AVAILABLE options to help control grass and broadleaf weeds have increased, with multiple new chemistries expected to be released to growers in the next few years.
In the past decade, resistance to pre-emergent herbicides has increased across SA, according to University of Adelaide weed researcher Chris Preston.
"Resistance to trifluralin is now common across many cropping regions of SA and resistance to Group J and K pre-emergent herbicides has also been detected in random weed surveys - in some parts of SA, resistance to triallate is also becoming common," he said.
Prof Preston said sustaining new products was "crucial".
"In the past five years, 60 per cent of paddocks in SA have trifuralin-resistant ryegrass, so these new options cannot be used across each paddock, year in, year out, or it the same thing will happen," he said.
At a recent GRDC research update at Balaklava, Professor Preston revealed understanding how to integrate herbicides into a farming system was integral to its performance.
Prof Preston said the difficulty that came with selecting pre-emergent herbicides was each product worked differently depending on the conditions of the surrounding environment, such as soil type and amount of rainfall.
Luximax was released this year and is suitable for grass weeds in wheat and Prof Preston said its active ingredient, cinmethylin, was an old chemistry that never made "tracks" until recently.
It will be available to growers next year as a Group Z herbicide and it relies heavily on binding organic matter.
"What stops this herbicide from disappearing into the soil profile is organic matter, the soil must have it for it to work and it will not work in durum, barley or oat crops," Prof Preston said.
"Wheat is not inherently tolerant of the active ingredient, so positional selectivity, keeping the herbicide and crop seed separate, is important," he said.
"It can only be used in a knife point and press-wheel sowing system and it needs to be sown at three centimetres or deeper."
Luximax is not suited to lighter soils with low organic matter, and heavy rainfall after application can also cause the chemical to move into the crop row and cause damage.
It is also not suited for dry seeding conditions and Prof Preston said it needed to be applied slowly.
"You cannot speed through to get the job done, care needs to be taken to not throw treated soil from one sowing furrow into another while sowing," he said.
RELATED READING: GRDC grains research update - Balaklava| Photos
Latest herbicides set for release
NEW pre-emergent herbicide Overwatch is set to be released to growers in 2021 and the University of Adelaide's Chris Preston hopes it could provide an effective alternative to Sakura for annual ryegrass control.
Overwatch has a new active ingredient called bixlozone and it will be released as a Group Q herbicide.
Prof Preston said wheat was the most tolerant to the active ingredient, followed by barley, and to be suitable for canola, a knife point or press-wheel system was needed.
"Some bleaching of an emerging crop occurred but in our trials it did not create yield loss," he said.
"If a crop grows poorly because of waterlogging and high root diseases, the crop might have difficulty growing away from the initial bleaching effect.
"It is more soluble than Sakura but less than Boxer Gold, low water solubility means it will not move around the soil profile from where it was applied unless there is soil movement or exceptionally heavy rain."
BAY167 is an experimental pre- and post-emergent product from Bayer for the control of grass weeds and some broadleaf weeds and is expected to be released in 2023.
"It is suitable for early post-emergent application, at the one to two leaf stage of annual ryegrass," Prof Preston said.
"It will require more rainfall after application than Boxer Gold so it will be suited to higher rainfall areas," he said.
- VANESSA BINKS
Start the day with all the big news in agriculture. Click here to sign up to receive our daily Stock Journal newsletter.
