I have around 40 Emerald Green Arbovitaes that were planted in April 2016 in my backyard in the New York area. Overall they seem to be doing pretty well. One of my trees this year and two last year have started to brown on one of the main branches. The other branches on the tree seem to look OK. Do you know why this browning is happening? Is the tree dying? Should I prune off the brown? Thank you for any ideas or suggestions.