The last time dryland cotton producers experienced a summer like this was in 2016 when weed pressure on bare fallow was enormous leading up to Christmas.
With tens of thousands of hectares at risk of soil moisture loss from burgeoning weeds the spray rigs were sent out with a vengeance, and the drift from hormone sprays like 2,4-D caused significant damage to cotton crops a long way from the offending operator.
This year's climatic conditions appear very similar, with rain events in November spawning a plethora of tough weeds just as the Christmas holidays loom close.
Mark Congreve from Independent Consultants Australian Network, contracted by the GRDC to facilitate best spray practice to farmers, expects this season to dish up real proof about how far the cropping industry has progressed since APVMA label changes for 2,4-D and industry extension helped steer the industry onto a more sustainable path.
"Back in 2016-17, it seemed every paddock had an application of 2,4-D and the spray rigs were often going 24/7 under a wide range of environmental conditions to cover the area required," he recalled. "Especially as the adjacent cotton was at a really sensitive growth stage at the time.
"While there are now new label requirements to follow and the industry says it has moved forward, we really haven't had a season since with heavy weed pressure over extensive areas of NSW to test where we are at."
Agronomist for the Inverell and Delungra region, Alice Jorgensen at McGregor Gourlay believes the industry has moved well down the track since 2016, but she expects 2021-22 to be a big year for learning, with a record 1500 hectares of dryland crop already planted in the Delungra area.
A cool spring and cloudy start to summer has delayed development, with fewer heat units to drive plant growth. These issues, rather than fear of spray drift, are posing greater concern to growers.
"There are a lot of different crops grown around here, and a lot of sensitive broadleaf crops," said the former Moree-based cotton agronomist. "Along with sunflowers we have soybeans and mung beans. In many cases mung beans are just as sensitive as cotton to drift from off-target spray.
"Farmers are aware of selecting appropriate products. Here there are so many smaller blocks and a very diverse array of production."
At the same time she says the superb growing season has spawned healthy weeds with big root zones and vigour not easy to kill, so growers are trying different chemistry in a strategic way. In addition, some producers are using strategic mechanical weed control, considering their full soil moisture profile.
"We're not 100 per cent no-till here," Mrs Jorgensen said.
Gwydir cotton grower Charles Boileau, Bella, Delungra, planted cotton for the second year as part of a new wave of dryland production in the district.
Having previously farmed near Gunnedah and before that Coolah, he is experienced in the ways landscape and climate can affect spray drift. Here at Delungra, rolling hills play tricks with wind direction and strength.
A wind sock near the sheds and visible in the paddock might well be telling a very different story to the one circulating over the spray rig itself, so Mr Boileau made his own indicator to give him a visual reference. An injection of diesel directly into the exhaust manifold sends up a puff of smoke and this gives the operator a clear picture of wind direction.
Manager of Lambrook Pastoral at Mullaley, James Vince, recalls the problems during 2016 but says growers are more aware now of how to spray safe these days, in spite of this season's ability to grow problem weeds.
A double knock is sometimes required, with glyphosate and 2,4-D in the first application followed by paraquat or even a strategic till, particularly on bigger acreages - like the 4000 hectare Lambrook Station.
"We are all more aware of chemical drift," Mr Vince says, pointing to the wider use of ultra coarse spray-nozzles and the adherence to strict label requirements during the cotton season
"We put away all hormone sprays during this time. We also adhere to maximum wind requirements and buffer zones.
"Post emergence we're using more expensive chemistry. With our optical sprayer we're using 10-15pc of that so the impact from spray is much less," he says.
Correct technique key
Mark Congreve from ICAN says chemical spray drift should not happen under correct application, pointing to growers on Queensland's Darling Downs who often strip crop and are able to spray 2,4-D onto bare follow right next to sensitive cotton, with no ill-effect. Key to good technique is using a minimum of very coarse nozzles on the spray boom, with water rates at least 50 litres to the hectare.
"However, if a sensitive crop is right next door, then I would advise extra coarse or even ultra coarse spray quality, with spray volume increasing proportionally with larger droplet size, and wind direction away from the sensitive crop," he said.
Vehicle speed should be 16-18km/hr at most in drift sensitive situations. This reduces turbulence behind the boom and also allows boom height to be as low as possible, while still achieving double overlap.
High travel speed with a high release height leads to the risk of any driftable spray fines being released into prevailing winds or inversions, increasing the risk of product moving off the paddock where it was applied.
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