ryt wen i saw this i started cuttin all the busy growth out of the middle so ii cud get rid ofthe white,i also removed lots of dead rotting bud and leaves from before the reveg. I fink it has appened because i spray my plants and then the heat dusnt get to the middle so it really moist. I have lost one of the main colas coz this stuff rotted the stem, it was all wilting so i removed it