Caused by pathogens which are fungal in nature Yellow spots on cannabis leaves are caused by pathogens which are fungal in nature, and which are classified in the Septoria genus. The two are specifically known as Septoria cannabis and Septoria neocannabina. The two will often affect cannabis plants in the outdoors, so the risk is greatly minimized for cannabis plants in an indoor garden. The trigger factors for this infection are warm weather and rainy weather when the conditions are warm and ...