Fungus gnats
Do you see small black flies in your house? Are they flying nearby your houseplants? Is the condition of your plants declining quickly? Then you are dealing with fungus gnats. Also known as sciarid flies, these small black flies are quite irritating, but the adult flies actually cause little damage. It is the larvae of the flies that are the real problem. The fungus gnat larvae eat the roots of your plants, causing them to wilt and deteriorate. When these larvae are present in large numbers, your plants can even die.
The best solution for these pests is to use beneficial nematodes. Beneficial pathogenic nematodes attack and kill fungus gnat larvae. This tackles the problem at its source by interrupting the life cycle of the gnats, killing the larvae before they can develop into adult flies that can reproduce.
Stenema nematodes for fungus gnats
Stenema consists of beneficial nematodes that attack the larvae of different species of sciarid flies. The nematode species is Steinernema feltiae, a parasitoid species that penetrates the larvae of fungus gnats, infecting them and subsequently killing them.
Benefits of Stenema nematodes
How many nematodes do I need?
One small package of Stenema for 10m² is usually sufficient to treat all of your houseplants. You can treat 500 liters of potting soil with this quantity of nematodes. This is already quite a large area. If the infestation is very heavy or if you have a larger area to treat, you should use a dose for 100m². These are enough nematodes for up to 5000 liters of potting soil.
How fast does Stenema work?
This depends on how bad the infestation is. If there are many adult flies, then you will need to remain patient for 2 to 3 weeks for all of the larvae to become infected and die off. A light infestation may already be resolved after a few days.
A second factor is the amount of nematodes used. Using a higher dose of nematodes concentrated on a smaller area will give a quicker result, as all of the larvae will be infected faster. It's impossible to overdose with nematodes. If the infestation is quite heavy, we recommend it in fact.
How to use Stenema nematodes
- Moisten the potting soil of the plants ahead of time so that the nematode solution will not run out underneath the pot when applied.
- Dissolve the contents of the package of nematodes in water to make a concentrated solution.
- Dilute the solution if necessary (this depends on the number of pots that you need to treat).
- Pour the solution over the entire surface area of the potting soil of your plants. You will need to treat all of your plants that are planted in potting soil, not just the ones showing signs of infestation.
- Keep the soil moist for as long as you still see fungus gnats. Don't overwater! The potting soil should feel slightly damp, comparable to the forest floor in the shade.
Using this method, the nematodes will keep working for a period of 4 weeks. Indoors, you can use Stenema nematodes year-round. The soil temperature must be at least 10 to 12°C in order to be able to use Stenema nematodes outdoors.
Treating fungus gnats when starting seeds & young plants
Stenema can be used both preventively and curatively for treating fungus gnat larvae. We've outlined treatments here so you can choose the best option for your situation.
Preventive care
Fungus gnats / sciarid flies are usually a problem with young seedlings and cuttings during the first six weeks of cultivation. By applying Stenema preventatively, fungus gnats have no chance to develop. Usually one application is sufficient. For slow-growing plants, a second treatment is recommended after 4 to 5 weeks.
Tip: Fungus gnats are usually brought in from the grower when acquiring new plants, or sometimes they come in bags of potting soil. Avoid this by treating preventively when you repot plants or bring new plants home.
Curative care
If fungus gnats are already present, it will take 2 to 3 weeks for the adult flies to die off and for all larvae to be killed by the nematodes. The disadvantage here is that young plants have vulnerable root systems, and they may have already been destroyed by the time the gnats have been eradicated.
How to store Stenema
Stenema is a living product and therefore has a limited shelf life. If you need to store it for later use, you can keep it in the refrigerator at 5°C until the date printed on the bag of nematodes. If you apply Stenema promptly after you receive it, there is no need to refrigerate the product. You should order Stenema when you need it.
Help! I still have fungus gnats
It is very rare for fungus gnats to persist after a correct application of Stenema. What does happen from time to time is that a new infestation of fungus gnats emerges. These flies occur naturally in many environments and may fly back inside to infest your plants once again. This can happen:
- When taking home new houseplants or potted herb plants from the grocery store.
- If you cultivate a lot of young plants and grow from seed: this automatically attracts fungus gnats.
Questions?
At Biogrowi, we have more than 30 years of experience in biological pest control. You can always send us an email, call or contact us
another way. We will be happy to answer all of your questions and give you personalized advice. We speak English, Dutch, French and German!
