THE launch of a new pre-emergent herbicide this season is giving pulse growers more mix-and-rotate options to tackle resistance in key grass weeds.
According to Adama market development manager South Australia Ashley Pilkington, the commercial release of Ultro (carbetamide) puts a completely different mode of action into the weed control program for pulses.
Carbetamide, a Group 23 herbicide, has been developed and trialled successfully for several years in southern farming systems, Mr Pilkington said.
It gives pulse growers another rotational tool and will easily slot into their weed control program.
Ultro offers increased flexibility in application timing, particularly in years with a dry start.
Carbetamide provides effective control of three major grass weeds - annual ryegrass, barley grass and brome grass - including populations resistant to other herbicide groups.
Mixing and rotating herbicide modes of action (MoA)is central to sustainable herbicide use in cropping systems, Mr Pilkington said.
Implementing the WeedSmart Big 6 throughout the crop rotation is the best way to minimise the impact of herbicide resistance in weeds.
Having more modes of action available in the pulse phase means growers can follow a more diverse herbicide program.
Adama has reintroduced carbetamide to the Australian market with a new registration for pre-emergent use in broad beans, chickpeas, faba beans, field peas, lentils, lupins and vetch and in winter fallow.
Carbetamide was formerly registered in Australia for selective weed control in lucerne, clovers and medics, as well as a long history of blackgrass control in the United Kingdom.
The pre-emergent use pattern in winter pulses introduces a new mode of action to winter broadacre cropping rotations.
Mr Pilkington said the herbicide could be applied up to seven days before being incorporated by sowing (IBS) and requires rainfall within two or three weeks to complete incorporation and activation of the product and initiate weed seed germination.
Carbetamide is taken up primarily in the plant roots and most of the grass weed control comes through failed emergence of weed seedlings, he said.
Plants that do emerge will suffer stunted growth and severe root pruning and these plants rarely produce seed panicles and usually die within a few weeks of germinating.
Carbetamide provides reliable pre-emergent control of the target grass weeds for at least 10 to 12 weeks, giving the crop a competitive edge.
All pre-emergent herbicides perform best when crops are sown in the most competitive configuration possible.
With that in mind, it is recommended by WeedSmart to scout for, and eliminate, survivors of any herbicide treatment.
An in-crop application of clethodim, or clethodim and butroxydim, provides effective control of survivors or very late weed germinations.
Carbetamide adds to the suite of pre-emergent options for pulse growers.
Currently, trifluralin and propyzamide, both Group 3 (D), simazine and pyroxasulfone are the only options for pre-emergent control of grass weeds in pulses.
Trials have demonstrated that carbetamide is equal to or slightly better than propyzamide, the current industry standard, which gives growers an immediate alternative to rotate chemistry in their pulse program.
Carbetamide is effective against ryegrass, barley grass and brome grass with resistance to Group 15 herbicide MoA, providing an opportunity to drive down numbers of resistant populations in the pulse phase, Mr Pilkington said.
Since carbetamide is active only on grasses, it is useful to tank mix it with a broadleaf herbicide such as simazine and with paraquat, a knockdown herbicide, however its important to note that carbetamide is not compatible with K-salt glyphosate formulations.
Adding carbetamide to paraquat in the second application in a double-knock tactic will ensure crops can get off to a clean start.
To make the new mode of action sustainable, growers should rotate and restrict use in the same paddock to no more than one application in four years.
Carbetamide is subject to microbial degradation in the soil.
More frequent use of the product promotes the buildup of the specific microbial species that degrade the herbicide molecule, reducing the longevity of future weed control with this MoA.
Although microbial degradation also affects propyzamide, the suite of microbes are different, so these two herbicides can be safely rotated in the pulse phase.
Be sure to check the re-cropping interval and rainfall requirements for safe planting of the following crop, Mr Pilkington said.
For example, there is a nine month and 250 millimetre rainfall requirement before planting barley, oats, wheat, soybeans and sunflowers.
If in doubt, canola is a safe option, requiring only a six month re-cropping interval which offers a double-break opportunity to put heavy pressure on the grass weed seed bank.
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