Diatomaceous Earth! It has worked really well for me in getting rid of all my pests! I'm not sure if you are able to use it during flowering though.
Diatomaceous Earth (DE) is great, can be applied as a topping on soil, it will act like tiny microscopic razor blades on bugs and will stop them from hatching or laying their eggs in over watered plants (fungus gnats), I've also read that DE can be safely applied to leaves by sprinkling directly on leaves during veg stage. It is very effective, but there is one problem, it is not safe to breathe into your lungs. They say it can be consumed orally by humans, but inhaling it is much like inhaling fiber glass. It is powdery and very soft to the touch, but on a microscopic level it very abrassavive and mostly made of silica. While it is very good for the plant and effective at killing bugs, you don't want it on, or in your buds because it will harm your lungs if smoked.
I've used it as a topping in pots, worked it into the soil, and have sprinkled it on leaves during veg stage. Sprinkling is effective, but then you have to try to remove it before the plants start to flower, so you have to be carefull how you choose to apply it. While it is completely safe and considered food grade (you can even eat it), you don't want to get it into your lungs. Once you sprinkle it around in your garden, the fans spread the fine dust everywhere and it is difficult to get rid of it. So, my experience with this DE has shown me to use it carefully as a soil additive (silica) and as a topping to deal with bugs. The silica makes the plant stronger. But you really don't want to smoke buds that contain DE. It does work remarkably well to eliminate fungus gnats as a soil topping when used carefully, but it must be dry to be effective, ineffective on bugs when wet. If I use it again, I think I'd pass on sprinkling it all over the plant, even during veg, it's nearly impossible to clean it up after because the fans keep spreading the fine dust all over the plants and you're bound to end up smoking it, not a good idea.
That's my take on DE, it's available on Amazon.
