I was working on a professional size matte in V6 (4000 pixels x 1500 cinemascope)

and I started getting severe grain in the dark shadow parts of the forest...(I started hand painting mist to cover for the grain....which starts to look very prodecural)

Can this tree grain be flushed out?

Under Atmosphere editor I punched up the sky, fog, haze "quality boost" up to 8......which kills rendering times...I heard for rendering HDRIs you have to go even hire than "8"...

Can this tree grain be flushed out?
Has anyone else gotten grain in vegatation before? (especially in wide hirez shots)