Sales Hotline +1 (760) 313-7455
Excellent [9.6 out of 10 based on 100 reviews]


How To Get Rid Of Fungus Gnats

How to Get Rid of Fungus Gnats

Encountering cultivation stumbling block happens to even the best of growers. No matter how meticulous one is in rearing cannabis plants, experiencing a few setbacks is inevitable.

The presence of fungus gnat in a marijuana growery is one of those snags cultivators may chance upon. Like other pests, it hinders one from achieving optimal yields. Growers need not worry, though, as combatting such bother is quite simple. And, if the problem is resolved before it becomes a full-blown crisis, an abundant harvest is still possible.

What Are Fungus Gnats

Getting to know fungus gnats before initiating an attack is necessary. Also known as sciarid flies, the common agricultural pest targets soil-grown plants. It most often resides in humid areas with high levels of moisture.

Fungus Gnat On A Leaf


At only around 2mm long, a full-grown fungus gnat is no larger than the thickness of a regular quarter. It resembles typical mosquitoes due to its long legs and pair of transparent wings.

On the other hand, its larvae or maggots are 1/4 inch in length. Sporting a whitish transparent body, their shiny black head is most distinguishable.

Although of minuscule size, fungus gnat populations can cause significant harm to a plant or an entire garden.

Life Cycle

Fungus gnats reproduce profusely and prefer to give birth in fertile, moist soils. An adult typically lives up to a week and can lay as much as two hundred to three hundred eggs each. After only four to six days, tiny larvae will emerge from the eggs and continuously feed for the next two weeks. The maggots will then enter the pupal stage for three to four days to repeat the life cycle.

The entire life cycle of a fungus gnat can reach up to only three to four weeks, depending on the temperature. Additionally, due to its short gestation period, a potted plant can easily host multiple generations of the pest.

How To Spot Fungus Gnats

It can be confusing to distinguish a fungus gnat from a common fruit fly. There are, however, some identifiable differences. The most apparent dissemblance is their color and size. A fungus gnat has a grayish black hue and is much smaller than the yellowish or tan fruit fly.

Moreover, the living and feeding patterns of the two are also distinct from one another. Fungus gnats situate their homes in wet, damp soil. Fruit flies, on the other hand, live around and lay eggs on ripe or rotting fruits and vegetables.

Additionally, the latter also buzzes around moist areas such as drains, empty containers, and even garbage bins. So, unless there’s a decaying produce in a grow room, a fruit fly would not have any business in such place.

Why Fungus Gnats Attack Cannabis Plants

Fungus Gnats

Pests infest an area or a plant for food and home, and fungus gnats are no different. Unfortunately, time and time again, growers make the ultimate mistake of overwatering plants making it desirable to this breed of insects.

Overwatering causes the soil to be perpetually damp. Hence, it becomes the perfect home for fungus and decaying matter – the fungus gnats’ maggots’ primary food source. When fungal elements start growing and organic materials disintegrate, the pests begin laying their eggs.

Moreover, gnats are also attracted to soil mixes which many growers use to nurture their cannabis floras. Composts, peats, and coco coir contain plenty of organic matter.

When the eggs hatch, the larvae go on a feast. And, although cannabis root hairs are not the squiggly ones’ main diet, they devour them anyway. This act of gluttony damages the roots which causes foliage and growth problems.

Not only that, the fecal matter clogs the drainage of the soil as well. As such, the earth remains damp, causing fungal matters to grow once again. With a new supply of food, the pest community thrives and grows.

Telltale Signs Of Fungus Gnat Infestation

Say that one has been grossly unprepared for the unprecedented attack of fungus gnats – here’s how growers will know if the pest has already harbored in their plants.

Gnat Sighting

The most obvious sign of an infestation is a sight of fungus gnats buzzing all over a marijuana flora or crawling through the soil. Growers must get rid of them regardless if the plant is showing the symptoms of distress or not.

Adult insects are not a threat to the plants. However, their presence indicates two possibilities. First, the insects may have successfully laid their eggs. And, second, the soil may already be infested with larvae.

Plant Damage

A visible plant deterioration is another hint of a fungus gnat infestation. Cultivators need to look out for disfigurations on the foliage. The leaves become droopy and pale or yellow while developing brown edges and dark spots. These physical downturns are often signs of nutrient deficiency but are unrelated to pH, nutrient, or any recognizable nourishment problem.

The infected plant may also show development issues and withering. Symptoms include stunted bud and overall growth. If left untreated, growers must expect reduced yields and weak, dead, or dying seedlings.

How To Get Rid Of An Infestation

Watering Marijuana Plant

Once a grower had identified the signs of fungus gnat infestation, the following course of action should be promptly set in motion.

Water Appropriately

As mentioned, overwatering is the primary cause of this pest dilemma. Hence, to combat the infestation, growers must only irrigate the plants when the topsoil has dried out. Although other methods will help the topsoil dry, it is still essential to prevent oversoaking in the first place. This helps in killing as many larvae as possible.

Place Yellow Sticky Cards In The Grow Area

Fungus gnats are attracted to the yellow hue. As such, placing a yellow sticky card lures the insects away from the plant. It also traps the adult fungus gnats, preventing them from reproducing any further.

Growers can also keep track of how bad the infestation is going with the amount of pests attached to the sheet. It will be the basis whether the number of fungus gnats has increased or decreased over time.

Blow Air Over The Top Soil

To dry out the topsoil, simply have a fan blow over it. An unmoist earth is uninhabitable to gnat eggs and larvae. Moreover, the stronger breeze will also blow away the adult fungus gnats. Of course, this step can is not necessary if one correctly waters the plant.

Kill The Larvae

This measure involves eliminating as many larvae in the soil as possible. One cannot employ the following steps unless the soil of the cannabis plant has completely dried out.

Neem Oil

Neem oil is safe to use, and it kills gnats almost immediately. Do note, however, that it emits a displeasing odor that lingers for a few days. As such, growers must not spray it on the buds when harvest is nearing.

On the side note, neem oil is practical to have in one’s gardening kit. Apart from fungus gnats, it also wipes out aphids, caterpillars, mealybugs, and the likes.

Food-Grade Diatomaceous Earth

Diatomaceous earth is an organic insect killer made from fossilized shells. It pierces the exoskeleton of insects on a microscopic level. Once punctured, the pests lose body fluids and eventually die.

Despite sounding lethal, the product is safe for humans and pets. To apply, spread it over the exposed parts if the soil using a powder duster.


Like diatomaceous earth, SM-90 is safe to humans even when ingested. The product effectively kills the larvae in the soil while being healthy for the roots. Mix 1 part of SM-90 to 5 parts water and spray it on the topsoil no more than once a week.

Essentria IC3 Insecticide

Although marketed as a “bed-bug killer,” Essentria IC3 insecticide efficiently eradicates fungus gnat larvae as well. Like the prior products, it is also safe for humans as it is an organic mix of various horticultural oils.

Use a one-hand pressure sprayer to make sure that the soil is evenly doused with the insecticide. It can be applied every other day and combined with other products, too.

BT Bacteria

BT Bacteria stands for Bacillus thuringienesis var. israelensis, which is a type of bacteria that produces toxins that hurt the larvae within the soil. The product hinders the maggots from being able to eat, causing them to slowly die.

There is a variation of BT Bacteria that can kill caterpillars and not fungus gnat larvae. Growers must always make sure to get the one that’s for Mosquito Bits or Dunks for it to work. Crush the pellets into powder to mix well with the water before administering it on the soil.

Food-Grade Hydrogen Peroxide

Although not as forceful as the solutions made especially for killing pests, Hydrogen Peroxide still does the job quite well. The suggested ratio of Hydrogen Peroxide to water is 1:4 when dealing with 3% pure H2O2. Choosing a food grade brand is highly recommended.

Preventive Measures

Once growers have successfully rid themselves of fungus gnats, preventing another attack is critical. This, of course, is only possible with the employment of preventive measures.

First and foremost, stop overwatering the plants. With proper irrigation, fungus gnats will cease to exist. Cultivators must also ensure that the area where the site of infestation is spotless and rid of even a single fungus gnat egg.

To keep the inside safe, keeping dangers out and as far away as possible is essential as well. Never purchase soil or bring in clones with any signs of flying bugs or larvae. Some growers will even go as far as cooking the new soil to kill all larvae and eggs before planting.

Being Prepared Is Key

Prevention is the mother of all cures. As such, nipping the trouble in the bud before it manifests is the best way to assure an excellent yield.

High Potency Cannabis

Alas, cultivating problems are inevitable even to the most precautious of growers. Learning from the experience, though, makes one better and helps prevent a repeat. With the resolve to eliminate the issue and the right materials on hand, an abundant harvest is still achievable.

Back to top