Fungus gnats(?) and food-safe removal from indoor potted vegetables - Ask Extension
I've moved some potted vegetable plants (tomatoes, herbs, spinach, watercress, etc.) indoors for the winter. There are little black flies/gnats that a...
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Fungus gnats(?) and food-safe removal from indoor potted vegetables #817557
Asked December 15, 2022, 2:39 PM EST
I've moved some potted vegetable plants (tomatoes, herbs, spinach, watercress, etc.) indoors for the winter. There are little black flies/gnats that are not quite like fruit flies. These bugs are flying around the pots and sometimes wandering further into the house and causing annoyances. Based on a little bit of Internet research, it seems like these might be fungus gnats, and some folks are suggesting various treatment methods for getting rid of the gnats. I am concerned about putting anything on my plants or soil that could be unsafe for eating the plant leaves or fruit. I saved a video of the flies if you'd like me to share a link to it.
Do you have any suggestions for getting rid of fungus gnats in pots that are growing food that humans will be eating?
Poweshiek County Iowa
Expert Response
The best way to manage fungus gnats is to eliminate the breeding spots. The immature stage of the fungus gnat is a small white maggot that lives in very moist areas high in decaying organic matter. This can be a number of places indoors, but plants are one of the most common breeding sites.
When houseplants are infested, it is typically because they are overwatered. Fungus gnats cannot survive in houseplants if the soil is permitted to dry out almost to the leaf-wilting point between waterings. Be sure to allow the soil to dry completely before watering. In most cases, if this is done, control of these pests can be obtained with no chemical use. Allowing the soil to dry completely between waterings is also good for the plant's health.
Make sure also that the saucers, trays, or sleeves under the pots are not full of water - that can also become a breeding ground for these annoying pests if they always have a little water in them.
Fungus gnats also originate from non-plant sources. This can include wet areas like furnace or refrigerator condensate pans and hoses, slow-moving or rarely used drains, and wet corners, cracks, or crevices in the basement or other indoor areas. These potential breeding grounds should be cleaned or dried. In the case of slow-moving drains, physically cleaning the drains with a stiff brush will be of more benefit than chemical drainer openers.
Thankfully, fungus gnats are completely harmless, both for plants and people....except for the fact that they are extremely annoying!
Further questions can be directed to your local county Extension office. This local resource is very helpful since they are familiar with trends and issues in your part of the state. Click on this link to get connected directly with a staff person in your county Extension office and ask your gardening question. https://hortnews.extension.iastate.edu/ask-gardening-question
Happy gardening!
--Aaron
When houseplants are infested, it is typically because they are overwatered. Fungus gnats cannot survive in houseplants if the soil is permitted to dry out almost to the leaf-wilting point between waterings. Be sure to allow the soil to dry completely before watering. In most cases, if this is done, control of these pests can be obtained with no chemical use. Allowing the soil to dry completely between waterings is also good for the plant's health.
Make sure also that the saucers, trays, or sleeves under the pots are not full of water - that can also become a breeding ground for these annoying pests if they always have a little water in them.
Fungus gnats also originate from non-plant sources. This can include wet areas like furnace or refrigerator condensate pans and hoses, slow-moving or rarely used drains, and wet corners, cracks, or crevices in the basement or other indoor areas. These potential breeding grounds should be cleaned or dried. In the case of slow-moving drains, physically cleaning the drains with a stiff brush will be of more benefit than chemical drainer openers.
Thankfully, fungus gnats are completely harmless, both for plants and people....except for the fact that they are extremely annoying!
Further questions can be directed to your local county Extension office. This local resource is very helpful since they are familiar with trends and issues in your part of the state. Click on this link to get connected directly with a staff person in your county Extension office and ask your gardening question. https://hortnews.extension.iastate.edu/ask-gardening-question
Happy gardening!
--Aaron
