Western Australian research has revealed that cost-effective options are available for the herbicide management of the foul-smelling weed matricaria in pasture and fallow situations.
Trials have demonstrated that herbicide treatments are available to control the small matricaria plants that usually germinate in autumn, and there are effective options to achieve seed set control later in the season during the weed's early flowering stages.
Research officer Alex Douglas, from the Department of Primary Industries and Regional Development (DPIRD), is studying matricaria as a part of a five-year 'locally important' weeds project that has Grains Research and Development Corporation (GRDC) investment.
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She said that, since appearing in Western Australia's eastern grainbelt in the late 1960s, matricaria - including the species Oncosiphon piluliferum and Oncosiphon suffruticosum - had spread widely and was now a serious weed.
"It is also spreading into neighbouring regions, including WA's Northern Agricultural Region, where the farming systems and seasonal conditions are similar to that of the eastern grainbelt," Ms Douglas said.
"Most matricaria seed germinates in autumn, although a few plants may germinate in late winter or early spring and continue to grow over summer."
Ms Douglas said research into the species Oncosiphon piluliferum had shown that treatments were most effective when applied to small plants at the six-to-eight leaf stage up to the eight-centimetre rosette stage.
"WA field trials have shown that, in sub-clover pastures, bromoxynil and Jaguar(r) (bromoxynil and diflufenican) are both viable options when applied to small rosettes of matricaria," she said.
"Trials have also shown that, in fallow situations, a three-way mix of glyphosate applied with 2,4-D and carfentrazone, as well as paraquat mixed with carfentrazone, provided the greatest level of control.
"Growers who are unsure whether matricaria has spread onto their farm can help identify the weed by rubbing the small plants between their fingers, as matricaria has a rank, herby smell."
WA field trials have shown that, in sub-clover pastures, bromoxynil and Jaguar(r) (bromoxynil and diflufenican) are both viable options when applied to small rosettes of matricaria.
Ms Douglas said research had shown growers were also able to reduce the viable seed set of larger plants - by up to 99 per cent - in fallow situations later in the season by applying glyphosate during the flowering stages (at bud formation with 10-20 per cent yellow buttons).
"This is positive news for growers who may not have been able to control matricaria at an earlier stage," she said.
"In the trials, glyphosate was generally more effective than paraquat in reducing the viable seed set of flowering matricaria - glyphosate provided 99 per cent reduction in seed set compared with paraquat that provided a 40 per cent reduction in seed set."
Other research results showed matricaria is unlikely to become a significant summer weed, given it only germinated in trials at temperatures between 10C and 25C.
"We also found matricaria seed survives well when buried at two to 10 centimetres beneath the soil surface and that, under laboratory conditions, darkness inhibits its germination," Ms Douglas said.
"Matricaria seed is likely to survive in the soil for several years if it is buried, and cultivation treatments like soil inversion could bury seed to depths where it remains viable and potentially germinate years later if brought to the soil surface."
More information about matricaria is contained in the GRDC Grains Research Update paper 'Biology and management of matricaria (Oncosiphon piluliferum) available at http://bit.ly/2TOHT05.