AusBonsai

Hey everyone. My Japanese maples have been hit with powder mildew for the first time this year. I tried stuff like nature soap and pest oil, I’ve tried thinning out the leaves and moving to a position where airflow is ok. Two questions - liquid copper fungicide - yes or no? And ... almost total defoliation at this time of year - yes or no? Thanks I’m advance.


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You can defoliate but it puts more stress on plants imo.
At this time of year I use milk with no detrimental effect to the plants. Milk is as good as any chemical in some cases better. JP are very delicate and easily detest chemicals so try this.
Mix 60 parts water with 40 parts milk and spray onto the affected plants fortnightly including top of soil. Whole milk or Skinny doesn’t matter whole milk will be a stronger mix. Or mix 1 oz/ or 30g powdered milk to 2 liters of water, and spray onto affected plants fortnightly.
Cheers
Kirky

Frankly it’s somewhat of a miracle you haven’t had it up until now mate. They are wildly susceptible to it I have found with the only cultivar exception of what I‘ve tried being shishigashira. Thus far I’ve not had mildew on it *touch wood* and Shindeshojo was the worst affected.

Each Powdery Mildew is quite specific to what host plant it attacks, so it shouldn’t spread from your maples to other things. Some tend to be easier to control than others; I’ve found maple mildew not the hardest but not necessarily easy either. Make sure you coat as much as you possibly can, any spores left will just multiply again. It will take multiple applications over many weeks to control it.

As mentioned the leaves are likely to burn with chemical use, so trying milk first isn’t a bad idea. Defoliation should be a last resort thing in my opinion as when I’ve tried it I’ve always had uneven regrowth with some parts being very strong and others very weak.

Copper, at least how I use it at work is more preventative than curative but that’s on bedding plants not maples. Otherwise at work it’s an imaginative range of strong fungicides that would roast maple leaves.

You can use copper / copper sulphate when dormant but nit now.
Cheers
Kirky

I use copper fungicide on bedding plants at work with no ill effects to foliage, but I have not tried it on maples being so delicate.

I’ve used lime sulphur at 15% solution too during dormancy as a basic preventative, but certainly not now!

I've used copper fungicide on a maple when the branches started turning black, which I'd read could be caused by a fungal infection. It didn't seem to affect the leaves but the whole thing eventually ended up dying anyway so make of that what you will.

Thanks everyone - much appreciated. I'll let you know how I go.

Cheers,

Mark

See if you can track down a product called EcoCarb. I use it as one of my less aggressive (read toxic) treatments and I have had some success with it. It almost instantly knocked out PM on Dahlia, but has been totally ineffective on the PM that affects Carnations so no promises with this one but it is a relatively gentle spray option compared to the really hardcore ones. It’s just potassium bicarbonate as the active.

Edit: Bunnings stocks it, or a version of it, as a product called Eco-Fungicide

Thanks Tim.


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