Crepe Myrtle’s trunk is cracking
by
K Hinson
+3
The local nursery said to check branches & trunk for “anything green” On a 9
year old, well established myrtle.
I did see green when I scratched off a small piece off the trunk Before winter 2018.
Winter hit and the trunk & branches are literally cracking in lots of places.
We had tons of rain in the summer & fall of 2017.
i hate to lose the tree 
https://www.sandyoaks.com/the-causes-of-bark-splitting-on-trees/
Don't do anything. These trees are TOUGH! In fact, Myrtle Beach is so named because after a hurricane, these were the only trees left standing.
Here's a link that might help you rescue your tree. Good luck!
https://www.plantmegreen.com/blogs/news/crape-myrtles-saving-a-split-tree
You can also contact your local Home Extension agent for the best way to help with this problem. The service is free and you can find it under local government agency.
Don't worry too much about the splitting. The tree has absorbed a lot of water and it's tissues are expanding. That's kind of normal for a Crepe Myrtle. The thing you should be concerned about is an attack by insects or other disease. To prevent that, I'd try spraying it with a horticultural oil like the one made by Bonide. I get mine at Home Depot. You just mix it up and spray it on the dormant plant. It will control lots of diseases and pests. Be careful of larger pests like ants. You may need to treat the surrounding ground to keep them at bay. Diatomaceous earth or boric acid powder works really well for that. Cheers!