Jack Herer Auto - Subirrigation - 4h Sun

Yeah that's quite normal to have the lower leaves yellow and fall off towards the end of harvest, if you're near the end which looks like you are, it's really nothing to worry about and completely natural

Health is the most important factor in preventing fungal, mildew problems. Of course, environment affects that health (consistently too much moisture, not enough light, too much light causing metabolic stress, cycles of too wet, too dry, nutrient imbalances etc). So basically...uh try make it easier for the plant environmentally, and improve its overall health.