Weed control methods

This application is a 371 of International Application No. PCT/EP2014/055705, filed 21 Mar. 2014, which claims priority to 61/804,917, filed 25 Mar., 2013, the contents of which are incorporated herein by reference herein.

The present invention relates, inter alia, to improved weed control methods which employ p-hydroxyphenylpyruvate dioxygenase (HPPD) inhibiting herbicides. Plants that have been genetically engineered to be tolerant to HPPD-inhibiting herbicides are known, for example, from WO02/46387, WO2012/082542 and WO2012/082548. In these cases, the tolerance is achieved by over-expression of HPPD. Whilst the tolerance observed in respect of the engineered plants is often very good, there exists an opportunity to improve the tolerance further, in order to improve crop safety and enable the commercial use of a broader range of HPPD inhibitors in conjunction with the engineered plants across extended use patterns relative to the innate tolerance expressed by these engineered plants. It has surprisingly been found that the tolerance of such engineered plants can be improved (safened) significantly by applying to the engineered plants a water-soluble iron-containing compound.

Thus, according to the present invention there is provided a method of improving the tolerance of a plant, which has been genetically engineered to over-express a HPPD, to a HPPD inhibiting herbicide, said method comprising applying to said plant a water-soluble iron-containing compound.

Several examples of plants which are tolerant to HPPD-inhibiting herbicides, achieved via over-expression of HPPD, are known for example as disclosed in WO02/46387. Suitable HPPDs can thus be derived from bacteria, more particularly from Pseudomonas fluorescens or Shewanella colwelliana , or from a plant, more particularly, derived from a monocot plant or, yet more particularly, from a barley, maize, wheat, rice, Brachiaria, Chenchrus, Lolium, Festuca, Setaria, Eleusine, Sorghum or Avena species. The HPPD may also have been mutated to increase the tolerance of the enzyme to HPPD-inhibiting herbicides. The plants which are tolerant to HPPD-inhibiting herbicides via over-expression of HPPD will typically be crop plants, such as cereals, for example barley and wheat, cotton, oilseed rape, sunflower, maize, rice, soybeans, sugar beet and sugar cane. In a preferred aspect of the present invention, the plant is soybean. Several HPPD-tolerant soybean transgenic “events” are known, and include for example SYHT04R (WO2012/082542), SYHT0H2 (WO2012/082548) and FG72.

The crop plants may also have been rendered tolerant to other herbicides or classes of herbicides (e.g. ALS-, GS-, EPSPS-, PPO-Auxins, and ACCase-inhibitors) by conventional methods of breeding or by genetic engineering. Examples of crops that have been rendered tolerant to herbicides by genetic engineering methods include e.g. glyphosate, glufosinate, isoxaflutole, dicamba, imidazolinone and 2,4-D resistant soybean varieties commercially or soon to be commercially available under the trade names RoundupReady®, LibertyLink®, BalanceGT®, RoundupReady® Xtend, Cultivance® and Enlist® respectively.

Thus, in another aspect of the present invention there is provided a method of selectively controlling weeds at a locus (typically a field), the locus comprising weeds and crop plants, the crop plants having been genetically engineered to overexpress a HPPD which confers tolerance to a HPPD-inhibiting herbicide, the method comprising application to the locus of (i) a weed controlling amount of a HPPD-inhibiting herbicide and (ii) a water-soluble iron-containing compound. One surprising aspect of the present invention is that it appears that the safening observed upon application of the water-soluble iron-containing compound to the locus is specific for the plant which has been genetically engineered to overexpress a HPPD. No significant safening is observed in respect of the weed species being controlled.

It should be understood that, if desired, the water-soluble iron-containing compound can be applied to the locus before application of the HPPD-inhibiting herbicide is made. For example, the water-soluble iron-containing compound can be applied to the locus up to seven days before the HPPD-inhibiting herbicide is applied. It may be applied as a broadcast foliar application but is also possible to apply the iron-containing compound as a seed treatment/dressing to the crop plant.

In a preferred aspect of the invention, the water-soluble iron-containing compound is applied to the locus comprising the crop plant simultaneously with the HPPD-inhibiting herbicide. Typically, this will be achieved by tank-mixing a herbicidal composition comprising the HPPD-inhibiting herbicide with the water-soluble iron-containing compound. It is also possible that the HPPD-inhibiting herbicide be provided as a “pre-mix” herbicidal composition which also includes the iron-containing compound and which is simply diluted appropriately in the spray tank. Thus, according to the present invention there is also provided a herbicidal composition, including a pre-mix (concentrate) composition, comprising a HPPD-inhibiting herbicide and a water-soluble iron-containing compound. The herbicidal composition, diluted where necessary, is typically applied to the relevant locus by spraying, for example via a tractor mounted sprayer for large areas, but other methods such as dusting (for powders), drip or drench can also be used. The application may be made to the locus pre-emergence or post-emergence of the plant which has been genetically engineered to over-express a HPPD.

Suitable water-soluble iron-containing compounds include, for example, ionic iron salts and iron chelates, wherein the iron may have the oxidation number of +2 or +3. Suitable iron salts include, for example, iron (II) sulphate (ferrous sulphate) and ferric ammonium citrate. Iron chelates are particularly preferred in the context of the present invention, especially those formed with e.g ethylenediamine tetraacetic acid (EDTA): 2-[2-[[2-Hydroxy-1-(2-hydroxyphenyl)-2-oxoethyl]amino]ethylamino]-2-(2-hydroxyphenyl)acetic acid (EDDHA); ethylenediamine-di (o-hydroxy-o-methylphenylacetic) acid (EDDHMA); ethylenediamine-N,N′-bis(2-hydroxy-5-sulfonylphenyl) (EDDHSA); ethylenediamine-di-(2-hydroxy-4-carboxyphenylacetic) acid (EDDCHA) and diethylenetriaminepentacetic acid (DTPA). Iron chelates may be a mixture of isomers, for example EDDHA is a mixture of iron (III) complexes of the two diasteroisomers of ethylene-N,N′-di(2-hydro-phenyl acetate) and iron (III) complexes of the two diasteroisomers of ethylenediamine-N-(2-hydroxyphenylacetate)-N′-(4-hydroxyphenyl acetate). Depending on the pH of the composition, the iron chelate may be present in the form of a salt, for example an alkali metal salt such as a sodium salt. The preparation of such iron chelates and there use as micronutrients in agriculture is known, for example, from U.S. Pat. No. 2,921,847. Several commercial forms of the above-mentioned iron chelates are known in the art. For example, an iron DTPA mixture is available as Sequestrene® 330. In a preferred aspect of the invention, the water soluble iron-containing compound is selected from the group consisting of iron DTPA (Sequestrene® 330), EDDHA-FeNa (Sequestrene® 138) and ferrous sulfate. In the context of the present invention, use of EDDHA-FeNa (a ferric sodium complex of EDDHA), commercially available as Sequestrene® 138Fe, which contains 6% iron in the form of EDDHA (ethylenediamine-N—N′-bis (2 hydroxyphenylacetic acid) chelated product), is particularly preferred. EDDHA chelated iron is also commercially available as Soygreen®. The iron can typically be applied to the locus at an equivalent rate of from 1 g to 1000 g/ha, more typically from 6 g to 240 g/ha. Thus, in the context of iron chelate such as Sequestrene® 138Fe, the actual product is typically applied at a rate of from 100 g to 4000 g/ha, more preferably from 200 to 2000 g/ha.

Herbicides that act by inhibiting HPPD are well known in the art. Inhibition of HPPD blocks the biosynthesis of plastoquinone (PQ) from tyrosine. PQ is an essential cofactor in the biosynthesis of carotenoid pigments which are essential for photoprotection of the photosynthetic centres. HPPD-inhibiting herbicides are phloem-mobile bleachers which cause the light-exposed new meristems and leaves to emerge white where, in the absence of carotenoids, chlorophyll is photo-destroyed and becomes itself an agent of photo-destruction via the photo-generation of singlet oxygen.

The safening effect conferred by the iron-containing compound has been observed in respect of a broad range of chemically diverse HPPD-inhibiting herbicides, indicating that the iron-containing compounds have broad utility with regard to safening HPPD-inhibiting herbicides in plants. HPPD-inhibiting herbicides include, for example, benzobicyclon (CAS RN 156963-66-5), mesotrione (CAS RN 104206-82-8), sulcotrione (CAS RN 99105-77-8), tefuryltrione (CAS RN 473278-76-1), tembotrione (CAS RN 335104-84-2), fenquinotrione (1342891-70-6), bicyclopyrone (CAS RN 352010-68-5), ketospiradox (CAS RN 192708-91-1) or its free acid (CAS RN 187270-87-7), benzofenap (CAS RN 82692-44-2), pyrasulfotole (CAS RN 365400-11-9), pyrazolynate (CAS RN 58011-68-0), pyrazoxyfen (CAS RN 71561-11-0), topramezone (CAS RN 210631-68-8), isoxachlortole (CAS RN 141112-06-3) and isoxaflutole (CAS RN 141112-29-0). More recent examples of HPPD-inhibiting herbicides which can also be used in the context of the present invention are reported in WO2009/016841, WO2009/115788, WO2010/089993, WO2010/116122, WO2011/031658, WO2011/035874, WO2012/002096, WO2012/033548, WO2012/028579 and WO2012136703.

Preferably, the HPPD-inhibiting herbicide is selected from the group consisting of mesotrione, sulcotrione, tembotrione, bicyclopyrone, pyrasulfotole, topramezone and isoxaflutole, more preferably selected from the group consisting of mesotrione, bicyclopyrone, tembotrione and isoxaflutole.

The rate of application of the HPPD-inhibiting herbicide may vary within wide limits and depend on the nature of the soil, the method of application (pre- or post-emergence; seed dressing; application to the seed furrow; no tillage application etc.), the crop plant, the weed(s) to be controlled, the prevailing climatic conditions, and other factors governed by the method of application, the time of application and the target crop. The herbicide is typically applied at a rate of from 10 to 2000 g active ingredient/ha, especially from 50 to 1000 g active ingredient/ha and more typically from 50 to 500 g active ingredient/ha.

In a preferred aspect of the present invention, the herbicidal composition of the present invention referred to above comprises a HPPD-inhibiting herbicide as defined above. In a more preferred aspect, the HPPD-inhibitor is selected from the group consisting of mesotrione, sulcotrione, tembotrione, bicyclopyrone, pyrasulfotole, topramezone and isoxaflutole, more preferably selected from the group consisting of mesotrione, bicyclopyrone, tembotrione and isoxaflutole. The actual concentration of the HPPD-inhibitor within the herbicide composition will vary, for example depending on the exact nature of the HPPD-inhibitor, and the exact composition type. In the context of a pre-mix (concentrate) composition, the HPPD-inhibitor will typically be present from 0.5% w/w to 50% w/w, more typically from 5% to 50% w/w and even more typically from 10 to 40% w/w.

In another preferred aspect of the present invention, the herbicidal composition of the present invention referred to above comprises a water-soluble iron-containing compound as defined above. In a more preferred embodiment, the water-soluble iron-containing compound in the herbicidal composition is selected from the group consisting of iron DTPA (Sequestrene® 330), EDDHA-FeNa (Sequestrene® 138) and ferrous sulfate. The actual concentration of the water-soluble iron-containing compound within the herbicide composition will vary, for example depending on the exact nature of the water-soluble iron-containing compound, and the exact composition type. In the context of a pre-mix (concentrate) composition, the water-soluble iron-containing compound will typically be present at an amount which provides from 1% to 10% w/w iron in the form of the chelate or the ionic salt.

The herbicidal composition of the present invention may also comprise further conventional agrochemical adjuvants such as wetters, dispersants, surface-active agents and other activity enhancers. The herbicidal composition may further comprise further herbicidal components that are appropriate for the crop to which the herbicidal composition is applied. Thus, with regard to soybean the herbicidal composition may further comprise, for example, glyphosate, glufosinate and fomesafen or agrochemically acceptable salts thereof. In some crop applications, the addition of a herbicide safener may also be beneficial.

The pre-mix (concentrate) herbicidal composition of the present invention may be provided in a wide variety of formulation types, for example a liquid formulation (e.g an aqueous formulation type such as a suspension concentrate (SC)), or in a solid formulation such as a wettable powder (WP) or granule (WG). If a granule is employed, this can be directly applied to the locus or diluted in a spray tank.