How to eliminate fungus gnats?

How to eliminate fungus gnats?

The most effective method is a combination of water control and spraying. Spraying alone without water control is unlikely to succeed, as eggs continuously hatch in the soil — insecticides only kill existing adults and larvae but cannot stop the source.

Step 1: Water control (most critical)

• Fungus gnats breed in damp soil; drying out the soil cuts off their survival.
• Water only when the top 2-3 cm of soil is dry — larvae mainly live in this surface layer; keeping it dry prevents eggs from hatching.
• Use a bamboo skewer or finger to check moisture depth; don't just judge by the surface (the surface may look dry but still be wet underneath).
• Water thoroughly, but empty any standing water from trays immediately after watering.
• For succulents and drought-tolerant plants, wait until the soil is completely dry before watering; better too dry than too wet.
• In winter, plants need less water; extend watering intervals by more than double compared to summer.

Step 2: Spray insecticide

• Spray dinotefuran-containing household insecticide on the soil surface of pots, allowing the solution to penetrate the topsoil.
• Also spray pot edges, trays, and surrounding countertops.
• Adults resting on the soil surface or pot edges die upon contact with the film.
• Larvae moving in the soil die upon contact with the penetrated insecticide.
• Spray every 5-7 days, 2-3 times consecutively — eggs hatch in about a week; timing applications to this cycle is essential for complete elimination.

Step 3: Physical control

• Cover the soil surface with a 1-2 cm layer of coarse sand or gravel — this physically prevents adults from reaching moist soil to lay eggs, and the dry surface is unfavorable for larval survival.
• Place yellow sticky traps near pots to trap adults.
• Reduce use of uncomposted organic fertilizers (such as unfermented tea leaves or rice water).

Step 4: Persistence

• Fungus gnats have a breeding cycle of about 3-4 weeks; maintaining water control + spraying for 3-4 weeks can basically eliminate them.
• As long as soil remains consistently wet, fungus gnats will keep returning.
• After elimination, continue the wet-dry watering cycle to prevent recurrence.