House Plants With Thrips or Fungus Gnats - Knowledgebase Question

Brooklyn, NY
Question by grendel
January 21, 1998
I live in an apartment in NYC, and am frequently discovering small bugs that look like miniature houseflies (they fly, and seem to crawl in and out of the soil) in my potted plants. I have had several plants die after I have noticed the bugs; the roots are being eaten. Can you tell me what these bugs are, where they are coming from (in the middle of the winter) and if they eat the roots? Would a beneficial insect, such as a ladybug, help keep house plants healthy? I always get these bugs if I try to growpansies; I have lost an orchid and a begonia also. I have tried mite spray but it doesn't have any effect on the bugs.


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Answer from NGA
January 21, 1998

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It sounds like you could have an infestation of fungus gnats, which lay eggs in the soil. In small numbers, the insect is merely a nuisance. The larvae, howver, devour young roots, and a severe infestation can harm plants.

Any house plant pestscan be brought into your home on new plants. They can also come inside with your plants after a summer in the garden. Fungus gnat seem to come out of nowhere, and appear on houseplants and seedlings.

One 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.


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