What is eating away the leaves on my Salix

Ordinary garden soil, don't plant close to drains, prefers soil which doesn't get bone dry, likes sun or half sun/shade, needs a bit of room to accommodate its spread, prone to rust infection. Can't say why the leaves are eaten away - may be something local to where you purchased it. If the problem continues, post a photograph, but incorporate some compost into the planting hole and feed it when planting, keep well watered. Prune back badly affected branches if you wish, but I'd wait and see if they put out new growth within a month.