Seasons permitting, the intensity of summer and winter cropping is at its greatest anywhere in Australia on the Darling Downs of southern Queensland.
Here, dryland cotton is the second-most-popular summer crop behind sorghum and the most susceptible to damage from drift from all Group I herbicides, including 2,4-D (2,4-Dichlorophenoxyacetic acid).
With as little as one metre separating cotton from fallow or neighbouring plantings, it is a crop which, like grapevines and vegetables, can suffer collateral damage from phenoxy herbicides, the primary active ingredients in spray mixes used to control broadleaf weeds in summer fallow.
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New Australian Pesticides and Veterinary Medicines Authority (APVMA) regulations have been introduced to minimise the risk of 2,4-D drift and a GRDC fact sheet has given growers and contract sprayers such as John Cameron the low-down on how to adhere to them.
"They are easy to follow, and they work," John says.
From their base at Bongeen, 50 kilometres west of Toowoomba, John and Ros Cameron crop 2000 hectares, with dryland cotton, sorghum and millet the crops grown over the 2018-19 summer.
Their switch 12 years ago to ultra-coarse (UC) nozzles, which produce bigger droplets than their predecessors, means they are already meeting the new hardware requirement for 2,4-D to be sprayed from nozzles no finer than very-coarse (VC).
They are acutely aware of the damage spray drift can cause, and were responsible for some of it themselves before they changed nozzles.
John says the new 2,4-D guidelines' focus on efficacy rather than coverage stands to benefit the industry by encouraging sprayers to get their pressures and tank mixes right.
He says this means they can minimise the risk of drift, and improve their own efficiency.
They are easy to follow, and they work.
"Efficacy is what we chase and, because of that, we have not had a herbicide failure in recent years we can attribute to poor coverage in anything from bare fallow to heavy stubble," John says.
That stubble comes from wheat crops which can yield up to five tonnes per hectare and sorghum crops which can get to 6 to 8t/ha.
John normally mixes LI700 adjuvant with 55 litres per hectare of their bore water when applying 2,4-D.
He says he can generally control broadleaf growth in fallow with two sprays over summer.
While he has had success with 55L/ha, research recommendations indicate water volume should be at least 80L/ha to maintain efficacy when using VC, extra-coarse (XC) and UC spray quality nozzles.
The Camerons farm on a 12-metre system, with sorghum and cotton planted on one-metre rows, and rotation crops and nozzles on their 36m boom spray on 50cm spacings.
The Camerons' target summer weeds are milk thistle, wild turnip and seedling and ratoon cotton.
The general ground speed for spraying is about 18 to 20 kilometres per hour, which gives 250 to 400 kilopascals at the TeeJet TTI 110-02 air-induction nozzle.
"Our objective is to keep our product within our own boundary," John says. "How can we justify our right to farm if we can't do that?"
New regulations came into effect in October last year, and require 2,4-D users to abide by the conditions in APVMA permit 87174, and record each spray.
More information: Vicki Green, 0429 046 007, firstname.lastname@example.org
Useful resources: GRDC Fact Sheet.