GB2288980A - Process for controlling Mycosphaerella diseases in plant crops using fenpropidin - Google Patents

Abstract

The Mycosphaerella diseases, in particular M.fijiensis ("black Sigatoka"), constitute an epidemic danger to plant crops, especially to banana cultivation, in the tropical belt. The disease can be effectively controlled and prevented by fenpropidin, (RS)-1-[3-(4-tert-butylphenyl)-2-methylpropyl]piperidine.

Description

Process for controllina Mycosphaerella diseases in plant crops The present invention relates to a process for controlling Mycosphaerella diseases, in particilar M.fijiensis, which attacks banana plantations as so-called black Sigatoka and results in high losses or makes banana cultivation impossible in certain tropical crop producing regions.

For several decades the less dangerous yellow Sigatoka - a fungal disease that is caused by Mycosphaerella musicola - occurred in banana plantations. The disease attacks leaves during the entire growth period up to the time of harvesting. It initially causes spotting and blotching of the leaf surfaces that results in necrosis and withering of the leaf tissue. The course of the disease is usually slow, but on account of the reduction of the active leaf surface leads to a weakening of the plant and an associated loss in yield. Because of its slow development, it was possible to control the disease well by spraying the plants with pure mineral oil or with a mixture of mineral oil and fungicides, and with minimum effort.

Infection of plants for the production of the plantain fruit by yellow Sigatoka was tolerated and control was usually not necessary.

In the years from 1972 to 1979, black Sigatoka (M.fijiensis) occurred for the first time here and there in some Central Americal countries. Within 10 years, from 1980 to 1990, black Sigatoka became the predominant leaf disease in bananas with a self-accelerating spread to all important banana growing areas in Central and South America, Central and West Africa and wide areas of Asia.

Black Sigatoka differs from yellow Sigatoka in its very much more aggressive occurrence and in a disease cycle that proceeds about twice as rapidly. The young leaves are infected even during formation and wither within 4-5 weeks. In addition to attacking all worldwide important table banana varieties, the disease also attacks the plantain fruit that constitutes the staple diet of the native population in wide areas of the tropical belt. Black Sigatoka has completely displaced yellow Sigatoka in the most important banana growing areas.

The aggressive and epidemic occurrence of black Sigatoka, especally in the tropical growing regions of America, Africa and Asia with their high rainfalls, leads to a rapid destruction of the banana plants. Infected leaves blacken, become necrotic, and wither.

Planned production of bananas without affording appropriate protection against black Sigatoka is no longer possible.

Especially during the rainy season, with its regularly recurring rainfalls and the attendant correspondingly high rate of infection, the standard residual fungicides are insufficiently effective to control the disease with adequate success. The benzimidazole fungicides introduced at the beginning of the 1980's were very effective when sprayed at intervals of 2 to 3 weeks. However, owing to the mechanism of action of this class of products and to their frequent application, black Sigatoka developed an almost complete resistance to the benzimidazole derivatives within a few years. At the present time only occasional use of these products in a few regions is possible.

For some years triazole fungicides have been used with good success against black Sigatoka. Especially during the rainy season when the danger of infection is very high, these products achieve impressive results by keeping the leaf surfaces healthy and ensuring regular crop yields. However, the number of spray applications per year of triazole fungicides has had to be severely limited since their introduction on to the market in order to prevent the development of resistance to them. Despite this measure, a certain deterioriation in sensitivity has already been observed.

The mineral oil used to control yellow Sigatoka has no effect against black Sigatoka. In all important banana-growing regions the fungicides are sprayed mainly from aircraft. At a rate of application of 15-30 litres/ha the spray volume is kept extremely low to enhance aircraft performance and to keep application costs low. To ensure good wetting of the plants, the fungicide is mixed with mineral oil or with a mixture of oil and water as carrier.

The oil ensures that the free spray droplets fall on the leaf surface and prevents them from immediately evaporating in the air. Oil concentrations of 5-15 litres/ha are used.

As certain fungicides used in conunction with oil can result in damage to plants, the number of products available for controlling black Sigatoka is so severely reduced that adequate protection can no longer be guaranteed for the entire growth period of the bananas.

The present invention solves this problem in surprising manner by providing a process for controlling Mycosphaerellaflflensis and musicola, which comprises the use of (RS )- 1 -[3-(4-tert-butylphenyl)-2-methylpropyl]piperidine, a compound which, under the generic name fenpropidin, is used for controlling mildew and rust in cereals (cf.

USP 4 241 058).

Fenpropidin is sprayed at a rate of application of 300-600 g a.i./ha, preferably of 375-525 g a.i./ha, at intervals of 10-12 days, when the risk of infection by M. fjiensis is high. When the risk of infection is lower outside the rainy season, the spray intervals may be greater, e.g. 18-21 days. Fenpropidin can be sprayed preventively. The particular advantage of fenpropidin resides in the possibility of curative control, i.e. the compound counteracts infection even after the crops have already been infected by the disease.

Fenpropidin also controls yellow Sigatoka (M. musicola). In the acute stage, spray intervals of 20-25 days will suffice to counteract infection of this species. Quite generally, however, fenpropidin is able to control and prevent Mycosphaerella diseases. The S-enantiomer of fenpropidin is particularly preferred for this utility.

Fenpropidin further has a novel biochemical mechanism of action that differs from the residual products and triazole fungicides. It is therefore particularly suitable for a combined control strategy.

Fenpropidin is found in all cases to be a long-acting compound and is superior to tridemorph (= 2,6-dimethyl-4-tridecylmorpholine, "Pesticide Manual" 9th. Ed.), which is also used on occasion.

Fenpropidin is normally used in the form of compositions with an agriculturally suitable carrier and/or other application promoting adjuvants.

Suitable carriers and adjuvants may be solid or liquid and correspond to the appropriate substances ordinarily employed in formulation technology, including natural or regenerated mineral substances, solvents, dispersants, wetting agents, tackifiers, thickeners, binders or fertilisers.

Suitable solvents are: aromatic hydrocarbons, the fractions containing 8 to 12 carbon atoms, typically xylene mixtures or substituted naphthalenes, phthalates such as dibutyl or dioctyl phthalate, aliphatic hydrocarbons such as cyclohexane or paraffins; also alcohols and glycols and their ethers and esters, such as ethanol, ethylene glycol, ethylene glycol monomethyl or monoethyl ether, ketones such as cyclohexanone, strongly polar solvents such as N-methyl-2-pyrrolidone, dimethyl sulfoxide or dimethyl formamide, as well as vegetable oils or epoxidised vegetable oils such as epoxidised coconut oil; castor oil or soybean oil; or water.

The solid carriers typically used for dusts and dispersible powders are usually natural mineral fillers such as calcite, talcum, kaolin, montmorillonite or attapulgite.

Further especially useful application-promoting adjuvants that may lead to a reduction of the concentration of active ingredient are natural (animal or vegetable) or synthetic phospholipids of the series of the cephalins and lecithins which can conveniently be isolated from soybeans.

Depending on the nature of the compound of formula I to be formulated, suitable surface-active compounds are nonionic, cationic and/or anionic surfactants having good emulsifying, dispersing and wetting properties. The term "surfactants" will also be understood as comprising mixtures of surfactants.

Suitable anionic surfactants can be water-soluble soaps as well as water-soluble synthetic surface-active compounds.

Suitable soaps are the alkali metal salts, alkaline earth metal salts or ammonium salts or substituted ammonium salts of higher fatty acids (C10-C22), typically the sodium or potassium salts of oleic or stearic acid, or of natural fatty acid mixtures which can be obtained, inter alia, from coconut oil or tallow oil. Further suitable surfactants are also the fatty acid methyltaurin salts.

Nonionic surfactants are polyglycol ether derivatives of aliphatic or cycloaliphatic alcohols, or saturated or unsaturated fatty acids and alkylphenols, said derivatives containing 3 to 30 glycol ether groups and 8 to 20 carbon atoms in the (aliphatic) hydrocarbon moiety and 6 to 18 carbon atoms in the alkyl moiety of the alkylphenols.

Typical examples of nonionic surfactants are nonylphenolpolyethoxyethanols, polyethoxylated castor oil, polyadducts of polypropylene and polyethylene oxide, tributylphenoxypolyethoxyethanol, polyethylene glycol and octylphenoxypolyethoxyethanol.

Fatty acid esters of polyoxyethylene sorbitan are also suitable nonionic surfactants, typically polyoxyethylene sorbitan trioleate.

Cationic surfactants are preferably quaternary ammonium salts carrying, as N-substituents, at least one C8-C22alkyl radical and, as further substituents, optionally halogenated lower alkyl, benzyl or hydroxy-lower alkyl radicals.

The anionic, nonionic or cationic surfactants customarily employed in formulation technology are familiar to those skilled in the art or may be found in the relevant literature.

- "Mc Cutcheon's Detergents and Emulsifiers Annual", Mc Publishing Corp., Glen Rock, New Jersey, 1988.

- M. and J. Ash, "Encyclopedia of Surfactants", Vol. I-Ill, Chemical Publishing Co., New York, 1980-1981.

- Dr. Helmut Stache "Tensid-Taschenbuch" (Handbook of Surfactants), Carl Hanser Verlag, Munich/Vienna 1981.

The agrochemical compositions usually contain 0.1 to 99 % by weight, preferably 0.1 to 95 % by weight, of a compound of formula I, 99.9 % to 1 % by weight, preferably 99.9 to 5 % by weight, of a solid or liquid adjuvant, and 0 to 25 % by weight, preferably 0.1 to 25 % by weight, of a surfactant.

Whereas commercial products will preferably be formulated as concentrates, the end user will normally use dilute formulations.

The compositions may also contain further ingredients such as stabilisers, antifoams, viscosity regulators, binders, tackifiers as well as fertilisers or other chemical agents to obtain special effects.

1. Formulation examples for fenpropidin for the treatment of banana croPs (throughout percentazes are by weight) 1.1. Wettable powders a) b) c) active ingredient 25 % 50 % 75 % sodium ligninsulfonate 5% 5% - sodium lauryl sulfate 3% - 5% sodium diisobutylnaphthalene sulfonate - 6 % 10 % octylphenol polyethoxylate - 2% - (7-8 mol ethylene oxide) highly dispersed silica 5 % 10 % 10 % kaolin 62 % 27 % The compound is thoroughly mixed with the adjuvants and the mixture is well ground in a suitable mill to give wettable powders which can be diluted with water to suspensions of any desired concentration.

1.2. Emulsifiable concentrate active ingredient 10%% octylphenol polyethoxylate 3% (4-5 mol ethylene oxide) calcium dodecyl benzenesulfonate 3 % cyclohexanone 34 % xylene mixture 50 % Emulsions of any desired concentration can be prepared by diluting such concentrates with water.

1.3 .Susension concentrate acvtive ingredient 40% ethylene glycol 10 % nonylphenol polyethoxylate (15 mol EO) 6 % sodium ligninsulfonate 10 % carboxymethyl cellulose 1% 37 % aqueous solution of formaldehyde 0.2 % silicone oil in the form of a 75 % aqueous emulsion 0.8 % water 32 % The finely ground active ingredient is intimately mixed with the adjuvants to give a suspension concentrate from which suspensions of any desired concentration can be prepared by dilution with water.

1.4 Oil formulation (% = percent by volume) active ingredient 75 % isotridecanol-8 -ethoxylate 3% castor oil (lust pressing) 22 % The finely ground active ingredient is intimately mixed with the adjuvants to give an oil concentrate which is diluted with water and can be sprayed over a wide area from e.g. an aircraft, conveniently with the addition of mineral oils.

Biological Examples B-1: Curative action of fenyropidin against M. fijiensis Test location: Ombu Farm, San Antonio, Costa Rica.

Method: Monofoliar application At regular intervals of a few days, the newly developing leaves in a banana plot are each marked so as to give a test series of leaves of different age that are subject to the natural risk of infestation by M.fijiensis. On the day of spraying, the oldest marked leaf is 22-days-old and the youngest is 0-days old. In an Airbrush spray tower, 50 % of the surface of a marked leaf is treated (50 % remains as control zone); the underside is not sprayed. The rate of application is 525 g of fenpropidin/ha. The spray volume is 21.6 litre of oil/water emulsion/ha. The evaluation after 32 days on infected and necrotic leaf surfaces shows the following curative action of fenpropidin in accordance with the Abbott formula: Date of leaf develop- Curative period Activity (%) ment and infection October 15 22 days 78.6 October 19 18 days 78.3 October 23 14 days 66.5 October 25 12 days 92.1 October 27 10 days 93.3 October 29 8 days 96.7 October 31 6 days 94.2 November 4 2 days 96.7 November 6 0 days 100 The very good curative action of fenpropidin extends up to 12 days (92.1 - 100 % activity). Only after this time does the curative action decrease slightly owing to the high rate of infection by the pathogen.

B-2: Curative action of fenpropidin against M. fiiiensis Test location: Canton Pococi, Provinz Lim6n, Costa Rica.

Method: 40 banana plants in a 302 m2 plot were each sprayed at intervals of 15-19 days at a rate of application of 375 g of fenpropidin/ha. The spray volume was 20 litre of oil/water (1:3) emulsion. 7 spray applications were made in 122 days. 4 replicates were carried out and the 10 youngest leaves of a plant were each finally assessed for infection and necrosis (1600 leaves). The following results were obtained: infection after infection after the 4th spray the 7th spray application application untreated control 38.2 % 24.5 % treated plants 15.8 % 5.0 % Despite very long spray intervals of 15-19 days, fenpropidin substantially counteracted the already established disease under conditions of high infection.

B-3: Curative action of fenpropidin against M. musicola (yellow Sigatoka) Test location: Research Station Rembau, Malaysia.

Method: Plots of 30 banana plants were each sprayed at intervals of 12-16 days at a rate of application of a) 300 g of fenpropidin/ha and b) 450 g of fenpropidin/ha. The spray volume was, per hectare, 5 litres of Shell white oil in 20 litres of water. 12 spray applications were made in 170 days. Four replicates of each of trials a) and b) were carried out. In the evaluations of infection, the state of the entire plant and not just some of its parts was taken into account. The following results were obtained: Infected leaf area in % after 42 days* 117 days* 146 days* untreated control 36 % 40 % 46 % 300ga.i./ha 10% 6% 6% 450 g a.i./ha 5 % 2.5 % 3 % *after the first spraying Fenpropidin is also found to be highly effective in counteracting yellow Sigatoka.

Claims (7)

What is claimed is:

1. A process for the control and prevention of Mycosphaerella diseases in plant crops, which comprises applying fenpropidin as active ingredient to said plants, to parts of plants or to the locus of thereof.

2. A process according to claim 1, wherein the S-enantiomer of fenpropidin is applied.

3. A process according to either claim 1 or claim 2, which comprises controlling Mycosphaerellafiflensis and M. musicola in banana crops.

4. A process according to any preceding claim, wherein fenpropidin is used together with an agriculturally suitable carrier.

5. A process according to any preceding claim, wherein fenpropidin is applied at a rate of application of 300-600g per hectare.

6. A process according to any preceding claim, wherein fenpropidin is applied to the plant crop after onset of the disease to effect curative control.

7. Use of fenpropidin for the control or prevention of infection of plants by Mycosphaerella.