Heads turning brown and dying

Hi I live in south africa and im growing 3 plants outdoor , they are a weaker strain of durban poisen.my one plants heads are turning brown and dying should i pluck them now and smoke them or is this normal on a weed plant.It has only affected 3 heads so far and theres plenty left i dont really want to pluck the yet as they not fully matured and the right season is three or four months away they have been growing for about 8 months now. theres no bugs on them or parasites. has anyone else had a few dying heads on there weed plants and if so is it going to spread?
 
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