It happens. It’s a little embarrassing but to be perfectly honest, I’ve had it happen. Particularly in the winter months or right before a vacation. You get stressed and anxious and you have lots on your mind. I’m here to tell you it’s okay and no one is judging you. You’ve overwatered your potted houseplants and now you have fungus gnats.
While this is a year-round problem, I think it happens a bit more in the winter. People bring in plants from outside. MaryJane doesn’t want her lemon tree to freeze and it needs to be watered so it survives. Unfortunately, overwatering can lead to a moist environment perfect for fungal growth. And that fungal growth means food material for fungus gnats. Just like fruit and phorid flies, fungus gnats seem to spontaneously appear out of nowhere. You aren’t bugging out, they have been there.
Let’s back up a minute and talk about the basics of fungus gnats. Fungus flies are true flies (only one set of wings) and are in the families Sciaridae, Keroplatidae, and Mycetophilidae as well as a few other small orders. This means there are literally thousands of species. They are small and larvae are thin little maggots. They are definitely not blunt.
Once it has been established that the issue is fungus gnats, you have to smoke out the infested pot. Once adult flies are seen, it’s likely not just one pot, it’s many. A high point is that adults don’t fly very well or very far, so the source of the infestation is likely close by. They do like to fly to windows and are often found dead on window sills. The low point is that most homes aren’t that big and have multiple, scattered houseplants throughout. In some cases of office buildings with lots of plants, it could be a widespread problem across a large area. It’s often a good idea to address all the potted plants at the site.
To deal with fungus gnat issues, just get rid of all the plants. Easy.
Wait, the customer doesn’t want to ditch the weeds? Okay then. All the plants need to be dried out as much as possible for as long as possible. That means NO watering. The longer they can go, the drier the soil can get, the better. To kill off all the lingering eggs and have the larvae waste away, the fungus needs to die. Once the soil has dried down a bit, sticky cards can be used in the vicinity to monitor where the highest concentrations of flies are. This way, you can see the reduction in numbers, and hash out what plants still have moisture/fungus issues. Plus, the sticky traps will reduce the number of flying adults to a small degree so the customer will be seeing a few less.
Some resources say to use Bt products, insecticidal soaps, and other DIY remedies, but these rarely do more than temporarily reduce the problem. You can always get carnivorous plants.
Some fun facts on fungus flies:
Some species are bioluminescent as larvae – this is where the term “glow worm” comes from.
These can be very cold tolerant – some species have a natural “antifreeze” to help them survive.
Fossilized flies in amber have been dated back to the Cretaceous period.
Mushroom farms are particularly susceptible to massive outbreaks of fungus gnats – with folks doing a lot more home growing projects, there may be mushrooms or other cultivated plants in homes now.
I wish I could say that I’ve never had pot problems. As a pest control professional, it’s a bit awkward to admit I have the occasional pest problem. It just goes to show that it’s a problem that can happen to anyone at almost any time. Try to chill out, find the budding problem, and don’t try to blow smoke at it.
You don’t have to huff and puff with frustration, we can help so you don’t get burnt out.
Lagniappe – if you are still munchie for more, I've decided to move to Tifton because they have a "Gnat Drop"!
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