The term “gnat” is used to refer to several types of miniscule flying insects. Also known as no-see-ums or midges, gnats tend to travel in swarms, infesting local vegetation and annoying both pets and people. Dining on roots, stems and leaves, these tiny insects are capable of inflicting a great deal of damage to your plants. Tender seedlings or new plants are particularly vulnerable to this sort of attack. Luckily, there are a number of things you can do to get rid of any gnats that are plaguing your plants.
Adjust your watering schedule. Gnats are attracted to fungus and decomposing organic material in the soil. The damp conditions are perfect for the growth and development of young gnat larvae. Allowing the soil to become fairly dry between watering sessions not only makes the environment much less inviting for gnats, it will encourage root development in your seedlings.
Place small disposable dishes filled with vinegar around the plants. Choose either apple cider vinegar or white vinegar as gnats seem to be drawn in by the fragrance of either. Add a squirt of liquid dish soap as this changes the surface tension of the liquid, inhibiting the gnat's ability get back out of the bowl and effectively drowning them.
Replace the vinegar with soda if you happen to have some on hand. Or use both, alternating the placement of the baits to draw in as many of the insects as possible. As an added bonus, the sugary smell of the soda will also draw in and trap other garden pests such as wasps and bees.
Remove the soil immediately surrounding the plant and replace it with sterilized potting soil, sand, gravel or perlite. This will remove any soil in which fungus has taken root, replacing it with clean growing medium.
Add 2 cups of isopropyl alcohol to 1 qt. of distilled water and stir until the two are well blended. Then transfer the mixture to a bottle with a spray attachment. Spray the foliage of the seedlings liberally with the alcohol solution to kill any gnats that may be present. Repeat this treatment once a week or after every rain.