Did sunburn kill my new bud?

[pandacular]

This Saturday, I noticed a new bud on the trunk of my tree (Azara microphylla). I was excited, as this back bud was in the exact right spot on the trunk where I eventually want to develop a new branch. This piece was facing away from the sun before, so I happily turned it around to get some more sun.

Today, I checked in on the tree and noticed that it was fried black



I know there's likely no saving this bud (turned it back around just to be safe though), but I want to know if my suspicion is right that this was killed off by the sun due to lack of cuticle or shade.

 

[caffeinated]

Most likely, since we were just coming out of a long spell of damp overcast weather until the end of last week. I got some crispy leaves on a couple trees that can usually handle mid eighties when it comes on gradually.

 

[pandacular]

Makes sense. Something similar happened to my red maple at the end of May when we got a blast of heat. I should be more diligent about protecting new growth in heavy sun, as I only have a little shade on my rooftop garden. Probably will settle for an umbrella for now.

 

[Shibui]

If sun is to blame I would expect to see more black leaves that were previously shaded. I guess it is possible that this shoot is the only part of the tree that was previously shaded but that has got to be a long shot.
Just because it is a young shoot does not mean it is more tender than an older branch. Leaves are leaves wherever they are on the tree.

Low shoots are usually inherently weak because of apical dominance. Trees put most resources into high branches and auxins flow down to suppress lower shoots. If I really want to promote low shoots I trim upper shoots harder to remove the auxins and allow the low shoots easier growth till they get going strong.

 

[pandacular]

It's possible that I damaged this shoot while handling or water the tree the other day. I don't see any other damaged foliage (though will be keeping an eye on it) and it really hasn't been *that* sunny, so I wonder if the damage is consistent with damage to the petiol or branch.

 

[pandacular]

Just because it is a young shoot does not mean it is more tender than an older branch. Leaves are leaves wherever they are on the tree.

is this true even with respect to the formation of cuticle? This shoot is a noticeably different color than the older growth. Or I should say was, before it turned black.

 

[Shibui]

I wonder if the damage is consistent with damage to the petiol or branch.

Probably more likely, especially given there's no other sign of sun damage anywhere else and that it has not been overly hot or sunny.

is this true even with respect to the formation of cuticle? This shoot is a noticeably different color than the older growth.

Pretty much true. Each leaf develops hardiness depending what it is exposed to rather than the age of the shoot it is on. Differences in color are usually the result of different amounts of sun in much the same way as our skins provide protective coloring in response to increased exposure. Leaves also develop some sort of sun screen that protects them from UV. Trees that are moved from shade to direct sun usually suffer sun damage unless the change is slow enough for them to develop protection.
Bark color is a bit different. Age seems to be the determining factor for stems and bark to change color but a similar length of similar new shoot should exist at the tips of most branches because all should be growing at similar rates.