Question
Hi Jim, I have 3 locust trees in my yard out in the country that have yellowed their leaves in the last 5 days. I planted these trees 8 years ago and are approx. 25'. The yellowing started on
the south side of the tree and is progressing to most of it. Even new stems seem to be affected. I am concerned that about a herbicide that was used on a field across the road from me on a pasture possibly being the problem, but see no other damage in my yard or even any yellowing in their field. I'm stumped, and seek your input. Thank-you for all of your great information that helps so many of us.

Answer
IF it is a herbicide you should see a pattern toward where the herbicide was a[[lied. Brown on that side a and green on the other side. Unless the herbicide was applied around the tree such as a product called Weed  and Feed, a lawn fertilizer that contains a herbicide that will kill tree.

IF this is not happening I would check for an insect called leaf miner. or leaf bug, Feeding by the honey locust plant bug results in severe leaf distortion, dwarfed leaflets, chlorosis, and yellow-to-brown spots. Irregular holes may result when dead tissue falls out of the infected leaves. Heavy plant bug infestations may cause premature leaf drop, but typically a second flush of leaves is produced. Despite the damage to the foliage, tree death rarely occurs. Unfortunately, the honey locust plant bug is an unpredictable pest because weather conditions influence the bug抯 survival and activity. An outbreak one year does not ensure an outbreak in subsequent years.' Here is is a web link to plant bugs. http://learningstore.uwex.edu/assets/pdfs/A3636.pdf

Leaf miner damage looks like the leaves have turned but looking closer the leaf has been partially eaten Here is a web link with pictures. http://www.state.sc.us/forest/idleafminer.htm

A picture might help.