Defoliation of Cottonwood leaves
My Cottonwood has been loosing 4-5 large branches a year for several years now. Coming home from a weekend trip, we saw that all the leaves are yellow and rapidly falling. The yard looks more like the end of October rather than mid-July. Is the tree dying, or do we need a tree doctor? The tree is probably 40 years old. About 4 years ago, a local tree removal company shaved down about three tree roots that were above ground making it difficult to mow. Could that have severely injured the tree?
There is not much that can be done for roots damaged by digging or mechanical damage. A minor amount of damage may have no visible effect but severe damage will cause branch dieback. The best help for root damaged trees is to prevent any additional stress. Keep the tree well watered during dry periods. Make sure mulch is not thicker than several inches and keep away from the trunk.
Also, Cottonwood trees drop leaves during heat stress. They are usually grown more around stream banks and not so much in upland areas.
You also have the option of consulting with a certified arborist for an onsite diagnosis, making sure the tree is not a hazard, and the best way to proceed http://www.treesaregood.org/
Here is a good publication on When to Remove a Tree http://extension.umd.edu/node/2273