Fungus gnats indoors: how to recognise them and how to get rid of them
Photograph the plant and the potting surface, answer a few questions, and receive a named diagnosis with a confidence level plus a dated plan of action.
Start plant diagnosis →How to tell fungus gnats from lookalikes
Fungus gnats are small, dark, slender flies with long legs and long antennae. They fly poorly, drift rather than dart, and they stay close to the pot: you see them walking over the substrate or resting on the pot rim, not hovering around a fruit bowl. Fruit flies are stouter and go for ripening fruit; whitefly sits on the undersides of leaves and flies up as a white cloud when you touch them.
The confirmation is in the soil, not in the air. In the top centimetres of damp substrate you may find translucent, legless larvae with a dark head capsule. Yellow sticky cards laid flat on the surface help you see whether adults are actually emerging from that pot and whether numbers are rising or falling over the following days.
Why your flat is such a good habitat
Indoors there is no winter. Steady room temperature, potting substrate rich in organic matter, saucers that stay filled and a watering habit that keeps the surface permanently moist give the insects everything they need to breed without a pause, generation after generation.
Newly bought plants and fresh bags of substrate that were stored damp are the usual point of entry. That is why an outbreak often appears a couple of weeks after a plant purchase or a repotting session rather than out of nowhere.
What you can change before reaching for any product
Let the top layer of substrate dry out between waterings so the eggs and youngest larvae lose their habitat, water from below where the plant tolerates it, and empty saucers instead of leaving a reservoir. Remove fallen leaves from the surface, consider a coarse mineral top layer, and repot plants whose substrate has broken down into a permanently soggy mass.
Keep new arrivals apart from the rest of your collection for a while and check the substrate surface before you place them next to other plants. None of this works overnight: several overlapping generations may still be in the pot, so judge success by trap counts over time rather than by a single evening. We cannot promise that a weakened plant will recover, and if the root system is already lost, it is fairer to say so than to keep treating.
When a plant protection product comes into play
We do not name products. Authorisations differ from country to country, and the same substance may be approved in one European market and not in another, so a recommendation without an authorisation check would be a legal problem for you and for us. For anything you intend to apply, ask the competent national plant protection authority, talk it through with an agronomist, or ask us directly and we will tell you which questions to put to them.
For anything you grow for harvest, the authorised use, the dose and the waiting period belong to the advice from the start. And if a diagnosis ever points towards a notifiable quarantine organism under Regulation (EU) 2019/2072, the reporting duty stands: the competent national authority has to be informed, and affected material must not simply be disposed of, moved or sold on your own initiative.
What Dr. Phyto actually does for you
You snap a photo of the struggling plant and, ideally, of the substrate surface. Dr. Phyto asks a few follow-up questions about watering, light, substrate and how long the symptoms have been visible, then names the most likely cause, explains exactly what is wrong, and states a confidence level instead of presenting a result as settled.
From there you get a step by step treatment plan with dates, so you know what to check and when, and a differential view of the causes that look similar. The knowledge base behind it is a verified European one rather than the guesswork of a general chatbot, and the web app is used across Europe, the Americas and Australia.
Who this is built for
Hobby growers with balconies, gardens and houseplants get a plain answer to the question of what is crawling in the pot. Professional growers in viticulture, fruit growing, greenhouses and market gardening get a fast first read before a site visit.
Public bodies and municipalities can use citizen photos for early detection and for the reporting obligations that follow from EU law. Agronomists and advisors get a quick second opinion and a differential diagnosis to argue against.
Are fungus gnats actually damaging my plants?
The adults are mostly a nuisance, the larvae are the issue: in large numbers they feed on fine roots and on the stem base of seedlings and cuttings. Established plants often tolerate a light infestation, young plants may not, and no recovery can be guaranteed once roots are damaged.
How do I know it is not fruit flies?
Look at the behaviour and the location. Fungus gnats are slender, fly weakly and stay near the pot and the soil surface, while fruit flies are stouter and gather around ripening fruit. A yellow sticky card placed flat on the substrate shows which pot the insects are emerging from.
Will Dr. Phyto tell me which spray to use?
No. Product authorisations are national and differ across countries, so we point you to the competent national authority, suggest you discuss it with an agronomist, or you can ask us directly. Every diagnosis comes with a confidence level, never as a guaranteed result.
Is drying out the soil enough on its own?
Letting the top layer dry between waterings removes the habitat for eggs and young larvae and is usually the most effective single change, but overlapping generations mean it takes patience. Track trap counts over several days instead of judging after one evening.