Q.locust tree
My locust tree is losing its leaves in site of treatment with Bayer tree and shrub food /insecticide. Leaves start dropping in early May.

Certified GKH Gardening Expert
What insect are you spraying for - the honeylocust spider mite? Heavy infestations of spider mites cause early leaf drop, so it may not necessarily be the insecticide, but the insect you are spraying for.
For more information on locust trees, please visit the following link:
https://www.gardeningknowhow.com/ornamental/trees/locust/locust-tree-information.htm