Answer: In small numbers, the fungus gnat is merely a nuisance. The larvae, howver, devour young roots, and a severe infestation can harm plants. You are on the right track with the sticky traps, keep using those. Another control is called Knock-Out Gnats (available from Gardens Alive, ph# 812-537-8650, address 5100 Schenley Pl., Lawrenceburg, IN 47025); this product contains a strain of Bt, a biological control, that controls the larvae. Fungus gnats usually show up when the soil is too moist, so you may need to cut back a bit on your watering. Also consider using beneficial "predator" insects to be released in your greenhouse...they are extremely effective. Burpee carries them (ph. # 1-800-888-1447) as does Planet Natural (ph. # 1-800-289-6656).
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