Paper birch & bronze birch borer

(Question)

My 40+yr old birch that suffered damage to the roots. I tried to save it, but it was so weakened the dreaded birch borer moved in. I had the tree cut down last fall (2014) and the stump removed (they just grind it up right in the ground). I would like to plant another paper birch but am concerned the borer might be alive in the ground. Is this a valid concern or would I be safe to plant another paper birch in the same location?

(Answer)

So sorry to hear of the loss of your lovely tree!

It is recommended that all wood from heavily infested trees be burned, chipped or removed from the property. Dead wood will not be reinfested. Presumably grinding the remaining bits of the tree (stump and roots) not only killed the tree, but also destroyed the borer larvae or adults, but it is possible that some may have survived.  The literature I located on borers notes that larvae may over-winter under tree bark, but does not address whether the pest can survive in dead tree detritus or soil.

In any event, experts recommend planting borer-resistant varieties of birch, e.g., the river birch, Betula nigra.  It is critical to keep your tree healthy, to make it less susceptible to attack by the pest.  This includes using adequate water and fertilizer, planting the tree in a semi-shaded spot, where the soil is relatively cool and moist, and controlling other insects that might attack the tree.  One example that illustrates how healthy trees fight off the borers is that – even where larvae have bored holes — good sap flow can drown the critters!  It is the sick, weak trees that are more likely to be targeted by borers.

If you are determined to have a paper birch (Betula papyrifera) in your yard, you might want to consult an arborist, to ensure that your birch has the best possible chance of thriving.  Landscape Ontario or your local nursery may be able to help you find one.

See Bronze Birch Borer: A Toronto Master Gardeners Guide,  which provides details about this horrid pest and how to prevent infestation.

Here are a few more helpful references you might want to consult: