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Gnats in office

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From: Mimi Lope
Philadelphia , PA
We have an infestation of tiny gnats that congregate right where the wall meets the cieling and just inside the window frames (both at the very top and along the bottom). There are no plants in this room and the room is on the 2nd floor. There are plants elsewhere in the building, but not this room. No obvious water leak anywhere. I vacuum them away only for there to be a hundred present a few days later. There is an AC vent near the base of the window but I haven't noticed any more near this vent vs anywhere else in the room. How to get rid of them completely? Is it possible that they might be breeding in a plant somewhere else and are attracted to this sunny room? I have checked rooms w plants and can't find any tiny flies (maybe one or two, not tons like here).

Extension Message
From: Richard Hentschel
Extension Educator, Horticulture
DuPage/Kane/Kendall Unit
These are likely a fungus gnat. The good clue you provided is there is a AC vent near by. These gnats can feed on debris in the vent system in the presence of moisture. Check to be sure the system is functioning properly, especially where the moisture condenses and drains away. These areas collect whatever is in the air and get dirty.

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