I`ve tried to place a villager, even a builder on the dead plant area but they are not doing anything to it. All it says that they can see some strange dead plants. Any solutions?

This puzzle is dependent on the completion of a different puzzle. Also, if I remember correctly, in addition you also need to be sure your villager has the correct skills. Since this topic isn't tagged spoiler, I'll say no more here -- in the 'guides' section of the forum are detailed solutions, if that's what you want.

Sorry, I forgot to tag it. I have done that specific puzzle with the lagoon, so that`s not the problem, and the skills of the villager were correct, as I said in my first post of this topic.

Nevermind, solved. It seems that I placed the villager on the wrong spot.