Resistance needs an aggressive campaign
GroundCover™ Issue: 112 | Author: Sarah Clarry
When the Sustainable Agriculture Fund bought the 10,000-hectare North Star Aggregation back in 2009, manager Tom Murphy quickly learnt they had also taken on a substantial herbicide-resistance problem.
In addition to glyphosate-resistant barnyard grass, Group A-resistant black oats (wild oats) and Group B-resistant phalaris, there were herbicide-tolerant populations of feathertop Rhodes grass and fleabane.
“We first sprayed a fallow with a reasonably robust rate and found the barnyard grass remained in the paddock, so we knew straight away we had a problem,” Mr Murphy says.
“The same year we put a Group B herbicide across a winter crop and the phalaris did nothing, despite there being 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.”
The dryland property features about 8500 arable hectares under rotation, with 75 per cent sown to winter crops – wheat, barley, canola and chickpeas – and the remainder to sorghum and cotton in summer. It has productive, grey, self-mulching soils, which can store 150 to 180 millimetres of soil moisture from an average 620mm of winter-dominant rainfall.
Despite the country’s productive potential, the added work and chemicals required to control problem weeds was adding $40/ha in costs.
Mr Murphy devised an aggressive integrated weed management (IWM) plan incorporating crop and chemical rotation, precise herbicide rates and double knocks, as well as non-chemical methods such as strategic tillage and windrow burning.
“You need to think outside the square. If someone told me a couple of years ago that windrow burning was the way to go around here I would have laughed at them,” he says.
However, in 2014 Mr Murphy trialled windrow burning for the first time: he windrowed about 50ha, burned half and left half untreated. A later inspection of the test areas with agronomist Rob Long found there were negligible grass weed species in the crops. Mr Murphy hopes this means their range of other controls is working well, as the test paddock had a history of resistant black oats. From the $40/ha cost of tackling the herbicide resistance problem in 2009, Mr Murphy estimates that the range of IWM approaches he has employed has meant additional costs are now down to about $10/ha or even lower.
“Longer term, and once we get on top of it completely, I believe we can get that back to the original baseline cost per hectare,” he says.
As a result of his success in tackling herbicide-resistant weeds, Mr Murphy has been chosen as a WeedSmart Champion.
“We got involved in the WeedSmart program because we’ve been through some tough lessons,” he says. “If I can share those lessons with other growers so they can get on top of their weed problems sooner, that’s a win for industry. WeedSmart also allows me to meet people who have tackled these problems differently. If I can find a way of doing something that’s more cost-effective, that’s great for the business I run.”
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