WO2004026033A1

WO2004026033A1 - Plant pesticides and uses thereof

Info

Publication number: WO2004026033A1
Application number: PCT/AU2003/001245
Authority: WO
Inventors: Paul Agostino; Sam Papandrea
Original assignee: Artpharm Pty Ltd
Priority date: 2002-09-20
Filing date: 2003-09-22
Publication date: 2004-04-01
Also published as: AU2002951533A0

Abstract

The present invention relates to pesticides and in particular to a plant pesticide comprising (a) avermectin, ivermectin, abamectin or emamectin and (b) sulphur (e.g. ThivoitR (a micronised sulfur formulation)) or a sulfur containing compound (e.g. captan, captafol, or dimethyldithiocarbonic acid). The invention also relates to uses of these pesticides in the treatment of plant diseases.

Description

PLANT PESTICIDES AND USES THEREOF TECHNICAL FIELD

The present invention relates to pesticides and in particular to a plant pesticide comprising (a) an avermectin and (b) sulphur or a sulphur-containing compound. The invention also relates to uses of these pesticides in the treatment of plant diseases. BACKGROUND

Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field. Agriculturists commonly observe outbreaks of diseases and pests in a wide range of plants, including ornamental, vegetable and fruit plants. Some common pest diseases and treatments, in particular treatment with sulphur (eg. Thiovit®), are discussed below.

Thiovit® is a registered product of a Syngenta Group Company and its active constituent is 80% elemental sulphur. It is a micronised sulphur formulation that mixes easily with water to form a spray with good spreading and sticking properties. It is classified as a fungicide/miticide, used for the control of powdery mildew, rust, mites, aphids and thrips in pome and stone fruit, citrus, grapevines, kiwifruit, strawberries and some vegetables.

Powdered Mildew. This fungal disease produces a fine white coating on the surface of leaves and buds. The concentration of Thiovit® recommended to treat this disease ranges between 20g - 40g per 10L of spray. It is recommended that it be applied at intervals between 10 days and 2-3 weeks or as necessary. However, in general practice, the concentrations used are much higher and the rates of applications are much more frequent than those recommended. Because of its low efficacy, Thiovit® is not commonly used by growers to treat powdered mildew. Rusts. There are hundreds of different fungi that cause the disease called rust.

They generally cause a small yellow patch or spot on the upper surface of the leaf. The concentration of Thiovit® recommended to treat this disease ranges between 20g - 40g per 10L and it is recommended that it be applied when the pest or disease is first seen and then repeating as necessary.

Mites. The group of mites which cause plant damage include the eriophyid mites, such as grape leaf blister mite and citrus bud mite; the tarsonemid mites such as cyclamen mite, the spider mites, and the two— spotted mite. Two-spotted mite known as

"red spider" occurs on the underside of leaves. Tomato russet mite is extremely small. The first sign of infection occurs on the lower leaves.

Broad mite feed on the lower surfaces of young soft leaves, which become bronze in colour. The leaf edges of affected Dahlias curl in and the leaves remain narrow. Growth is stunted. Flowers may be deformed and discoloured. Specific miticides can be used but mites seem to develop resistance to pesticides very rapidly. The concentration of Thiovit® recommended to treat mites ranges between 15g-50g per 10L and it is recommended that it be applied at intervals of 10 to 21 days, or as necessary.

Aphids. These small insects are sometimes referred to as plant lice. The concentration of Thiovit® recommended to treat this disease ranges between 20g - 40g per 10L and it is recommended that plants be treated at intervals between 10 days and 2- 3 weeks or as necessary. Aphids are also commonly treated with broad spectrum systemic pesticides such a Rogor® or Lebaycid®, which are both odorous organophosphates.

Thrips. These plant pests have a variety of feeding habits. Some thrips feed on leaves only and others on flowers only. Others feed on decaying organic matter such as dead leaves or fungi. Others feed on aphids or mites. Western flower thrips attack a wide range of ornamental plants and many fruit and vegetable crops. These thrips are about 1 mm long and form pale yellow to brownish in colour, like many other thrips. Infected plants show flecking, silvering and deformation of flowers, buds and fruit. Thrips prefer to feed on floral parts, but will also attack young leaves and stems. Treatment for thrips is similar to that for aphids. The most commonly used pesticides are the systemic organophosphates Rogor® and/or Lebaycid®.

Sulphur has been used as a contact fungicide and insecticide on plants for at least 2,500 years. More recently agents that release sulphur such as dimethyldithiocarbamic acid have been used. A related sulphur-containing compound, captan, has been used as a fungicide. Captafol, another organic sulphur-containing compound, has been used as an agricultural fungicide, especially for potatoes.

It has been observed over the course of many years that the use of traditional toxic pesticides, such as the organophosphates and sulphur fungicides, is becoming almost ineffective in the treatment and prevention of plant diseases leading to poor, unsatisfactory yields. For example, it has now evident that the use of the sulphur- containing fungicide, Thiovit®, even at concentrations and application frequencies higher than those commercially recommended, often does not provide the desired degree of protection or yield of plant crops. Pesticides can cause serious damage to the environment - particularly when they are applied excessively and repeatedly. For example, in active growth conditions, leaf tissues expand and the sulphur coverage on the leaves has to be very dense to achieve disease control. Under these conditions, the frequency of sulphur applications has to be increased from the standard application regime and the interval between applications reduced from 14 to 4-7 days. Excessive use of such sulphur compounds results in acidification of the soil, which requires neutralisation with lime, enriched with compost and other fertilizers in order for it to sustain plant crops.

As indicated above, the recommended use of Thiovit® for ornamental and vegetable plants is to spray as soon as pest or disease (Powdery Mildew, Two-spotted Mite, Bean Rust, Tomato Russet Mite, Bean Spider Mite) is first noticed with further applications every 10 to 21 days, or as necessary, at concentrations of 20g-40g/10L. However, this recommended spraying regime is not effective at all in many cases.

Specifically, for example, growers reported difficulties controlling powdery mildew in their vineyards despite following recommended spray regimes. Researchers at the Institute for Horticultural Development, Knoxfield, Victoria, Australia investigated the relationship between sulphur (Thiovit®) deposits and powdery mildew control on grapevines (because sulphur is the most commonly used fungicide). Dose- response curves were generated to determine how much sulphur needed to be deposited onto a leaf to achieve powdery mildew control. Grapevines were sprayed with various concentrations of Thiovit®, inoculated with powdery mildew spores and kept under conditions favourable for infection. From the results obtained, the dose of sulphur per cm² of leaf area needed to prevent 99% of the spores from germinating (ED⁹⁹) was estimated as 300g/m².

Deposits applied by typical commercial applications were measured in a series of field trials to determine if this effective dose of sulphur was achieved. It was found that the amount of sulphur deposited by the spray applications were below the ED⁹⁹ value and, hence, would not provide adequate control of powdery mildew on inner leaves. The results suggested that the poor efficacy of sulphur in the control of powdery mildew reported by many growers was perhaps due to the application of an inadequate dose. However, as mentioned above, the application of increased amounts of compounds such as Thiovit® is undesirable due to its effect on the environment.

Further, resistance to chemicals has evolved in more than 500 species of insects and mites, and 100 species of plant pathogens. The most serious resistance problems have occurred in pests that are frequently treated. For example, resistance to insecticides such as Diazinon®, Talstar® and sulphur formulations is common in exactly those pests (eg. whiteflies, western flower thrips, spider mites and aphids) that cause such serious damage to the plants that they are often sprayed. Some resistant mechanisms are effective against entire classes of chemicals - this is called "cross-resistance" and allows pests to be resistant even to pesticides to which they have never been exposed. Once resistance evolves, it rarely declines enough to allow the pesticide to be used again to any significant extent.

Not only is resistance on the rise, fewer pesticides are being developed for the future. New insecticides and fungicides are developed mainly on the basis of their efficacy in the treatment of crops of major economic significance such as maize, wheat, rice, cotton, and soybeans.

The increased pesticide use on crops also increases the risk of plant damage due to phytotoxicity. It may also accelerate selection for resistance, and eventually the pesticide can become completely ineffective. The long and excessive use of fungicides like Thiovit®, has led to the production of resistant strains. These resistant fungi may not be controlled by Thiovit® or other groups of fungicides and, as a consequence, there will be a reduction in the efficacy of the pesticide and yield loss. Avermectins

Avermectins are a class of highly active broad - spectrum anti-parasitic agents isolated from fermentation broths of Steptomyces avermitilis. The avermectins have anthelmintic and insecticidal activity. Their potency varies with the avermectin and with the organism they are used to treat. Stromectol®, containing the ivermectin (22, 23- dihydroavermectin Bla and 22, 23-dihydroavermectin Bib), is indicated in humans for the treatment of onchocerciasis and intestinal strongyloidiasis. It is incompletely absorbed (50% bioavailability) following oral doses of ivermectin tablets. It is metabolised in humans, and both ivermectin and its metabolites are excreted almost exclusively in the faeces, with less than 1% of the administered dose being excreted in the urine. The plasma half-life of ivermectin in man is about 12 hours, and that of the metabolites is about 3 days. Parasitic diseases are common in animals and can affect the skin, ears, stomach, intestines, heart, lungs and liver. Ivermectin is used to kill and prevent parasites such as fleas, ticks, mites and worms. An ivermectin commonly used in agriculture is Ivomec® liquid for sheep. This topically applied, systemically active, parasiticide for sheep consists of a 0.08% solution of ivermectin, and is formulated for external application to sheep only. Ivomec® Pour-on for cattle is formulated only for cattle, and consists of a 0.5% solution of ivermectin, a more highly concentrated solution than the one for sheep. The recommended dosage of Ivomec® is 0.5mg ivermectin per kilogram of body weight, with the concentration of ivermectin in Ivomec® Pour-on for cattle being 5mg per ml of solution. Abamectin consists of a mixture of avermectin Bι_a and B^ (not the dihydro derivatives mentioned above) obtained through fermentation of Streptomyces avermitilis. Abamectin has been considered a useful chemical for controlling leafininer fly. Since it is derived from a biological source, it is a bio-rational product that can be used in an environmentally friendly manner in pest management programs. Abamectin has been effective against a number of pests, such as mites, ants, cockroaches, and selected pest species of lepidoptera (Lasota and Dybas, 1991), and is considered a selective insecticide with relatively low toxicity to many non-target arthropods.

In 1999 Mujica et al evaluated the effectiveness of abamectin when applied alone or mixed with plant oil on leafminer fly, Liriomyxa huidobrensis Blanchard, on bean plants under laboratory and greenhouse conditions. The addition of plant oil to abamectin sprays to obtain 1% oil spray concentration, increased the effectiveness of the insecticide to the extent that the active ingredient of the insecticide could be reduced by one-half to three-fourths of the normal dosage (0.15%). Abamectin normal concentration (commercially recommended) 0.15% Abamectin concentration with l% plant oil 0.075%) and 0.1125%

Both eggs and fly larvae were affected with leafminer fly. The synergistic effect shown by the mixture of abamectin and plant oil allowed a reduction in the commercially recommended concentration of abamectin without any loss in effectiveness. In addition, emamectin, a semi-synthetic second generation avermectin (derived from avermectin Aj_a and sold under the brand name PROCLAIM by Syngenta), has been shown to be useful as a plant pesticide. It is claimed to be highly potent against a range of Lepidopteran species that attack grape vines, in particular Light Brown Apple Moth (LBAM) and Nine Moth. Chemical pesticides, including fungicides, insecticides, and miticides, continue to be heavily relied upon for pest control in agriculture. As such, and in light of the above, we should be concerned about the efficacy of chemical treatments in terms of quantity and frequency of application of the pesticide as well as the development of pesticide resistance. It is important for those managing pest control, such as agriculturists and nursery operators as well as domestic gardeners, to reduce the amounts of chemicals used in order to implement more environmentally friendly control practices and, by doing so, to reduce the incidence of resistance development.

Clearly, therefore, there is a need for pesticides that can effectively eradicate or significantly reduce the damage caused to plants by pests, preferably using reduced amounts of low toxicity pesticide and reduced applications of the pesticide.

It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.

SUMMARY OF THE INVENTION

It has been surprisingly found that a composition comprising an avermectin and sulphur has a synergistic effect in controlling pest infestation in a wide variety of agricultural and horticultural species i.e. a composition comprising an avermectin and sulphur was more effective in the control and treatment of plant pest diseases than a composition comprising either avermectin or sulphur alone. Further, it was found that the concentration of the avermectin required for the above-mentioned purpose may be reduced to a surprisingly low level while still achieving synergism.

It was unexpected shown, for example, that ivermectin in combination with sulphur can be used as a plant pesticide. Ivermectin was previously known to be useful as an anthelmintic for both veterinary and human purposes and has been used both internally and externally. It has also previously been used to treat sea lice infestation on marine fish. Its application in the agricultural field as a pesticide in combination with sulphur, however, was not previously considered and the benefits of such a combination were therefore not recognised.

According to a first aspect, the present invention provides a plant pesticide comprising (a) avermectin and (b) sulphur or a sulphur-containing compound. Preferably, the pesticide comprises 0.0001% to 0.002% (w/v) avermectin. More preferably, the pesticide comprises 0.0008% (w/v) avermectin.

Preferably the avermectin is ivermectin. The skilled addressee will understand, however, that other avermectins may also be useful in the present invention including, but not limited to, abamectin and emamectin.

In one embodiment, the pesticide may be in the form of a solid granular pellet or pellet-like form.

Preferably, the sulphur is micronised sulphur and, more preferably, it is wettable micronised sulphur. Most preferably, it is microgranule elemental sulphur. The skilled addressee will be able to identify other sources of sulphur that may be useful in the invention eg. a sulphur-containing compound such as captan or captafol or a sulphur release agent such as dimethyldithiocarbamic acid. In light of the description of the present invention, the skilled addressee will be able to determine which sulphur or sulphur-containing agents are useful for specific applications. The skilled addressee will be able to determine a suitable amount of sulphur.

For example, the pesticide may comprise 0.1 to 1.0% (w/v) sulphur. Preferably, the pesticide comprises about 0.3% (w/v) sulphur.

Preferably the pesticide also comprises a carrier. While it is clear that the skilled addressee will be able to identify suitable carriers, preferably, the carrier is selected from the group consisting of: water, stabilizers, emulsifiers, oils, surfactants, antioxidants and UV screens.

When the carrier is a surfactant, preferably the surfactant is a non-ionic surfactant, and more preferably it is a non-ionic organic surfactant. A large number of agents are capable of acting as surfactants. These include anionic surfactants (e.g. soap, sodium cetostearyl sulphate); cationic surfactants (e.g. benzalkonium chloride); and non- ionic surfactants (e.g. glyceryl monostearate). The skilled addressee will be able to identify the surfactant most suitable for the desired application through simple routine experimentation. Most preferably, the surfactant is nonylphenoxy polyethoxyethanol.

The skilled addressee will be able to determine the amount of surfactant required for a particular pesticide. The pesticide may comprise, for example, 0.01 to 0.P/o of the surfactant. Preferably, the pesticide comprises about 0.03% (w/v) surfactant.

The plant may be any suitable plant and the skilled addressee will be able to identify such plants.

In one embodiment of the invention, the plant is an ornamental plant. Preferably the ornamental plant is a carnation, rose, lavender, tulip, delphinium or dahlia.

In another embodiment of the invention, the plant is a fruit plant. Preferably, the fruit plant is a stone fruit tree, citrus fruit tree, grape vine, strawberry, coffee, banana, tomato, rockmelon or watermelon plant.

In another embodiment of the invention, the plant is an herb or medicinal plant. Preferably, the herb or medicinal plant is a red clover, chamomile, aloe, evening primrose, skullcap, Echinacea, saw palmetto, feverfew, witch hazel, valerian, tea tree, garlic, eucalyptus, basil, parsley or ginseng plant.

In yet another embodiment, the plant is a vegetable plant. Preferably, the vegetable plant is a bean, corn, carrot, cucumber, potato, radish, spinach, pea, lettuce, onion, cabbage, broccoli, cauliflower, zucchini or turnip plant.

According to a second aspect, the present invention provides a method for the prevention and/or treatment of a plant disease comprising applying to the plant, or the environment of the plant, an effective amount of a pesticide according to the first aspect. According to a third aspect, the present invention provides a method for the prevention and/or treatment of a plant disease comprising applying a pesticide to the plant, or the environment of the plant, wherein the pesticide comprises two separate components: (a) an avermectin and (b) sulphur or a sulphur-containing compound, and the method comprises the simultaneous or sequential application of (a) and (b) such that a synergistic pesticidal effect between (a) and (b) is achieved. Preferably, the disease results from a parasite, insect, fungi, worm or mite infestation.

Preferably, the pesticide is applied to a surface of the foliage of the plant. More preferably, it is applied to substantially all surfaces of the plant foliage.

The skilled addressee will be able to determine the best means of application of the pesticide. In so doing, consideration may be given to the plant species, type or extent of disease, environmental conditions such as humidity, temperature, type of soil, size of plant and/or season. In light of the description of the invention and standard agriculture practices, it will be well within the competence of the skilled addressee to develop a treatment regime. Preferably, the pesticide is applied by a spray technique.

Preferably, the pesticide is applied to the plant at a rate of 10-300ml per m². More preferably, it is applied at a rate of 30-50ml per m².

Preferably, the pesticide is applied to the plant in more than one application. In a preferred embodiment, the pesticide is applied according to different stages of plant growth and disease progression. Three treatment stages may be identified ie. pre- infection, maintenance and post-infection treatments. Typically, the pre-infection treatment commences at about 4-5 weeks of plant growth and before disease or pest infection is noticed. Preferably, the pesticide is applied in the pre-infection treatment at intervals of 1 to 10 days. More preferably, the pesticide is applied twice during the pre- infection treatment at about a 4-day interval. Preferably, the maintenance treatment is applied 2 to 10 weeks after the pre- infection treatment. More preferably, it is applied 4-5 weeks after the pre-infection treatment. The maintenance treatment may be repeated. When maintenance treatments are repeated, preferably the pesticide is applied at 2 to 8 week intervals, more preferably, 4-5 week intervals.

Preferably, a first post-infection treatment is applied upon the appearance of signs of pest infection. These signs may be observed by the naked human eye eg. by checking the plant for the presence of the pest or damage done by the pest or for the presence of related organisms that normally precede attack by the pest in question. Signs of pest infection may also be observed, for example, by microscopic analysis. Further post-infection treatments may be applied. Preferably a further post- infection treatment is carried out 3 to 6 weeks after the first post-infection treatment. More preferably, the further post-infection treatment is carried out 4 to 5 weeks after the first post-infection treatment. It will be clear to the skilled addressee that the three treatments i.e. pre-infection, maintenance and post-infection treatment, may be applied at any suitable frequency and while some treatments may be repeated, others may not always be required. In particular, more than one maintenance treatment may be required but if no infection occurs, the post-infection treatment will not be required. In a preferred embodiment, two pre-infection treatments are carried out at an interval of 4 days, followed by a first maintenance treatment 4 to 5 weeks after the last pre-infection treatment, and a further maintenance treatment 4 to 5 weeks after the first maintenance treatment. According to a fourth aspect, the present invention provides a process for preparing a plant pesticide according to the first aspect comprising combining an avermectin, sulphur and a surfactant.

According to a fifth aspect, the present invention provides a plant pesticide comprising about 0.0008% (w/v) avermectin, about 0.3% (w/v) sulphur and about 0.03% (w/v) non-ionic organic surfactant.

It will be clear to the skilled addressee that in the context of the present application, the term "plant" refers to any plant or part thereof including aerial and subterranean parts of the plant. It is contemplated that the parts of the plant may be, for example, flowers, fruits or vegetables, and that the parts of the plant may or may not be attached to the remainder of the plant.

In the context of the present invention, the term "plant pesticide" includes, but is not limited to, a substance which may be used for inhibiting the proliferation of, killing, or otherwise affecting the growth of, organisms considered to be undesirable or harmful to plants such as, for example, parasites, insects, fungi, worms or mites.

In the context of the present invention, the term "plant disease" includes, but is not limited to, states in which a plant is exposed to organisms considered to be undesirable or harmful to the plant such as, for example, parasites, insects, fungi, worms or mites. The skilled addressee will understand that a plant disease may occur when a pest or undesirable organism is present on, in, or in the environment of, the plant.

Unless the context clearly requires otherwise, throughout the description and the claims, the words 'comprise', 'comprising', and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to". BRIEF DESCRIPTION OF THE FIGURES

Figure 1 Treatments required to maintain plants substantially pest-free using Compositions 1, 2 and 3.

Figure 2. Use of a preferred composition of the invention to prevent infestation - synergistic effect and sulphur-sparing factor

Figure 3. Use of a preferred composition of the invention to treat severe pest infestation

DETAILED DESCRIPTION OF THE INVENTION

Preferred embodiments of the invention will now be described by way of example only with reference to the accompanying figures. Example 1 : Preparation of Pesticidal Compositions

The following are examples of the types of compositions studied. Those skilled in the art will recognize that the compositions and treatments may be varied considerably and still remain within the ambit of the claims defining this invention. The compositions studied were prepared using mixtures of commercial products including:

Thiovit™. This is a micronized form of sulphur comprising 80%) w/w of elemental sulphur. Ivomec™. This is a veterinary product comprising 0.08%) ivermectin. Agral™. This is a non-ionic detergent comprising 60% nonylphenoxy polyethyoxyethanol.

Composition 1 (sulphur as the sole active) Thiovit™ (80% elemental sulphur) 6 g

Agral™ (non-ionic detergent) 0.5 mL

Water to 1 L Composition 2 (low concentration ivermectin as the sole active)

Ivomec™ (0.08% ivermectin) 10 mL

Agral™ (non-ionic detergent) 0.5 mL

Water to 1 L

Composition 3 (sulphur + low concentration ivermectin as sole actives)

Thiovit™ (80%) elemental sulphur) 3 g

Ivomec™ (0.08% ivermectin) 10 mL

Agral™ (non-ionic detergent) 0.5 mL Water to 1 L

Briefly, to make the Thiovit/Ivomec combination, 48g of a wettable micronised

sulphur compound Thiovit® (a registered product of the Syngenta Group Company) was

combined with 160 ml of Ivermectin (Ivomec® liquid for sheep solution) and 8 ml of

Agral® and brought to a final volume of 16 L with water. Agral is a standard, well-

known surfactant used widely by plant growers as a carrier for pesticides. This solution was mixed and shaken vigorously to a homogenous mixture. Agitation and mixing of the solution also continued during the application of the composition to plants.

Pressurised equipment was used as a spray applicator to deliver the 16 L of solution over crops occupying a surface area of 300-500 square metres, depending on the age and active growth (rapid leaf expansion) of the plant. Spraying technique and quantity delivered to the surface and under-surface of the foliage was, inasmuch as it is practically possible, maintained the same. Both top and under surfaces of the leaves of the plants were sprayed. Example 2: Spraying Regime for Pesticides

The compositions described in Example 1 were applied to several plants. The application of the Thiovit/Ivomec composition is described below. The spraying programme was separated into three treatment stages. The first stage of spraying was regarded as the pre-infection period, and began at 4-5 weeks of plant growth, before infection was noticed. Pre-infection applications were considered to be more effective than post-infection. The objective of the experiments was to have a crop as free from visible signs of pests as possible.

At the pre-infection treatment stage, after 4-5 weeks of plant growth, the plants were sprayed irrespective of the presence of infection. This was repeated one more time at a 4-day interval. Therefore, the interval between pre-infection applications was 4 days. For example, if the first pre-infection application was made on 01-05-99, the second pre-infection application was made on 05-05-1999.

The next stage of spraying was considered the maintenance treatment. This was applied 4-5 weeks after the last pre-infection application, even in the absence of disease. This was repeated one more time if it was considered necessary. The necessity of repeating the maintenance treatment depended on the visual appearance of infection, the visual appearance of plant damage, and climatic changes e.g. wind, rain and humidity. The interval between maintenance treatments was 4-5 weeks. At the end of the maintenance treatment, the plants were generally substantially free from visible infection for a period of 7-8 weeks or more.

Any sign of insect emergence or infection indicated that an application was necessary. This was regarded as the post-infection period. Intervals between post- infection treatments, if they occur, will typically depend on the severity of the disease. The regimen for post-infection treatment was to spray once, then wait 4-5 weeks for a further treatment if necessary.

If there were no infections, further applications of the pesticide were carried out at 7-8 week intervals, or at even longer intervals depending on the crop and the risk that one was prepared to take, to protect the yield of the crop. If rain occurred after spraying, it was regarded as a non-application, and reapplied the next day.

In the present example, the pesticides described in Example 1 were applied without dilution. Spraying was not carried out in very hot weather, in wet or cold frosty weather, or on a windy day; warm days were preferably chosen, where temperatures were about 15-20°C, and spraying was carried out at the end of the day. Each crop sprayed was examined daily for the presence of insects and for any undesirable damage to any part of the plant and surrounding environment.

Example 3: Effectiveness of the Ivermectin/Thiovit® Combination The effectiveness of the Thiovit/Ivomec combination (Composition 3) pesticide was evaluated on dahlias, a bulbous ornamental plant susceptible to diseases. Using the spraying regime described above to avoid pest and disease problems, the plant performed well under these conditions.

Diseases on this ornamental plant vary from place to place and season to season. Pests such as aphids, thrips, whiteflies and mites of various sorts are always considered possible problems with any flower crop. Unprotected leaves are chewed by green loopes, cluster caterpillars. Earwigs and black field crickets also cause problems at times.

Dahlia seedlings were randomly placed in three beds and spraying commenced after the plants had become established (the index week) according to the following schedule:

Spray 1: applied during day 1 of the index week.

Spray 2: applied during day 4 of the index week.

Subsequent sprays: applied as needed, but not more frequently than once weekly. The compositions were applied by pressure spraying to all parts of the plants up to the point of run off.

Results are presented in Figure 1 in terms of the treatments required to maintain plants substantially pest free. Figure 1 shows that after 4-5 weeks of plant growth, and two pre-infection treatments at intervals of 4 days, Composition 3 showed an increased effectiveness in insecticidal activity over Compositions 1 and 2, by reducing the next maintenance treatment, from one application per week, to an application every 4-5 weeks (with some crops 7-8 weeks); and a reduction in the required Thiovit® concentration, from 60g/10L to 30g/10L. Other plants were also tested. All treated plants (e.g. dahlias, delphiniums, roses, tomatoes, carnations, beans, corn, carrots, strawberries, basil, parsley; and a variety of citrus and stone fruit trees and banana plants) were free from common diseases and pests for intervals of 4-5 weeks before re-applications; some ornamentals were free of disease up to 7-8 weeks before re-applications. The physical health appearance and yields of the crops treated were also far superior when Composition 3 was used compared to Compositions 1 and 2.

Without wishing to be bound by theory, it would appear that the effects seen in Figure 1 are due to the synergistic interaction of the avermectin (ivermectin) with sulphur. This is beneficial because it results in a reduction of the amount of sulphur required to treat the plants and, hence, a reduction in environmental damage. It is likely to follow that there would be a reduction in the development of resistance to the pesticides if they are used in lower quantities.

Figure 1 represents the culmination of many years of research in which the optimum treatment regime to maintain plants free from pesticides was achieved with compositions 1, 2 and 3 as described in Example 1. It was noted (results not shown) that when compositions 1 and 2 were used according to the same treatment regime as Composition 3, significantly more pests were present on the plants and the plants displayed a higher degree of plant damage than those treated with the combination.

The data in Figure 2 are provided by way of more clearly illustrating the relative effectiveness of the compositions described in Example 1 (Compositions 1, 2, and 3). The effects of the compositions were compared in terms of the total amount of sulphur needed to maintain the plants substantially pest- free over an 8-week period. The reciprocal of this figure (called the Sulphur-sparing Factor) was taken as a measure of the effectiveness of the mixture. As can be seen from Figure 2, not only did Composition 3 have a pesticidal effect greater than would be expected from a combination of the two active ingredients (ie. a synergistic effect) but, further, as a consequence, there was a significant reduction in the amount of sulphur required when Composition 3 is utilised i.e. the sulphur-sparing effect.

Synergistic effects comparable to those shown for Composition 3 in Figure 2 were observed with the following horticultural and agricultural crops grown under market garden conditions: dahlias, carnations, roses, tomatoes, capsicums, egg plants, beans, lettuce, spinach, cabbage, broccoli, and strawberries. Those skilled in the art will recognize that this wide selection of plants studied indicates a wide horticultural and agricultural use of the invention.

Example 4

The results in Figure 2 demonstrate the effectiveness of the invention (as exemplified by Composition 3) in preventing pest infestation. The results provided in Figure 3 demonstrate that the invention has therapeutic as well as prophylactic activity. An opportunity to demonstrate the therapeutic efficacy of Composition 3 occurred when a severe pest infestation afflicted an unattended crop of mature fruiting tomato plants grown under glasshouse conditions. Examination of the plants showed severe infestation with spider mites, aphids, and other forms of pests. The plants were sprayed according to the treatment regimes described in Figures 1 and 2. The plants recovered rapidly, with early improvement being seen after five days, and full recovery of the crop within 17-20 days.

Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms, in keeping with the broad principles and the spirit of the invention described herein.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS :-

I . A plant pesticide comprising (a) an avermectin and (b) sulphur or a sulphur- containing compound.

2. A plant pesticide according to claim 1 wherein the pesticide comprises 0.0001% to 0.002% (w/v) avermectin.

3. A plant pesticide according to claim 2 wherein the pesticide comprises about 0.0008% (w/v) avermectin.

4. A plant pesticide according to any one of claims 1 to 3 wherein the avermectin is ivermectin.

5. A plant pesticide according to any one of claims 1 to 4 wherein the pesticide is in the form of a solid granular pellet or pellet-like form.

6. A plant pesticide according to any one of claims 1 to 4 wherein the sulphur is micronised sulphur.

7. A plant pesticide according to claim 6 wherein the sulphur is wettable micronised sulphur.

8. A plant pesticide according to claim 7 wherein the sulphur is microgranule elemental sulphur.

9. A plant pesticide according to any one of claims 1 to 8 wherein the pesticide comprises 0.1 to 1.0% (w/v) sulphur.

10. A plant pesticide according to claim 9 wherein the pesticide comprises about 0.3% (w/v) sulphur.

I I. A plant pesticide according to any one of claims 1 to 10 wherein the pesticide further comprises a carrier.

12. A plant pesticide according to claim 11 wherein the carrier is selected from the group consisting of: water, stabilizers, emulsifiers, oils, surfactants, antioxidants and UN screens.

13. A plant pesticide according to claim 12 wherein the surfactant is a non-ionic surfactant.

14. A plant pesticide according to claim 13 wherein the surfactant is a non-ionic organic surfactant.

15. A plant pesticide according to claim 14 wherein the surfactant is nonylphenoxy polyethoxyethanol.

16. A plant pesticide according to any one of claims 12 to 15 wherein the pesticide comprises 0.01 to 0.1 % surfactant.

17. A plant pesticide according to claim 16 wherein the pesticide comprises about 0.03% (w/v) surfactant.

18. A plant pesticide according to any one of claims 1 to 17 wherein the plant is an ornamental plant.

19. A plant pesticide according to claim 18 wherein the ornamental plant is a carnation, rose, lavender, tulip, delphinium or dahlia.

20. A plant pesticide according to any one of claims 1 to 17 wherein the plant is a fruit plant.

21. A plant pesticide according to claim 20 wherein the fruit plant is a stone fruit tree, citrus fruit tree, grape vine, strawberry, coffee, banana, tomato, rockmelon or watermelon plant.

22. A plant pesticide according to any one of claims 1 to 17 wherein the plant is an herb or a medicinal plant.

23. A plant pesticide according to claim 22 wherein the herb or medicinal plant is a red clover, chamomile, aloe, evening primrose, skullcap, Echinacea, saw palmetto, feverfew, witch hazel, valerian, tea tree, garlic, eucalyptus, basil, parsley or ginseng plant.

24. A plant pesticide according to any one of claims 1 to 17 wherein the plant is a vegetable plant.

25. A plant pesticide according to claim 24 wherein the vegetable plant is a bean, corn, carrot, cucumber, potato, radish, spinach, pea, lettuce, onion, cabbage, broccoli, cauliflower, zucchini or turnip plant.

26. A method for the prevention and/or treatment of a plant disease comprising applying to the plant, or the environment of the plant, an effective amount of a pesticide according to any one of claims 1 to 25.

27. A method for the prevention and/or treatment of a plant disease comprising applying a pesticide to the plant, or the environment of the plant, wherein the pesticide comprises two separate components: (a) an avermectin and (b) sulphur or a sulphur-containing compound, and the method comprises the simultaneous or sequential application of (a) and (b) such that a synergistic pesticidal effect between (a) and (b) is achieved.

28. A method according to claim 26 or claim 27 wherein the disease results from a parasite, insect, fungi, worm or mite infestation.

29. A method according to any one of claims 26 to 28 wherein the pesticide is applied to a surface of the foliage of the plant.

30. A method according to any one of claims 26 to 28 wherein the pesticide is applied to substantially all surfaces of the plant foliage.

31. A method according to any one of claims 26 to 30 wherein the pesticide is applied by a spray technique.

32. A method according to any one of claims 26 to 31 wherein the pesticide is applied to the plant at a rate of 10-300ml per m².

33. A method according to claim 32 wherein the pesticide is applied at a rate of 30-50ml per m².

34. A method according to any one of claims 26 to 33 wherein the pesticide is applied to the plant in more than one application.

35. A method according to any one of claims 26 to 34 wherein the pesticide is applied according to different stages of plant growth and disease progression.

36. A method according to any one of claims 26 to 35 wherein the pesticide is applied in three treatment stages identified as pre-infection, maintenance and post-infection treatments.

37. A method according to claim 36 wherein the pesticide is applied in the pre-infection treatment at intervals of 1 to 10 days.

38. A method according to claim 37 wherein the pesticide is applied twice during the pre-infection treatment at about a 4-day interval.

39. A method according to claim 36 wherein the maintenance treatment is applied 2 to 10 weeks after the pre-infection treatment.

40. A method according to claim 39 wherein the maintenance treatment is applied 4-5 weeks after the pre-infection treatment and optionally reapplied at 2 to 8 week intervals or 4-5 week intervals.

41. A method according to claim 36 wherein a first post-infection treatment is applied upon the appearance of signs of pest infection.

42. A method according to claim 37 wherein a further post-infection treatment is applied.

43. A method according to claim 42 wherein the further post-infection treatment is carried out 3 to 6 weeks after the first post-infection treatment.

44. A method according to claim 44 wherein the further post-infection treatment is carried out 4 to 5 weeks after the first post-infection treatment.

45. A method according to claim 36 wherein two pre-infection treatments are carried out at an interval of 4 days, followed by a first maintenance treatment 4 to 5 weeks after the last pre-infection treatment, and a further maintenance treatment 4 to 5 weeks after the first maintenance treatment.

46. A process for preparing a plant pesticide according any one of claims 1 to 25 comprising combining an avermectin with sulphur or a sulphur-containing compound.

47. A plant pesticide comprising about 0.0008% (w/v) avermectin, about 0.3%> (w/v) sulphur and about 0.03% (w/v) non-ionic organic surfactant.