WO2003005821A1

WO2003005821A1 - Weed control process

Info

Publication number: WO2003005821A1
Application number: PCT/GB2002/003154
Authority: WO
Inventors: Peter Bernard Sutton; Rex Alan Wichert
Original assignee: Syngenta Ltd
Current assignee: Syngenta Ltd
Priority date: 2001-07-11
Filing date: 2002-07-08
Publication date: 2003-01-23
Anticipated expiration: 2004-01-11
Also published as: GB0116955D0; AR034751A1

Abstract

A novel process of controlling triazine-tolerant weeds by the application of a composition comprising mesotrione to the locus of said weeds is disclosed.

Description

Weed Control Process

This invention relates to the use of mesotrione to control the growth of undesired target plants that show triazine tolerance.

The protection of crops from weeds and other vegetation that inhibits crop growth is a constantly recurring problem in agriculture. To help combat this problem, researchers in the field of synthetic chemistry have produced an extensive variety of chemicals and chemical formulations effective in the control of such unwanted growth. Chemical herbicides of many types have been disclosed in the literature and a large number are in commercial use. Commercial herbicides and some that are still in development are described in The Pesticide Manual, 12th edition, published in 2000 by the British Crop Protection Council. All the herbicides specifically named in this application can be found in The Pesticide Manual.

Triazines are one known class of herbicides. In normal use, these have proved to be very effective across a wide range of weeds. However, an increasing problem encountered in agriculture is the appearance of weeds that have developed a tolerance to triazines. By 'tolerance' is meant that these weeds are less easily damaged or killed by the application of triazine than the normal phenotype. Typically, these weeds show little or no damage when triazines are applied at normal application rates. This tolerance arises naturally and occurs because of the selection pressure exerted on the weed population by repeated application of triazine herbicides. Some weeds have developed almost complete tolerance to triazines, that is, they are virtually undamaged by triazines at the normal commercial application rates. Sometimes the word 'resistant' is also used to describe such weeds, in particular where they have the inherited ability to survive treatment by a triazine.

Triazine tolerance is obviously a problem, because either the weeds thrive to an increasing degree, which can drive down crop yields, or alternatively increased quantities of triazine must be used, which increases cost and risks environmental damage.

We have now discovered that mesotrione can be used to control triazine-tolerant weeds to a surprising degree. Mesotrione is a known herbicide, and as such would be expected to kill weeds. However, we have discovered that it is unexpectedly more effective against triazine-tolerant weeds than it is against ordinary weeds. Hence the use of mesotrione to control triazine resistant weeds represents a surprising advance in the continuing efforts to control triazine-resistant weeds in agriculture and elsewhere.

According to the present invention there is provided a process of controlling triazine-tolerant weeds by the application of a herbicidal composition comprising mesotrione to the locus of said weeds.

The mesotrione can be in the form of a metal salt, for example a copper salt as disclosed in US 5 912 207.

Preferably, in the field, the composition is applied at a rate such as to apply the mesotrione at above 50g/ha, more preferably above 75g/ha and most preferably above 105g/ha. Preferably, in the field, the composition is applied at a rate such as to apply the mesotrione at below 250g/ha, more preferably below 210g ha and most preferably below 180g ha. In glasshouse tests, much lower levels can be used. For example, in glasshouse tests, the mesotrione can be applied at as little as 0.1 to 10 g ha. The process of the invention involves applying the composition by a convenient method to the locus of the tolerant weeds where control is desired. The "locus" is intended to include soil, seeds, and seedlings, as well as established vegetation.

The process can be used in areas where there are no desired plants, such as crops, or where desired plants, such as crops, have been planted, but have not yet emerged Cpreemergence'). The process can also be used over a wide range of growing desired plants, such as crops (postemergence). Examples of crops include (but not limited to) corn (maize), wheat and rice. Suitable desired plants include those that are tolerant to mesotrione, particularly when the process is used postemergence, and/or tolerant to any other herbicide, such as glyphosate that can be additionally included in the composition. The tolerance can be natural tolerance which is inherent or which is produced by selective breeding or can be artificially introduced by genetic modification of the desired plants. Tolerance means a low susceptibility to damage caused by a particular herbicide. Plants can be modified or bred so as to be tolerant, for example to HPPD inhibitors like mesotrione, or EPSPS inhibitors like glyphosate. Corn (maize) is inherently tolerant to mesotrione, and the process is particularly useful for controlling triazine tolerant weeds in corn. Examples of weeds with tolerant phenotypes include Redroot pigweed

(AMARE), common lambsquarters (CHEAL) and black nightshade (SOLNI). The process is particularly effective over AMARE. Tolerant phenotypes are well know in the art and are easily identified by applying a triazine herbicide, such as atrazine, terbuthylazine or simazine and comparing the effect with application to a non-tolerant phenotype, also well known in the art, at a similar stage of growth.

The composition employed in the practice of the present invention can be applied in a variety of ways known to those skilled in the art, at various concentrations. The composition is useful in controlling the growth of undesirable vegetation by preemergence or postemergence application to the locus where control is desired.

The composition applied according to the present invention preferably also comprises an agriculturally acceptable carrier therefor. In practice, the composition is applied as a formulation containing the various adjuvants and carriers known to or used in the industry for facilitating dispersion. The choice of formulation and mode of application for any given compound may affect its activity, and selection will be made accordingly. The compositions of the invention may thus be formulated as granules, as wettable powders, as emulsifiable concentrates, as powders or dusts, as flowables, as solutions, as suspensions or emulsions, or as controlled release forms such as microcapsules. These formulations may contain as little as about 0.5% to as much as about 95% or more by weight of active ingredient. The optimum amount for any given compound will depend upon formulation, application equipment, and nature of the plants to be controlled.

Wettable powders are in the form of finely divided particles that disperse readily in water or other liquid carriers. The particles contain the active ingredient retained in a solid matrix. Typical solid matrices include fuller's earth, kaolin clays, silicas and other readily wet organic or inorganic solids. Wettable powders normally contain about 5% to about 95% of the active ingredient plus a small amount of wetting, dispersing, or emulsifying agent.

Emulsifiable concentrates are homogeneous liquid compositions dispersible in water or other liquid, and may consist entirely of the active compound with a liquid or solid emulsifying agent, or may also contain a liquid carrier, such as xylene, heavy aromatic naphthas, isophorone and other non-volatile organic solvents. In use, these concentrates are dispersed in water or other liquid and normally applied as a spray to the area to be treated. The amount of active ingredient may range from about 0.5% to about

95% of the concentrate.

Granular formulations include both extrudates and relatively coarse particles, and are usually applied without dilution to the area in which suppression of vegetation is desired. Typical carriers for granular formulations include sand, fuller's earth, attapulgite clay, bentonite clays, montmorillonite clay, vermiculite, perlite and other organic or inorganic materials which absorb or which can be coated with the active compound. Granular formulations normally contain about 5% to about 25% active ingredients which may include surface-active agents such as heavy aromatic naphthas, kerosene and other petroleum fractions, or vegetable oils; and/or stickers such as dextrins, glue or synthetic resins.

Dusts are free-flowing admixtures of the active ingredient with finely divided solids such as talc, clays, flours and other organic and inorganic solids that act as dispersants and carriers.

Microcapsules are typically droplets or granules of the active material enclosed in an inert porous shell which allows escape of the enclosed material to the surroundings at controlled rates. Encapsulated droplets are typically about 1 to 50 microns in diameter. The enclosed liquid typically constitutes about 50 to 95% of the weight of the capsule, and may include solvent in addition to the active compound. Encapsulated granules are generally porous granules with porous membranes sealing the granule pore openings, retaining the active species in liquid form inside the granule pores. Granules typically range from 1 millimeter to 1 centimeter, preferably 1 to 2 millimeters in diameter. Granules are formed by extrusion, agglomeration or prilling, or are naturally occurring. Examples of such materials are vermiculite, sintered clay, kaolin, attapulgite clay, sawdust and granular carbon. Shell or membrane materials include natural and synthetic rubbers, cellulosic materials, styrene-butadiene copolymers, polyacrylonitriles, polyacrylates, polyesters, polyamides, polyureas, polyurethanes and starch xanthates.

Other useful formulations for herbicidal applications include simple solutions of the active ingredient in a solvent in which it is completely soluble at the desired concentration, such as acetone, alkylated naphthalenes, xylene and other organic solvents. Pressurized sprayers, wherein the active ingredient is dispersed in finely- divided form as a result of vaporization of a low boiling dispersant solvent carrier, may also be used.

Many of these formulations include wetting, dispersing or emulsifying agents. Examples are alkyl and alkylaryl sulfonates and sulfates and their salts; polyhydric alcohols; polyethoxylated alcohols; esters and fatty amines. These agents, when used, normally comprise from 0.1% to 15% by weight of the formulation.

Each of the above formulations can be prepared as a package containing the herbicide together with other ingredients of the formulation (diluents, emulsifiers, surfactants, etc.). The formulations can also be prepared by a tank mix method, in which the ingredients are obtained separately and combined at the grower site.

A commercial formulation of mesotrione is available as Callisto from Syngenta (formerly Zeneca Agrochemicals). Callisto is a suspension concentrate of mesotrione.

These formulations can be applied to the areas where control is desired by conventional methods. Dust and liquid compositions, for example, can be applied by the use of power-dusters, broom and hand sprayers and spray dusters. The formulations can also be applied from airplanes as a dust or a spray or by rope wick applications. To modify or control growth of germinating seeds or emerging seedlings, dust and liquid formulations can be distributed in the soil to a depth of at least one-half inch below the soil surface or applied to the soil surface only, by spraying or sprinkling. The formulations can also be applied by addition to irrigation water. This permits penetration of the formulations into the soil together with the irrigation water. Dust compositions, granular compositions or liquid formulations applied to the surface of the soil can be distributed below the surface of the soil by conventional means such as disking, dragging or mixing operations.

If necessary or desired for a particular application or crop, the composition of the present invention may contain an antidotally effective amount of an antidote (also known as a 'safener') for mesotrione. Those skilled in the art will be familiar with suitable antidotes.

Further, other biocidally active ingredients or compositions may be combined with the synergistic herbicidal composition of this invention. For example, the compositions may contain, in addition to mesotrione, insecticides, fungicides, bactericides, acaracides or nematicides, in order to broaden the spectrum of activity.

As one skilled in the art is aware, in herbicidal testing, a significant number of factors that are not readily controllable can affect the results of individual tests and render them non-reproducible. For example, the results may vary depending on environmental factors, such as amount of sunlight and water, soil type, pH of the soil, temperature, and humidity, among other factors. Also, the depth of planting, the application rate of individual and combined herbicides, the application rate of any antidote, and the ratio of the individual herbicides to one another and/or to an antidote, as well as the nature of crops or weeds being tested, can affect the results of the test. Results may vary from crop to crop within the crop varieties.

Although the invention has been described with reference to preferred embodiments and examples thereof, the scope of the present invention is not limited only to those described embodiments. As will be apparent to persons skilled in the art, modifications and adaptations to the above-described invention can be made without departing from the spirit and scope of the invention, which is defined by the appended claims.

EXAMPLES

Several different greenhouse trials were carried out to evaluate the effectiveness of mesotrione over triazine tolerant (T) and triazine susceptible (S) weeds. The example target weeds were redroot pigweed (Amaranthus retroflexus L.; AMARE), common lambsquarters {Chenopodium album L.; CHEAL) and black nightshade (Solanum nigrum L.; SOLNI). Each trial was a randomised complete block with treatments replicated four times. The original source of triazine-resistant and non-resistant seed was Herbiseed.

Seeds for these tests came from plants grown from those seed lots. The soil type in each case was a clay loam (loam:Nichol's clay; 2:1). The soil was mixed with a full rate (128g of 12-12-12 per 10 gallons of soil) of fertilizer. The mesotrione dosage was noted in grams of active ingredient (mesotrione) per hectare (g a.i/ha). The dosages of mesotrione needed to control all types of weed under these ideal greenhouse conditions were much lower that one would normally use in the field. It should be noted that due to the rates used being very low, significant re-growth of the weeds (and hence reduction in the percentage of weed control) is possible.

In each case visual ratings, using a 0% (no injury) to 100% (dead plants) scale, were recorded 10 DAA and 21 DAA. These are shown in the tables to each example. Example 1

1.1 Seeds from the T seed lot were planted on 23 March and seeds from the S seed lot were planted on 30 March 2001. These timings were based on earlier observations of differences in time-to-germination and growth rate.

1.2 Application The plants were grown and treated with mesotrione on 19 April 2001, when the S plants were in the 4-5-leaf stage and the T plants were in the 6-7-leaf stage. Tap water containing 0.5% Tween 20 was used to prepare all spray solutions. The treatment solutions were applied at 200 1/ha and 40 psi using an 80015E nozzle. Rates of mesotrione (as Callisto 4SC from Syngenta; a suspension concentrate of finely divided mesotrione powder in water) were 1, 2, 3, and 8 g a.i./ha. After spraying, the plants were placed in a glasshouse, under environmental conditions of 29/20°C (84/68^*^ day/night temperatures, 56/84% day/night relative humidity and a photoperiod of 14 hours.

Table 1: Mean Control (%) of AMARE at 10 and 21 DAA

Example 2

2.1 Seeds from the T seed lot were planted on 23 March and seeds from the S seed lot were planted on 30 March 2001. These timings were based on earlier observations of differences in time-to-germination and growth rate 2.2 Application Notes

The plants were grown and treated with mesotrione, on 23 April 2001, when the S plants were in the 6-7-leaf stage and 100 mm tall and the T plants were in the 7-leaf stage and 65-75 mm tall. Tap water containing 0.5% Tween 20 was used to prepare all spray solutions. The treatment solutions were applied at 200 1/ha and 40 psi using an 80015E nozzle. Rates of mesotrione (as Callisto 4SC from Syngenta) were 1, 2, 4, and 8 g a.i./ha. After spraying, the plants were placed in a glasshouse, under environmental conditions of 29/20°C (84/68°F day/night temperatures, 56/84% day/night relative humidity and a photoperiod of 14 hours.

Table 2: Mean Control (%) of AMARE at 10 and 21 DAA

Example 3 3.1 The seeding dates are shown in Table 3 A. These timings were based on earlier observations of differences in time-to-germination and growth rate. 3.2 Application

CHEAL and SOLNI plants were grown and treated with mesotrione (as Callisto 4SC from Syngenta) on 20 April 2001. The stage of growth for each species and seed lot (biotype) was as shown in Table 3A.

Table 3A

Species Biotype Seeded Growth stage on 20 April 2001

CHEAL T 23 March 2001 10-12 leaf; very occasional terminal flower bud

CHEAL S 30 March 2001 8-10 leaf; flower buds and some flowering

SOLNI T 28 March 2001 5-leaf; a few flower buds

SOLNI S 28 March 2001 6-leaf; a few flower buds (larger than T plants Tap water containing 0.5% Tween 20 was used to prepare all spray solutions. The treatment solutions were applied at 200 1 ha and 40 psi using an 80015E nozzle. Rates of mesotrione were 0.1, 0.3, 0.6 and 0.9 g a.iVha. After spraying, the plants were placed in WRC glasshouse 16B, under environmental conditions of 26/18°C (78/65^ day/night 5 temperatures, 44/68% day/night relative humidity and a photoperiod of 14 hours.

Table 3B:Mean control (%) of CHEAL and SOLNI at 10 and 21 DAA

Example 4

10 4.1 Seeds from the T seed lot were planted on 27 March and seeds from the S seed lot were planted on 30 March 2001. 4.2 Application

The plants were grown and treated with mesotrione, on 24 April 2001, when the S plants were in the 6-leaf stage and 90-100 mm tall and the T plants were in the 6-leaf stage and

15 65-75 mm tall. Tap water containing 0.5% Tween 20 was used to prepare all spray solutions. The treatment solutions were applied at 200 1/ha and 40 psi using an 80015E nozzle. Rates of mesotrione (as Callisto 4SC from Syngenta) were 1, 2, 3, and 8 g a.i./ha. After spraying, the plants were placed in a glasshouse, under environmental conditions of 29/20°C (84/68^ day/night temperatures, 56/84% day/night relative

20 humidity and a photoperiod of 14 hours.

Table 4: Mean Control (%) of AMARE at 10 and 21 DAA

Example 5

5.1 Seeds from the T seed lot were planted on 23 March and seeds from the S seed lot were planted on 30 March 2001. These timings were based on earlier observations of differences in time-to-germination and growth rate

5.2 Application

The plants were grown and treated with mesotrione, on 25 April 2001, when the S plants were in the 6-leaf stage and 45-55 mm tall and the T plants were in the 4-7-leaf stage and 25-40 mm tall. Tap water containing 0.5% Tween 20 was used to prepare all spray solutions. The treatment solutions were applied at 200 1/ha and 40 psi using an 80015E nozzle. Rates of mesotrione (as Callisto 4SC) were 1, 2, 3, and 8 g a.i./ha. After spraying, the plants were placed in glasshouse, under environmental conditions of 29/20°C (84/68^ day/night temperatures, 56/84% day/night relative humidity and a photoperiod of 14 hours.

Table 5: Mean Control (%) of AMARE at 10 and 21 DAA

Example 6

6.1 The seeding dates are shown in Table 6A. These timings were based on earlier observations of differences in time-to-germination and growth rate. 6.2 Application Notes

CHEAL and SOLNI plants were grown and treated with mesotrione (as Callisto 4SC; from Syngenta) on 20 April 2001. The stage of growth for each species and seed lot (biotype) is shown below. Table 6A

Species Biotype Seeded Growth stage on 20 April 2001 CHEAL T 23 March 2001 10-12 leaf; very occasional flower bud, 40-60mm CHEAL S 30 March 2001 9-11 leaf, 110-125 mm §OLNI T 28 March 2001 9-leaf, 70-90 mm SOLNI S 28 March 2001 9-leaf, 70-90 mm

Tap water containing 0.5% Tween 20 was used to prepare all spray solutions. The treatment solutions were applied at 200 1/ha and 40 psi using an 80015E nozzle. Rates of mesotrione were 0.1, 0.3, 0.6 and 0.9 g a.i./ha. After spraying, the plants were placed in a glasshouse, under environmental conditions of 29/20°C (84/68*^ day/night temperatures, 56/84% day/night relative humidity and a photoperiod of 14 hours.

Table 6B:Mean control (%) of CHEAL and SOLNI at 10 and 21 DAA

Claims

1. A process of controlling triazine-tolerant weeds by the application of a composition comprising mesotrione to the locus of said weeds.

2. A process according to claim 1 in which the mesotrione is applied at a rate of 50 to 250g/ha.

3. A process according to claim 1 in which the triazine-tolerant weeds are tolerant phenotypes of one or more of Redroot pigweed, Common

Lambsquarters and Black Nightshade.

4. A process according to claim 1 carried out in the presence of desired plants.

5. A process according to claim 4 carried out in the presence of com.