My three year old Ivy, although looking healthy and robust, has started giving off a sticky substance. It grows in a light filled windowsill and is watered once a week with feed once a month.
This is called honeydew and it's the residue from pests. Spider Mites are a common pest on Ivy, though it could be others.
Treat the Ivy with Neem Oil.
Make sure you keep this plant away from others until the pests are gone.