Treatment on fungus gnats
What's Happening
Fungus gnat control must target larvae in soil rather than adults flying around plants. Adult gnats live only 7-10 days and do not damage plants, but each female lays 100-200 eggs in moist soil. Killing adults with sprays provides temporary relief but fails to stop reproduction. The key to eradication is breaking the life cycle by eliminating larvae in the soil while reducing moisture that supports breeding. Multiple methods work best in combination: biological controls for larvae, sticky traps for adults, and cultural changes to prevent recurrence.
How to Fix It
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Step 1: Allow top 1-2 inches of soil to dry completely—this alone kills many larvae through desiccation
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Step 2: Apply Bacillus thuringiensis israelensis (BTI) such as Mosquito Bits to soil—bacteria kill larvae but are safe for plants
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Step 3: Deploy yellow sticky traps near soil surface to capture adults and reduce egg-laying
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Step 4: Top-dress soil with 1/4 inch sand or diatomaceous earth to create physical barrier that kills hatching larvae
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Step 5: If severe, repot in fresh sterile soil after removing all old soil and larvae
How to Prevent It
Continue BTI treatments monthly during warm seasons; maintain dry soil surface; avoid overwatering; use well-draining mixes. Bottom water to keep surface dry. Add sticky traps preventively. Monitor with potato slice test quarterly.