Problem with Level 30 Kill TaskFollow

I'm a level 31 Enchanter, and I'm unable to carry out the "Black Swirling Orbs" kill task, supposedly open to Level 30 and above. The NPC who supposedly assigns the task, a treant named Regan, won't talk to me at all, except to say "I'm talking to the forest. Please leave me alone."

The blurb in the Quests area of this website says "it helps to have neutral or hostile faction with the treants", but shouldn't friendly be better still - since I'm expected to kill the treants' enemies??