Hundreds of species of willow trees (Salix spp.) grow throughout the world, and 54 of them are native to North America. Generally, willow trees are deciduous trees or shrubs that bear single scale buds. Willow trees lose their leaves for a number of reasons, and most of them are not serious health issues. With the proper corrective measures, you can restore your willow tree to health and prevent further leaf loss.
To properly care for your tree, you need to first learn the exact type of willow tree that is growing in your landscape. If you don't know the species of the willow that is growing in your landscape, send a picture of the tree to your local university extension service centre. They may be able to help you identify your tree and give you advice for that tree's care.
Lack of water can be one of the main reasons for a willow tree dropping leaves. Check your tree's water supply. If you live in a hot and dry region, you will need to water more frequently than if you live in a cooler, more humid region. Water deeply, until you see the water just beginning to pool at the trunk. Young trees and trees that have been recently planted may need additional water, so check the soil often to make sure that it is not dry to the touch.
Prune away any leaves that have olive-green spore masses on the leaf veins. These spores are a disease known as willow scab and can easily kill young leaves very quickly. You don't need to treat the leaves with a fungicide, but as soon as you notice the scab, prune the infected leaves with garden shears to make sure that the disease doesn't spread to healthy leaves. If you notice a powdery mildew or yellow or black spots on the leaves, these are usually harmless diseases that will cause some leaf drop. Rake all of the fallen leaves away from the tree and dispose of the leaves.
Normal Leaf Drop
If your willow tree's leaves are changing colour and falling off of the tree in the fall, then don't panic. This is the natural process for deciduous trees and it does not mean that your tree is ill or suffering. The leaves should return healthy in the spring.