I am sorry for this delayed reply to your gardening question. We are transitioning to a new Q&A system and your question was unfortunately lost in the transition. I have discovered it now and hope this reply is not too late to be of help.
When a tree turns brown suddenly it is usually due to a major root problem and there is little that is in your power to do for it. Dry soil, soggy wet soil (poor drainage), physical injury to roots, damage from weed killers used nearby, or root rot diseases are among the possible causes. If the browning is gradual and general you may be seeing damage from mites or some other such pest in which case the tree will recover and be fine.
Finally, dig down around the base of the tree trunk about 6 inches deep and look for something strangling the trunk such as plastic tags, wire, or other such materials. If you find such and can remove it the tree may be able to recover although it will take a year or more.
Thanks for the question. Please stop in again soon!
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