The Easiest Way to Get Rid of Fungus Gnats from Houseplants with a Bug Zapper

Fungus gnats (Bradysia spp.) are annoying tiny, delicate looking little flies are around 1.5 – 3.0mm (1⁄16 to 1⁄8”) often seen flying slowly around indoor plants. They look like and are often mistaken to be tiny ‘fruit flies’ when they land on the sides of pots and surrounding areas. They’re a nuisance and have an annoying habit of landing in your cup of tea, but it’s their larvae are the true pests.

The larvae of fungus gnats are tiny little grubs that mainly eat fungi growing in rotting potting mix in over-watered pots, but they’ll also eat the roots of houseplants. When their numbers increase to high levels, they can cause significant root damage, weakening plants and stunting their growth, as well as spreading root diseases.

fungus gnat indoor plant pest close up macro photography
An adult fungus gnat magnified more than 20x, these flies are really tiny!

In a previous article, How to Control Fungus Gnats in Indoor Plants, we discussed nearly every possible method of getting rid of fungus gnats from houseplants.

In this article, we’ll look at an additional method that I discovered, which is one of the easiest to use, but please have a look at the previous article for ways to prevent the problem in the first place, and for other methods to use in combination to clean up the problem faster!

Using Portable Bug Zappers for Fungus Gnat Control

Bug zappers, more commonly known as fly or mosquito zappers, are electric devices that use a purple-blue ultraviolet (UV) light of 365nm wavelength to attract flying insects into a high voltage grid that electrocutes them.

These traditionally have been large wall mounted indoor units seen in shops, or lantern shaped outdoor units hung from overhead, that are plugged into the 120/220/240V mains power supply, use glass fluorescent UV tubes that a fair bit of power to protect large areas, and also use widely spaced wires in their high voltage grids to handle large flies and mosquitos which small insects can fly through unharmed.

With the progression of technology, we’ve seen lots of innovation in rechargeable battery design and low-power LED lighting, which come together to make possible devices such as USB rechargeable portable indoor/camping mosquito zappers!

These are designed to be safe, battery-powered devices that can be used indoors on a bedside, or hung inside a tent when camping, and usually feature a second switch that turns on a gentle night light, or soft camping light for reading. They’re also quite affordable, costing around $20, which makes them great value.

USB rechargeable portable mosquito zappers can run from their internal battery or be kept plugged into a USB charger to run the continuously

What makes these small-scale, portable mosquito zappers useful for controlling fungus gnats around houseplants is the very fine grid, which will capture even the smallest of flying insects.

Pictured below is an extreme close up of the high voltage grid with the closely spaced wires being the right distance apart to be able to capture the fungus gnats that are stuck in there. These zappers all come with a narrow cleaning brush which is used to clean the insects out from the electric grid, it’s fast and easy, and takes about a minute to brush them out.

The finely spaced high voltage grid is very effective on tiny flies that bigger bug zappers won’t get!

These portable mosquito zappers are very effective at reducing the population of fungus gnats. The picture below shows the number of insects one of my bug zappers collected near some indoor plants. Reducing the adult population prevents them breeding, and quickly helps get fungus gnat infestations under control, especially when they seem to be everywhere in the home!

A large number of fungus gnats cleaned out from a portable mosquito zapper after a few weeks

Remember that the mosquito zappers work well at night, because there are no other lights to attract the fungus gnats, so they head straight for the highly attractive UV light that draws them in.

At night the UV light is brighter and attracts fungus gnats very well, run your zappers at night too!

To increase the effectiveness of this fungus gnat control and get rid of them faster, combine this with other methods such as physical (and trapping) controls, cultural controls, biological controls and chemical controls described in the article How to Control Fungus Gnats in Indoor Plants.

As an additional bonus, these portable mosquito zappers do also work on mosquitos too, as that’s what they’re designed for. The openings in the protective safety grids on the outside are too closely spaced for flies to get in though, which does save having to clean them out, which is a benefit in my mind!

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