A SPRAY application expert has warned farmers they will need to virtually rule out night application of 2,4-D based products in order to limit the risk of drift due to inversion events.
Mary O’Brien, of Mary O’Brien Rural Enterprises, Queensland, said in light of proposed Australian Pesticides and Veterinary Medicines Authority (APVMA) changes to 2,4-D application, farmers needed to do everything right if they wanted the chemistry to remain as readily available as it is today.
2,4-D is a widely used herbicide used primarily in Australian systems for fallow weed control, particularly in summer.
The APVMA review comes because of high profile reports of spray drift from farmers using the product killing highly susceptible crops, such as cotton, grape vines or horticultural produce.
“2,4-D is a really important piece of chemistry and for the growers they need to be doing everything they can to show they are using it responsibly,” Ms O’Brien said.
“For me that would mean no spraying at night because the risk of inversion is just too great.
“In virtually all instances in Australian conditions over the summer, the risk of inversion grows at night, so it is something you have to weigh up very carefully.”
Ms O’Brien said people had disagreed with her on the matter, saying it was too hot to apply the product effectively in the day time in the Australian summer, but she said the risk and reward showed a slight reduction in efficacy may be the price they had to pay to keep the chemistry.
“2,4-D use is under the microscope at present and if I was them I would not be providing any reasons to have the restrictions tightened once again.
“If you won’t stop spraying at night you have to do absolutely everything right in terms of application, make sure your sprayer is putting out that extra coarse droplet, have the boom right down as low as you can go and slow down.
“You can have the best nozzle set up in the world but if you are spraying at 30 kilometres per hour at night there is still the risk of inversion.”
Ms O’Brien said she did believe farmers would have particular problems adjusting to the proposed APVMA changes which included a minimum mandatory use of nozzles distributing ‘very coarse’ droplets and widened buffer zones, but said she was not sure the changes addressed the problem of 2,4-D drift.
“Compliance with buffer zones will not be a major issue but I am just worried that it probably does not address the problem of drift, given most drift damage is occurring via inversions not through off-target spray being blown on the wind.”
Grains Research and Development Corporation (GRDC) manager of plant health technologies, Ken Young said farmers had to take the necessary steps to comply with the new rules.
“It is very important chemistry and GRDC will be doing everything it can in terms of providing resources and educating farmers on how to comply,” Dr Young said.
He was confident farmers would transition to the new regulations seamlessly.
“Growers have been excellent at adapting new technologies and new nozzle types according to best practice, so I think with the right information it should be something they can work with.”
Ms O’Brien said the droplet requirements were a more difficult area to work through because of the variable formulas used to calculate droplet size.
“We talk about ‘very coarse’ droplets and an advisory message for extra coarse, but obviously different spray set ups will mean different droplet size,” Ms O’Brien said.
Droplet size is affected by both the actual nozzle type and size, as well as the spray volume and pressure.
Ms O’Brien said other variables could also affect droplet size and efficacy, which needed to be taken into account.
“Surfactants in the mix may mean you end up with finer droplets than you would using just the chemical so people are going to have to do their homework.”
Dr Young agreed.
“It is not going to be a one nozzle fits all strategy, people are going to have to find out how to comply but still put their herbicide out in the most effective manner,” he said.
Dr Young said the GRDC continued to research inversion event prediction techniques but said that work was ongoing.