If you mean that attack, where the tree jumps on his ass, then I thought so as well, till I found out that he only spreads the rot in front of him and maybe to the sides. If you roll, so that you end up behind him, you're safe to apply some hits.
Running away also works fine. I think a lot of issues people might have with certain attacks can be summed by : they try to dodge everything instead of dodging away once then maintaining the sprint button and bugging out.
Sprinting is also the only reasonable way of avoiding its magic attack that spams fast targeted projectiles.
Then just wait until it catches up to you instead of walking on the shit it spread on the ground.
Running away also helps a lot with certain enemy combos, it's how I dealt with all the assassins, dodge once, then run, then jump attack them once they hit the last hit of their combo in the air. Why dodge if you can just walk it out?