Inversion risk should give sprayers night terrors

Inversion risk should give 2,4-D sprayers night terrors

Farmers need to have a thorough knowledge of their sprayer and how to manage droplet size to comply with new 2,4-D application requirements.

Farmers need to have a thorough knowledge of their sprayer and how to manage droplet size to comply with new 2,4-D application requirements.


Farmers looking to maintain the use of 2,4-D should carefully consider whether they need to spray at night says a spray drift expert.


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, 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 virtually all year, the risk of inversion grows at night so it is something you have to weigh up very carefully.”

She 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 there may not be any other option in order 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 at the correct height and slow down.

Nozzle set-up is critical to getting spray droplet size right.

Nozzle set-up is critical to getting spray droplet size right.

“You can have the best nozzle set up in the world but if you are spraying at 30kph at night and the boom is too high there is still the risk of inversion.”

Ms O’Brien said she did not think farmers would have particular problems adjusting to the APVMA changes which include 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.”

Ken Young, Grains Research and Development Corporation (GRDC) manager of plant health technologies, 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 formulas used to calculate droplet size that can vary according to the tank mix.

“We talk about 'very coarse' droplets and an advisory message for extra coarse, but obviously different chemical set ups will mean different droplet size.”

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, such as the use of adjuvants could also affect droplet size and efficacy, which needed to be taken into account when choosing the correct nozzle.

"Certain 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 GRDC continued to research inversion event prediction techniques but said that work was ongoing.


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