21/11/23: Yorke Peninsula (South Australia) 26 reports of spray drift. Pesticide: Overwatch (Bixlozone)

Spray drift: not on our watch

Yorke Peninsula Country Times 21/11/23

Prompted by its investigation into 26 reports of off-target impacts of the herbicide Overwatch on Yorke Peninsula, Primary Industries and Regions South Australia says it will crackdown on non-compliant use of agricultural chemicals.

PIRSA biosecurity executive director Nathan Rhodes said the reports had come from throughout YP, including Alford, Balgowan, Edithburgh, Kulpara, Moonta and surrounds, Maitland, Minlaton, Port Vincent, Point Turton, Tiddy Widdy Beach, Wallaroo, Warooka and Wool Bay.

Overwatch damage has also been reported in the Mid North at Snowtown, Balaklava, Hart and Manoora.

No complaints or reports have been received from outside these two regions.

PIRSA has referred the reports to the Australian Pesticides and Veterinary Medicines Authority but has not yet received feedback.

Manufactured by FMC Australia, Overwatch is a pre-emergent herbicide which is applied during seeding time in April/May to control annual ryegrass and some broadleaf weeds in broadacre crops.

Mr Rhodes said PIRSA has a renewed focus on preventing drift of any agricultural chemicals by ensuring chemical users comply with mandatory instructions.

“Users identified to not be following mandatory label instructions can expect PIRSA to use the strongest possible regulatory enforcement options, which include prosecution,” he said.

Most of the reported damage was to garden plants in townships, often some distance from cropping paddocks.

“Damage is considered likely to have resulted from a combination of use during hazardous inversion weather conditions and/or application practices resulting in unacceptable production of fine droplets with a higher potential to drift,” Mr Rhodes said.

“Spray drift damage is highly visible for Overwatch — with some plant species being particularly susceptible to very low amounts of Overwatch drift — as the bleaching symptoms are easily observable.”

PIRSA contacted crop producers across YP believed to have used Overwatch in 2023, largely based on their location near reported damage, but this did not imply they were the source of the damage, he said.

No evidence was found by PIRSA to indicate the users checked during the investigation had contravened mandatory label instructions.

“All producers interviewed by PIRSA were aware of the potential of Overwatch to produce visible symptoms on non-target vegetation and were concerned about it, with one farmer choosing not to use the herbicide again due to this off-target damage risk,” Mr Rhodes said.

More training to stop spray drift

“Overwatch is a relatively new herbicide product and has a unique mode of action that enables it to control some weeds that are not well controlled by other herbicides,” PIRSA biosecurity executive director Nathan Rhodes said.

“This makes it useful where weed resistance to other herbicide groups has developed.”

It is expected Overwatch will be used again in 2024, and PIRSA is working with Grain Producers SA to improve awareness and training for chemical users.

FMC head of development Geoff Robertson said the company had shared information with PIRSA during the investigation.

He said many factors — such as soil, nutrition, environmental conditions and use of other agricultural chemicals — can also cause plant symptoms which may be mistaken as signs of contact with Overwatch.

FMC has provided chemical-user training over the past three seasons and will run another series of workshops in 2024, Mr Robertson said.

These will be held at Crystal Brook on February 27, at Paskeville on February 28 and at Minlaton on February 29.

Mr Robertson said Overwatch does not pose any threat to human health when applied in accordance with label instructions.

“APVMA and the Department of Health determined that Overwatch has a very low toxicity profile,” he said.

“If any small amount of spray drift was to contact drinking water collection areas or fruit in nearby fields, the risk would be extremely low due to its very low toxicity to humans.”