Larvae feed on root hairs, rootlets, and tender root, stem, and leaf tissue. Feeding by later instars may extend to plant stems. This tissue damage creates entry points for fungal pathogens.

Localized plant death, especially in the area of larval feeding.

Damage is most severe in young plants, particularly in humid, overwatered conditions.

Larvae and adults transfer fungal pathogens such as Fusarium, Botrytis, and Verticillium between plants.

Increased susceptibility to root rot and other soil-borne diseases due to feeding wounds

The life cycle of fungus gnats consists of several stages: egg, four larval instars, pupal stage, and adult. Adults are small, grey-black flies measuring 1–5 mm in length, with long legs and antennae. Their wings have distinct venation, and although equipped with sucking mouthparts, they feed very little during their short lifespan. Males are typically smaller than females. Adults are weak fliers and are most active in damp, dark environments rich in organic matter. Fungus gnats can be present year-round in controlled environments like greenhouses.

Eggs are tiny—ranging from 0.1 to 0.25 mm—and yellowish-white in colour. They are laid on or just below the soil surface, near plant roots. Larvae hatch from the eggs and grow to 5–12 mm long and 0.5–1.5 mm wide. They are legless, translucent white, and feature a distinct black head with strong chewing mouthparts used to feed on organic matter and sometimes living plant tissue.

Pupation occurs in the soil within a small cavity. Initially white, the pupae gradually turn yellow to brown as they mature. Notably, the posterior end of the pupa remains mobile, a trait typical of this family.

Preventing fungus gnat infestations begins with environmental and cultural controls focused on disrupting their ideal breeding conditions. Fungus gnats are drawn to damp, organically rich soil, so maintaining proper irrigation practices is key. Avoid overwatering and allow the top layer of growing media to dry between waterings, as this discourages females from laying eggs. Good drainage and the use of well-structured media also help reduce excess moisture retention.

Sanitation is another critical component. Remove plant debris, decaying organic matter, and any algae growth from the growing area, as these provide food sources for fungus gnat larvae. Keep the space tidy, especially around propagation areas where young plants and humid conditions are more vulnerable to pest activity.

Yellow Horiver sticky cards are a valuable tool for early detection and control. Place them just above the soil line to capture adult gnats as they emerge. These cards help monitor population levels and can give early warning before larvae become established. Checking and replacing cards regularly ensures continued effectiveness and supports a strong prevention program.

Biological control offers effective, sustainable solutions for managing fungus gnat populations without relying on chemical inputs. A well-rounded biocontrol strategy targets both the adult and larval stages of the pest to reduce reproduction and prevent crop damage.

Yellow Horiver sticky cards play a continued role in biocontrol by capturing adult fungus gnats before they can reproduce. Strategically placing these cards near the soil surface helps monitor populations and reduces adult numbers over time. However, because adult fungus gnats cause little direct damage, targeting the larval stage is essential for effective long-term suppression.

Entomite-M (containing the predatory mite Stratiolaelaps scimitus) is highly effective at reducing fungus gnat larvae in the soil. These mites dwell in the top layer of the substrate and actively seek out larvae and pupae, disrupting the life cycle at its most damaging stage. They're especially useful in propagation areas and potted crops where larvae are likely to be concentrated.

For added control, Entonem—which contains entomopathogenic nematodes (Steinernema feltiae)—can be applied as a drench to growing media. These microscopic worms penetrate fungus gnat larvae and release symbiotic bacteria that kill the host within 48 hours. Entonem is ideal for hotspots or widespread infestations, working quickly and efficiently in a wide range of growing systems, including hydroponics.

Together, this integrated biological approach—combining monitoring, predatory mites, and nematodes—offers a powerful defense against fungus gnats while supporting plant health and environmental sustainability.