The mention of fungus gnats is sometimes enough to make a plant owner grumble and say curse words. These little nuisances are the bane of many homeowners and seem to put up a brave fight to maintain their presence.
Thankfully, there are effective ways to eliminate fungus gnats and stop them from swarming when it’s time to water your plants.
What are Fungus Gnats?
Quite similar in size to fruit flies, fungus grants are tiny dark brown or black flies that look like itty bitty tiny mosquitos. They are often found in homes where moist houseplant soil creates high humidity spots. The adults are an annoyance, but they rarely cause damage. It’s the fungus gnat larvae that are problematic.
Fungus gnat larvae live in the soil, feeding on decaying plant matter and naturally occurring soil fungi. In the case of minor infestations, they usually cause minor, if any, damage at all. But when infestations become severe, the larvae will feed on the roots, creating wounds and inviting pathogens into the plant.
Why Do Fungus Gnats Infest Plants?
Adult gnats are attracted to the moisture in potting soil because they’re looking for damp organic matter that will serve as a food source for larvae and pupa. They lay up to 200 eggs near the soil surface when they find suitable conditions. The eggs hatch into larvae and burrow in the soil three days later, searching for food.
Over the next two weeks, the larvae transition to pupa and then adults. The adult gnats then emerge from the soil and repeat the process during their one-week lifespan. This brief lifespan is the main reason they are so hard to get rid of.
What Does Fungus Gnat Damage Look Like?
Fungus gnats typically don’t cause much damage to plants, but if the infestation is severe and larvae are feeding extensively on the roots, your plants will show symptoms. Damage appears similar to other root-related issues: leaves yellow and drop, growth slows or stops, and the entire plant can wilt even with plenty of water in the soil.
How to Get Rid of Gnats
Fungus gnats always seem tenacious. Homeowners will treat the problems, eliminating the gnats they see flying around. It may seem like their efforts were effective, but then a week or two later, these pesky little buggers reappear. To effectively get rid of them, you need to eradicate the adults and the larvae.
The likelihood is high that you’ll need to try more than one method and possibly repeat it a couple of times. Without a doubt, fungus gnats are one of the most challenging indoor plant pests to control.
Quarantine Problem Plants
If you are struggling with fungus gnats in a plant, one of the best things to do—and one of the first things you should do—is put it in a quarantined spot during treatment. Creating some distance between it and uninfested plants helps prevent bugs from flying to another pot and creating a more significant problem to handle.
Natural Treatment Options
Neem oil
Neem oil is a botanical pesticide made from the pressed seeds of a neem tree. Its active ingredient blocks the production and subsequent release of hormones needed for larvae to transition to pupa and then adults but doesn’t harm beneficial plant organisms. Dilute the neem oil according to the label directions and then drench the soil.
Insecticidal soap
Insecticidal soaps contain fatty acids that suffocate small soft-bodied insects, disrupting the permeability and structure of cellular membranes. Mix one tablespoon of “pure” liquid soap (avoid dish soaps that claim to cut grease) per quart of distilled water in a spray bottle. Then spray the entire plant, including the bottoms of the leaves, until the solution drips from the foliage.
Sticky traps
Sticky traps consist of yellow paper covered in adhesive. Adult gnats are attracted to yellow, causing them to crawl or fly onto the card, sticking to the glue. Traps are available at most places that sell plants. Cut them into small squares and then put them on the soil surface or attach them to skewers in the potting soil.
Apple cider vinegar traps
Mix equal parts water and apple cider vinegar with a few drops of liquid dish soap, filling a shallow container with at least ¼” of this mixture. Place the trap close to infected plants or on the soil surface of larger containers. The sweet smell of the vinegar attracts the gnats; the soap traps them, so they drown in the water.
Mosquito dunks
Mosquito dunks contain a beneficial bacteria called Bacillus thuringiensis subspecies isrealensis. The bacteria infects and kills the larvae of flying insects and are commonly used to keep mosquitos from populating fish ponds, fountains, and animal troughs. Toss a mosquito dunk in a gallon of water overnight. The following day remove the dunk and use this water on gnat-infested plants.
Diatomaceous earth
Diatomaceous earth is a commonly used non-toxic pest killer. This all-natural product is made from crushed diatom fossils. Powdered diatomaceous earth has shards of silica that cut up and kill gnats when they crawl through it. Sprinkle a layer on dry soil before your plant needs watering, and dust some under the container to keep the pests from using the drainage holes.
How to Prevent Fungus Gnat Infestations
Prevention is key to dealing with fungus grants. It’s easier to prevent problems instead of treating an infestation, especially when fungus gnats feel like they’re impossible to get rid of completely. The following basic practices are the best ways to prevent all pest problems. After all, an ounce of prevention is worth a pound of cure.
- Quarantine incoming plants. Any time you introduce a new plant into your home, it’s recommended you keep it separate from the other houseplants for at least two weeks. Like quarantining infested plants, keeping them distanced from your healthy plants minimizes the chance of spreading problems if they have pests.
- Water from the bottom. Switching to bottom watering gives your plant’s roots enough water without saturating the top of the soil. A slightly dry soil surface is significantly less appealing to gnats.
- Maintain good air circulation between plants. Arrange your plants, so there is some space between containers and if possible, turn a small fan on them to create gentle airflow. The air circulation helps prevent damp soil conditions and makes it harder for gnats to land on the soil surface.
- Cover the soil surface. Some people claim that covering the potting soil with at least a ¾” thick layer of sand, small pebbles, or decorative aquarium rocks keeps adult gnats from getting to the soil and laying eggs.
- Clean all equipment after every use. It doesn’t matter if you’re working with healthy plants or those struggling with fungus grants. Any time you prune plants or take cuttings for propagation, clean and sterilize all tools before moving to a new plant and when your project is done.
