 Many diseases like "Septoria" thrive in an area that provides excess decaying material, by removing dead leaves you are leaving the disease with less survival structures.Since "Septoria" relies on the proximity of suitable hosts, increasing the spacing of your cannabis plants and rotating crops annually will decrease the likelihood that the disease will move next door.The use of fungicides (Bordeaux Mixture, or Daconil 2787) are also applicable when the disease has infected your plants.