The challenges with herbicides in recent seasons have seen WA farmers adjusting their spray application techniques for better results
Agrarian Management Agronomist, Craig Topham, of Geraldton, said the 2021 season, in particular, had a major wind event which caused erosion and furrow fill.
“We saw quite a lot of damage from all pre-emergent chemicals that year,” he said. “But we learnt a lot about how to apply products, looking at spray and droplet movement. We’ve learnt a lot and, in hindsight, we’re way better off.”
Like many areas in Australia, annual ryegrass is the major challenge for growers and pre-emergent herbicides are the backbone of any weed management strategy.
“As we have very few effective post-emergent options, you have to get good pre-emergent control. If you don’t, the ryegrass gets away and it out-competes the crop. There can be huge losses if you don’t get on top of it early. Pre-emergent control of ryegrass is the number one tool we have.”
Mr Topham said ryegrass is a multi-season challenge and control strategies include using pre-emergent chemicals as well as crop rotation, cultural practices, seed management and crop competition.
“We’re using every bit of technology we've got and not just relying on any one product or system.”
He said in terms of pre-emergent options, Sakura* Herbicide was used in up to 75 per cent of the paddocks each year and there was concern it was being overused.
“Trifluralin was a major product 15 years ago, but its use is dropping off rapidly – particularly on our lighter soils.
Overwatch® Herbicide has emerged as a good alternative in the area and is regularly being used as part of the pre-emergent mix.
“We watched Overwatch® through the development phase, did all the trials and did the demos,” Mr Topham said. “We love the product. It was looking really good.”
He said Overwatch® Herbicide was launched in the challenging 2021 season and, as a bleacher, the crop effect of the herbicide was very visual where you did not get adequately seed to treated soil separation.
“You can see the bleaching from Overwatch® when driving past in the ute, whereas you need to hop out and dig up plants to see the chemical damage caused by Sakura*, Trifluralin or any of the other products.”
The Bleaching symptoms of Overwatch® are more visible than the below ground chemical effects from any of the other pre-em product.
Mr Topham said with new pre-emergent herbicides they have had to pick up their game with seeding accuracy and a visual product like Overwatch® has focused farmers on their application and planting techniques.
“It's actually made everyone stop and think about how these products work, where they end up in the soil, where they move in the soil and what moves them. It's increased the level of professionalism and accuracy with our seeding system across the whole state.”
Four years after its launch, Overwatch® Herbicide has become an important tool for weed management in the Geraldton region.
“Overwatch® has got two real fits,” Mr Topham said. “It's a great product underneath canola, but it's also a great product the year before we go into canola.”
As Overwatch® Herbicide is registered in wheat, barley, canola and certain pulses, the fit before or during a canola crop addresses any risk of carryover during dry conditions.
“We try to go Overwatch® / Treflan* or Overwatch® / Prosulfocarb in the year before canola so there aren’t any issues with carryover if we get a dry year.”
He said they will always mix Overwatch® with other chemistry to maximise weed control and help with resistance management.
“Overwatch® works great in some of the mixes. I love the Overwatch® / Sakura* mix. We've done a lot of that this year. We use Overwatch®/ Prosulfocarb on the heavier country out east and we do a lot of Overwatch® / Triallate which works well on the right soil type.”
“Some 95% of the paddocks in WA get a full dose of two pre-emergent herbicides, so the mixing and rotating of pre-emergent’s is now standard practice in WA.
“Overwatch® has certainly increased in its popularity, and that's because people are getting used to it. We know where it fits, and the awareness of resistance and the need to rotate is pushing people down that line.”
Mr Topham said the control of Overwatch® on ryegrass was excellent and it had some additional benefits on other problematic weeds in the area.
“One of the coolest things is watching Overwatch® hold back Wild radish in a canola crop. It stunts the radish, holds it back and it keeps it small. The post-emergent herbicides then work a lot better because the Wild radish has not taken off.”
“The third major weed in Geraldton is brome grass. Overwatch® is quite handy on brome grass and wild oats.”
“The Overwatch® and Sakura* tank-mix on brome grass is very good. We are using a lot of that to hold back brome and often those cases are in non-wetting sands which has Wild radish as well.”