UPDATE (3:15 p.m. PT) – The U.S. Forest Service has finalized a decision to fell about 2,100 poisoned pines in the Deschutes National Forest along Highway 20, where officials have long worried about hazard trees falling over on the road.

“Our primary objective is to mitigate a public safety hazard, and our No. 1 priority is getting the trees down,” said Ian Reid, Sisters District ranger with the Forest Service.

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The trees died from exposure to herbicide. The federal plan is to turn them into forest products, but proposed state regulations may prevent that from happening.

According to the Oregon Department of Agriculture, the primary threat posed by milling poisoned trees isn’t from the wood, but rather from the sawdust, said Rose Kachadoorian, a pesticides program manager with the agency.

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She said the sawdust could easily go to the nursery industry, or to a farm as animal bedding, and from there become compost. She pointed out two studies showing that can lead to unintended plant die-offs.

For some backstory: state contractors inadvertently killed the mature ponderosa pines near Highway 20 with herbicide meant to control weeds, applied from 2011 until 2015. At that time, aminocyclopyrachlor, or ACP, was widely applied to rights of way in Oregon and the Pacific Northwest. The compound had already been linked to tree deaths in other states and was even pulled from the market under one brand name until it reappeared through a different manufacturer, and again got federal approval from the Environmental Protection Agency for use on roadsides.

Kachadoorian said ACP is of low toxicity to animals and fish. But it moves through soil and water, into the roots of trees. After a few years of applications, the road to Sisters changed. Centuries-old ponderosa pines died; some of them hundreds of feet from where spraying occurred. The number of affected trees has grown in recent years.

After public complaints and pressure from the advocacy group Beyond Toxics, the Oregon Department of Agriculture ordered a temporary stop to ACP applications on roadsides and other rights of way in 2018. In January, ODA proposed making the rule permanent and added a prohibition on milling wood from ACP exposed trees. That's because it's not entirely clear how the compound lingers and moves in the environment.

ODA has received over 3,000 comments about the proposed rule, Kachadoorian said. The public comment period closes Feb. 26. The rule could be finalized by the end of March, before the Forest Service timber harvest near Sisters takes place during its planned April start. Reid and Kachadoorian said the agencies are in communication.

This story has been updated to include comments from the Oregon Department of Agriculture.