Answer: Based on your description I think the tree may be infested by scale insects, possibly accompanied by sooty mold. These can be controlled with applications of horticultural oil or insecticidal soap when they are in the soft crawler stage, some types can also be controlled by applying a horticultural oil spray during the dormant season. I would suggest you work with a local professionally trained nurseryman for a more specific identification of the pest(s) and based on knowing that, determine how to proceed. I'm sorry you are having trouble with your little willow.
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