Thanks for reaching out to Cooperative Extension. I will need more information from you before I can assist. Please respond back to the following questions
Which species of willow is it?
Is it being irrigated?
If so, how much per week?
How was it planted and how big was the tree at planting?
Would you say the soil is sandy and well drained or soggy and has lots of clay?
Why did you plant it - shade, fast growth, other reason?
Any other factors that you think might be relevant could also be helpful. Some additional photos of the trunk and overall tree appearance would also be helpful. Please send your response to email@example.com. I will also connect to your county office once we get more information.