Trident maple leaf turning black

[hellorp1990]

Hi everyone, one of my trident maple leaves are turning black.
I performed root over rock in March. And then leaves came out nicely but since last week the leaves are droopy and turning black.
I did the scratch test on bark and it’s green.
I already put the tree under shade.
Can anyone help me in diagnosing ?

 

[Gabler]

I don't know what it is, but I had the same problem with some Japanese maple seedlings this spring. A foliar fungicide treatment seems to have arrested the wilting problem. I had already applied a systemic fungicide about a week before I started seeing the wilting.

 

[hellorp1990]

@Gabler should I use a fungicide then?

 

[bonsaiwood]

What is your location? This will help others better understand what your climate is like and how to best answer your questions.
If you are misting the tree or excessively wetting the foliage, this could cause early season shoot rot. I would remove anything diseased now and only apply water to the soil when it feels dry.

 

[hellorp1990]

@bonsaiwood i am in zone 7A (Maryland).

 

[bonsaiwood]

I already put the tree under shade.

Trident maples prefer sun. Keeping it in a mostly shaded and damp environment could make the problem worse. Search for a place in your garden where it can receive plenty of morning sun and filtered afternoon shade. The suns UV combined with removal of diseased plant material can significantly help. If you have sprinklers running nearby, try not to let the tree get doused. Stick to a watering can/wand or even better, a drip system. The healthy green growth at the tips of the branches tell me the tree is not deficient in water, but it does appear to be reaching for sunlight.
Your tree would also benefit from late summer pruning i.e. shortening or complete removal of leggy branches and training up a single leader. Search the forums for references, you will find a wealth of information on growing and caring for Trident maples.

 

[hellorp1990]

@bonsaiwood thank you so much for your detailed response. My other tridents are doing fine in morning/afternoon sun. I pruned them as well.
This trident I did some pruning but I didn’t prune much as I did root over rock and buried it deep.
I will put it in sun (it was under sun but it was wilting and black leaves, that’s why put it in shade) now.

 

[bonsaiwood]

I will put it in sun (it was under sun but it was wilting and black leaves, that’s why put it in shade) now.

Nothing wrong there since you do not know what exactly is causing the problem,
hence, the need to ask the forum. Take my two cents with a grain of salt- after all, we are on opposite ends of the country in two very different climates. However the same principles for growing maples still apply, be it in Cali, Maryland, or Australia. I’m newer to the forum (not so new with plants) and have found a few folks who seem to have a good grasp on working with maples, particularly @Shibui , @SeanS
Welcome to Bnut.

 

[Jrmcmich]

Is it drying out during day? Hard to tell how large pot is. Also wonder if buried too deep if that could impact? @Shibui and @SeanS definitely have much more experience so hopefully they might respond as @bonsaiwood mentioned.

 

[Shibui]

Looks more like dehydration than fungus to me.

Also wonder if buried too deep if that could impact

I don't think it is possible to bury a trident too deep. If the trunk is buried they just grow a whole new set of roots just under the surface.

I performed root over rock in March. And then leaves came out nicely but since last week the leaves are droopy and turning black.

Without knowing how or what you did with the roots and rock my guess is this is the real reason here, especially as you mention the other tridents are unaffected.
Reducing roots but not the top just before leaves sprout can cause imbalance between water use (leaves) and water supply (roots) The tree then adjusts demand to match supply by letting a few leaves die. I've seen similar results after trying late spring root pruning. All the leaves turned brown but after a few weeks when the tree had regenerated enough roots new shoots emerged.

You may also not be aware that any pot with a rock will need lots more water than a similar tree/pot without a rock. Rocks absorb water. when part of the rock, including a rock slab, is exposed to the air it then evaporates water into the air so acts as a wick to suck moisture out of the soil and dehydrate the tree.
In this case the rock is buried so can't transfer water to the air but have you considered how much space that rock is taking up in the pot? In essence your tree is growing in a much smaller pocket of soil than trees in similar post without rocks. The space taken up by the rock cannot store water. The tree is reliant on a much smaller volume of soil to hold and supply water. Have you increased watering to compensate?

My recommendation would be to leave it alone now and let the tree adjust. Increase watering if necessary.

BTW, I am NOT in favour of the so called scratch test. Scratch test will not cure an ailing tree so it's of no real benefit. It can't tell you anything more than tree is alive or dead which will be obvious without scraping through the bark anyway. A tree will either live or die with or without the scratch test so the test is of no benefit. Scratch test cannot tell you what is wrong or how to treat it so of no real benefit. Scraping through the protective bark can admit more pathogens so is probably much more detrimental than of any practical use.

 

[Gabler]

which will be obvious without scraping through the bark anyway

It's not obvious if you don't spend much time around trees. There's a shift in color and a dried out look to dead branches, and that's obvious to anyone who spends a lot of time looking at tree branches, but it's not obvious to newcomers who can't tell an elm from a maple.

Otherwise, I agree. I just figure it's worth mentioning that it takes time to learn to distinguish a live tree from a dead one at a glance.

 

[Gabler]

@Gabler should I use a fungicide then?

It doesn't look to me like it's caused by a lack of water or by overwatering, since the highest leaves are least affected. I would guess that it's from a pathogen, and tree pathogens tend to be fungal. @Shibui knows better than I do, so take that with a grain of salt.

 

[hellorp1990]

Is it drying out during day? Hard to tell how large pot is. Also wonder if buried too deep if that could impact? @Shibui and @SeanS definitely have much more experience so hopefully they might respond as @bonsaiwood mentioned.

I buried deep due to the root over rock procedure. I hope this is not the cause . Will keep you all posted

 

[hellorp1990]

Looks more like dehydration than fungus to me.

I don't think it is possible to bury a trident too deep. If the trunk is buried they just grow a whole new set of roots just under the surface.


Without knowing how or what you did with the roots and rock my guess is this is the real reason here, especially as you mention the other tridents are unaffected.
Reducing roots but not the top just before leaves sprout can cause imbalance between water use (leaves) and water supply (roots) The tree then adjusts demand to match supply by letting a few leaves die. I've seen similar results after trying late spring root pruning. All the leaves turned brown but after a few weeks when the tree had regenerated enough roots new shoots emerged.

You may also not be aware that any pot with a rock will need lots more water than a similar tree/pot without a rock. Rocks absorb water. when part of the rock, including a rock slab, is exposed to the air it then evaporates water into the air so acts as a wick to suck moisture out of the soil and dehydrate the tree.
In this case the rock is buried so can't transfer water to the air but have you considered how much space that rock is taking up in the pot? In essence your tree is growing in a much smaller pocket of soil than trees in similar post without rocks. The space taken up by the rock cannot store water. The tree is reliant on a much smaller volume of soil to hold and supply water. Have you increased watering to compensate?

My recommendation would be to leave it alone now and let the tree adjust. Increase watering if necessary.

BTW, I am NOT in favour of the so called scratch test. Scratch test will not cure an ailing tree so it's of no real benefit. It can't tell you anything more than tree is alive or dead which will be obvious without scraping through the bark anyway. A tree will either live or die with or without the scratch test so the test is of no benefit. Scratch test cannot tell you what is wrong or how to treat it so of no real benefit. Scraping through the protective bark can admit more pathogens so is probably much more detrimental than of any practical use.

Thank you so much for your reponse. I usually check all my trees with finger test and then put water.
I was not aware of the information regarding the watering and rock. I will keep it in mind.
Great information on the bark test . I will keep it in mind. Also I am attaching a pics during the root over rock procedure. I am pretty much a beginner in this procedure.

 

[Shibui]

Thanks for the follow up pic. You've left plenty of roots which should rule out one of the possible issues of a tree trying to support new leaves and growth with limited roots, though tridents can usually cope with massive root reduction in winter and spring.
I would usually try to get a few more main roots around the rock where possible. A single root running down the rock may end up looking OK but I think several looks more natural.
Something you may find is that tridents tend to throw more roots right at soil level when planted deep. Often those new roots grow way better than the deeper root wrapped around the rock. I've developed the foil wrap method to counteract those 2 issues. If you have not used foil or some other wrap I would recommend checking roots next spring to make sure your trident is not doing anything unwanted.

Fingers crossed that there's nothing fatal happening.

 

[hellorp1990]

Thanks for the follow up pic. You've left plenty of roots which should rule out one of the possible issues of a tree trying to support new leaves and growth with limited roots, though tridents can usually cope with massive root reduction in winter and spring.
I would usually try to get a few more main roots around the rock where possible. A single root running down the rock may end up looking OK but I think several looks more natural.
Something you may find is that tridents tend to throw more roots right at soil level when planted deep. Often those new roots grow way better than the deeper root wrapped around the rock. I've developed the foil wrap method to counteract those 2 issues. If you have not used foil or some other wrap I would recommend checking roots next spring to make sure your trident is not doing anything unwanted.

Fingers crossed that there's nothing fatal happening.

Can you please explain the foil wrap method?

 

[Shibui]

Can you please explain the foil wrap method?

Here's one page on Shibui Bonsai with some details - https://shibuibonsai.com.au/?p=188
If you search 'foil' on the Shibui Bonsai blog you'll find a few pages of info at various stages in ROR production.