newsticker-treeview-automatically-mark-displayed-items-as-old

newsticker-treeview-automatically-mark-displayed-items-as-old is a variable defined in `newst-treeview.el'.
Its value is

t

Documentation:
Decides whether to automatically mark displayed items as old.
If t an item is marked as old as soon as it is displayed. This
applies to newsticker only.

You can customize this variable.