Early herbicide strategy boosts northern WA cereal cropping

February 21, 2024 5 min read Bayer Crop Science

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Problems controlling annual ryegrass and wild radish weeds in WA’s northern agricultural zone after years of narrow cropping rotations and repeated use of popular herbicides is well-known across the country.

21 February 2024, AU: However, a new early crop establishment herbicide strategy in cereals is finally turning the dial for the region’s growers. This strategy allows them to confidently sow earlier rather than wait for double knockdown weed control opportunities, as well as plant cereals in high weed pressure paddocks that otherwise may have been substituted for alternative crops.

Grant Thompson, a leading farm consultant in the region who has been operating his Crop Circle Consulting business since 2000, said brome and barley grasses as well as turnip, capeweed and doublegee broadleaf species also were a factor through the region, but were not as prevalent.

Grant said typical grass weed herbicide applications in cereals had included tank mixes of trifluralin and Sakura^® or trifluralin and prosulfocarb incorporated by sowing (IBS), followed by the post-emergent application of Boxer Gold^®, if it was not used pre-sowing. For wild radish control, Jaguar^® herbicide has been applied early post-emergent (EPE), generally followed by a tank mix application of Velocity^® with either LVE MCPA or 2,4-D.

However, the arrival and impact in recent seasons of the grass and broadleaf weed herbicide, Mateno^® Complete, is changing up herbicide strategies and improving weed control efficacy.

Mateno Complete contains aclonifen in a unique, complementary co-formulation with pyroxasulfone and diflufenican herbicides, and it can be applied IBS or EPE in wheat and barley.

“Mateno Complete has given us a really robust EPE grass control option and it’s worked particularly well under high ryegrass pressures, where our traditional pre-emergent chemical options may not control ryegrass in the drill row,” Grant said.

“It provides 100 per cent coverage across the whole paddock, so we are picking up grasses that are emerging with the crop in the drill row; it’s picking up later emerging grasses because it has very good length of residual in the soil; and we’re getting extremely good suppression of other grass species like barley grass as well.

“Depending on the broadleaf weed scenario at the same time, there are also some tank mix partners that provide additional control of broadleaf weeds, so it’s essentially given us a one pass option for early grass and broadleaf weed control.

“Fortunately, we have been involved with R&D work with Bayer and some of the trials in wheat in recent years showed lower rates of bromoxynil were very helpful for broadleaf weed control and putting some Logran^® or Lontrel^® in that mix helped control the volunteer legumes. We are pretty much wiping the slate clean for broadleaf weeds when we do that.”

Grant said difficult early seasonal conditions in the region in 2022 for various growers also provided valuable understanding to help maximise the benefit of the Mateno Complete applications.

“Some growers applied Mateno Complete and then there was no substantial rainfall for five weeks, so efficacy was quite poor. Others waited for a solid rainfall event before application and got an inferior level of control to what we would expect purely because the weeds had grown in size so much.”

“We learned that the very early post-emergent window is the ideal timing for Mateno Complete – generally going at the one-and-a-half to two-leaf stage of the wheat crop, before there is much canopy closure and while the weeds are small.

“By waiting until early to mid-tillering of the crop and tillering ryegrass, we would expect a 30-50% reduction in control just by missing the right timing.”

He said the ideal early herbicide strategy for growers would be at least a pre-emergent application of trifluralin, or a mix of trifluralin and prosulfocarb under higher weed pressure scenarios, followed by an EPE application of Mateno Complete.

“It’s quite specific to conditions and timing, so growers can’t necessarily spray it over their entire program and nor should they, but it does allow them to confidently plant cereal crops earlier than usual and without waiting to double knock.”

“They could seed a couple of weeks earlier knowing they have got a very reliable post- emergent herbicide option to tidy up once the crop has emerged, so it can essentially give growers a tool to plant earlier. Earlier-sown crops are better in this region because generally they get heat-stress at the end of the season. Achieving grainfill in winter, rather than relying on spring rainfall, is generally a winner.”

Crop phytotoxicity levels following the EPE application of Mateno Complete also are “more than commercially acceptable” provided follow-up rainfall is received and crops are actively growing.

Grant said conditions during the 2022 growing season were good and paddocks treated with Mateno Complete showed no significant secondary germinations of annual ryegrass.

“The herbicidal control lasted throughout the season and crop competition took over at the end, so growers were quite happy with the residual control of grass by Mateno Complete.”

“In some situations, we saw later germination of broadleaf weeds, which is to be expected with most herbicides. You often anticipate a late broadleaf spray if you have high pressure.”

He said in research trials, Mateno Complete had achieved high 90% plus annual ryegrass control, compared with 70% with some other herbicide options, and this had translated to at least 1-1.5 tonnes per hectare extra grain yield in high yielding scenarios and a substantial investment return.

“It’s also not only the short-term spin-off of high yield, but the fact you are not replenishing the seedbank with survivors.” Grant said.