Looks like I have a case of mildew on an English oak. This is the first
time I've seen this. It started as small yellow dots on the leaves of a
branch in the apex, now those leaves are covered in yellow and
distorted. Now other leaves are showing yellow dots.

This tree was wintered outside last winter(buried + mulched). Seven
other Q. robur were wintered in a garage and show no sign of mildew.

I suppose I could defoliate the tree either gradually or completely(this
hasn't been done for a few years on this tree).

Any ideas on a fungicide or baking soda solution?

Powdery mildew on Oak:
http://www.mykopat.slu.se/mycorrhiza...er/mildew.html

Regards,
Alan

Blue Mountain Bonsai
Ontario, Canada
Zone 6