area accounts for 11 to 20 percent of the whole leaf area;

and 7, stage: the lesion area accounts for 21-40% of the whole leaf area;

and 9, stage: the lesion area accounts for more than 40% of the whole leaf area.

Disease index ∑[ (number of diseased leaves at each stage x number of relative stage) ]/(number of investigated total leaves x 9) × 100

The prevention and treatment effect is (blank control disease index-treatment disease index)/blank control disease index multiplied by 100 percent

Example 1 controlling Effect of L-azetidine-2-carboxylic acid on cucumber powdery mildew

In this example, cucumber was selected as a test plant, and the control effects of L-azetidine-2-carboxylic acid, D-azetidine-2-carboxylic acid and azetidine-3-carboxylic acid on cucumber powdery mildew were compared at the same concentrations, and the results are shown in table 1 below. As can be seen from the results in table 1, the control effect of azetidine-3-carboxylic acid is similar to that of the blank control group, i.e., it has almost no powdery mildew control effect on cucumber, D-azetidine-2-carboxylic acid has a weaker powdery mildew control effect, whereas the L-azetidine-2-carboxylic acid of the present invention has a control effect of up to about 84%, which is stronger than about 62% of that of tebuconazole of the positive control group.

TABLE 1

Example 2 controlling Effect of L-azetidine-2-carboxylic acid on cucumber powdery mildew at different concentrations

In this example, cucumber was selected as the plant to be tested, and the control effect of L-azetidine-2-carboxylic acid on cucumber powdery mildew was compared at different concentrations, and the results are shown in table 2 below. As can be seen from the results in Table 2, the control effect is gradually enhanced with the increase of the concentration of the L-azetidine-2-carboxylic acid, and the control effect reaches about 97% at a concentration of 200. mu.g/mL, which is obviously higher than about 68% of the control effect of the tebuconazole of the positive control group with the same concentration.

TABLE 2

Example 3 controlling Effect of L-azetidine-2-carboxylic acid on powdery mildew of melon

In this example, melons were selected as plants to be tested, and the control effects of L-azetidine-2-carboxylic acid, D-azetidine-2-carboxylic acid and azetidine-3-carboxylic acid on cucumber powdery mildew were compared at the same concentrations, and the results are shown in table 3 below. As can be seen from the results in table 3, the control effect of azetidine-3-carboxylic acid was similar to that of the blank control group, i.e., almost no powdery mildew control effect on melon, and D-azetidine-2-carboxylic acid had a weaker powdery mildew control effect, whereas the L-azetidine-2-carboxylic acid of the present invention had a control effect of up to about 83%, which was stronger than that of tebuconazole of the positive control group by about 64%.

TABLE 3

Example 4 controlling Effect of L-azetidine-2-carboxylic acid on powdery mildew of pumpkin

In this example, cucurbita pepo was selected as a test plant, and the control effects of L-azetidine-2-carboxylic acid, D-azetidine-2-carboxylic acid and azetidine-3-carboxylic acid on cucumber powdery mildew were compared at the same concentrations, and the results are shown in table 4 below. As can be seen from the results in table 4, the control effect of azetidine-3-carboxylic acid was similar to that of the blank control group, i.e., it had almost no powdery mildew control effect on cucurbita pepo, and D-azetidine-2-carboxylic acid had a weaker powdery mildew control effect, whereas the L-azetidine-2-carboxylic acid of the present invention had a control effect of up to about 86%, which was stronger than that of tebuconazole of the positive control group by about 65%.

TABLE 4

The preferred embodiments of the present invention have been described in detail, however, the present invention is not limited to the specific details of the above embodiments, and various simple modifications may be made to the technical solution of the present invention within the technical idea of the present invention, and these simple modifications are within the protective scope of the present invention.

It should be noted that the various technical features described in the above embodiments can be combined in any suitable manner without contradiction, and the invention is not described in any way for the possible combinations in order to avoid unnecessary repetition.

In addition, any combination of the various embodiments of the present invention is also possible, and the same should be considered as the disclosure of the present invention as long as it does not depart from the spirit of the present invention.

Reference to the literature

[1] The biological prevention and treatment research of powdery mildew of melons is developed by Buxus, Zhuhaiyun, Libo, and the like [ J ]. J.J.Microbiol.2016, 36(01): 106-.

[2]Fowden L.Azetidine-2-carboxylic acid:a new cyclic imino acid occurring in plants[J].The Biochemical journal.1956,64(2):323-332.

[3]Rubenstein E,Zhou H,Krasinska K M,et al.Azetidine-2-carboxylic acid in garden beets(Beta vulgaris)[J].Phytochemistry.2006,67(9):898-903.

[4]Bouazaoui M,Martinez J,Cavelier F.Direct Access to L-Azetidine-2-carboxylic Acid[J].European Journal of Organic Chemistry.2009,2009(17):2729-2732.

[5]Jin J Z,Zhang J.Synthesis of L-Azetidine-2-Carboxylic Acid[J].Advanced Materials Research.2012,455-456:635-638.

[6] The pesticide field efficacy test criterion (I) is that the bactericide prevents and treats cucumber powdery mildew, GB/T17980.30-2000.

Claims

1. A method of controlling powdery mildew of a plant, comprising applying to said plant an effective amount of L-azetidine-2-carboxylic acid, or an agriculturally pharmaceutically acceptable salt thereof.

2. The method of claim 1, wherein the agriculturally pharmaceutically acceptable salt comprises an inorganic salt and an organic salt.

3. The method of claim 2, wherein the inorganic salt comprises at least one of ammonium, lithium, sodium, potassium, cesium, calcium, magnesium, copper, aluminum, zinc, barium, and quaternary ammonium salts.

4. The method of claim 2, wherein the organic salt comprises at least one of arginine, t-butylamine, dimethylamine, diethanolamine, ethanolamine, ethylenediamine, imidazole, lysine, methylamine, pyridine, picolinate, piperazine, triethylamine, triethanolamine, trimethylamine, and urea salts.

5. The method of claim 1, wherein the plant is barley, wheat, strawberry, grape, rose, apple, rubber or melon.

6. The method of claim 5, wherein the melon plant is cucumber, melon, balsam pear, wax gourd, pumpkin, luffa, hami melon, or pumpkin.

7. The method of claim 1, wherein the L-azetidine-2-carboxylic acid, or an agriculturally-pharmaceutically acceptable salt thereof, is formulated as a pesticide formulation.

8. The method of claim 7, wherein the pesticide formulation is at least one of an aqueous agent, a dust, a granule, a wettable powder, and a soluble powder.

9. The method of claim 7 or 8, wherein the pesticide formulation is configured as a spray for use and the L-azetidine-2-carboxylic acid, or an agriculturally pharmaceutically acceptable salt thereof, is present in the spray in an amount of 20-2000 μ g/mL.

Use of L-azetidine-2-carboxylic acid, or an agriculturally pharmaceutically acceptable salt thereof, for controlling powdery mildew of plants.