At What Temperature Do Fungus Gnats Die?
Fungus gnats thrive best in temperatures between 70 degrees and 80 degrees Fahrenheit. However, they can survive at any temperature above the freezing point. If you wish to use temperatures to kill them, you have to lower it to well below the freezing point.
Fungus gnats will die at any temperature below -25 degrees Fahrenheit. However, some species will survive up to -60 degrees Fahrenheit. On the other side, gnats cannot survive beyond 140 degrees Fahrenheit. Thus, it is the easier method to use to get rid of the fungus gnat. If they exist in potting soil, place it in a furnace and heat it to 140 degrees Fahrenheit for about 30 minutes. This kills the pests and their larvae.
Pasteurizing the soil has more advantages than killing the gnats. You will also get rid of bacteria and viruses in the soil. However, you cannot pasteurize infested plants as they will die in the high heat.
Freezing soil is the wrong approach to killing gnats. Instead, the larvae will become dormant and wait for temperatures to rise. Once you unfreeze your soil, all the dormant fungus gnat larvae will come back right back.