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.

Powdery mildew isn't yellow, and I have NEVER heard of it on an
oak! Tho the page you supplied says it does infect oaks -- in
Europe, at least -- it also doesn't indicate that it's yellow.
Powdery mildew is a gray "dust" on leaves, and that's what the
picture seems to show.

The page also suggests some fungicides, but if you have lime
sulfur on hand, it should do the trick (IF it is powdery
mildew!!!!!).

Jim Lewis - - Tallahassee, FL - Who has
several crape myrtles with PM (in the yard -- and they're about
to get cut down!)

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

That shouldn't have made a difference, unless the other trees stayed
in the garage during the spring infection period, or unless the
buried tree was mulched in infected oak leaves.


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

Powdery mildew isn't harmful on oaks (it's more unsightly than
anything else); what you should do is to wait until fall and remove
the leaves as they senesce; those yellow dots are the over-wintering
stage, and will be infective next spring.


Any ideas on a fungicide or baking soda solution?

Too late for this year; next year you could treat the leaves
prophyllactically, but home-recipe baking soda won't work on oak
leaves; you should buy a formulated baking soda fungicide with
adjuvants to allow better penetration, or find a fungicide labeled
for powdery mildew on ornamentals.

Nina, who just took her applicator's license test, hence use of words
like "prophyllactic" and "adjuvant".

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Powdery mildew isn't yellow, and I have NEVER heard of it on an
oak!

Powdery mildew is common on oak, but the "powdery" stage is hard to
see- whereas the sexual state is large and distinct. It starts out
bright yellow, and then, as it matures, it turns chestnut brown.

The Tulasne brothers, pioneers in plant pathology, figured out that
the powdery stage and the sexual stage were parts of the same
organism in 1861, and the "Father of Mycology", Anton de Bary, nailed
the details in 1863. I am very proud to be an academic descendant of
de Bary's, since my chair was a student of Fitzpatrick, who was a
student of one of de Bary's students.

Nina, who is now studying the genus Phytophthora, which De Bary named in 1876.

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************************************************** ******************************
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+++++ Questions? Help? e-mail +++++

Powdery mildew isn't yellow, and I have NEVER heard of it on
an
oak!

Powdery mildew is common on oak, but the "powdery" stage is
hard to
see- whereas the sexual state is large and distinct. It starts
out
bright yellow, and then, as it matures, it turns chestnut
brown.

The Tulasne brothers, pioneers in plant pathology, figured out
that
the powdery stage and the sexual stage were parts of the same
organism in 1861, and the "Father of Mycology", Anton de Bary,
nailed
the details in 1863. I am very proud to be an academic
descendant of
de Bary's, since my chair was a student of Fitzpatrick, who was
a
student of one of de Bary's students.

Nina, who is now studying the genus Phytophthora, which De Bary
named in 1876.


OK. Wow, I try to learn something new every day! Today, it got
fed to me (hope that counts). I guess my books don't like to
talk about sex.

FORGET WHAT I WROTE! Listen to Dr. Nina!

Jim Lewis - - Tallahassee, FL - "People,
when Columbus discovered this country, it was plum full of nuts
and berries. And I'm right here to tell you the berries are just
about all gone." -- Uncle Dave Macon, old-time musician

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Nina,
Thanks, I'll follow your advice. All this mycology is way more
complicated than bonsai!

Now, if I can just find out what ate the truffles(mushrooms), in the
pots. Those nasty little squirrels no doubt!

Best regards,
Alan

Blue Mountain Bonsai
Ontario, Canada
Zone 6