Q.What Is A Good Bug Spray For House Plants To Kill Gnats?
I have gnats on my house plants and need a spray to control them.

Certified GKH Gardening Expert
It is important to know the role of fungus gnats, and what causes them to appear.
Fungus gnats serve an important function to the soil. They eat rotting material, and fungus. Some of these fungi are known to infect and kill plants.
Now, these gnats don't really like to be outside of the soil. Seeing them to a degree that becomes an annoyance will signify that their home is too wet to live comfortably for them. They are suffocating in wet soil.
Killing off the gnats may reveal a soil infection that will likely kill the plant if not controlled.
To restore the balance of your soil may take a little work. The first step will be to let the soil dry out thoroughly down to about 3 or 4 inches. You will, then, treat with a fungicide. Make sure to follow all packaging instructions. This article will help you with fungicide use:
https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm
Once you remove their food source (fungus) and restore proper soil moisture, they will gladly leave to find food elsewhere.
This article will help you with watering houseplants:https://www.gardeningknowhow.com/houseplants/hpgen/watering-your-houseplants-properly.htm
These articles will help you to use insecticides, should you still choose to get rid of the gnats:
https://www.gardeningknowhow.com/special/organic/what-are-organic-pesticides.htm