Fungus Gnats in a Greenhouse

Fungus gnats (Mycetophilidae and Sciaridae families) are unwelcome greenhouse visitors. Although gnats look like tiny mosquitoes, they do not bite or snack. Adult gnats are harmless, but their presence indicates the certainty of unseen seams that attack roots and compromise plant health. Although enclosed greenhouse environments pose challenges to controlling fungus gnats, early detection permits you to act swiftly before initial populations cause infestations.


Adult fungus gnats fly across potting soil that is high in organic matter, like peat moss, which can be a main part in many greenhouse soilless mixtures. You’re able to detect their presence almost immediately by mounting yellow sticky cards through your own greenhouse, which pull and trap gnats. The University of Connecticut proposes using one to four traps per 1,000 feet, put in a grid pattern, with extra cards attached near doors and ports. Potato slices pressed to potting mixtures around plants pull fungus gnat larvae. Checking the pieces weekly is a simple early-detection system.


Adult fungus gnats are irritation insects to people, but they do not damage plants. Female gnats lay eggs in potting soil that hatch into maggots, which are larval life stages of the insect. Larvae eat fungi, mulch and plant origins. The University of California warns that fungus gnat larvae can lead to serious damage in greenhouses. Since they feed on roots, they destroy a plant’s nutrient transfer system, which causes stunted growth, yellow leaves and, in serious cases, plant death.


The most effective control is also the easiest. Fungus gnat larvae cannot reside in the absence of moisture. If you allow plant press to dry before watering again, larvae will perish. Pyrethroid-based insecticides kill adults but have no impact on larvae. Bacillus thuringiensis subsp. Israelensis (Bti) is a microbial insecticide that is applied to soil media as a drench. It is frequently tough to find in retail shops, but an option is imidacloprid, which is a systemic insecticide that is also applied to soil to control fungus gnat larvae.


Preventing fungus gnats from populating your greenhouse is the best line of defense. All nursery pots, plug ins and seed flats ought to hold well-draining potting mixtures. If your irrigation or mist process is on a timer, make certain that it’s set properly so that you don’t over-water plants. Filling containers with pasteurized soil mixes and compost prevents the introduction of infested media to your greenhouse. Properly screened windows and ports disallow fungus gnats from coming inside.

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