Technical Field

The invention relates to novel synergistic herbicidal combinations containing carbetamide ([(2S)-l-(ethylamino)-l-oxopropan-2-yl] N-phenylcarbamate).

Background Art

Carbetamide is generally used as a selective herbicide to control a range of grass weeds and some broad leaf weeds. Grass weeds which carbetamide may control include Barley Grasses (Hordeum spp.), Cocksfoot (Doctylis glomerato ), Lesser Canary Grass (Phalaris minor), Madrid Brome (Bromus madritensis), Perennial Ryegrass (Lolium perenne), Prairie Grass ( Bromus unioloides), Rats Tail Fescue (Vulpia myuros), Shivery Grass (Briza minor), Silvery Hairgrass ( Aira caryophyliea), Soft Brome ( Bromus mollis), Squirrel-tail Fescue (Vulpio bromoides), Sterile Brome (Bromus sterilis), Wimmera Ryegrass (Annual Ryegrass) (Lolium rigidum), Winter Grass (Poa annua), Yakka Grass (Sporobolus caroli) and Yorkshire Fog (Holcus lanatus). Broad leaf weeds which carbetamide may control include Chickweed (Stellaria media), Climbing Buckwheat ( Fallopia convolvulus), Mouse-ear Chickweed (Cerastium glomeratum), Shepherds Purse (Capsella bursa-pastoris), Sorrel (Rumex acetosella) and Wireweed (Hogweed) (Polygonum aviculare).

Carbetamide is generally used to control such weeds in crops and pastures after the crop or pasture has emerged. It has been used in situations such as pasture/grain legumes and canola/oilseed rape (OSR), as well as under tree and vine crops in regions such as the European Union. Post-emergent application of carbetamide can carry with it a risk of phytotoxicity (undesirable crop or pasture damage) in legumes and canola/OSR. This risk has been accepted as a consequence of carbetamide use, in view of the effectiveness of carbetamide in controlling such weeds.

Since the introduction of carbetamide globally, a wide range of alternative herbicides have been introduced from a range of other modes of action. One of the more popular modes of action are the inhibitors of acetyl co-enzyme A carboxylase (ACC'ase inhibitors), which are broadly referred to as Group A herbicides in Australia. Examples of ACC'ase inhibitor herbicides that were introduced into Australia are set out in the table below:

The ACC'ase inhibitors became popular due to their high level of selectivity in some crops for controlling problem grass weeds, low use rates and ability to be applied after both crop/pasture and target grass weeds had emerged.

While highly effective, resistance to ACC'ase inhibitor herbicides has become a major problem globally in a wide range of grass weed species. In Australia, there are at least nine species of grass weeds that have be reported as resistant to one or more ACC'ase inhibitor herbicides. Cross resistance within the ACC'ase inhibitor mode of action group is also common in species such as Annual Ryegrass (Lolium rigidum) and the use of alternative mode of action herbicides is often required to manage resistant weed populations.

Farming methods have also diversified over the years so that there are alternatives to the traditional tillage techniques, in which soil is prepared for crops by mechanical agitation (usually ploughing). One such option is no-till farming, in which the remnants of the previous crop are allowed to remain in the soil to act as mulch. To sow the next crop, the soil is disturbed as little as possible by using special equipment with discs or tine coulters to form shallow slots for the seed. Another option is low-till or minimum tillage farming, which also avoids ploughing but which may use a limited amount of shallow disc harrowing. For convenience, no-till and low-till farming are referred to generally below as minimum tillage farming.

At the same time, crop development has resulted in some herbicide-tolerant crops, for example, under the Clearfield (trademark) management system, or crops bred by traditional plant breeding methods, or through genetic engineering. Such crops can be grown in areas where major weed problems occur. Canola is one such crop.

Herbicide-tolerant crops may be tolerant to glyphosate ('Roundup Ready') and /or triazine and/or glufosinate-ammonium, for example. Herbicide-tolerant crops can be advantageous in no-till or low-till farming, as well as in other farming methods. However, some herbicide-tolerant weeds have also developed, causing problems in weed control.

The present invention provides a synergistic combination containing carbetamide which can be particularly effective in the control of Annual Ryegrass (Lolium rigidum). In some embodiments the combination of the invention is particularly suitable for minimum tillage farming and/or for weed control in herbicide-tolerant crops.

It is expected that use of the combination of the invention and of the method of the invention will also be effective on hybrids of Lolium rigidum, for example with L multiflorum, L. perenne, L. orundinoceum and some species of Festuco. The terms 'annual ryegrass' and 'Lolium rigidum' as used herein in the specification (excluding the examples) and claims include hybrids developed therefrom.

Summary of the Invention

Accordingly, the invention provides a synergistic herbicidal combination for controlling Annual Ryegrass (Lolium rigidum) in a crop, wherein the combination includes an effective quantity of carbetamide and an effective quantity of clethodim or butroxydim. The invention also provides a method of controlling Annual Ryegrass (Lolium rigidum), the method including the step of applying to a crop post-emergent, a synergistic herbicidal combination for controlling Annual Ryegrass (Lolium rigidum), wherein the combination includes an effective quantity of carbetamide and an effective quantity of clethodim or butroxydim

It has been found that the use of the invention can provide improved control of Lolium rigidum, including in herbicide-tolerant crops. Lolium rigidum has become multiple- herbicide-resistant, being resistant to glyphosate, triazines, imidazolines and other herbicides for which herbicide-tolerant traits have been incorporated into commercial cultivars.

Trial results have shown the safety and effectiveness of carbetamide in RR (Roundup Ready) canola, TT (triazine-tolerant) canola and "stacked trait" varieties such as RT canola (tolerant to both glyphosate and triazines).

The synergistic use of carbetamide in herbicide-tolerant crops can extend the useful life of the herbicide tolerance trait technology. It allows farmers to continue to grow such herbicide-tolerant crops while being able to control resistant weeds, such as Lolium rigidum, while providing residual weed control for any subsequent target weed germinations that occur post-application.

Preferably, the synergistic combination contains carbetamide in an amount enabling application at the rate of about 800 to 1800 g ai/hectare in a tank mix with clethodim at about 50-150 g ai/hectare. More particularly, the combination is either a tank mix or co-formulation enabling application of carbetamide at a rate of 870 to 1740 g ai/hectare and clethodim at about 60-120 g ai/hectare. The most preferred combination is a mixture enabling application of carbetamide at a rate of about 1740 g ai/hectare and clethodim at about 60 g ai/hectare, or carbetamide at a rate of about 870 g ai/hectare and clethodim at about 120 g ai/hectare. In another embodiment, the combination is a mixture enabling application of carbetamide at a rate of about 1450 to 2900 g ai/hectare and butroxydim at about 20 to 80 g ai/hectare.

Field trials have shown that when carbetamide is applied as a tank mix with clethodim or butroxydim, the level of control of Lolium rigidum is significantly improved, when compared to standalone applications of each active ingredient. This in turn can result in improved crop yield due to improved weed control.

The combination may include any other desirable ingredient, including adjuvants.

The crop includes canola, examples being Brassica nopus cv. 44Y84 and Brassica napus cv. Crusher , as well as grain legumes and other crops too where carbetamide, clethodim and butroxydim are safe for use on the crop.

By way of example, clethodim is regarded as safe for use on chickpeas, faba beans, field peas, lentils, lupins, cotton, peanuts, mung beans, soybeans, beetroot, cabbage, celery, lettuce, potatoes, onions, forestry, non-bearing fruit trees and ornamentals. By way of further example, butroxydim is regarded as safe for use on chickpeas, faba beans, field peas, lentils, linseed, lucerne, lupins, vetches (Vicia spp.), white and subterranean clover, medic pastures, mung beans, navy beans, peanuts, soybeans, cotton and sunflowers.

In order that the invention in its various aspects may be more readily understood and put into practice, one or more preferred embodiments thereof will now be described.

Detailed Description of Preferred Embodiments Example 1

In this non-limiting example, carbetamide compositions were applied post-emergently to test control of annual ryegrass in triazine-tolerant canola (Brassica napus cv. Crusher). The treatments were compared with each other, with clethodim, registered for use in herbicide-tolerant crops, and with tank mixes of carbetamide and clethodim.

The treatments are set out in table 1: Table 1: Treatment List

The treatments were applied to the crop at 4-5 leaf stage. Assessments of crop damage, crop vigour and weed control were made at 7, 14, 29, 44 and 56 days after application (DAA). Weed density was counted at 56 and 121 DAA.

No crop phytotoxicity was observed for standalone clethodim treatments. There was some low crop damage initially from the carbetamide standalone treatments, observed at 7 DAA and peaking at 14 DAA, but these were well within the range of damage seen in commercial canola crops. The tank mixes including carbetamide at 1740 g ai/ha resulted in some delayed phytotoxicity, peaking at 29 DAA. On the whole, phytotoxicity disappeared and was not present in any treatment by the last assessment at 56 DAA.

There was some reduction in crop vigour - minimal for clethodim and more significant for carbetamide standalone and carbetamide tank mixes. However, treatments with the greatest phytotoxicity and vigour reduction were also the treatments resulting in the highest yield.

Control of annual ryegrass was good for clethodim at the higher rate of 120 g ai/ha and increased yield significantly. Carbetamide standalone compared favourably with clethodim with commensurate yields, especially at the higher rate of 1740 g ai/ha. Some evidence suggested that ryegrass survivors were much smaller compared to clethodim use and there were significantly less ryegrass panicles when applied at the higher rate.

Table 2 shows percent ryegrass control for the treatments:

Table 2: Annual Ryegrass Control Percent

Tank mixes including carbetamide and clethodim were among the best performer treatments in this trial. Increasing the rate of either clethodim or carbetamide in a tank mix improved ryegrass efficacy compared to clethodim 120 g ai/ha along with a significant yield improvement. The highest yields were consistently achieved by carbetamide at 1740 g ai/ha or tank mixes of carbetamide at 870 g ai/ha with clethodim at 120 g ai/ha.

Colby test values for clethodim at 60 g ai/ha and carbetamide at 1740 g ai/ha showed a Colby ratio of 1.01 to 1.03. Colby test values for clethodim at 60 g ai/ha and carbetamide at 870 g ai/ha showed a Colby ratio of 1.05.

Colby test values for clethodim at 120 g ai/ha and carbetamide at 1740 g ai/ha showed a Colby ratio of 1.03 to 1.06. Colby test values for clethodim at 120 g ai/ha and carbetamide at 870 g ai/ha showed a Colby ratio of 1.20.

Example 2 In this non-limiting example, carbetamide compositions were applied post-emergently to test control of annual ryegrass in triazine-tolerant canola (Brassica napus cv. Crusher). The trial site had a known history of ACC'ase inhibitor herbicide use. The treatments were compared with each other, with butroxydim and with tank mixes of carbetamide and butroxydim. The treatments are set out in Table 3: Table 3: Treatment List

In this trial, carbetamide significantly reduced annual ryegrass counts compared to the untreated control, with a significant increase in efficacy in response to the higher application rate.

The standalone application of butroxydim was effective, but performance was enhanced when combined in a tank mix with carbetamide, especially at carbetamide application of 1740 g ai/ha.

Table 4 shows percent ryegrass control for the treatments:

Table 4: Annual Ryegrass Control Percent

Yield response reflected weed control in response to treatment applications, with the untreated control having significantly lower yield than all treatment applications.

Some crop phytotoxicity was observe in response to the applications but was considered minor (<10%) and was not observed at later assessment timings.

Reductions in crop vigour were not significantly different to the untreated control.

Colby test values for butroxydim at 20 g ai/ha and carbetamide at 1740 g ai/ha showed a Colby ratio of 1.10.

The foregoing embodiments are intended to be illustrative of the invention, without limiting the scope thereof. The invention is capable of being practised with various modifications and additions as will readily occur to those skilled in the art.

Accordingly, it is to be understood that the scope of the invention is not to be limited to the exact construction and operation described and illustrated.

Reference to prior art disclosures in this specification is not an admission that the disclosures constitute common general knowledge in Australia or elsewhere. Industrial Applicability

There is an urgent need for herbicides effective against herbicide-resistant weeds, especially Annual Ryegrass (Lolium rigidum) as defined herein. The synergistic combination and method of the invention can enable effective control of Annual Ryegrass ( Lolium rigidum) in a range of crops.