STORED moisture in summer fallow is critical to the success of a winter crop, so weed control especially of flaxleaf fleabane at its earliest stage of growth is essential and this summer has seen a rise in the weed in different areas of the state.
However, prevention is always better than cure according to Narromine agronomist, Ryan Pratten of Muldoon Pratten Ag Consultants.
“Fleabane is on the radar this summer and some farmers are on their third fallow spray.
“We can prevent the weed by getting good winter crop establishment and use the correct herbicide products pre and post emergence,” he said.
Mr Pratten said no-til farmers learnt from the heavy infestations of the 2011/12 summer that the use of certain residual products applied in winter were successfully reducing spring germinations of fleabane” he said.
“We learned back then that products like Lontrel or Balance were doing a lot of the good work on fleabane prevention.
“Whenever we use them in winter we get significantly less fleabane germination in spring.”
Mr Pratten said the other common denominator with fleabane was crop competition.
“Anyone who had poor winter crop establishment would have a lot more fleabane germinate in spring,” he said.
“It’s the same pattern you always see, if you have a good thick crop you’ll generally not see much fleabane in spring.
"When it germinates in autumn we control it easily with glyphosate when it is small, but when it germinates in spring it is much older when we can target it after harvest and it often has been damaged by harvest.”
Therefore, the “double knock” spray is the only way to gain effective control when infestations occur in summer.
“We have found it brilliant,” he said.
“And the double knock herbicide which is most affective is Gramoxone.
“The active in this is paraquat.”
Mr Pratten said the first pass is of glyphosate with certain other products to improve the efficacy on the fleabane.
“This pass is followed with a spray of Gramoxone however, we do need to be very cautious of drift towards summer crops when using this strategy".
South Australian field tests have shown the control of fleabane could save up to 70 millimetres of moisture, field tests have shown.
University of Adelaide weeds researcher, Ben Fleet, said tests in the Bute and Pinnaroo areas found that controlling fleabane in summer conserved 45mm to 71mm of soil moisture at the Bute and Pinnaroo site respectively.
“The timing and staggered germination plus the need to treat plants when they are small were the combination that made the weed very difficult to control with herbicides, Mr Fleet said.
“These plants have a natural tolerance to herbicides but they are much more susceptible to herbicide control at an early age of less than a month.”
Plants at rosette stage can be easily killed with lower rates of glyphosate however, once stem elongation begins a far greater dose is required to achieve similar results.
Mr Fleet said a plant could produce up to 120,000 viable light fluffy seeds which disperse on the wind and in runoff water during summer and autumn.
