When / how to apply imidacloprid as soil drench for birch trees? - Ask Extension
Hi! I have ~15 very large birch trees lining my driveway, and was recently advised by my tree service to begin treating for bronze birch borer as a pr...
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When / how to apply imidacloprid as soil drench for birch trees? #631751
Asked May 05, 2020, 6:58 PM EDT
Hi! I have ~15 very large birch trees lining my driveway, and was recently advised by my tree service to begin treating for bronze birch borer as a preventative. No sign of the borer at this time but I'm hoping to keep these trees going as long as possible. The trees have an average diameter of ~22 inches (65 inch circumference) at chest height.
Data sheets on imidacloprid indicate how toxic it is for bees, and there are many honeybee hives in my area that I do not wish to harm. There are many flowering plants around the base of these trees so I worry that a soil drench will be taken up by the flowers and pass imidacloprid into the pollen.
Given all this, do you recommend I treat these trees with imidacloprid? And is there a safe time to do so, given the bee concern? Thanks, as always, for any advice you can provide!
Clackamas County Oregon
Expert Response
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 incidental, but to reduce risk of exposure it
is best to wait until after flowering.
In terms of the other flowering plants at the base of the birches, wait until they are done flowering to apply the drench.
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.
For more information on control of Bronze Birch Borer, check out
this homeowners guide: https://catalog.extension.oregonstate.edu/sites/catalog/files/project/pdf/em9189.pdf
Thank you, Weston! I appreciate your quick and expert reply. I have checked out the homeowners guide you provided, and will schedule the soil drench as soon as the plants beneath the trees are finished flowering. Hopefully we'll still be in the rainy season but if not I can do the deep watering via drip hoses as needed.
Thanks again!
Thanks again!
