Q.Kilmarnock Willow is dying!
I have had my willow for 7 years and it has been lovely; however, over the last couple of weeks I noticed a section wilting and the leaves turning brown. This is now spreading rapidly. Please can you give me advice?

These links will help you pinpoint the cause.
https://extension.psu.edu/pests/plant-diseases/all-fact-sheets/willow-diseases
https://www.gardeningknowhow.com/ornamental/trees/willow/treat-peeling-willow-bark.htm
https://www.gardeningknowhow.com/ornamental/trees/willow/grow-a-willow-tree.htm