Stuck on Poison Ivy's second plant to get rid of the toxic cloud burst.

Am stuck trying to break free Poison Ivy's second plant on Founder's Island, get to the actual location, only I can't break it free as I keep getting Batman's message about using the sonic burst for it to work. I got a guide book, and it said I can do that
by finding this tunnel to get to the roots. But found that I can't reach this tunnel and am losing patience with this. So want to complete this great game but stuck on a simple task. Any tips or advice please?

:)

 

Can I backtrack to get every Riddler trophy?

I am going through my second playthrough, and I want to get 100% of Riddler trophies. The one trophy I am having issues with is in the southern point of Arkham North. In the cave. I have seen on a YouTube walkthrough that I must enter the lower entrance
of the cave and pull down a wall with the Ultra Batclaw, yet I am blocked by Poison Ivy's titan plant. Is there anything I can do to reach this trophy? It would be quite frustrating to have to restart the game to make sure that I get this 1 trophy earlier
on...

Thanks for any responses...

 

Green Thugs

Are you talking about the thug to be interrogated for Riddler secrets, or Poison Ivy's Minions?...