bad news 5 weeks into flowering

I'm 5 weeks into flowering and of my 4 plants 2 have devoloped black powder all over the buds and leaves. All four have some problems with their leaves. what do i do? I think it might be magnesium def. with the leaves but can i do anything for the budrot. Ive been nuting and using molasses, could this be the problem? How do i fix all this stuff? Do i have to kill the ones with bud rot, are they infectious? Any help will be appreciated.

sorry to say but those plants are goners
the ones with budrot are not even smokable
the humidity is probably to high in the room
do u have fans for circulation?
yes kill the ones that dont have budrot
so that the good ones dont get it