Answer: Peeling bark is natural - it means the tree is growing rapidly. Lichen or green algae means the soil is too wet because it is not draining well or you are watering too frequently. Pecan trees are drought tolerant so you will only need to water every few weeks. When you do water, apply water slowly so it has a chance to trickle down and wet the entire root system. Here's a publication from Texas A & M with information about growing pecan trees. Hope you find it helpful.
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