Brand new classes of pre-emergents overcome resistance
Pre-emergent herbicides are on the menu for croppers right now and the good news is that there’s a suite of new chemistry available this season, says Elders Kingscote, SA, agronomist Maree Gifford.
Decisions around pre-emergent choices revolved around a number of factors, Ms Gifford said, which include weed burdens, the chemical history of the paddock, the planned crop and any chemical residuals.
Of the new chemicals available this year, Ms Gifford said Overwatch, Luximax, Ultro and Reflex were the most anticipated.
Luximax herbicide released in 2020 controls annual ryegrass in wheat (other than durum). Its maker, BASF, says Luximax is the only herbicide in a class of chemistry known as the cineoles, which have no known cross-resistance. For resistance management purposes, Luximax is currently classified as a Group Z.
Similarly, Overwatch controls annual ryegrass and some broadleaf weeds and, with a Group Q mode of action, overcomes resistance to other chemicals. It can be used as a preemergent for incorporated by sowing (IBS) treatment in wheat, barley and canola.
Ultro from ADAMA introduces an old chemistry with a new purpose, offering a new mode of action in pulses (Group E) as a pre-emergent control option for annual ryegrass, barley grass and brome grass in winter pulses and fallow.
Ms Gifford said a fourth herbicide, Reflex, due for registration later this month, would also play a key role in controlling wild radish in beans when it became broadly available.
“We get a lot of wild radish through beans, which you really can’t do much about, but this is going to have an 8-10 week residual period controlling broadleaf weeds, including wild radish, in bean crops,” she said.
“It’s going to be extremely advantageous for us.”
Aside from dealing with existing herbicide resistance, Ms Gifford hoped the new options would extend the effective life of current chemistries.
“It’s going to help slow down the rate we’ll get resistance occurring in those crops because we can rotate our chemistry, meaning we’re not always having to hit them with the same group,” she said.
As with any other herbicide, it was critical to observe the manufacturer’s label and application rates and Ms Gifford said producers also needed to be careful with seed placement in relation to treated soil.
“These chemicals are all incorporation by sowing (IBS) and it is important to avoid treated soil being thrown into furrow,” she said.
“Some transient crop effect may be observed. Reflex will also have a post sow, pre-emergence option in all registered crops except lentils.”
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