Tree killing insect found in pool parking lot

The invasive emerald ash borer was spotted in Portland for the first time in the Aquatics Center parking lot by a local arborist during a routine tree inventory, raising concern for the future of ash trees in the city.

Originating from Asia, the ash eating larvae of the beetle have been responsible for millions of tree deaths across the country, ultimately reaching the west coast in recent years. The first emerald ash borer sighting in Oregon was in Forest Grove in 2022 and has since spread to other counties such as Marion, Yamhill, Clackamas, Washington and now Multnomah county.

Despite not planting any ash trees after 2019, using proactive pesticides on ash trees since 2023 and installing emerald ash borer traps in 2024, local arborist Peter van Oss noticed signs of infestation on a tree in the Aquatics Center parking lot while inventorying the trees.

There are an estimated 95,000 ash trees in Portland, and with the infestation of the emerald ash borer, almost all of them could die. The beetle doesn’t usually travel far on its own though, the infestation is commonly spread by moving firewood between counties.

The emerald ash borer larvae kills trees by feeding on the trees' cambium, the layer of cells between the bark and the wood that’s responsible for tree growth, making it impossible for the tree to take in its needed nutrients. This causes a thinning in branches, woodpecker damage, split bark and D-shaped exit holes. Not only does the emerald ash borer attack ash trees, but there is also evidence supporting that white fringe and olive trees may be susceptible to ash borer infestation.

“When I came closer to the tree I started looking for some D-shaped exit holes,” said Van Oss, “and I did find a D-shaped exit hole that was about the size of a ballpoint pen tip.”

“From what we can tell, we caught it early,” said City of Portland forest pest and pathogens coordinator Anya Moucha when asked about the infested tree in the parking lot. Despite research that shows you can potentially save lightly infested trees, Moucha recommends removal of the tree to protect the surrounding trees.

“Without any action,” said Moucha, “We will lose all these trees at the same time.”