Fungus gnats are annoying yet typical apartment pests. They can be easy to overlook at first and reproduce at an alarming rate. The larvae feed on the roots of potted plants, and if untreated, the plants may eventually perish due to shrinking further and further with each passing day.
A part from the damage they inflict to cherished plants, these tiny critters are simply bothersome to have in any living space. If you are interested in eradicating fungus gnats, this guide will provide you with the necessary information.
What are fungus gnats?
Fungus gnats are tiny brown or black two-winged flies often misidentified as fruit flies, drain flies, or even small mosquitoes. Unlike these other insects, fungus gnats tend to have a longer and slimmer thorax along with relatively more elongated legs and antennae than fruit flies.
Although smaller than mosquitoes, fungus gnats do not bite people, which is a plus. Unlike many other plant pests, fungus gnats do not attack the stems or leaves of a plant. Problem is, most gnat larvae prey on the roots of plants, making them far more difficult to spot during a cursory glance.
Why do they appear?
A fungus gnat infestation is a direct consequence of having decaying organic matter within the vicinity. More specifically, fungus gnats flourish in moist soils and stagnant water.
If you overwater your indoor plants consistently, fungus gnats will infest the plants that are frequently watered, as opposed to those which are neglected.
What damage do fungus gnats cause plants?
The adults pose no danger to anything, as they do not damage anything, plants or people. The larvae, however, are quite dangerous. As with the vast majority of pests, the fungus gnat larvae seek out the roots of plants and eat them.
The plant may go through a stage where it refuses to mature and attempts to “hibernate.” In timeless terms, it will slowly curl and lose foliage until death.
Lesser known, young plants or seedlings are comparatively susceptible to suffering irreversible harm. Cotyledons and seedlings do not possess many root structures – and thus their ability to sustain root degradation due to gnat larvae is limited.
This is a phenomenon not observable in older plants, which are bound to have a larger root system, and thus are able to withstand more temporary damage inflicted by gnats.
How to know if you have a fungus gnat problem
Plants suffering from a fungus gnat infestation will show the following signs early on:
- Fungus gnats crawling on the soil surface or pot
- Fungus gnats hovering around the plant
- Abnormal drooping or shedding of leaves
- When repotting, you see tiny white specks (fungus gnat larvae) wriggling around the roots
To confirm an infestation, visually check for the described signs, focusing on plants with moist soil.
Plants like jade are especially vulnerable because their soil is consistently moist from routine watering. However, don’t discount other plants that aren’t watered as frequently. Any plant with damp soil, or a saucer that often contains standing water, will attract fungus gnats.
How to prevent fungus gnats in the first place
The best way to deal with fungus gnats is to prevent them in the first place, mind your plant P’s and Q’s.
Healthy plants are the ones which are vibrant in color. Thus, when purchasing from garden centers, it is useful to check for these indicators. Also check the foliage of the plant.
Avoid plants that are wilted or droopy, and do not select those with brown spots on leaves or stems. Unhealthy plants will only attract pests such as fungus gnats.
If you are purchasing a plant, ensure you’re checking whether you can visibly see the plant roots. Examine the roots for small white larvae wriggling around, as this indicates an infestation. Plants that are infested with fungus gnats will only spread the infestation to others, if left unchecked.
To contain the spread of fungus gnats, encourage conditions that are unfavorable to fungus gnats. Familiarize yourself with your plants, and pay attention to their specific watering needs. Ensure the soil drains well and choose pots with drainage holes over ones without.
Fungus gnat larvae can be deterred with a 1-2 inch layer of sand on top of the soil, as the layer dries quickly and does not provide the organic matter fungus gnats relish.
Avoid overwatering plants and lean towards benign neglect whenever possible. While watering, it is best to use a towel to blot excess water from saucers or water plants in a sink and return them to their saucers after draining. Both of these approaches work well. Sitting water is equivalent to a ‘help yourself’ sign to fungus gnats.
How to get rid of fungus gnats
Simply allowing more drying time between waterings is more than adequate when addressing a mild infestation. For larger issues, consider hydrogen peroxide soil soaks, yellow sticky traps, or both. Be patient as fungus gnat infestations take several days to fully cycle through their population.
Soil soaks with hydrogen peroxide as a treatment hydrogen peroxide helps eliminate the root problem of fungus gnats: larvae. Hydrogen peroxide soil soak solutions undergoes a cleansing process to eliminate stubborn fungus gnat larvae ingrained within the soil.
A solution of 4:1 (water to hydrogen peroxide at 3% strength) will safely eradicate fungus gnat larvae while remaining non harmful to plants. You can either water the soil directly with the solution while avoiding the leaves or place the pot in the solution so that the soil can soak it and make its way to the roots.
Capture of adults with yellow sticky traps and any similar trap, like the ones sold here, is also an acceptable way of controlling fungus gnat populations. Adult fungus gnats are lured in with yellow sticky traps and thus become incapable of flying away to lay more eggs.
A slow yet efficient method of dealing with infestations is cutting yellow sticky sheets to size, and placing them on soil surface. As fungus gnats, both adult and juvenile, crawl onto the traps, they get stuck. However, these traps target solely adult fungus gnats.
Summary
Fungus gnats are an ongoing problem for greenhouse and indoor pot plants, notably for delicate young plants with little rooting. While appearing similar to mosquitos, they are benign to humans.
Allowing the plants to dry out more prevents them from being comfortable homes for fungus gnats and is helpful in avoiding initial infestations. For those already infested, hydrogen peroxide soil soaks and yellow sticky traps effectively eliminate fungus gnats. Happy hunting!