If you’re a houseplant owner, you’ve probably encountered black winged bugs hovering around your plants. Especially if the humidity and moisture levels are high. For this reason, they’re notorious in and near the bathrooms as well.
Wondering what these flying nuisances are? They are probably fungus gnats. Their larval stage attack and feed on the roots of your houseplants making them vulnerable to sudden wilting, yellowing, loss of vigor, and poor growth. Although the adults don’t bite their constant hovering around is quite irritating.
In today’s post, I’m going to discuss what are fungus gnats, how to properly identify them, and some of the measures you can take to control them. But first, we’ll cover what these black flies are.
What Are Fungus Gnats?
If you’re like most folks I know, you probably may not know what fungus gnats are. At least not for sure. Probably the reason why they’re just generally referred to as “black-winged bugs.”
But essentially, Fungus gnats (Bradysia species), also known as dark-winged fungus gnats, are small flies that infest soil, potting mix, and other sources of organic decomposition. Adults aren’t harmful since they don’t bite or transmit any known disease but their constant flight near the windows and around the plants is quite irritating.
However, it’s their larval stage you have to worry about. This is because they primarily feed on fungi and organic matter in the soil. Once exhausted they’ll begin to chew the roots of your houseplants causing unrepairable damage. Therefore, it’s important to correctly identify them so that you can take action.
How to Identify the Fungus gnats
Fungus gnats belong to the same order (Diptera) as mosquitoes. For this reason, they resemble in appearance. They have light grey to clear wings with a Y-shaped wing vein. Like most Diptera members, adult fungus gnats are attracted to light.
Hence, you might first notice them flying near your windows indoors. On the contrary, they’re relatively weak fliers compared to the common housefly. To properly identify them, regularly check near your potted plants, the surface of the potting mix, wet mulch piles, or your houseplant foliage.
If you notice small black flies that have slender legs with segmented antennae longer than their head, then you probably have fungus gnat infestation.
Females lay tiny eggs in moist organic debris or potting soil. Larvae have a shiny black head and an elongated, whitish-to-clear, legless body. They eat organic mulch, leaf mold, grass clippings, compost, root hairs, and fungi.
Fungus gnats thrive in humid and moist conditions in the house and around the indoor plants.
What Damage do Fungus Gnats Cause?
In small infestations, fungus gnats don’t cause any noticeable damage. Moreover, the adults which don’t feed on the plants nor bite. The larvae, if present in large numbers, can attack and feed on the roots of your houseplants making them vulnerable to sudden wilting, yellowing, loss of vigor, and stunt growth.
If you don’t the necessary control measures promptly, the affected plants will eventually die. The damage is particularly detrimental in seedlings, young plants, and most interior plantscapes. The most susceptible plants to fungus gnats include carnations, African violets, poinsettias, and geraniums.
How to Get Rid of Black winged bugs (Fungus gnats)
Prevention by regulating the moisture and improving the sanitation
When it comes to pest management, prevention is almost always the best cause of action. Especially when you know the cause and effect of the infestation. Which by now, you’re well aware of where fungus gnats come from and what conditions favor them.
You can take the following measures to prevent fungus gnats infestation:
- Inspect all the plants before taking them indoors
- Since these black winged bugs thrive in moist conditions, only water your plants when the soil feels dry. Also, make sure there’s optimum drainage in the pot at all times.
- Eliminate any pipe leakages or areas with stagnant water.
- Avoid using fresh mulches, excessive organic fertilizers, fresh grass clippings, and compost that isn’t properly decomposed
- Discards severely infested plants
- If the bugs are present in small numbers, isolate the infested plants from clean plants to avoid any spread.
Trapping and monitoring
This is one of my favorite ways to get rid of most black winged bugs either indoors and outdoors. You can achieve it using yellow sticky traps. By doing so, you’ll achieve two objectives. The first one is adult bugs are trapped and killed thus altering the life cycle.
The second objective is monitoring since the more the adult fungus gnats get trapped, you’re ultimately able to determine the severity of infestation. Some of the commercial sticky traps are coated with pheromones for extra effectiveness and are available online or in garden centers.
Here is my best recommendation – Kensizer Dual-sided Yellow Sticky Trap for indoor and outdoor use.
You should cut the yellow sticky traps into smaller squares, attach to wooden skewers or sticks and place them in pots to trap the adult gnats. After a few days in a pot, remove infested chunks, dispose of them, and replace them with fresh ones.
Pasteurizing the potting soil (where possible)
One of the most common sources of fungus gnats is untreated potting soil. To avoid this, commercial potting mixes are often pasteurized to kill flies and the algae and microorganisms they feed on. You should therefore purchase and use only pasteurized container mix or potting mix.
If it’s not possible or practical for you may consider solarizing the soil/mix. To solarize the soil at home, follow the following steps:
-Moisten the potting soil.
- Place it in a bag of transparent plastic or black plastic.
- Make the pile no deeper than about 8 inches.
- Place the bagged soil on a slightly elevated surface, such as a pallet in a sunny location, for about 4 to 6 weeks.
- Congratulations, your mix will be ready to use without having to worry.
Use of natural enemies (biological control)
The use of natural enemies is the way nature is meant to self-regulate. This makes this strategy one of the eco-friendliest approaches to control most pests in our homes and gardens. The most effective biological control of fungus gnats is the use of Bacillus sp. Others include Hypoapsis and Steinernema sp.
Bacillus thuringiensis subspecies israelensis (Bti) (Gnatrol) is a naturally occurring, spore-forming bacterium produced commercially by fermentation. It provides control and is toxic only to the larvae of fungus gnats.
Pro Tip: This Bt is a different subspecies from that applied to foliage to control caterpillars or beetles. Bt labeled for caterpillars is not effective against fly larvae.
Hypoaspis (=Geolaelaps or Stratiolaelaps) miles - A light-brownish predaceous mite adapted to feeding in the upper layers of moist soil. Preys on fungus gnat larvae and pupae. However, Hypoaspis won’t perform very well in individual houseplants and probably isn’t a good choice for use in homes.
Steinernema feltiae – According to UC IPM division, this nematode is effective when temperatures are between 60° to 90°F and conditions are moist. You can apply it as a soil drench and to media using conventional spray equipment.
Use cinnamon to get rid of fungus gnats
Most herbs including cinnamon are very effective in controlling damping-off in seedlings. This is because they all have antifungal characteristics. Here’s how to use cinnamon to control fungus gnats
- Sprinkle the cinnamon powder on top of the soil surface.
- Alternatively, you can mix the powder with water and then pour the solution on the soil surface.
- According to this research journal, cinnamon is effective in the treatment of damping-off with stellar antifungal properties.
- Therefore, cinnamon works by destroying the soil-borne fungi which feed the larvae of fungus gnats. With no source of food, the gnats will starve to death.
Use Hydrogen Peroxide
Hydrogen peroxide is a common disinfectant readily available in most homes or pharmaceuticals. Aside from its diverse uses, you can use it to control fungus gnats at home.
Just mix 1-part hydrogen peroxide and 4-parts water. Pour the solution on the soil surface and watch as the solution form and fizzle. By the time this stops, all the gnats’ eggs will be rendered unviable and the larvae killed thus disrupting the life cycle.
Rest assured your plants won’t be injured in any way or form.
Spraying with organic insecticides (chemical control)
As the last resort, you may consider spraying your houseplants or the potting mix with nature-friendly organic insecticides. Pyrethrins, for instance, offer effective protection against most black winged bugs. Alternatively, you can spray with Spinosad-based insecticide that provides natural control of gnats.
My best recommendation is Monterey’s Garden Insect Spray which contains Spinosad as an active ingredient.
Spinosad is a natural substance made by a soil bacterium that can be toxic to insects. It is a mixture of two chemicals called spinosyn A and spinosyn D. It is used to control a wide variety of pests.
Spinosad affects the nervous system of flea beetles that eat or touch it. It causes their muscles to flex uncontrollably. This leads to paralysis and ultimately their death, typically within 1-2 days. For an abundance of caution, move your plants outdoor before the spray.
And, above all always read the instructions given on the label carefully.
You’ve just read about what fungus gnats are, how to properly identify them, and most importantly, how to get rid of these irritating black winged bugs flying around your houseplants. Now, the next you notice your houseplants suddenly begin to wilt, yellowing, loss of vigor, or stunt in growth, you’ll know what to check.
However, these symptoms can also indicate other problems including excess moisture as a result of poor cultural practices. Let me know which strategy resonates well with you.