Treants kicking my butt

[Servellious]

I just hit 29 and decided to give the treants a try. I seem to kill the lower level ones np but every 3 kills i get a really hard one where i will have 75 health and the mob about 10-15 and he starts healing himself next thing i know im getting wrecked by the dot and his knockback nuke.

I fully buff myself including haste, magic and fire resist, i have a poison wind censor (thanks franswa going away party). i pull with slow, send a pet in (having charmed animal helps a bit) put my envenomed breath on and go to work. If i miss 1 slam it seems to go downhill. I was trying to nuke him when he was at low health but 2 times i got the message my spell landed yet no damage was dealth not sure if this is a bug or not because it worked on some of them.

Anyway any advice would help, i wanted to farm these guys for a bit but not sure if i suck or i should find something else for a couple of levels.

PS if any clerics near south karana i could use a rez, i can donate.