Time to Change our thoughts in the placement of the white birches that we have so over used the last few decades! Thanks to one FEISTY little insect, Agrilus Anxius, or the Bronze Birch Borer. In truth this guy probably belongs anywhere certain birch species occur, and we brought the birches!
-the crown of the birch tree, one side of it, will often begin to die first.
Agrilus Anxius has been in the Northwest for almost a decade but because of its life cycle tends to be noticed 4-5 years after starting infestations. The female lives 3-4 weeks after leaving her pupae cell in a warm week of May or June,from the tree where she grew up. She is attracted to the strong scent of a birch trees rapid early summer growth, but irresistibly is drawn to trees that have fresh wounds, or that are oozing sap. We are deep into the second and third generations here in Portland, they have spread with light manifestations for the last 6-10 years, now that the population is strong we can expect all but the most healthy and well suited trees to die in the next two-three years.
The Larvae kill a birch tree by eating the conductive tissue under the bark, thus cutting the root off from the branches. If left untreated, this will kill the tree within a few years. If you have any type of birch trees, keep an eye on them, look in the top third to show first, they will be inside working their way down the trunk.
This pest will target trees under stress. One of the primary reasons for stress is drought and the resulting slow growth.
Some 'Experts' advise extra watering, this may provide some (probably very small) benefit. But shows us the importance of placing the tree within the right system. Birch are water loving trees, and somewhat intolerant of high soil temps, mostly just due to having very shallow roots.
This is a prescription lifted off a local tree service companies website:
To protect or begin the control process for Bronze Birch Borer, the trees must be treated with an approved soil active systemic product during the cool months, which is then absorbed by the root system in the early Spring. Not all systemic products will work. Most 'over-the-counter' Rose type systemics will do nothing. Foliar spray treatments will do little. Because this pest is so severe I recommend preventative treatments yearly. If the pest invades to the point of severe damage, it may be too late.
While this borer is part of the midwest ecosystem, it may not have ever established here in near history, certainly looks like this is the first incursion- wil be permanent, and severe.
Chemical treatments year after year for tree varietals, and or individuals, placed in unsuitable situations???, does not constitute much of a plan. And sounds expensive!
I think we need to realign our thinking on the design intent/ usage of the tree. Can you plant F. Latifolia anywhere on a site? No and that is a tree native and suited to our little climate here. Same for the birches- which grow in wet places on banks and slopes, and require full canopy shade, or heavy ground cover.
New rules are in place! Placing a birch near a hard surface(sidewalk/ Asphalt), or alone in the middle of a lawn, will tend to just give your bugs plenty of food!
As a commercial landscape contractor- I will not warrantee Betula J. or some of the others, on a new project.
Comments about the bronze birch borer possibly eliminating a species, have no validity- at most this borer has the ability to make us quit throwing non- native birch species indiscriminately through the landscape- or even force an industry moratorium on the ornamental useage. We have already vastly altered the prevalence, by introduction of non- natives throughout the Genus, and the trees are so prolific that there will always be plenty of seedlings. And those will have a far better chance of success that the most fussed over tree in the landscape. Just another example of paying attention to the way things were created, we learn again and again that success depends on study and understanding of nature.
The adult Bronze Birch Borer leaves a distinctive 'D'-shaped exit hole as it burrows out of the tree. Many times, the area around the exit hole is stained this bronze color.
