Something strange keeps happening to the huge peppercorn tree on Harry Barclay’s farm.
For at least a decade, he has seen the evergreen shed most of its leaves around March and April.
He believes it is linked to spraying nearby cotton crops with a defoliant for harvest.
Harry Barclay says the huge evergreen peppercorn tree sheds most of its leaves around the time the nearby cotton farms defoliate. (ABC Western Plains: Catherine James)
“As soon as the cotton defoliation goes on, the peppercorn drops most of its leaves a day or two after and then slowly loses the rest over three or four weeks,” Mr Barclay says.
“It’s not a deciduous tree. It’s not supposed to suddenly lose its leaves like that.”
The grazier from Bundemar, north-west of Dubbo, fears the tree and others he has seen shedding leaves in nearby towns like Warren may be a sign of chemical spray drift.
“The peppercorn is like the canary in the coalmine,” Mr Barclay says.
In Nevertire, a village south of Warren, Bruce Hopley keeps a notebook documenting a peppercorn and other trees on his property losing their crowns in cycles that he says mirrors defoliation of cotton crops 4.5 kilometres away.
Bruce Hopley records changes in trees on his property. (ABC Western Plains: Catherine James)
Cotton Australia chief executive Adam Kay says cotton growers are being unfairly blamed.
“We’ve heard of these complaints, and there’s no evidence that cotton is implicated in any wrongdoing,” Mr Kay says.
“The [NSW Environment Protection Authority] is the proper authority on this issue and they’ve shown there’s no linkage there.”
But proving any of this is difficult.
Call for a national chemical register
Independent environmental consultant Peter Ampt wants a national registry to help track the purchase and use of agricultural chemicals.
“Part of the problem with [investigating spray drift] is that we don’t know who sprayed what where and how much did they spray?” Dr Ampt says.
“There’s nowhere you can go to know which pesticide or herbicide is being used.”
Peter Ampt wants a national chemical register to help investigate vegetation damaged by agricultural spraying. (Supplied: Peter Ampt)
Farmers are already required to keep a rigorous register of what chemicals they use.
However, Dr Ampt says a public registry could provide traceability, much like the National Livestock Identification System (NLIS), which tracks sheep and cattle from birth to slaughter to ensure the integrity of Australia’s red meat.
History of spray drift complaints
Spray drift has been a long-standing concern in the farm-dense region with cotton often the brunt of allegations.
A report in 2018 by the then NSW Department of Industry found “large-area agricultural spraying” was “most likely” causing major leaf drop among peppercorns and leaf necrosis in other tree species in the Lower Macquarie Valley.
It described the peppercorn as “an excellent indicator species” for spray drift, noting trees in residential Trangie were visibly affected, while symptoms “were not apparent in other non-cotton areas such as Dubbo”.
This peppercorn tree suddenly lost most of its leaves, which is uncommon for evergreen trees. (ABC Western Plains: Catherine James)
In 2021, the NSW Environment Protection Authority (EPA) launched the Macquarie Valley monitoring program with five air sampling stations: two in Trangie, one in Gin Gin, one in Gilgandra, and one on Mr Barclay’s farm north-east of Warren.
The results have provided no insight into the shedding peppercorn.
Monitoring only set up to detect
The EPA identified four agricultural compounds in the air over Mr Barclay’s property in March and April 2024, around the time of the cotton harvest.
Only one of them, 2.4-D, is known for defoliant action, although it is not typically applied as a defoliant on cotton, and is instead used by a number of farming sectors for weed control.
“2.4-D is a herbicide that controls broadleaf plants. So it’s used for brambles, blackberry, and any broadleaf weed in a cereal crop [like wheat] because cereal crops are grasses, so 2.4-D doesn’t affect them,” Dr Ampt says.
The EPA set up five air sampling stations to detect spray drift in Western NSW. (ABC Western Plains: Catherine James)
In a statement to the ABC, an EPA spokesperson says the air-monitoring program was set up to detect more than 600 pesticides, herbicides, and insecticides that might be in the ambient environment.
But it does not measure concentration levels, and detection does not point to spray drift.
“It is important to note that the presence of pesticides in the environment does not mean that they have caused defoliation or that there is a risk to the environment or human health,” the spokesperson says.
Bales of raw cotton in Western NSW await processing after the cotton harvest. (ABC Western Plains: Catherine James)
Even in cases of visible change to vegetation, spray drift is rarely confirmed as the cause.
For the two years to December 2024, the EPA received 31 direct reports of suspected spray drift from the Macquarie Valley’s local government areas of Warren, Dubbo, Narromine, and Gilgandra.
Of these, 13 reports were flagged for further investigation and three advisory letters were issued.
“It can be challenging to pinpoint the source, particularly as the movement of spray drift depends on several environmental factors including wind speed and direction, atmospheric conditions, temperature, and rain events,” the EPA said.
Spray drift doesn’t discriminate
Mr Kay says cotton growers are themselves the victims of widespread spray drift.
“I think it’s pretty ordinary to point at cotton when there’s over 40 different crops in the area,” he says.
Adam Kay says cotton growers are being unfairly blamed. (Supplied: Cotton Australia)
Warren cotton grower Gus O’Brien says his crops were mildly affected in the 2022–23 season.
“Damage on cotton is very obvious, but sometimes it doesn’t show up until there’s been a rain event,” he says.
“Personally, I think the biggest contributor to spray drift is people spraying Amine 2.4-D at night.
“Particles can drift for hundreds of kilometres sometimes and they generally get drawn to the most cool environment down the valley and that’s normally an irrigated cotton crop.”
Gus O’Brien says farmers spraying crops at night are more likely to cause spray drift damage. (Supplied: Gus O’Brien)
Rigorous testing required
Scientists are more circumspect about the EPA’s findings, saying further investigation is needed to rule out spray drift.
Asad Asaduzzaman has been researching the effects that intermittent chemical exposure could have on plants and crops. (Supplied: Asad Asaduzzaman)
Research done by Charles Sturt University’s Asad Asaduzzaman has suggested that a “sudden” spray drift event could have been building up over time through low levels of chemical exposure.
The lecturer in crop science found that intermittent small chemical doses might not kill a plant, but they can throw hormones off-balance and render it far more sensitive to a low dose of herbicide or other stressors through climate or pests.
“This could explain … why the defoliation happens regularly and appears to align with spray cycles in the region,” Dr Asaduzzaman says.
He says proper testing is “most effective” soon after spray drift is suspected but requires testing the leaves and soil around affected vegetation “because some chemicals break down relatively quickly”.
Dr Ampt says the process of testing for spray drift is expensive and is chemical specific, making it important to be able to properly conduct tests with data about who, what, and where has been recently sprayed.
Editor’s note 29/01/2025: This story has been amended to clarify that the chemical 2.4-D is not typically used as a defoliant on cotton crops.
The leaves on the peppercorn tree after defoliating are curled up and show signs of damage. (ABC Western Plains: Catherine James)
