Bottom leaves droopy and dying?

Hi all,

Im into my 6th week with my lowryder and it has been going great untill yesterday...all my bottom leaves including my biggest fan leaves are starting to die??? I have been using half strength mother earth organic nutes for the last two weeks every other watering... there are nutes in my soil (its organic plagron royalty mix)

The top of the plants and buds seem fine but the bottom half all the leaves are droopy or dying? any help would be great as I dont have much longer to go till harvest and would be terrible to lose it now.