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Albany's birch trees are fighting off an invader bent on destruction, but city officials are fighting back.

The trees are under attack from the bronze birch borer beetle, a critter native to eastern Oregon whose larvae like to munch on the inner layer of a tree called the cambium. They've been plaguing the western half of the state since the early 2000s.

The bugs feed on the cambium, which is the part of the tree that grows new cells. By the time they emerge through the outer bark — leaving a tiny, telltale hole shaped like a letter D lying on its side — plenty of damage has been done.

Birch borer beetles have a harder time killing healthy trees with lots of water at their disposal. Drought-stricken trees are much more vulnerable, said Emily Day, a natural resources specialist for Albany.

"Watering trees is the biggest defense," she said. "We've been in a drought since 2015. It stresses the tree out and makes it more susceptible to infestation." 

Day can see the effects of the beetle particularly in the Lexington subdivision in the southeast corner of town. Whole streets lined with birch trees have been affected to one degree or another.

Once a tree has lost more than 50 percent of its foliage, it's pretty much a goner and needs to be pulled out and replaced, Day said. The city is doing that with several trees it planted on that side of town.

However, if the foliage dieback is just beginning, there may be time to save the tree.

Day said the city will be spending part of the winter on soil injections, contracting with a licensed spray service that will inject a pesticide into the soil at the base of some 40 affected trees it owns. That's so the tree can draw the insecticide into its cells and take out the larvae in the process. It's a process crews began last year and are waiting to see if it has an effect.

"We'll keep monitoring," she said. "See if they can make a comeback."

Homeowners with birch trees in their yards can do the same, Day said. First, check out the tree's overall health — are the leaves dying back, especially at the crown? Losing any branches? — and then look for the D-shaped holes.

Watering is key, but certified arborists can help if homeowners want to try the pesticide route, Day said.  

The city has removed birch trees from its list of approved trees for city sidewalks.

Ash trees are also off the list, a preventative strike against the emerald ash borer, which is on its way west from Colorado, Day said. The city is working on an street and park tree inventory of ash trees to help monitor for the bug.

"Our Urban Forestry Program is working on implementing guidelines and recommendations outlined in the Emerald Ash Borer State Preparedness Plan issued by the Oregon Invasive Species Council to prepare for a potential introduction," she said. "Citizens can help protect ash trees by keeping an eye out" for the Emerald Ash Borer and not transporting firewood from areas that have been affected.

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