Aggressive and innovative approach tackles resistant weeds
An aggressive and innovative approach to weed control is helping northern NSW farmer Tom Murphy win the war on herbicide resistant weeds.
Mr Murphy manages the 10,000 hectare North Star Aggregation for the Sustainable Agriculture Fund, which purchased the property four years ago.
Unknowingly, they inherited populations of glyphosate resistant barnyard grass, Group A-resistant black oats (wild oats) and Group B-resistant phalaris, as well as ‘herbicide tolerant’ populations of fleabane and feathertop Rhodes grass.
“A lot of this was discovered purely when we went and did the first spray of a fallow with a reasonably robust rate and found that the barnyard grass would still remain in the paddock – we knew straight away we had a problem,” Mr Murphy said.
“The same year we put a Group B herbicide across a winter crop and the phalaris just did nothing, and that was with little or no Group B history on the farm as well.
“So we sent that seed away for testing and came up with a plan to deal with it.”
As a result of his subsequent success in tackling resistant weeds, Mr Murphy has been chosen as a WeedSmart Champion. WeedSmart is an industry-led initiative managed by the Australian Herbicide Resistance Initiative (AHRI) aimed at enhancing on-farm practices and promoting the long term sustainability of herbicide use in Australian agriculture.
“We got involved in the Weedsmart program purely because we’ve been through the tough lessons,” he said. “We encountered the problem and had to be very quick on our feet to try and get around it.
“If I can share those lessons with other farmers so they can get on top of their problem weeds sooner then that’s a win for industry.
“WeedSmart also allows me to meet people who have tackled these problems differently. If I can find a different way of doing something that’s more cost effective then that’s great for the business that I run.”
The dryland North Star Aggregation property features about 8500 arable hectares under rotation, with 75 per cent each year sown to winter crops of wheat, barley, canola and chickpeas, and the remainder to sorghum and cotton in summer.
The Brigalow-Belah country features highly productive, grey self-mulching soils, which can store 150-180mm of soil moisture, with most of the 620mm average annual rainfall arriving in winter.
Despite the productive potential of the country, the added work and chemical required to control the range of problem weeds was loading $40/ha in costs to the bottom line.
Mr Murphy devised an aggressive integrated weed management plan, featuring crop and chemical rotation, very precise herbicide applications and double-knock treatments, as well as non-chemical methods such as strategic tillage and windrow burning.
“One thing we’ve definitely done is be really aggressive with these weeds,” Mr Murphy said. “It does cost more and while you might not win all of your battles, with that aggressive approach you will win the war.
“The other feature of the plan has been a willingness to think outside the square. If someone told me that windrow burning was the way to go around here I would have laughed at them a couple of years ago.
“But we’re giving it a crack and if it doesn’t work then at least we know. And if it does work and it’s a winner for us then we’re ahead.”
Mr Murphy’s strategy features a strict, managed approach to chemical use.
“We’re managing our use of herbicides through a couple of options. One is the double knock approach, which we’re finding is working very well; the other is mixing up the chemistry – we try not to be too reliant on one active group too much.
“It’s also very important to get your spray rig set up right and to use the correct rates.
“We’ve taken a very aggressive approach to our resistant weeds so we use nothing but the top rates. We found out the hard way that if you try and reduce your rates with any resistant weeds you’ll run into trouble again.”
The ability to grow summer crops as part of the rotation has also delivered benefits to herbicide rotations as well as non-chemical treatments.
“For example, for cotton you have a long fallow leading into it; you’ve got a crop period where you can use different chemistry; and you’ve got a long fallow after it, as well as a mandatory cultivation,” he said.
“Having sorghum in there as well also changes the fallow period and introduces new residual chemicals, so the summer rotation is really key to what we’re doing.”
The non-chemical control method of windrow burning is also being trialled, and although early signs are it may not be suited to the environment, Mr Murphy is maintaining an open mind.
“At this stage I don’t see that it’s a great fit for our circumstances because a lot of our weeds have lost their seed come harvest time or they’re not a problem in crop, but we are looking at it and we are trialling it.
“It’s really important that when you’ve got a herbicide resistance problem that you don’t stick your head in the sand – you need to be proactive about it.”