I have several plants indoors and altho I have had a gnat issue in the past.....lately it has been horrible. So have taken them outside to dry out some. I keep a jar of apple cider vinegar on kitchen counter....which does catch them....but I want to kill them all...pronto. Have not seen any indication that anything is attached to under side of leaves. Found recipe for lemon soap and water to spray them with after they dry out. Does anyone else ever have this issue ?
We use tall and medium metal plant stakes and attach a fly/nat sticky thing, pulled out of a small container, to it. Nats are really attracted to these sticky traps and stick to them.
Every year around this time, when the night temperature drops to really cold, all the gnats (I call them 'flying fleas') and fruitflies look to invade, and overwinter with me. Once they get established indoors its a major chore to be rid of them, and not cheap to do it. I use a multi-prong attack. First I have a great bug zapper (Flowtron BK-7). Unfortunately for you, its no longer available: https://www.amazon.com/dp/B00005CFGI/ This one looks to have the right grid (the spacing cannot be more than 1/8 inch apart), and might be an adequate substitute: https://www.amazon.com/Enshey-Mosqu...521861807&sr=8-89&keywords=gnat+zapper+indoor Secondly, when a breeding pair make it inside, they head straight for a drain to lay eggs. So for that I mix 1 cup Creolina to 3 cups hot water, and pour that down each drain (sink, shower, lavatory, etc.) If you you cannot find Creolina, use ammonia, but you will have to do that like every couple days for two or three times. Lastly, I fumigate my place with Raid Fumigator: https://www.walmart.com/ip/Raid-Fumigator-Fumigating-Fogger-3-Pack/11045996 Be sure to get this specific product...the various aerosol-based junk will not work, and make a big mess. You will need one 'can' per room, and open all drawers, cupboard doors, and so on to give the critters no sanctuary from the fog. If you have a heavy infestation, you may need to repeat this a week later.
If you have fungus gnats, they most likely live and breed in the soil, not on the plants. The only way I have heard that will get rid of them short of re-potting in everything down to bare roots into fresh, clean soil is to "tent" the plant with a plastic bag then fill the bag with a plant-friendly insecticide ad leave it out of the sun for several days--up to a week. You can respray daily. Putting moth balls/crystals into a jar lid and placing it under the tent may work as well, but I have not tried that. If you are dealing with food plants or want to be organic, you could get parasitic nematodes and try those. Ask at your local garden center or Extension Service office if you have one around.
I make traps for the fruit flies using apple vinegar in a glass or jar, covered by cling, with small hole cut into it. Attracted to the vinegar, the fruit flies are able to get in through the holes but, probably because their brains aren't very large, they aren't able to get back out and end up floating in the vinegar. It takes a while, but eventually their numbers thin out, and they disappear.
That works great for fruit flies, but not for gnats. Wine works slightly better than vinegar, and I sometimes put a small funnel on top of the glass to accomplish the same thing.
I had not thought of fungus gnats. For anything that lives in the soil, a thin layer of 'Diatomaceous Earth' spread over the surface will likely kill the critters, as they will have to bury through it to get to the soil, and back through it to get out. https://richsoil.com/diatomaceous-earth.jsp
Haha...that's what I have but not because of bugs but because watering is an issue. Also...I'm good at killing indoor plants....brown thumb.
@Don Alaska Speaking of which, it always amazes us how fruit flies suddenly show up in the house out of nowhere, when I start up a new batch of wine, almost as though they "come out of the woodwork"! The wine is contained in 5-gallon glass carboys, equipped with water-traps to keep air (and flies) out, while allowing the CO2 produced to escape. I suppose a variety of fragrances other than CO2 are present.......