Air Layer Trouble?

[Warnold]

I started an air layer 4 1/2 weeks ago of a branch on my large Liquidamber (Sweet Gum) tree. Today I'm noticing the leaves at the end of the branch are turning reddish brown. I added some water to the sphagnum moss but the package looks fine. Should I consider cutting off some of the outer branch or just let it go? I was expecting another 4 to 6 weeks before seeing new roots. Thanks!
How it looked before adding some water.


Branch as it comes off the tree.


Leaves at end of branch.

 

[19Mateo83]

When you stripped the bark did you damage the wood underneath? It looks like it’s not getting fed by the tree and is drying out.

 

[AJL]

It looks ok to me - the tree is bound to react by showing some colour change in the leaves - just ensure its not drying out between waterings and have patience!

 

[Tieball]

That’s a huge branch.

 

[Tums]

Stupid question: how is the bag sealed at the top? It's not like wire that would choke into the branch above your desired layer?

 

[Warnold]

When you stripped the bark did you damage the wood underneath? It looks like it’s not getting fed by the tree and is drying out.

I stripped the bark and them removed the cambium layer. It peeled off leaving a smooth layer that I did not have to scrape anything off of.

 

[penumbra]

I believe the layering attempt is failed. Sweet gum is a tough candidate for layering.

 

[Warnold]

Stupid question: how is the bag sealed at the top? It's not like wire that would choke into the branch above your desired layer?

The bag is just wired on around the branch, not too tight.

 

[Lorax7]

I stripped the bark and them removed the cambium layer. It peeled off leaving a smooth layer that I did not have to scrape anything off of.

Based on this description, I’m not entirely sure that you’ve removed the cambium. Usually, when you make the two cuts at the top and bottom of the girdle region there is a layer of bark that separates easily and leaves a smooth surface underneath. That layer that separates easily is not the cambium. The cambium is the surface layer of the smooth part underneath and you have to scrape it to remove the cambium.

 

[0soyoung]

This is a normal reaction to a girdle. It arises because the girdle causes an accumulation of auxin just above it. The high levels of auxin cause an ethylene precursor to be produced, some of which goes into the xylem water stream. The part left just above the girdle is converted to ethylene which causes the enhance radial growth (swelling) that you probably can see now, immediately above the girdle. The part that went into the xylem water stream gets converted to ethylene by an enzyme in the leaves, and causes them to change color like they do in fall,

Not to worry, though, high levels of auxin in the tissues immediately above the girdle are what causes cambium cells to morph into roots.

One (you) can demonstrate this by dusting a girdle/partial-girdle with high concentration IBA/NAA, If you wish. The stronger the powder, the stronger the color change. Also, a tight tourniquet and even just wire biting-in on a branch will cause similar effects, if you want to explore/experiment. And, of course, you can take the deep-dive into scholarly papers on the subject of the ethylene chain with the help of Google Scholar anytime you've got the will-power.

 

[Warnold]

This is a normal reaction to a girdle. It arises because the girdle causes an accumulation of auxin just above it. The high levels of auxin cause an ethylene precursor to be produced, some of which goes into the xylem water stream. The part left just above the girdle is converted to ethylene which causes the enhance radial growth (swelling) that you probably can see now, immediately above the girdle. The part that went into the xylem water stream gets converted to ethylene by an enzyme in the leaves, and causes them to change color like they do in fall,

Not to worry, though, high levels of auxin in the tissues immediately above the girdle are what causes cambium cells to morph into roots.

One (you) can demonstrate this by dusting a girdle/partial-girdle with high concentration IBA/NAA, If you wish. The stronger the powder, the stronger the color change. Also, a tight tourniquet and even just wire biting-in on a branch will cause similar effects, if you want to explore/experiment. And, of course, you can take the deep-dive into scholarly papers on the subject of the ethylene chain with the help of Google Scholar anytime you've got the will-power.

Thanks for your comprehensive reply. this gives me a lot to consider and learn!

 

[andrewiles]

Based on this description, I’m not entirely sure that you’ve removed the cambium. Usually, when you make the two cuts at the top and bottom of the girdle region there is a layer of bark that separates easily and leaves a smooth surface underneath. That layer that separates easily is not the cambium. The cambium is the surface layer of the smooth part underneath and you have to scrape it to remove the cambium.

This doesn't match my experience. I've done quite a few air layers over the past few years, mostly in spring when the ring of bark separates cleanly. I spray isopropyl alcohol on the exposed section to kill any lingering cambium cells but otherwise do not scrape any further into it. I haven't had problems with bridging, etc.

If I layer earlier in the season before the pholem and bark peel off easily, then I can be left with green layers that need to be scraped off. But that's rare once their tree wakes up.

 

[Lorax7]

This doesn't match my experience. I've done quite a few air layers over the past few years, mostly in spring when the ring of bark separates cleanly. I spray isopropyl alcohol on the exposed section to kill any lingering cambium cells but otherwise do not scrape any further into it. I haven't had problems with bridging, etc.

If I layer earlier in the season before the pholem and bark peel off easily, then I can be left with green layers that need to be scraped off. But that's rare once their tree wakes up.

OP made no mention of using isopropyl alcohol and stated that they did not scrape anything. That’s why I am uncertain if the cambium was actually removed. Don’t need to do both techniques, but should really do one of them to be certain no living cambium remains.