Question
Healthy appearing leaflets are falling off my 20 foot tall skyline honey locust the leaflets appear h althy  no chew marks no chlorosis there has been no herbicide or insecticide sprayed on   On or around the tree  .looking through magnifying glass I could see no sign of insect present nor could I see any sign that they were even there.no chew marks no  discoloration in the leaves   No boring holes in twigs ,branches or trunk of  tree The root collar and just below it seems healthy we have had no Abnormal cold or hot days. majority of leaflets are falling off the south west side of the tree it has lost almost 2/3 of its leaflets on that side leaving almost Baron petioles.The leaflets that have fallen off appear as healthy as the attached leaflets on the north side of the tree water does not seem to be an issue nor does wind could this be a genetic issue with the direct sun light on the south west side shading the north side of the tree and taking on all the sun .this tree has always want lost its leaflets early mid July through August never this early.Any info would be greatly appreciated thank you have a great day

Answer
Scott:
Your locust tree situation does sound strange. I am assuming it has been planted for sometime and has had the opportunity to get established in the present location.  This situation does not sound like a disease that I am familiar with, but rather some other stress perhaps root related like a moisture imbalance for example. Your issue will probably require an on-site visit to evaluate. Try contacting your local county Agricultural Extension office.  It is often located in the county courthouse. Often times there is someone who can make a house call and may find something that is overlooked or missed.  You may have some luck by posing this query to your local garden center/nursery.

Regards
Steve