Am no expert so hoping I might find a little help here. I have a most beautiful Salix and for the last ten years Ive had no problem with her. However the last couples of weeks she has started to drip a very sticky substance assuming thats the sap. On some of the branches and part of the trunk in patches its very dark in colour and sticky in colour. On a few of the stems there are what appears to be a tiny black creatures. Anyone have any ideas?