Willow trees are susceptible to several varieties of beetles including the willow leaf beetle, cottonwood leaf beetle and the blister beetle. Beetle damage on willows is characterised by holes in the leaves that are created when the beetles chew into them. Sometimes the leaf structure remains intact but all green parts are removed. Saving a willow from beetle damage must start as soon as the beetles are first detected and requires the use of chemical sprays.
Open a large garden sprayer tank and fill it with an insecticide containing acephate, diazinon, chlorpyrifos or carbaryl. Use the amount specified on the insecticide bottle and dilute it with water if the directions instruct you to do so.
Screw the top on the garden sprayer and shake it gently.
Spray all parts of the willow tree trunk and branches with the insecticide spray until the entire tree is covered. For taller trees you may need a ladder to reach the upper branches.
Examine the willow tree regularly and reapply the insecticide spray if the beetles do not all die. You may need to apply multiple applications if the beetles laid eggs that hatch.
If you are treating a weeping willow, prune back any branches that touch the ground, since they may allow more beetles to access the tree. Cut the branches back to at least 2 feet above the ground with hand pruners. If you want to use an organic control option, spray the willow tree with neem oil or an insecticidal soap.