Very bad white staining on Acer leaves

KL · August 2019

I have been away for 5 weeks and since my return noticed that the leaves on my purple Acers are covered very badly in white powder. Is there any way to get rid of this and is it harming the trees ?

fidgetbones · August 2019

Powdery mildew. The trees are probably too dry at the roots. The grass is competing for food and water. I would lift all the grass around those tress (the whole strip) water well and then use a mulch of crushed bark or composted manure. It is too late to save the leaves for this year(but could save the tree), but that should improve matters for next year. As they are deciduous trees, I would underplant with spring flowering bulbs which can then naturalise , and as they go dormant in summer, will not affect the trees at all.

JennyJ · August 2019

I agree. That strip of grass going right up the the wall and tree trunks must be a pain in the bum to mow and trim anyway. If you have to keep it, at least clear a large circle around each tree trunk. Grass outcompetes young trees, and there's also a risk of damaging the bark when you mow or trim near the trunks.

KL · August 2019

I was wandering if the grass was taking the water when I cut it yesterday as that strip was originally just earth but over a few years it has sprouted grass on its own at a hefty rate.

1. Do I put the mulch around the tree only or the whole strip ?
2. What do you mean by underplant ?
3. What does naturalising do

I’ve also just noticed green leaves on it this morning in large amounts.

Fairygirl · August 2019

Agree with the others. Put your mulch right along the full length of the space.
Underplanting just means putting other plants into that strip below your trees, once you've removed the grass.
Naturalising means those bulbs will spread of their own accord, without any input from you. Nice and easy

There are other groundcovering [clue's in the title

]plants you can use as well, which won't really affect the trees too. If you want to go down that route, you'll get plenty of suggestions on the forum, so don't hesistate to ask.

We're approaching bulb season, so you might want to invest in some shortly. Crocus are always a good bet - readily available everywhere, and some of the dwarf daffs are also good. The small bulbs are easier to put in when you have an established tree too, as they don't need much depth, and that avoids disturbing your tree's roots when you're making a hole for them

Bee witched · August 2019

Hi @KL,

Have you still got the label from these large leaved purple Acers?
If yes, then does it say what the ultimate height and spread will be?
The reason I'm asking is that your trees look very close to the wall.... and to each other.
Some of these acers get really big .... see this info from the RHS.

https://www.rhs.org.uk/Plants/89715/i-Acer-platanoides-i-Crimson-King/Details

So it would be worthwhile checking what yours are as they will be easier to put them somewhere with a bit more room now rather than when they've been in a few more years.

Bee x

JennyJ · August 2019

If it's specific branches that are producing green leaves then it could be reverting, or growing branches from the rootstock. If you want to keep the purple, you'll need to prune out the green-leaved branches. As they are standards, they could be grafted at the top of the trunks. Have a look at the top of the trunks, see if you can see a kind of knobbly lump - that will be the graft where the purple variety is grafted onto the rootstock. Any shoots or branches growing out from below the graft should be pruned right off or they will grow stronger than the purple variety and eventually take over. Post close-up pics if in doubt.

KL · August 2019

Thanks for all your replies. Since it’s a nice dry day I’m going to remove the grass and prepare it for the mulch. Is it purely a case of raking out the grass and covering with mulch or should I be doing more ? Also is the mulch just standard as what I can buy in B&Q or is there a specific type I should look out for ?

Fairygirl · August 2019

I doubt raking will be enough, you'll probably need a spade or similar to lift the turf Just be careful round the trunks, as you don't want to cause any damage. Your hands are more useful at that point

Bark is always a good mulch in a situation like that. There are various grades of it, so just choose which is most suitable for your budget.

JennyJ · August 2019

I think you'd need to lift the turf including roots, not just rake off the top growth, but be very careful not to damage any roots of the trees that are near the surface.

Any organic mulch would be fine. If you go for bark, the fine, composted stuff is better than coarse stuff that looks like raw wood chips. Give the trees a good watering before you put it on, and leave a small gap around each tree so it's not touching the tree trunks.

Fairygirl · August 2019

Snap @JennyJ

I forgot to mention watering though

Very bad white staining on Acer leaves

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