Fungus gnats are tiny black flies that nest in the soil of your houseplants and garden and lay eggs on your plants and in your soil. Their larvae do tremendous damage to roots & clones, and spread diseases. For people with plant nurseries or significant infestations, they’re a serious pest.
Fungus gnats are one of the few species native to all 7 continents. They breed and grow in nature anywhere there’s soil, water and plants. From the arctic and antarctic tundras, Egypt to South Africa, Europe, Canada and all over the US, there’s no escaping them. Whether or not they’re introduced to gardens is not a question of if, but when.
Fungus gnats enter gardens through contaminated soil and clones or they fly in from outside. Once they’re inside, if they have access to your soil or growing medium, they form breeding colonies inside and are a persistent plant pest.
Fungus gnats begin as tiny eggs laid on plants or moist soil. The eggs hatch into translucent whitish larvae that look like tiny maggots about 5mm long. Larvae that hatch on plant surfaces roll off leaves and stems to land on the soil. Once in the soil they burrow in to look for moisture and roots to eat.
Fungus gnat maggots are equipped with strong jaws and feed on living plant root tissue and fungus. As they devour root tissue and grow, the larvae molt several times, eventually pupating into dark, barrel-shaped pupae resembling tiny coffee beans. Finally, the adult gnats emerge from the cocoon, with delicate wings. They head to the surface of the soil to fly away, find a mate and lay hundreds of eggs in and on your garden.
Eggs: hatch in 1-3 days
Larvae: live 5-10 days
Pupae: pupate for 2-3 days
Adult fliers: Live 2-4 days
A single female gnat can lay up to 300 or more eggs in her lifetime. Optimal conditions can lead to multiple generations hatching within a month. This rapid reproduction rate fuels their potential to become formidable crop pests.
If you see a sticky trap with hundreds of fungus gnats on it, you’ve got hundreds of thousands in not millions of larvae feeding on your plant roots and spreading pathogens. They’re worth stopping.
Fungus gnats love moisture, soil, rockwool, peat, coco, fungus and roots. They’re simple creatures. If there’s food, water and a growing medium they’ll breed. They breed in dynamic temperature ranges (from 50°f to 88°f), although optimum temperature for them is 68°f to 77°f. Unfortunately, most plant species also like these temperatures. It’s important to remember the soil temperatures are often more moderate than ambient air temp. If the air is 90°f, wet soil is likely much cooler. Fungus gnats are known to survive freezing temperatures and bloom when they thaw in the Spring.
As a general rule of thumb, the drier you can run your garden, the less they’ll breed, but you can’t dry a plant out enough to kill fungus gnats off without harming your garden. Overwatering causes infestations to become worse. Drying soil completely in between plantings destroys most of the eggs left in the soil.
Fungus gnats and larvae don’t just cause problems in adult plants. If you’re cloning from mother plants, fungus gnats are a huge problem. The adults lay eggs on the stems and leaves of the mother plant.
When a clone is cut, the eggs hatch on the clone inside the humidity dome. With no roots present, fungus gnat maggots find their way to the base of the stem of the cutting. There they burrow into the open stem of the cutting and feed on the pithy tissue inside of the clone. More often than not, the larvae will introduce infection into the cut stem and the clone will rot off or callus and not root. If it does root, it will do so poorly, often contaminated with pathogens like fusarium, bacteria or plant viroids.
If you’ve experienced clones that are damping off, it is very likely due to fungus gnat larvae eating and contaminating cuttings.
Running a nursery in California for many years, we dealt with fungus gnats vectored in from store-bought soil. They were abundant in fresh bags of dirt. We invented Bio-shield for ourselves as a solution to this problem (along with root aphids and thrips).
Adult gnats fly around to mate, lay eggs and be annoying. They don’t eat like their larvae do. They will seek nectar from flowers for the sugar content and drink moisture from the soil and dew off leaves. Their larvae pose the most serious threat to your houseplants and clones. These ½ cm long maggots feed voraciously on delicate root hairs and beneficial fungal partners essential for plant growth. This stunts plant development, reduces nutrient uptake, and can even lead to wilting and death. If you have fungus gnats in your garden, the larvae are damaging your roots, plant health and crop yields.
The larvae puncture root tissue while feeding on roots and fungus. Their jaws create open wounds in the roots. These wounds allow bacteria, fungi and viruses/viroids to enter the cells of the roots and spread into your plants. Additionally, the mouth parts of the larvae become contaminated and directly introduce pathogens into the cell walls of your plants.
In every case, if there’s a way to stop fungus gnats and their larvae, it will benefit the plants and the gardener.
Fungus gnats used to require consistent time, effort and money.
Bio-shield is a one-step, reusable solution that stops them and other bugs cold. Bag your root balls to deny bugs access to their habitat and break their lifecycle.
Bio-shield is a 75-micron nylon mesh bag that secures the root-balls of your plants in a bag with pores small enough to stop fungus gnats and their larvae but large enough to allow air, water and nutrients to pass through freely. The bag cinches around the stalk of the plants and locks bugs out. If there are existing fungus gnats in your soil, they’ll turn into adults in a few weeks and be trapped. They can’t fly away to breed and finish their life-cycle and die trapped in the bags. This causes their population to rapidly decline.
Fungus gnats (along with most soil-dwelling bugs) don’t thrive in an environment where their life-cycle is disrupted. The swarm often abandons protected rooms entirely. Breeding happy insect pests release chemicals to attract mates. Scientists suspect stressed & dying insects emit volatile warning pheromones and sounds to dissuade other members of their species from trying to live there.
BIO-SHIELD™ lets you beat bugs without harsh chemicals and constant maintenance!
