I have dozens of succulents indoors. In nice weather, some plants are moved out to a balcony, and the windows are often open.
I have been trying to eliminate fungus gnats with several techniques, separately and in combination.
What techniques do you recommend to eliminate fungus gnat adults, eggs and larvae?
Fungus gnats LOVE wet soil, so if your succulents aren't in well-draining soil or don't dry out between watering, your pots can be a very attractive breeding ground for these pests.
Letting the soil dry out completely between watering will help to prevent this problem, and since they're already present, it will help to kill any larvae in your soil. Your succulents will be fine for a few days and even weeks without water.
To kill the gnats flying around, an apple cider vinegar trap will do the trick. Simply put a few tablespoons of apple cider vinegar in a plastic cup. Add a couple drops of dish soap. Cover the cup with a plastic bag, but poke a hole the size of your finger in it. This allows the gnats to fly in, but it's difficult to escape. The sweet smell of the vinegar lures them in and the dish soap traps them or weighs them down.
You can also place food-grade diatomaceous earth (DE) in the top of your soil, which will kill any adults or larvae that come into contact with it.