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Old June 22nd, 2010, 08:23 PM
Curious Arborist Curious Arborist is offline
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Powdery mildew on Crimson King Maple

How can I get rid of what appears to be powdery mildew on the leaves of my Crimson King maple. This mildew appears every year at this time. The tree was pollarded 3-4 years ago. Since then it has been selectively pruned in an attempt to perform a structural crown restoration. Any suggestions?
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Old June 22nd, 2010, 08:39 PM
ryansenechal ryansenechal is offline
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Re: Powdery mildew on Crimson King Maple

Pollarding is not a single event, but an annual technique starting with a young tree. Single event heavy reductions fall under two categories -- one being topping and the other being a crown reduction (which is usually a response to a declining tree dying from the crown tips inward). Proper pollarding puts enormous stress on a tree which can weaken defense to common pathogens and insects. Topping and crown reductions have a more drastic effect, amplified by large wounding.

Now for your Powdery Mildew issues:
Port Coquitlam's municipal cosmetic fungicide ban takes all chemical controls off of the table. Crimson King is naturally very susceptible to the pathogen and although the issue catches your eye, it likely is not much more than a cosmetic issue. Leaf wetness is the primary factor after this very wet, cool spring.
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Old June 22nd, 2010, 08:46 PM
Ron B Ron B is offline
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Re: Powdery mildew on Crimson King Maple

I'd say the mildew in this case is probably a byproduct of the pruning*, the one that really mildews too much down here - whether pruned or not - is the 'Crimson King' bud sport Crimson SentryTM. Since both are examples of Acer platanoides I would not grow either. This region does not so far have the Norway maple problem of eastern North America but there are places in and near Seattle where appalling numbers of the things have popped up - despite our dry summer conditions. In fact, these seedlings appear to be more drought resistant and much better at persisting through the first year than our native A. macrophyllum.

*Unless these are pretty much now all mildewing up there, perhaps with a different strain of mildew present than we have here
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Old June 22nd, 2010, 08:50 PM
ryansenechal ryansenechal is offline
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Re: Powdery mildew on Crimson King Maple

Quote:
Originally Posted by Ron B View Post
Since both are examples of Acer platanoides I would not grow either.
Likewise.
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Old June 23rd, 2010, 05:37 AM
Michael F Michael F is offline
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Re: Powdery mildew on Crimson King Maple

Agree, best to get rid of it, given its invasive habits.

Quote:
Pollarding is not a single event, but an annual technique starting with a young tree
For clarification, not necessarily (nor usually) annual; pollarding rotations are typically anything from 3-20 years.
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