WESTERN Australian growers are being urged to monitor paddocks for fleabane, which has become more prevalent throughout the grainbelt following significant spring and summer rainfall.
While hard to kill when mature, control can be achieved with a ‘double knock’ and the weed will otherwise use vital soil moisture and nitrogen.
Grains Research and Development Corporation (GRDC) supported surveys have found that, while originally restricted to WA’s southern cropping areas, fleabane has gradually spread throughout the grainbelt. Its numbers are higher than average this summer.
Department of Agriculture and Food Western Australia (DAFWA) researcher Sally Peltzer said the most common of three fleabane species present in WA was flaxleaf fleabane (Conyza bonariensis) and fleabane germination was favoured by conditions associated with minimum tillage cropping systems and good spring rainfall.
“Fleabane normally germinates in late August or early September, and this summer it has kept growing strongly due to continuing rainfall,” she said.
“The late harvest also allowed fleabane to grow massively within crops.”
Dr Peltzer said DAFWA research supported by the GRDC had shown that mature fleabane, with its large tap roots and hairy leaves, was difficult and expensive to kill, especially in mid to late summer.
“However, trials in 2009 indicated that the best control of large fleabane in stubble is achieved using a ‘double knock’ approach with a range of primary herbicides, followed by paraquat seven to 10 days later,” she said.
“It is important to control fleabane as large infestations of the weed significantly reduce soil moisture and nitrogen for the following crop, resulting in yield losses, and the weed may also get caught up in machinery at seeding time.”
Dr Peltzer said growers would need to monitor for fleabane in August and September this year, when it was possible high numbers of the weed would germinate.
“Fleabane can most effectively be controlled when plants are emerging, mainly in early spring while they are still small,” she said.
“Fleabane can be more difficult to control in late spring but this can be achieved if its rosettes are less than 5cm.”
Dr Peltzer said fleabane could spread rapidly due to its abundant production of wind-dispersed seeds, with mature flaxleaf fleabane plants producing, on average, 100,000 seeds each.
“Because the seeds are fine, they can also spread easily in grain and equipment,” she said.
More information about fleabane identification, characteristics and management is available in the DAFWA Farmnote Fleabane in Western Australia, available by searching ‘fleabane’ on the DAFWA website.
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