Go to Google Images and type in 'sapsucker holes'. They show a bunch of photos of the birds' handiwork on various types of bark. If you type in 'woodpecker holes', the photos show an entirely different type of pattern.
This looks like an informative site from UC Davis for Integrated Pest Management (and disease) for willows:
http://www.ipm.ucdavis.edu/PMG/GARDEN/PLANTS/willow.html You might have two separate problems, leaves and trunk.
If you can find a cavity in the trunk with ants, maybe filling it with Diatomaceous Earth (food grade) would help to discourage them. It's non-toxic to everything that doesn't have a hard shell; safe for people, pets, birds, earthworms, etc.
Sue