You've probably noticed that there are more of those little black flies floating around your plants now. Don't worry, you're not the only one who's bothered by them! Those fungus gnats, or sciarid flies , suddenly seem to be everywhere in the fall and winter. But why exactly? In this blog, we'll dive into the 'why' and give you practical tips to get this pest under control!
What are fungus gnats?
Fungus gnats are small, black flies that are often found in potted plants or moist soil. They are about 2 to 4 millimeters in size and resemble fruit flies, but you will usually find them around your houseplants instead of fruit. These flies lay their eggs in moist potting soil, and their larvae feed on organic matter and fungi in the soil. Although the flies themselves are harmless to humans, their larvae can cause damage to the roots of your plants.
Example of a mourning fly
Why do you see so many fungus gnats now?
Fungus gnats are present all year round, but they are more common in autumn and winter. This is because the conditions during this period are ideal for their reproduction. There are a few important reasons why autumn and winter create a fungus gnat heaven:
Indoor plants receive more water in autumn and winter
During the colder months, many people bring their plants indoors to protect them from the lower temperatures. In addition, many plants are in heated rooms with dry air during this period. In response, many people water their plants more, thinking that the plants will dry out due to the heated air.
However, this extra water creates a moist environment in the potting soil , which is ideal for fungus gnats to lay their eggs in. The moist soil provides the perfect breeding ground for the larvae, which feed on the organic matter and fungi in the soil. Overwatering is therefore one of the biggest causes of the increase in fungus gnats in the fall and winter.
Tip: Use a hygrometer to ensure you don't over (or under)water your plants!
Less ventilation in autumn and winter
During the colder months, we tend to keep our windows and doors closed more often to keep the heat in. This means there is less air circulation, and stagnant air contributes to moisture build-up around your plants. Poor ventilation creates a more humid environment, which gives fungus gnats more opportunity to breed. They can also survive more easily in enclosed spaces because they are not being blown outside.
Shorter days and less light
In autumn and winter, the days are shorter and the sun is more likely to be hidden behind clouds. Less sunlight means that the potting soil stays moist for longer – exactly the conditions in which fungus gnats thrive. In addition, many plants are in a dormant period in winter , which means that they absorb less water than normal. The soil therefore dries out less quickly and stays wet for longer, an invitation for fungus gnats to lay their eggs.
Use of organic fertilizers
We want to keep our plants healthy, so we often use organic fertilizers such as compost or potting soil with a lot of organic material . These types of fertilizers are great for your plants, but unfortunately also for the larvae of fungus gnats. The larvae feed on rotting material and fungi in the soil, and organic fertilizers can actually promote these fungi. A win-win situation for the larvae, but less fun for you and your plants.
How do you prevent a fungus gnat infestation in autumn and winter?
Luckily, there are ways to prevent fungus gnats from becoming a major problem. Here are some tips to keep your plants and home free of these pesky flies:
Or read our full blog here about how you can combat fungus gnats.
Adjust your watering routine
Fungus gnats like moist soil, so by watering them a little less often, you make their environment a lot less attractive. Water your plants a little less during the colder months. Let the top layer of soil dry out before watering again. This prevents the fungus gnats from breeding and breaks their cycle.
Ensure good ventilation
Get some fresh air in your home! Open a window occasionally, even if only for a short while, or use a fan to improve air circulation, especially in rooms where your plants are. This will help reduce humidity and make it much harder for fungus gnats to breed.
Yellow sticky traps of durable quality
Place yellow sticky traps near your plants. These sticky traps attract and catch adult fungus gnats. By catching the adult flies, you interrupt their reproductive cycle and reduce the number of new eggs they can lay.
An example of a sticky trap full of fungus gnats
Biological pesticides such as nematodes
One of the most effective methods to deal with fungus gnat larvae is with nematodes of the Steinernema feltiae type. These microscopic worms attack and kill the larvae of the fungus gnats. Nematodes are safe for your plants and a great natural enemy of fungus gnats, making them ideal for controlling and preventing new infestations.
Goodbye fungus gnats, hello healthy plants!
Fungus gnats are especially common in the fall and winter due to the combination of moist soil, less ventilation, and shorter days with less sunlight. By adjusting your watering routine, ventilating well, and using biological control methods such as nematodes and yellow sticky traps, you can effectively prevent and control these annoying flies. Do you have any other tips or experiences with controlling fungus gnats? Feel free to share them!
