My experiences of powdery mildew are limited to plants other than
Japanese maples and in the UK. However, powdery mildew over here is
usually on the upper side of leaves. I've got a dozen or so varieties of
palmatum and probably 300 or so plants of these dozen varieties. I've
never seen mildew on any of them. Oaks, crabapples, and a few other
species but never maples. I'd take a close up look with a lens or get an
expert near you to take a look. One thing that I have seen on the
underside of maple leaves is woolly aphid. Not sure if you get these in
Aus though?

As autumn is approaching for you, I wouldn't worry too much but keep a
close eye for the problem next year and be ready with the right remedy.

Good luck with the ID.

Kev Bailey
North Wales, UK


-----Original Message-----
From: Internet Bonsai Club ] On Behalf
Of jimitheskin
Sent: 11 April 2003 03:24
To:
Subject: [IBC] Powdery mildew on Japanese Maple (acer palmatum)

Hi guys,

I've just begun my love affair with bonsai, and am building up (i think)
a
good collection. I've had most of my plants for a few months now, and am
starting to experience a few problems. The one that concerns me tht most
is
one of my Japanese Maples, which seems to have a pretty bad case of
powdery
mildew (fine white powder on the underside of the leaves). I don't
really
know what has caused it - I have 2 maples and the other is fine (it is a
bit
more developed, perhaps more disease resistant). Anyway, I'm after
suggestions on what may have caused it and the best way to treat it.
I've
just begun praying with a fungicide (copper oxychloride), but I'm unsure
whether this is ok or will work (the guy at the nursery said it would,
but I
don't really trust him). I'm particularly concerned by the amount of
blue
powdery residue the spray is leaving on the leaves. The tree is a
sapling
about 9 inches high, still very slender in the trunk. I don't think it's
the
location, they get good part sun and virtually no wind, so it must be
something else. I was misting them regularly, and as it is now coming on
autumn here (I live in Newcastle, Australia) perhaps I've been keeping
it
too moist? Thanks in advance, any suggestions will be gratefully
received.

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