Australia
July 31, 2013
Growers are urged to monitor fleabane in-crop as research has identified the best time to control the weed is at the small seedling stage.
Fleabane is a major difficult-to-control weed infesting zero-tilled cropping systems from southern Queensland to the centre of the West Australian cropping belt.
The research, which was funded by the Grains Research and Development Corporation (GRDC), builds on work carried out in the northern grains region since 2006.
Flaxleaf fleabane in wheat stubble immediately after harvest in southern Western Australia.
Project leader, Dr Steve Walker, University of Queensland’s Queensland Alliance for Agriculture and Food Innovation (QAAFI) associate professor says fleabane is easily controlled by a range of post emergent herbicides when smaller than a five centimetre rosette.
“The real problem with fleabane is growers try to control plants that have bolted, usually after crop harvest,” Dr Walker says.
“This means the use of two consecutive herbicide applications, usually known as the ‘double-knock’, to control big fleabane.”
He says using the double knock is expensive and control in summer is complicated by stress from high temperatures and low available soil moisture. Also there is often a short time when spraying conditions suitable and a high risk of herbicide drift.
With this in mind controlling fleabane in winter crops is a golden opportunity as it germinates in late autumn and early spring, when the winter crop has established, he says.
Weed specialist Andrew Storrie, Australian Glyphosate Sustainability Working Group (AGSWG) executive officer says this presents growers with an opportunity to control fleabane with little additional cost to their weed management programs.
“Two options available to growers are use an early post emergent broadleaf herbicide that has some residual activity to control later germinations or use a late post emergent herbicide such as 2,4-D in wheat and barley up until flag leaf emergence to control seedlings,” Mr Storrie says.
Unfortunately there are only a few herbicides currently registered for control of fleabane in winter crops, however a number of companies are currently registering herbicides and some new products will be available within the next 12 months, he says.
Dr Walker said recent research looking at a range of Group I herbicides found the level of control by majority of herbicide treatments was reduced by an average of 30 per cent when five to 15cm diameter rosettes were sprayed compared with rosettes less than five cm diameter.
“In field trials a delay in herbicide treatment of two weeks reduced control consistently across herbicide treatments, due to weed age and size. Using higher crop densities also improved fleabane control by 90pc.”
He says rainfall greater than 10 millimetres in early spring is ideal for the germination of fleabane so growers need to check crops now and following significant early spring rain for fleabane seedlings and control them in-crop.
Early control keeps weed control costs down, makes for a cleaner harvest and reduces the need for post-harvest spraying under difficult conditions, he says.
GRDC Project Code: Glyphosate Sustainability Working Group ARN00001; Northern project UQ00055
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