Soil Drench for Bronze Birch Borer

Asked March 31, 2020, 10:17 PM EDT

Hi, I live in Eugene, Oregon and have 9, twelve year old birch trees in my yard. So far I have succeeded in keeping them relatively alive & healthy, although they are and have been attacked to varying degrees by the Bronze Birch Borer. The key to my success I believe, is a water drip system on each one every day throughout the summer. I also do a soil drench of Imidacloprid, per instructions every year, My question is, when is the best time to do the soil drench. I have done quite a bit of research on it, and there are many different answers. I have been doing it in spring, after the catkins have released most of their pollen and before leaf out. Haven't found any evidence of honey bees doing much if any harvesting of birch pollen. Another point on that is, I believe it can take a month or more for the Imidacloprid to reach the top of the tree? I will certainly appreciate you thoughts and advice on the best time to do a soil drench. Thank You, Stephen Bianco

Lane County Oregon

3 Responses

The best time to do a soil drench is when the tree starts to put out new growth in the spring. Generally, the best practice for protecting pollinators is to wait until after flowering to apply any pesticides. Birch trees are wind pollinated so most pollinator activity around birch trees is exploratory and incidental, but to reduce risk of exposure it is best to wait until after flowering. The important thing is to water regularly, via rain or irrigation, and deeply after the drench to ensure the product is being taken up by the tree. It will take a few months for the tree to take up all the product from the soil. I hope that helps. For more information on control of Bronze Birch Borer, check out this homeowners guide:

Thank you Erica. :)

Thank you Erica. :)