Street maple foliage problems

[thebonsaiproject]

I am a gardener in Toronto (zone 6) and have 5 maple trees across the city having the same foliage problems. Haven't been able to find anything yet and thought who better to ask then the maple lovers here who might have had something similar happen on their trees.

Ill do my best to describe it:

• Coming into spring, everything all the branches have good looking buds
• During spring a couple branches don't leaf out
  • Looks like all the buds on the branch dry out
  • Not sure if the branch is completely dead yet
  • Seems to always be mid way up the tree or closer to the apex
• Soil is clay-ish
• I don't think there was a hard frost
• Full sun - part shade
• Trees planted in the ground for 5 - 15+ years
• All over 7ft high
• I believe they are blood good maple
• I think this is the first year had any sort of issues like this
• Planted in front yards close-ish to the street and in back yards

Any thoughts would be awesome!

 

[Rivian]

Check dead branch cross section for discoloration

 

[SiccarPoint]

I had a potted (non-bonsai) maple that did this for four years before I finally cracked it (touch wood) this year. However, can't be quite the same case as you, because the issue was (spoiler) hot roots. I systematically worked my way through all the possibilities:
- Bad, easily saturated soil -> repotted into very freely draining mix (helped, but did not fix)
- Diseased? (no discolouration)
- Soil not draining well in concrete pot with only a single hole -> Drill more holes in pot. (No change to problem)
- Root system too weak to support all top foliage -> cut back hard (new growth initially strong, but then died back as before).
- Issue with direct sun. Here I got lucky in demonstrating the problem. I moved the pot to the lee of a south-facing wall, hoping I would get shade for a good chunk of the day. But, I didn't - the crown has been in the sun all year. But the pot is now 100% shaded. Moved it in March, and this year, it's growing like a weed without the dieback.

Having watched the dynamics for 5 years, I've concluded this kind of drying and blackening dieback is a maple's response to imbalance between foliage and roots. But of course, that means a bunch of possible causes. In your case, the combination of clay soil (unhappy roots) and direct sun (driving fast transpiration) is probably causing this. Neither of which is really fix-able per se. Has this year been particularly sunny/dry/hot in Canada? That might push them over the edge if previously happy, as in clay soil there's going to be a limit to the rate of water supply the roots can provide. Or could something have damaged the roots this year that has been previously absent?

 

[rodeolthr]

Is it possible that the trees experienced excessive drought/dry period last year. I've seen this happen the following year after landscape trees went through a drought period.

 

[Tums]

Check dead branch cross section for discoloration

You thinking verticillium wilt?

 

[Rivian]

It could be many things, but since the branches are dead anyway, theres no harm in cutting one up and maybe youll have your answer right away.

 

[thebonsaiproject]

Check dead branch cross section for discoloration

I'll try to check on a couple trees this week, and see what I find. Also, I had another look and most of the dying branches will be 90% dead with 1 or 2 leaves still on it (on a secondary/tertiary branch).

I had a potted (non-bonsai) maple that did this for four years before I finally cracked it (touch wood) this year. However, can't be quite the same case as you, because the issue was (spoiler) hot roots. I systematically worked my way through all the possibilities:
- Bad, easily saturated soil -> repotted into very freely draining mix (helped, but did not fix)
- Diseased? (no discolouration)
- Soil not draining well in concrete pot with only a single hole -> Drill more holes in pot. (No change to problem)
- Root system too weak to support all top foliage -> cut back hard (new growth initially strong, but then died back as before).
- Issue with direct sun. Here I got lucky in demonstrating the problem. I moved the pot to the lee of a south-facing wall, hoping I would get shade for a good chunk of the day. But, I didn't - the crown has been in the sun all year. But the pot is now 100% shaded. Moved it in March, and this year, it's growing like a weed without the dieback.

Having watched the dynamics for 5 years, I've concluded this kind of drying and blackening dieback is a maple's response to imbalance between foliage and roots. But of course, that means a bunch of possible causes. In your case, the combination of clay soil (unhappy roots) and direct sun (driving fast transpiration) is probably causing this. Neither of which is really fix-able per se. Has this year been particularly sunny/dry/hot in Canada? That might push them over the edge if previously happy, as in clay soil there's going to be a limit to the rate of water supply the roots can provide. Or could something have damaged the roots this year that has been previously absent?

Is it possible that the trees experienced excessive drought/dry period last year. I've seen this happen the following year after landscape trees went through a drought period.

Damn that's insightful, thanks for the info. I believe it has been a hotter this year (just arrived in Canada this year so I'll ask around). I also have a some other maples I can check in shadier conditions if they have the same symptoms. I guess my next problem is how do I resolve these issues on trees I can't dig up.

Something that might affirm what you are saying is on a particular site there are two larger and older maples starting to have this issue. A couple years ago a giant (~50ft) Norwegian maple was removed that would have shared a lot of the same root zone. Since it was taken out, the trees get much more sun and likely much more water (now that it is not sharing). I don't think the watering levels have been adjusted since.

 

[thebonsaiproject]

Check dead branch cross section for discoloration

Checked a couple trees and branches. No discoloration.