You have not given me enough information to give you a precise answer.  Your willows may be planted in poor soil/clay.  They like moisture but cannot sit in water or roots will rot.  They need full sun.  The roots are close to the surface so mulch is necessary to keep them moist and cool.  You have a leaf disease too.  Here a couple links to information for you: https://mortonarb.org/plant-and-protect/trees-and-plants/white-willow/#care-knowledge      https://www.uaex.uada.edu/yard-garden/plant-health-clinic/disease-notes/posts/willow-common-diseases.aspx