ALTHOUGH there were patches of good summer rain through southern and eastern Australia, crop researchers say there will be large areas of cropped land where farmers have to be aware of herbicide residue risks.
“We have areas where plant back will be a risk,” said Birchip Cropping Group (BCG) research manager Claire Browne.
The major herbicide of concern is imidazolinone (imi), used in the Clearfield cropping systems grown widely throughout the country.
Ms Browne said the herbicide needed to be in damp, warm soil for ten to 14 days to aid breakdown.
“There have been some places that have had that summer rain and will be fine, but others haven’t, so it is something growers need to be aware of when making their planting decisions.”
Chris Preston, head of the weed management team at the University of Adelaide, said growers who were planting a Clearfield variety this season to avoid chemical residues issues needed to resist the temptation to put another dose of imi on the paddock in season.
“It is tempting to get the Intervix (an imi based herbicide) out once again, because you have that option, but I would strongly encourage growers to consider alternative weed management options.”
Ms Browne said growers worried about herbicide residues could conduct simple planting tests.
“You could either get some soil from the paddock and plant seeds in it in pots or you could water up some seeds in the paddock and see if there are any issues,” she said.
“There is no doubt Clearfield is a great tool on the weedier paddocks but potential residue risk is something growers have to think about, especially with the run of dry springs and summers we have had of late.”
Ms Browne said while Clearfield herbicides were the primary concern, farmers also had to monitor levels of other products, such as clopyralid (trade name Lontrel).
The other major weed management issue as the autumn remains dry is combating cereal volunteers in cereal on cereal rotations.
In particular, Ms Browne said farmers were concerned about wheat volunteers in barley, as methods of control were limited.
“This is again a problem for guys who did not get summer rains to germinate the volunteers.”
She said farmers had prioritised planting of clean paddocks, but would soon need to make tough decisions regarding paddocks with potential high volunteer loads.
“They have to decide whether to sow later than the optimum or sow on time and have volunteers come up with the crop.”
Dr Preston said the dry start to the season was also putting a large load on pre-emergent herbicides.
He said products such as trifluralin and Sakura would work well in dry conditions and could reduce the need for a knockdown but added there could be issues if there was a small amount of moisture, especially for Sakura.
“Farmers need to make their decisions wisely and according to the conditions,” Dr Preston said.