What is Happening to the Birch Trees in Calgary?

Saturday, September 6th, 2014

Probably Birch Leafminer or Bronze Birch Borer

Is your Birch tree also infected?

Many city lawns once had a majestic birch tree gracing it. Now, one by one, the white barked beauties are dyeing off: first, the leaves disappear from the top, then, usually within a few years, the entire tree is consumed. By that point, not much can be done but to call an Arborist for removal and stump grinding.

So why are trees that have happily existed for many years in town suddenly dyeing off? Is it climate change? Is it herbicides? Well, these may be contributing factors to overall tree weakness: an ideal birch environment keeps the roots cool and moist while sunlight is able to hit the crown of the tree. Calgary is a naturally dry environment and many birch tree rooting areas are located in full sun. Additionally, the standard yard falls short on nutrients: a carpet of grass does little to mimic nutrition available on a forest floor. Many forest soils are teaming with microorganisms and nutrient- rich hummus from composting wood and leaves. City soils may have herbicides present that damage microorganism balance. Add all these factors together and a birch tree starts to lose its natural defense capabilities.
However, this alone does not lead to the rapid tree deaths we are seeing currently. These deaths are usually due to two insects: the Birch Leafminer and the Bronze Birch Borer. Both can destroy a stressed tree in as little as two years.

Birch Leafminer

Birch Leaf Miner Larvae

Birch Leafminer Larvae

The Leafminer is a wasp-like insect; they lay eggs in birch leaves and the larvae hatch and feast on the leaves. Affected trees often have brown leaf patches in the mid-summer. Pulling apart an infected leaf in the early summer exposes orange colored “caterpillars.” Birch leafminers are most active in the late spring/early summer. These pests have a medium rate of tree destruction.

Bronze Birch Borer

Bronze Birch Borer

Bronze Birch Borer beside exit hole

The Bronze Birch Borer is a member of the beetle family: it bores holes into the circulatory system of the tree. The damage inflicted is similar to the devastating pine beetle: just peel back affected bark to see multiple winding trails made by these insects. An infestation leads to the tree losing sap circulation and dyeing from the top down. The presence of this boring insect is usually detected by large “D” shaped exit holes (although these may be too high up the tree trunk to be seen). Bronze Birch Borers are active most of the growing season and have a high rate of tree destruction.

So how does the average birch owner avoid a rapid death of their beautiful tree at the hands of these insects?

Here are a few tips for keeping your birch happy and healthy in the future:
  • Ensure your birch is well watered throughout the growing season; a lack of water often begins the process of tree top die-back and stresses the tree. A healthy birch can heal itself from a small insect invasion. Mulching around the rooting areas to cool and retain moisture also is beneficial.
  • If you suspect an insect invasion call your Arborist immediately for a diagnosis and treatment. If caught early, your birch tree may still be able to be saved. Treatment recommended for both insects listed above is an organic, ecologically-friendly trunk injection.
  • Keep your birch healthy with preventative trunk injections every second year administered by your Arborist. During these visits, you can also request a fertilizer treatment.

 

Please pass this information along, we hope these suggestions help ensure Calgary’s old and new birch trees remain in good health.