Case Study of severe sunscald on a Liberty Apple Tree

[Native Hunter]

Sun scald is caused by the freezing of bark on a tree that was earlier heated up on a warm, sunny day in the winter. The result can be permanent damage to the tree.

Trees are exposed to the most sunlight on the southwest side of the tree. On a sunny winter day this side of the tree can thaw out and become heated to the point that the cells open up – somewhat like breaking dormancy.

The temperature required to wake up a tree depends on local conditions and surrounding vegetation, but typically the temperature will be just above freezing or even warmer. The opened up cells on the southwest side of the tree are unable to return to dormancy by nightfall when the temperatures fall again.

This sets up the perfect storm for problems – especially if the sequence is repeated. The difference in the bark on the southwest side compared to bark on the other side of the tree creates an effect that can cause the bark on the southwest side to separate from the tree trunk.

Even years ago before I got into growing many apples, I was aware of damage to trees I had planted for ornamental purposes in the yard. Even dogwood trees can be affected by this phenomenon.

Some of the methods of prevention are shown below. I won’t go into detail here, because you can find detailed information regarding this on the Internet. My purpose with this thread is to illustrate a severe case:

• Painting the tree trunk with white paint (various recommendations)
  
  
• Wrapping trunk with a protective covering (some wrap in the fall and remove in the spring)
  
  
• Setting up a board of piece of plywood on the southwest side to block sunlight. (this could be attached to the cage)

I seldom see sunscald injury in my farm tree planting, because during winter there is enough vegetation (and nearby trees) around to provide some shading. However, in my clean and fully exposed south facing yard at home, I have the perfect storm situation.

This thread documents the most severe case of sunscald I have ever observed. It happened on a six or seventh leaf Liberty on MM111 rootstock. The recommended treatment for dealing with this injury is to take a sharp knife and shave back the bark to the point it is still attached to the tree. The hope is that the wound will eventually heal over.

However, in this case – the bark separated around the entire tree – actually leaving an air space between the bark and the tree.

Rather than replace the tree right now I have decided to just let it stand until it eventually breaks off. Actually I have a Liberty sprout coming off above the graft that I will try to keep alive, and when the tree eventually breaks off, I will saw it off just above the sprout and pile dirt on top of that – in hopes that the sprout will take root above the graft and make a full sized Liberty tree.

If that fails, I will break down and plant another tree. Yes, I can be stubborn and don’t give up easily…LOL. Actually, this tree is still bearing nice apples – just as well as it ever did. Why should I be in a hurry to do anything else???

These pictures are 3 years (maybe 2, I don’t remember for sure) after the event occurred.

First picture show the air gap between bark and tree. Notice how the bark is now over 1.5 inches thick. This is the tree’s natural reaction – trying to compensate for what it has experienced. This tree is essentially dead, but just trying to hang on.




Second picture shows just another view of the same thing.




Third picture show my little sprout above the graft that I will try to nurture to start a new tree when the inevitable eventually occurs.




This last pic shows the tree still making apples. Actually, the top of the tree is very healthy, and the tree had a fine crop last year, but it’s just a matter of time until the death occurs.



I just got in the mood to talk apples today and decided to post this thread. I hope someone benefits from it and gains some knowledge. I’ve learned a lot with this.

 

[Neahawg]

I'd it happens again native you can do a bridge graft and it may help it heal better over the long term

 

[Native Hunter]

I'd it happens again native you can do a bridge graft and it may help it heal better over the long term

Yes.

At the time this happened someone else mentioned that, but I wasn't into any grafting back then. I also wondered how successful it would be with complete separation of the bark from the tree. If I had something similar happen now, I would likely try that process. If anyone has successfully done this where there was complete separation, I would like to know about it for future reference.

 

[Neahawg]

I never had to do a bridge graft but in theory I would think it would work if you 2 or three of them around the tree. As long as the grafts took the should heal and fill in the gaps.

 

[Native Hunter]

I never had to do a bridge graft but in theory I would think it would work if you 2 or three of them around the tree. As long as the grafts took the should heal and fill in the gaps.

Wonder if I could do it now?

 

[chickenlittle]

Since that dead section will eventually fail, I would cut it off just below that damage next winter. I can't tell exactly where the graft union is but if that is above the union, you should get several sprouts of Liberty. Select one and it will grow into a nice, solid tree in a few years.

 

[Native Hunter]

Since that dead section will eventually fail, I would cut it off just below that damage next winter. I can't tell exactly where the graft union is but if that is above the union, you should get several sprouts of Liberty. Select one and it will grow into a nice, solid tree in a few years.

That is kind of the plan I had, except that I might leave the tree a little longer based on how big the sprout is. I also noticed today that the rootstock has put out some sprouts a few inches away. If the Liberty sprout doesn't work, those rootstock sprout should grow rapidly, and I could pick the best one of those and graft it.

 

[sandbur]

Some recommend leaving a lower limb on the southwest side of the tree to reduce danger of sunscauld. I am not so sure that having the first scaffold at 5 or 6 feet for a wildlife tree is a good thing.

 

[chickenlittle]

The liberty sprout will probably grow slowly until you take the top off. The top is getting most of the resources. Worst case would be the top breaks under fruit load and does more damage below the sunscald.

 

[Native Hunter]

The liberty sprout will probably grow slowly until you take the top off. The top is getting most of the resources. Worst case would be the top breaks under fruit load and does more damage below the sunscald.

Yes, I agree that the growth of the sprout is being slowed by leaving the main tree. I will probably assess the situation at the end of the growing season this year and make a decision then on when to remove the damaged tree.

 

[Neahawg]

Wonder if I could do it now?

If you wanted to just try it I don't see anything wrong with it. The only trouble I can see is the middle portion is for sure dead so you would need to leave a big enough gap you could remove it later on before the gaps filled in.

 

[CrazyEd]

Trees don't leave my apple tree factory without white painted trunks and window screen to protect them.

 

[Appleman]

I have been trying to hash this out for years why some trees in the orchard develop sunscald and others have not. Here are some observations and would like to compare notes to see if their is any correlation. 1) Most all Trees grafted to M7 developed some degree of sunscald while only a few M111 had slight damage. 2) 90 percent of my trees in the orchard are grafted to B118 with zero showing any sunscald damage. 3) Use of aluminum screening to protect from vole damage has been used since first introduced B118 to the orchard. 4) Sunscald damage m7 and m111 seen prior to using screening. Conclusion: Aluminum screening my prevent or slow sap flow during winter thaw thus reducing chance of developing sunscald and/or B118 may promote less damage due to delayed sap flow inherent in the b118 root system. This hypothesis is from empirical observation at my site and is far from conclusive. What are your thoughts?

 

[sandbur]

I thought it occurred when we had very cold nights and sunshine during the day. One side (SW) of the tree warms up from sun in late afternoon or just before sunset as the rays hit the vertical trunk. Then a sudden drop in temperature occurs as the sun goes behind the trees. I thought it could occur with daytime highs that were well below freezing and perhaps even below zero.

Shading the trunk makes the difference, and weeds on the SW side can shade the trunk, leaving lower branches on the SW shades the trunk, and window screen shades the trunk.

I have a few trees with signs of sunscauld on the east side in an exposed location.

My thoughts are that pruning with long sections of exposed trunk might not be so good in the Minnesota climate if you are in the exposed, prairie type environ.

Maybe I am completely wrong.

There are probably different mechanisms for sunscauld in different climates.

 

[Native Hunter]

I have been trying to hash this out for years why some trees in the orchard develop sunscald and others have not. Here are some observations and would like to compare notes to see if their is any correlation. 1) Most all Trees grafted to M7 developed some degree of sunscald while only a few M111 had slight damage. 2) 90 percent of my trees in the orchard are grafted to B118 with zero showing any sunscald damage. 3) Use of aluminum screening to protect from vole damage has been used since first introduced B118 to the orchard. 4) Sunscald damage m7 and m111 seen prior to using screening. Conclusion: Aluminum screening my prevent or slow sap flow during winter thaw thus reducing chance of developing sunscald and/or B118 may promote less damage due to delayed sap flow inherent in the b118 root system. This hypothesis is from empirical observation at my site and is far from conclusive. What are your thoughts?

Those are some excellent observations Appleman. Unfortunately, I can't help much with the answers.

I am just beginning to grow trees on b118. Most of my trees are on mm111, with just a few on 106. My other experience is with old heritage cultivars grown on their own roots. I hope others respond to your post.

 

[Native Hunter]

The case study fun ended last night. We had a microburst to come through that knocked down enough trees to close a major highway passing by the house, and it got the Liberty.







Along with the big sprout coming off the main root, I left myself some insurance by leaving some of the other smaller sprouts for backup. I will eventually go with only one sprout.



I put 6 inches of dirt on top of everything and matted it.




Don't laugh at my screening job. I decided to just screen the whole thing for right now.

 

[Bowsnbucks]

Native - Sorry to see the Liberty down. Is that the only tree to get hammered at your place ?? The Liberty ?? I hope the rest of your trees rode out the storm OK.

 

[Native Hunter]

Native - Sorry to see the Liberty down. Is that the only tree to get hammered at your place ?? The Liberty ?? I hope the rest of your trees rode out the storm OK.

Thanks Bowsnbucks. I only had one other tree damaged. It was a Japanese Persimmon that I had caged with a 5 foot cage. It broke off and was hanging on the outside of the cage. It looked like a gust of wind must have slammed it so hard against the cage that it broke when it hit the cage.

But, all is well here and everything back to normal now. I knew it was just a matter to time before that Liberty broke off, so at least now I have gone ahead and got my sprouts growing. The wind probably did me a favor on that tree.

 

[Bowsnbucks]

Wind a blessing in disguise ?? Maybe in this case, Native. Glad no other big damage to your property. Sprouts look like they're taking off.

 

[Native Hunter]

This plan seems to have worked well. 3 months later: