Oregon is the first state in the nation to sharply restrict an herbicide known to kill trees, despite federal regulations still allowing the substance as roadside weed control. The product, known as Perspective, was effectively banned this week from wooded areas in Oregon.

“This certainly could set a precedent; other states would have to look at their authority to regulate the use beyond the federal requirements,” said Dale Mitchell of the Oregon Department of Agriculture’s pesticide program.

States are required to enforce federal pesticide regulations, but making the rules set by the Environmental Protection Agency any stricter is rare. If other places decide to adopt Oregon’s customized approach, they may soon run into federal roadblocks.

On March 19, the EPA announced plans to reevaluate localized power over pesticide regulation, with changes possible after 2019. The notification warned, “the [EPA] Administrator may suspend a state’s registration authority.” As Politico reported, “If the EPA decides to step in to overrule states on certain restrictions, Bayer, which recently purchased Monsanto and its product lines, could be one of the main beneficiaries of that change.”

Bayer manufactures Perspective; the active ingredient is aminocyclopyrachlor or ACP. Highly mobile in groundwater, it’s of low toxicity to animals but highly effective at killing plants. State investigators found ACP spraying was to blame for over 2,000 dead and dying pines in Deschutes National Forest near Sisters.

The die-off was high profile, with predominately old growth trees lost along a scenic road, and it triggered the state’s rule-making. The end result severely limits ACP use on rights of way and bans spraying “where roots of non-target trees or shrubs may extend,” among other natural areas. These limits were temporarily imposed in September, as more than 5,000 public comments poured into ODA’s pesticide program.

County road departments and others with existing stocks of ACP intended for weed control opposed the restrictions — as did Bayer. The day after the EPA signaled it might curtail state-specific regulation, Bayer appealed Oregon’s ACP rule, delaying permanent adoption until this month.

In the final rule, state regulators backed down on a provision to keep wood exposed to ACP out of mills. The Forest Service is in the midst of logging those poisoned pines near Sisters, with plans to sell them as lumber. ODA’s originally proposed rule would have prevented selling the lumber to a mill because ACP-affected wood has been shown to contaminate mulch and compost.

But the onus will be on the mill, according to Mitchell. 

“The facility that purchases and processes the logs will need to take measures that that material does not enter the composting stream,” he said. 

The trees that once towered between Sisters and Camp Sherman have been slowly dying from ACP exposure that occurred between 2013 and 2015. Four years later, all the standing dead and even the slash are being hauled out in an effort to stop the problem from spreading further and keep hazard trees from falling on the road.

ODA’s investigation focused on four locations near Sisters exhibiting damage attributed to the use of ACP. It’s unknown how the herbicide may have affected conifers across the Pacific Northwest. The label says not to apply near “desirable” roots — a warning that came after ACP was first linked to a wave of spruce tree deaths in the Midwest — eight years ago. That product made by DuPont was banned by the EPA in 2011, then Bayer launched a different brand in use today.