One summer we had a very bad infestation in a small university greenhouse. I tried regular sticky traps, but watched as half of the flies bounced off of new traps, and even more as the traps covered over with flies. I then took yellow solo cups and coated them with Tree Tanglefoot. Nothing bounced off and the cups stayed effective for years. The cups could be placed on the benches mouth down or put on sticks and placed in the pots. Its hard to say if the cups cut down the population faster than they were breeding on the plants, but they sure did catch whiteflies and fungus gnats. I would bump a plant and the cloud of flies mostly went for the cup.
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