Aerial applicator

An aerial applicator sprays a field. Oregon regulators have seen reduced pesticide levels in key waterways.

Pesticide levels in some key Oregon waterways have dropped to a fraction of their former concentrations due to changes voluntarily adopted by farmers, according to environmental regulators.

Monitoring by Oregon’s Department of Environmental Quality has found that growers are willing to alter spray regimens to achieve successful water quality results.

“Overall, we’ve seen improvements in a number of agricultural areas, particularly in the Columbia plateau. We’ve seen agriculture respond to the data,” said Kevin Masterson, DEQ’s toxics coordinator.

About 50% of the waterway sites tested under an interagency “pesticide stewardship partnership” program showed progress in pesticide detections and concentrations during the 2015-2017 sampling period, compared to the previous biennium.

Roughly 27% of the tested sites showed declines in water quality from pesticides, while 23% showed no change during that time, according to data compiled by DEQ.

Those numbers don’t tell the whole story, however, because the monitoring is targeted toward streams where pesticides are detected, while those without occurrences are dropped from testing, said Masterson.

“It is a targeted monitoring program,” he said, adding that the water quality improvements are noteworthy given that regulators are focusing on areas with problems. “What we don’t find is as important as what we do.”

The monitoring program has resulted in significant reductions in pesticide levels in such watersheds as the Walla Walla, where the concentration of diuron herbicide has effectively fallen to zero from a maximum level of 18.9 micrograms per liter and an average level of 1.5 micrograms per liter in 2010.

When presented with the diuron data, the local irrigation district stopped treating ditches with the herbicide during dry periods and instead switched to mechanical removal and spot-treatment with a less-toxic and -persistent chemical, Masterson said.

Concentrations of the malathion insecticide have likewise plummeted in the Wasco basin, where cherry growers are now more reliant on weather stations to time their spraying, according to DEQ. Aerial applications now occur on the interior of orchards while areas near streams are sprayed by hand.

Not every waterway under scrutiny has seen a decrease in pesticide levels — those in the Willamette Valley, for example, have generally seen concentrations rise and fall without a clear trajectory, said Masterson.

“In a lot of areas, we haven’t seen sustained trends for pesticides of interest,” he said. “Even though it’s a challenge in some watersheds, it’s been a success in others.”

Decreasing pesticide levels in water is generally more straightforward in regions primarily dedicated to certain crops — Walla Walla for apples, Hood River for pears, Wasco for cherries — compared to those where agricultural land use is less uniform, said Kirk Cook, pesticide stewardship specialist at the Oregon Department of Agriculture.

“Those are usually where we have a wide diversity of crops grown and chemicals used,” he said.

For the same reason, more progress has been seen among farmers compared to more numerous city dwellers, who are more difficult to communicate with on a large scale, said Masterson. “We’ve been able to see major declines in agricultural areas that we haven’t been able to see in urban areas.”

Farmers have generally taken pride in seeing a positive response from their efforts to keep pesticides out of water, said Cook of ODA. “Any regulatory action that you take is generally something that is forced on them. People are going to react negatively to something that is forced on them.”

There’s also an incentive to take voluntary action because growers know that a lack of improvement could result in regulatory action that cuts off access to pesticides, he said.

For pesticides subject to the federal Clean Water Act, exceeding benchmarks for concentrations in water could result in a more restrictive “total maximum daily load” process than the current voluntary approach, he said.

Exceeding benchmarks for other “pesticides of concern” identified by Oregon regulators could also cause those chemicals to be pulled from the market if voluntary action were ineffective, Cook said.

“That would not be available for the applicator community to use,” he said. “Our goal is to not have that happen.”

I've been working at Capital Press since 2006 and I primarily cover legislative, regulatory and legal issues.

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