Are there suddenly all sorts of small, black flies flying around your plants? Then your plant is probably suffering from fungus gnats. Many plant lovers have to deal with them and besides being an annoying sight they can be harmful to your plants. Prevention is better than cure, but how can you prevent this pest or, if it is already too late, control it? Read here what exactly fungus gnats are and how you can best combat these small potting soil flies.
What are fungus gnats?
Fungus gnats are actually not flies, but belong to the mosquitoes. They are also called sciarid flies and are tiny black insects that fly around the leaves and soil of your plant(s). You usually don't notice them until you water the plant or tap the pot: they suddenly appear. Although the animals seem quite harmless to humans, it may be that they have their sights set on your plant.
The female fungus gnat is super good at reproducing. She continues to reproduce throughout her short life, laying up to 200 eggs! Even though she only lives a few days, with so many eggs a day it can quickly become a major pest. Because they reproduce so quickly, it is difficult to get rid of them. The eggs of a fungus gnat hatch after a few days and the larvae are born. Unlike other species of fungus gnats, the sciarid fly feeds on living material in addition to dead plant material such as fungi. Due to its rapid reproduction, it quickly becomes an infestation. If the number of larvae becomes too large, there may not be enough fungi in the soil to feed the larvae. The small larvae then crawl towards the living roots of your plant and start eating them. First they start at the hair roots, but once they have grown into larger larvae, the larger roots are up for grabs as well. You will understand that this makes the roots super vulnerable and susceptible to fungi and bacteria. The roots are also less able to absorb water and nutrients, making the plant weaker and weaker.
After about 3 weeks the larvae will pupate into small, black flies. The flies, unlike the larvae, only eat dead plant matter. Once they become adults they only have a few days to live, but in those days they take care of the offspring! The larvae therefore cause the greatest damage "invisibly".
How do I recognise fungus gnats?
An adult fungus gnat is a flying insect and looks a bit like a fruit fly. They are about 3 millimeters long and black in color with black transparent wings. A fungus gnat is slightly darker than a fruit fly and don't like the overripe bananas in your fruit bowl, but have their eyes set on your plants! You recognise a fungus gnat only when the larva has developed into a fly, but they start as eggs. The eggs are laid in the top layer of soil and after about four to six days they have developed into larvae. If your plant's soil is moist, you can sometimes see the larvae slithering through the soil. A larva of a fungus gnat has a long, white or transparent body with a black head. After about two weeks the larvae will develop into adult fungus gnats. So it may be that you only find out after two weeks that you have a fungus gnats infestation!
How do fungus gnats damage my plants?
Fungus gnats, or rather the eggs or larvae of the fungus gnat, are often brought in through new plants or new potting soil. Eggs or larvae may already be present in the soil and spread to other plants. They can also just fly in, by the way.
So the female fungus gnats find potting soil the perfect place to lay their eggs. It is a moist environment, with many organic and biological substances where the larvae can grow well. These larvae are the biggest problem, because they can eventually cause the most damage to your plants. The youngest larvae mainly eat the algae and fungi from the potting soil, but the older larvae will also target the roots of the plant. Especially young plants and cuttings are often not strong enough yet to survive such an infestation. Because their small roots are affected, they can no longer absorb water and nutrients. A large plant also suffers from this, but fortunately has a very good chance of survival!
When the roots of a plant are affected, the health and resistance of the plant also deteriorate. It will weaken, making it more resistant to diseases and fungi. The symptoms your plant gives may be somewhat similar to those of root rot or over watering:
- The lower leaves turn yellow;
- The plant drops leaves;
- The plant grows slower or stops growing altogether;
- The plant wilts.
In addition, the fungus gnats can also carry and transmit other fungi and diseases to other plants. One common fungus that the critters carry is Pythium, better known as root rot. In addition to the damage caused by fungus gnats, it is also an annoying sight! The flies are always dancing around and the ground or windowsill may be covered with dead flies.
How can I prevent fungus gnats?
Prevention is better than cure, but unfortunately you can not 100% prevent fungus gnats. However, you can take a few precautions to reduce the chance of getting fungus gnats. Fungus gnats like warm, wet and nutritious soil. To combat your fungus gnats infestation faster and prevent a new infestation, it can help to take a closer look at the composition and moisture of your potting soil. You can also prevent a possible new plague by putting new plants in quarantine before you put them with your other plants. Should a plague develop then the rest of your green friends are not infected yet.
Fungus gnats feel completely at ease in moist, rich soil with a pleasant temperature around 21 degrees. Houseplants that like a higher temperature, are regularly watered and have their roots in fresh soil are therefore the greatest prey for the fungus gnat. In some cases there are already eggs and/or larvae in the potting soil you buy in the store. It is therefore better to open the bag, let excess water evaporate and put it away in a cool dry place. The chance that the eggs and larvae will hatch and that an adult fungus gnat will lay more eggs in the potting soil is smaller then.
Fungus gnats love a moist soil. Make sure you do not water your plants too much! A layer of water at the bottom of the pot is best avoided at all times: this way the roots can rot and you make it a paradise for fungus gnats. Try to choose a plant pot and potting soil that stores as little water as possible. A pot with (several) drainage holes is perfect.
A well cared for and healthy plant is the best protection against diseases and plagues. Therefore, make sure that your plant is in the right location, gets the right amount of light and water and once in a while give it some extra plant nutrition. If it should happen that a plague of fungus gnats arises, the plant is strong enough to survive the attack. Cuttings and young plants often do not have enough strength to withstand an attack on their delicate roots. If you suspect that you have a fungus gnat infestation, keep a super close eye on it and intervene as soon as possible!
How can I control fungus gnats?
Have you found fungus gnats in your houseplant? Then it is important to start fighting them as soon as possible! Fortunately, there is no reason to panic. Your green friend will not die immediately. However, the roots are affected and the chance of diseases and fungi is greater. With cuttings and young plants it can go wrong quickly: They are not as strong! It is therefore very important to treat them immediately.
If one of your plants is infected, there is a good chance that the fungus gnats will also infect your other plants. Therefore put the infected plant separate from your other plants, preferably in a separate room. Adult fungus gnats stay alive for only 1 to 2 days, but because they lay 200 eggs at a time, you will have to deal with a persistent infestation in no time. With the following tips, we hope that you will soon be rid of the fungus gnats so that your plant can live happily ever after!
Let your plant dry out
Because fungus gnats love moist soil, it is important never to overwater your plants. Always choose a pot with a hole at the bottom, so excess water can drain away and the roots of your plant won't rot. Have you already spotted fungus gnats near your plant? Then don't water the infected plant for a while and let the soil dry out. The fungus gnat will then look for another place to lay her eggs. Moreover, the larvae cannot move well in dry soil, so they die out. We also recommend that you renew the potting soil of your plant. Clean the roots and the pot well and spoil your plant with fresh potting soil.
Sprinkle sand over the potting soil
Sprinkle some white sand (like sandbox sand) on top of the potting soil. Fungus gnats cannot lay eggs in this. In addition, the white sand does not contain any nutrients, so the larvae cannot grow either. Do this with all your plants. Make sure you remove the white sand again.
When you no longer have trouble with fungus gnats, otherwise not only the fungus gnats but also your plants will die.
Nematodes against fungus gnats (biological pest control)
Have you tried everything but still suffer from fungus gnats? Then you can buy nematodes against fungus gnats.
Steinernema Feltiae nematodes are microscopic worms that parasitize the larvae of the sciarid fly. The larvae die and thus cannot grow into adult mourning flies. Depending on the size of the infestation, you are within a few days (for a light infestation) to 2-3 weeks (for a persistent infestation) of those pesky fungus gnats off.
First, moisten the potting soil of your houseplants a little. Then dissolve the nematodes in some water and pour this mixture on the wet soil. Make sure you keep the potting soil moist. When the fungus gnats have disappeared, the nematodes will also die out.
Nematodes against death flies are harmless to your plants and safe for children and pets. Nematodes against fungus gnats can be bought online easily. Gotten curious about what kind of pest control we also offer? Check out our blog: ‘Which natural and biological pest control against which pest?’
Suffering from fungus gnats in your plants? Then the PLNTSdoctor Kit is the perfect remedy! The kit contains, among other things, neem oil. This is a perfect remedy for pests and fungi on your plant. Make a Neem oil mixture with water and dish soap and pour it into a plant sprayer. Spray your plant and the potting soil with this. Keep in mind that the fungus gnats will not be gone immediately, it may take a few days. So spray several times!
PLNTS hacks against fungus gnats
If you search online for the best way to fight fungus gnats you will come across a huge number of options. It is good to know that there is not one specific method that works for everyone. For some plants, one method works better than the other. It's a matter of trying!
Below are a number of alternative hacks that will help you recognize and combat fungus gnats.
To find out if there are larvae in the soil of your plant you can put some thin slices of raw potato in the soil. After a few days mold will grow on the slices. This makes them an attractive snack for the larvae! Place a few slices in different places and/or in different pots. After a few days, check to see if there are larvae on the slices. They may be translucent, so use a small magnifying glass if necessary to inspect closely! Can you see the larvae? Time to remove/renew the slices!
Another option you'll often come across when looking for a natural way to control fungus gnats is with cinnamon. It seems to be super effective and it's easy to use. Add two tablespoons of cinnamon powder to 1 liter of boiled water. Let the water cool and pour it into a watering can. Make sure the residue at the bottom does not come with it. Give your plants a little cinnamon water the next time you water. The larvae hate cinnamon and will not survive!
Ground cover plants
Another top-tip: the use of ground covers! Replace the top layer of potting soil with a layer of gravel, sand or pebbles. The fungus gnats cannot lay their eggs on these. Make sure that you remove the covers when the infestation is resolved.
Fungus Gnats Catcher
Another great way to prevent fungus gnats from breeding are our 'Fungus Gnats Catcher'! These sticky insect strips ensure that insects are attracted by the bright color and then stick to it! Cut the strips into several small strips so you can put them in multiple plant pots.