WO2012007907A1

WO2012007907A1 - Weed control method

Info

Publication number: WO2012007907A1
Application number: PCT/IB2011/053113
Authority: WO
Inventors: Gordon Vail; Charles Foresman
Original assignee: Syngenta Participations Ag
Priority date: 2010-07-13
Filing date: 2011-07-12
Publication date: 2012-01-19

Abstract

The present invention relates to a method of controlling a HPPD recalcitrant weed at a locus, said method comprising applying to the locus a pre-emergence application of a herbicidal composition comprising a HPPD inhibiting herbicide. The present invention further provides a method of identifying and controlling HPPD recalcitrant weeds at a locus, said method comprising :- (i) applying a normal post-emergence application of a herbicidal composition comprising a HPPD-inhibiting herbicide; (ii) identifying HPPD recalcitrant weeds that survive at said locus; and (iii) subsequently applying to said locus at least one pre-emergence application of a herbicidal composition comprising a HPPD-inhibiting herbicide.

Description

Weed Control Method

The protection of crops from weeds and other vegetation that inhibit 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, 15th edition, published in 2009 by the British Crop Protection Council. Hydroxyphenylpyruvate dioxygenase (HPPD) inhibiting herbicides are a class of herbicides that can be used both pre- and/or post-emergence to provide effective control of a wide variety of weeds. It has recently been discovered, however, that certain weed biotypes do not seem to be adequately controlled by post-emergence applications of HPPD-inhibiting herbicides at application rates which would normally be expected to afford adequate control (by "normally" it is meant that the herbicide is applied at a typical commercial rate, as recommended by the herbicide manufacturer. Thus a normal post-emergence application rate for the HPPD-inhibiting herbicide mesotrione would be, for example, from 30 to 210 g/ha, more typically from 70 g/ha to 150 g/ha). For the purposes of the present invention, such weed biotypes are referred to as a "HPPD recalcitrant weeds". Thus, a HPPD recalcitrant weed is less easily damaged or killed by a post-emergence application of the HPPD-inhibitor than the normal weed phenotype. Thus, "HPPD recalcitrant weeds" are weeds (in particular Palmer amaranth or common waterhemp) that have increased tolerance to HPPD inhibitors applied pre or post but are not resistant to HPPD inhibitors.

We have now discovered that these HPPD recalcitrant weeds can be successfully controlled using a pre-emergence application of a herbicidal composition comprising a HPPD-inhibiting herbicide. This finding is surprising in that weed biotypes that are recalcitrant to post-emergence herbicide treatment would similarly be expected to be recalcitrant to pre-emergence herbicide treatment, which is not the case.

Thus, according to the present invention there is provided a method of controlling a HPPD recalcitrant weed at a locus, said method comprising applying to the locus at least one pre-emergence application of a herbicidal composition comprising a HPPD inhibiting herbicide. The term "locus" means the area in which the plants are growing or will grow. Thus the locus will typically be a field or fields. In the context of the present invention it should be understood that the locus may further comprise other weeds and/or crops such corn, cotton or soybeans.

In the context of the present invention, the term "post-emergence" is taken to mean that the herbicidal composition is applied once the HPPD recalcitrant weed has emerged from the locus. The term "pre-emergence" is taken to mean that the herbicide composition is applied before the HPPD recalcitrant weed has emerged from the locus.

The present invention further provides a method of identifying and controlling HPPD recalcitrant weeds at a locus, said method comprising:-

(i) applying a normal post-emergence application of a herbicidal composition comprising a HPPD-inhibiting herbicide to the locus;

(ii) identifying HPPD recalcitrant weeds that survive at said locus; and

(iii) subsequently applying to said locus at least one pre-emergence application of a herbicidal composition comprising a HPPD-inhibiting herbicide.

By "normal" it is meant that the herbicide is applied at a typical commercial rate, as recommended by the herbicide manufacturer. A normal post-emergence application rate for mesotrione would be, for example, from 30 to 210 g/ha, more preferably from 70 to 150 g/ha.

It should be appreciated, that in the context of this particular method, the identification, via post-emergence application, and control, via pre-emergence application, could take place at different locations within the locus (for example different fields). Also, the identification and control could take place in different growing seasons. For example, the grower may make the identification of the HPPD recalcitrant weed in one growing season on one particular field and then make the pre-emergence application (on the same field or a different field as a precautionary measure) in a subsequent growing season in order to control the HPPD recalcitrant weeds. HPPD recalcitrant weeds will typically be identified via a visual assessment following the post-emergence application. Numerous HPPD-inhibiting herbicides are known in the art and include, for example, benzofenap, bicyclopyrone, benzobicyclon, isoxachlotole, isoxaflutole, mesotrione, pyrazoxyfen, pyrasulfatole, pyrazolynate, sulcotrione, tembotrione, topramazone and tefuryltrione. In the context of the present invention it is preferred that the HPPD-inhibiting herbicide used in the pre-emergence application is selected from the group consisting of bicyclopyrone, isoxaflutole, mesotrione, tembotrione and topramezone. Mesotrione is particularly preferred. For the avoidance of doubt, the term HPPD-inhibiting herbicide should be taken to include agrochemically acceptable salts thereof, for example mesotrione can be in the form of a metal salt, for example a copper salt as disclosed in US 5,912,207.

The pre-emergence HPPD-inhibiting herbicide is typically applied to the locus at a rate from 20 g/ha to 500 g/ha, preferably from 100 g/ha to 250 g/ha. Thus, a typical pre- emergence application rate for mesotrione is from 50 g/ha to 250 g/ha.

The pre-emergence herbicidal composition may further comprise one or more additional herbicides in order to confer even better control of the HPPD recalcitrant weed. Examples of such additional herbicides include atrazine, ametryn, prometryn, terbuthylazine, metribuzin, fomesafen, alachlor, hexazinone, amicarbazone, pendimethalin, trifluralin, metolachlor, iS-metolachlor, acetochlor, flufenacet, mefenacet, dimethenamid, p- dimethenamid, pyroxasulfone and saflufenacil. In a particularly preferred embodiment of the present invention, the herbicidal composition applied pre-emergence comprises mesotrione (and/or other HPPD inhibiting herbicide e.g isoxaflutole, bicyclopyrone, tembotrione or topramezone) and atrazine and/or ^-metolachlor. In another embodiment, fomesafen, metribuzin, glyphosate and/or glufosinate can be integrated in to the pre-emergence composition or application regimen.

Where the pre-emergence composition comprises one or more additional herbicides then the individual components can be applied sequentially, in any order, to the locus. In this instance the components are typically applied within 3 days and most preferably within 24 hours of each other. Alternatively and preferably, the individual components are applied simultaneously in a single herbicidal composition.

In another embodiment of the present invention the pre-emergence application of the herbicidal composition comprising the HPPD-inhibiting herbicide is followed by a post- emergence application, to the locus, of one or more additional herbicidal compositions. The one or more additional herbicidal compositions could comprise a HPPD-inhibiting herbicide and/or other typical post-emergence herbicides such as glyphosate atrazine, glufosinate, dicamba and/or 2,4-D. The post-emergence application would typically be applied within 45 days of the pre-emergence application.

In another embodiment of the present invention for controlling HPPD recalcitrant weeds at a locus, the post emergence herbicides or post-directed herbicides that can follow the pre-emergence application of the herbicidal composition comprising the HPPD-inhibiting herbicide are selected from 2,4-D, acifluorofen, bromoxynil, lactofen, dicamba, paraquat, diquat, MSMA, DSMA, chlorpryralid, fluroxypyr, triclopyr, MCPA, butylate, prosulfocarb, imazapyr, imazaquin, imazethapyr, imazamox, pyrithiobac-Na, chlorimuron-ethyl, thifensulfuron-methyl, triasulfuron, cloransulam-methyl, oxyfluorfen, flumiclorac-pentyl, pyraflufen-ethyl and glufosinate.

Examples of HPPD recalcitrant weeds can include biotypes of the following species:- Amaranthus sp. (in particular Amaranthus palmeri, Amaranthus rudis, Amaranthus tuberculatus and Amaranthus tamariscinus), Ambrosia sp., Conyza sp. Digitaria sp., Chenopodium sp. and Xanthium sp., Solarium sp., Datura sp., Abutilon sp., kochia, Russian thistle and Polygonum sp.

The components of the combination according to the present invention (whether administered sequentially or together) are suitable applied as an agriculturally acceptable composition. The composition(s) preferably also comprise 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.

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 (sometimes also called a 'safener'). Those skilled in the art will be familiar with suitable antidotes.

Examples

Example 1

Greenhouse screens are conducted to evaluate the response of sensitive and recalcitrant waterhemp (AMATA) accessions to various pre-emergence (PRE) and post- emergence (POST) herbicide treatments. For POST treatments the herbicide is applied (with 1% v/v Crop Oil Concentrate) at a lx field application rate as indicated in the tables below when the waterhemp was 3-3.5" in height. An application volume of 150 1/ha is used. Plants are assessed for visual control (0% = no control, 100% = complete control) 23 days after application (DAA) of the herbicide. For PRE treatments the herbicide is also applied as a lx rate. Plants are assessed for visual control 20 DAA of the herbicide(s).

Table 1. POST Results.

This result indicates that the recalcitrant accession is significantly less well controlled v. the sensitive accession using a lx POST application rate of mesotrione.

Table 2. PRE Results.

This result indicates that both the sensitive and recalcitrant accessions are well controlled using lx PRE application rates of mesotrione. Example 2

Field tests

Field tests are conducted to evaluate the response of recalcitrant waterhemp (AMATA) accessions to pre-emergence (PRE) followed by (fb) post-emergence (POST) herbicide treatments. For POST treatments the herbicides are applied at rates indicated in the Table below (as LUMAX™) when the waterhemp was 2-3" in height. Plants are assessed for visual control (0% = no control, 100% = complete control) 28 days after the post application (DAA) of the herbicide (54 days after the PRE application). Treatment Rate g/ha Visual Control (%)

Mesotrione + S- 75 + 751 + 280 fb 91

metolachlor + 150 + 1502 + 560

Atrazine

113 + 1127 + 420 93

fb 113 + 1127 +

420

150 + 1502 + 560 94

fb 75 + 751 + 280

These results show that herbicidal compositions comprising mesotrione, applied PRE and POST emergence, are effective in controlling HPPD recalcitrant weeds.

Example 3

Field tests are conducted to evaluate the response of recalcitrant Palmer amaranth (AMAPA) accessions to pre-emergence (PRE) herbicide treatments. Herbicides are applied at the rates indicated in the Tables below (as LUMAX™ or LUMAX™ + AATREX™). Plants are assessed for visual control (0% = no control, 100% = complete control) 36 days after the herbicide application.

These results show that various herbicidal compositions comprising mesotrione applied pre- emergence are effective in controlling HPPD recalcitrant Palmer amaranth. Example 4 Greenhouse tests are conducted to evaluate the response of recalcitrant and sensitive Palmer amaranth (AMAPA) various to pre-emergence (PRE) herbicide treatments. Herbicides are applied using commercial formulations as indicated in the Table below and assessed for visual control (0% = no control, 100% = complete control). Herbicide synergy is assessed using the formula disclosed by Colby, S. R., "Calculating synergistic and antagonistic response of herbicide combinations", Weeds 15, pp 20-22 (1967). When the observed response is greater than expected the response (observed minus expected is a positive value), the combination is synergistic; when less than expected, it is antagonistic. If the observed and expected responses are equal, the combination is additive.

AMAPA % Control

Recalcitrant Acc. Sensitive Acc.

Rate (g Active

Herbicide(s) ai/ha) Ingredient Obs Exp Obs - Exp Obs Exp Obs - Exp

Callisto 6 Mesotrione 23 32

12 37 82

23 85 95

47 88 99

94 98 100

187 99 100

Dual II S-

Magnum 46 metolachlor 24 83

91 33 95

182 40 96

364 77 99

728 98 100

1456 100 100

Aatrex 46 Atrazine 2 18

91 15 12

182 12 19

364 12 45

728 7 95

1456 86 98

Callisto + Mesotrione

Aatrex 6 + 46 + Atrazine 6 25 -19 87 44 43

115 + 91 51 46 5 97 84 13

23 + 182 85 87 -2 100 96 4

47 + 364 99 90 9 99 99 0

94 + 728 100 98 2 100 100 0

187 + 1456 100 100 0 100 100 0

Callisto + mesotrione

Dual II + s-

Magnum 6 + 46 metolachlor 41 42 -1 93 88 5

115 + 91 96 58 38 100 99 1

23 + 182 98 91 7 100 100 0

47 + 364 99 97 2 100 100 0

94 + 728 100 100 0 100 100 0

187 + 1456 100 100 0 100 100 0 mesotrione

+ s- metolachlor

Lexar 97 + atrazine 91 43 48 97 91 6

194 97 64 33 99 99 0

388 100 92 8 100 100 0

775 100 98 2 100 100 0

1550 100 100 0 100 100 0

3100 100 100 0 100 100 0

Claims

1. A method of controlling a HPPD recalcitrant weed at a locus, said method comprising applying to the locus at least one pre-emergence application of a herbicidal composition comprising one or more HPPD-inhibiting herbicide(s).

2. A method of identifying and controlling HPPD recalcitrant weeds at a locus, said method comprising :-

(i) applying a normal post-emergence application of a herbicidal composition comprising a HPPD-inhibiting herbicide;

(ii) identifying HPPD recalcitrant weeds that survive at said locus; and

3. A method according to claim 1 or claim 2, wherein the HPPD-inhibiting herbicide is selected from the group consisting of benzofenap, bicyclopyrone, benzobicyclon, isoxachlotole, isoxaflutole, mesotrione, pyrazoxyfen, pyrasulfatole, pyrazolynate, sulcotrione, tembotrione, topramazone and tefuryltrione.

4. A method according to claim 3, wherein the HPPD-inhibiting herbicide is selected from the group consisting of bicyclopyrone, isoxaflutole, mesotrione, tembotrione and topramezone.

5. A method according to claim 4, wherein the HPPD-inhibiting herbicide is mesotrione.

6. A method according to any one of the previous claims, wherein the pre-emergence application of the HPPD inhibitor is from 20 to 500 g/ha.

7. A method according to any one of the previous claims, wherein the herbicidal composition applied pre-emergence further comprises one or more herbicides selected from the group consisting of atrazine, terbuthylazine, metribuzin, fomesafen, metolachlor, iS-metolachlor, acetochlor, flufenacet, mefenacet, dimethenamid, p- dimethenamid, pyroxasulfone and saflufenacil.

8. A method according to claim 7, wherein the herbicidal composition applied pre- emergence comprises mesotrione and atrazine and/or iS-metolachor.

9. A method according to any one of the previous claims, wherein the pre-emergence application is followed by the post-emergence application of one or more additional herbicidal composition(s).

10. A method according to any one of the previous claims, wherein the HPPD recalcitrant weed is selected from the group consisting of Amaranthus sp., Ambrosia sp., Conyza sp. Digitaria sp., Chenopodium sp. and Xanthium sp. , Solanum sp. , Datura sp., Abutilon sp., kochia, Russian thistle and Polygonum sp.

1 1. A method according to claim 10, wherein the HPPD recalcitrant weed is Amaranthus palmeri and/or Amaranthus rudis.