New Locust tree leaves
It takes a while for trees that have been transplanted to adjust to the stress associated with the move and new location. Sometimes the stress is significant enough to produce symptoms of what's called transplant shock. Go here to learn about transplant shock and what can be done to prevent it or reduce its effects:
It’s important to water newly planted trees but it’s best to avoid frequent light watering. Go here for useful guidelines:
If the tree continues to decline, bring its condition to the attention of those who sold it. Most reliable vendors warranty their perennial plants for at least one year after planting.