Fungus gnats are small, black insects from the Diptera family. This common houseplant pest is a nightmare for every plant owner so let us get to know our enemy!
Fungus gnats’ larvae live in soil and feed on organic matter, root hairs, or mouldy leaves. When there is not enough food and too many larvae, they start to damage the plants’ roots.
As a result, leaves turn yellow and can die. Larvae have around 7mm long, legless, clear see-through bodies with black heads. They stay in this stage for around 10-14 days then pupate for 3-4 days.
Adults emerge from the pupa and live for up to 3-7 days. They are tiny little things with a short life, but females can deposit up to 200 eggs if we assume that they will live for approximately 5 days.
Their favourite spots are soggy soil, the presence of fungus is beneficial for them. They thrive in 21C-28C and our homes are just perfect and cosy for them!
The easiest way to prevent fungus gnats is to not to give them the opportunity to lay eggs and survive.
Avoid overwatering plants and do not keep the soil wet for a long time. Consider changing your watering methods, instead of pouring water on the top of the soil start watering plants from the bottom.
Leca Clay Pebbles
They lay eggs in the top 2-3cm of the soil so putting Leca pebbles on the top of the soil, will help prevent them getting into the soil. It doesn’t have to be natural colour clay pebbles and you can get pink, yellow or another colour which will not only help with insects but also looks nice!
Quarantine all new plants to make sure that the soil is free from eggs, even if you bought the plant from a trusted source the soil can be infected at any point.
Use yellow sticky traps to catch adults, you can also use a dish with some old red wine (keep the good stuff to celebrate when you conquer the fungus gnat!) or a mix of apple cider vinegar and a few drops of soap, this draws them in and will kill them.
Make your own trap using an old plastic bottle to make it more difficult for them to escape. It is super easy, here is a short guide on how it is done:
1. You will need an old water bottle, vinegar (they like the apple cider kind) and liquid soap.
2. Cut the water bottle in half and remove the screw cap.
3. Mix up some soap and vinegar in the base.
4. Invert the top half of the bottle and place it inside the lower half and you are done.
5. Optionally you can tape around the bottles to make them a bit more solid and draw crossbones to let those pests know you aren’t messing around!
A few fungus gnats around many plants won’t make a lot of damage but sometimes 10 can become 100 very fast, then we have to be ready to use our final weapon!
Hydrogen peroxide can be used to kill many indoor plants pests and it is my favourite way to get rid of fungus gnats.
Use one part of hydrogen peroxide and two parts of water, mix, then pour slowly into the soil.
Make sure that it will soak well into the soil but also let the excess of water to go through drainage holes. You will hear buzzing, it’s oxygen killing eggs and breaking the life cycle of the fungus gnat.
To prevent it in the future, add 1-2 spoons of hydrogen peroxide to 1 litre of water every 2nd or 3rd watering, this will not only help with fungus but also provide more oxygen to roots.
If you haven’t already, check our pest prevention article with more information on how to make a hydrogen peroxide mix.
Diatomaceous earth is a mineralized fossil dust, make sure to get food grade which is natural and safe for environment and pets. Sprinkle on the top of the soil or even add to your homemade potting mix.
Both adults and larvae will die after contact with this white powder which is very sharp and damage their bodies. When dealing with Diatomaceous earth cover your nose and mouth, inhaling this stuff is not healthy!
Check out your kitchen cupboard and if you find some old cinnamon for those Christmas cookies which we promise to make every year, sprinkle on the top of the soil to make a thick, visible layer and repeat every 2-3 weeks if necessary.
Although it wont kill larvae it will help to reduce fungus in the soil which is their favourite food!
I have tested all of these methods myself over a long time, and I can promise that they work. However the number of insects you are dealing with will change how effective each method is. You may need to combine some methods to get a good result.
If you decide to repot your plants to get rid of infected soil you do not have to bin it! You can sterilize soil in the oven, 30 minutes in 190 degrees will kill everything and make soil safe to use again.
I hope you enjoyed reading this article, if you have your own experiences with fungus gnat, would like to share your methods or need some support in fighting pests check out our Instagram. If you tried our advice and found it helpful let us see your happy plants and tag #highlandmoss.
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