Fungus gnats are small, dark, short-lived flies, Fungus gnats are typically harmless to healthy plants - and humans - but can inflict extensive damage to seedlings; their presence can be indicative of more serious problems. In houseplants, the presence of fungus gnats may indicate overwatering; they may be feeding on roots that have sat in drain water too long and are thus rotting, or the gnats may be attracted to fungus growing in saturated topsoil. Symptoms of an infestation may be delayed plant growth, wilting, yellowing leaves and rotten roots.
Sticky traps : You can buy yellow sticky traps for indoor plants to control insects inside, they will work with fungus gnats. The idea is that the yellow color will attract and when they go to investigate, they will be caught by the sticky substance on the trap.
Killer Soap Spray Recipe : Mix 2 tablespoons of lemon dish detergent or Ivory liquid soap with 1 gallon of water, use this mixture to drench the soil hosting them. After about 1 hour, spray the leaves with clear water to rinse soap off.
Tobacco : Break some cigarettes and make a thin layer of tobacco over the soil , nicotine is repulsive. Do not use on herbs or plants that we eat.
Trap : Pour a tablespoon or two of apple cider vinegar in a cup, the top it with water. Leave the cup near the plants with the problem. They will be attracted to the vinegar and drown.
Dry There Home : Allow soil the to dry completely, so that your plants begin to wilt before watering them again (about one to two cm of soil is completely dry). You must obtain the dry larvae in the soil to dry completely (end of the cycle), adults cannot reproduced in dry soil, so the cycle will end.
Rubbing alcohol spray : Mix 1 cup of alcohol with 1 liter of water, pour into a spray bottle. Spray and treat every three days for two weeks. Be sure to test first on a sheet to check that the mixture is not too hard for them.