Lhaereth's forces have set up plague cauldrons in the Circle of Madness. The cauldrons should be destroyed to protect the Rangers of Ithilien.
'${PLAYER}, I fear that Lhaereth has brought her plague with her to Minas Morgul. I do not know if it is the same Great Plague you destroyed in Seregost, or some weaker strain she could concoct quickly, but we cannot take any chances! Destroy her cauldrons before the winged discover our encampments and use it on us instead of on Gothmog!'
Plague cauldrons have been setup in the Circle of Madness.
You should destroy plague cauldrons.
Rhadrog is stationed inside Barad Elenath, the Star-gazers' Spire.
You should talk to Rhadrog.