So there I was checking my plants after a hard days work.
Everything was going smoothly or so I thought.
Until I noticed something in the corner of my eye.
It couldn’t be.
There were FUNGUS GNATS on my plants!
These little buggers have decided to invade my plants right under my nose how could I have missed these bastards.
And so started the war.
But I have good news.
I was able to save my plants and have an OK harvest.
So not to worry if you have fungus gnats on cannabis plants there are simple ways to eradicate these F*&^ers and save your plants!
You will learn everything you need to know about fungus gnats on how to identify and determine if you have fungus gnats or another type of fly.
The causes of fungus gnats and how to prevent fungus gnats on marijuana and most importantly.
How to kill fungus gnats for good!
Now let’s get right into it,
What are Fungus Gnats
Fungus gnats are tiny black flies that if seen with a magnifying glass resemble the appearance of mosquitos.
When I mean tiny, they are anywhere from 1/16 of an inch to ⅛ an inch tall.
Where do fungus gnats come from ?
Gnats are your most common pest in the house when you bring home plants from the store or flowers they usually appear after a couple of days.
Then they start to go to work. In not only your houseplants but can make their way to the grow room.
Or from some store bought soils that are mass made, these soils will have these hidden invaders just waiting to be let loose on your plants.
How to Identify Fungus Gnats on Cannabis
A lot of people including myself have been confused if they have fungus gnats or fruit flies.
At first, that’s what I saw or thought when I first saw them years back. Not Fungus gnats.
Fungus Gnats vs. Fruit Flies
You can see the difference between the two different insects; one is black in color the other is more of a yellow, orange color.
Not only visually are they different they also feed and live differently.
The fruit fly lives around rotting fruit and vegetables.
Fruit Flies will lay eggs on the skin of the fruit such as bananas and not in soil.
Fungus gnats live around damp soil or coco coir, rock wool and can also be gray and brown in color.
Lifespan and Damage Fungus Gnats can do to Marijuana
The life cycle of the fungus gnat is an endless cycle unless it is stopped or they run out of food.
It all starts with the adult flies that are about a ⅛ inch in size and lay their eggs. Which then hatch in 4- 6 days.
The fungus gnat larvae are born, and they will immediately start to feed on the root hairs on your marijuana roots.
The larvae grow into a maggot like a form and are visible. Become fully grown within two weeks.
After that the cocoon and turn into the notorious fungus gnat in 7 days. And well you get it, the cycle continues.
Referenced from the University of Vermont
Fungus Gnat Damage
A simple question anyone can ask are fungus gnats harmful to cannabis? The answer is YES!
Fungus gnats infest the soil and decomposing organic matter.
The larvae feed off this and also eat roots hairs of your new marijuana seedlings or your growing plants.
Fungus gnat damage stunts growth and can start to turn leaves yellow.
The plant slowly dies as the roots cannot uptake the nutrients and water it needs due to root damage.
Causes of Fungus Gnats on Cannabis
Damp growing mediums caused by over watering.
It’s one of the primary reasons.
So it’s critical to control your water and how saturated the plants get.
Fungus gnats are also attracted to excessive carbon dioxide or CO2.
- Have you ever been is your house or outside and little flies come up to your face. Annoying yet this is a great warning sign!
If you are growing indoors, turn off CO2 tanks so you can root out the problem before your roots become the problem!
Make sure your grow tent or grow room is properly sealed.
Believe it or not, they are attracted to soil mixes with compost or peat.
Saturated soil or coco coir medium.
Houseplants and flowers bought at stores which were not properly looked after.
Open windows without screens.
Now onto my favorite part, and what you have been waiting for,
How to Kill Fungus Gnats
When I realized these flies were not fruit flies I immediately took action.
I knew they were already in my crop. So that was my priority.
Obviously, I have to protect my medicine at all costs.
I sealed the room and started to see if there were any air holes from the outside coming into the grow room and tents I had setup.
Also made sure all windows were sealed and closed properly.
Then I tried to see if all my plants are infested or just a one.
From what I could tell a couple had been infected.
There are many ways to kill fungus gnats you can go the natural way of remedies.
Or if you do not want to mess around go with organic food safe foliar sprays.
Each method is safe for your marijuana plants.
So not to worry if you are growing medical marijuana.
I will go over some of the best ways to get rid of fungus gnats on your cannabis.
Then I will give you my exact steps I used to win the war.
Home Remedies for Fungus Gnats
Yellow Sticky Trap paper is a great first solution as supposedly theses flies are attracted to the color yellow.
These fungus gnat traps are perfect cheap first defense.
Just place theses traps around your infected plants and watch them stick and die!
Apple cider vinegar smell also attracts the fungus gnats.
Mix in a jar or cup or bowl, the apple cider vinegar about two tablespoons or more with some dish soap and water. Then place it around your plants.
Hydrogen Peroxide can be used if the fungus gnats have infected the soil and you suspect larvae are growing.
One of the ways to get rid of the fungus gnats in larvae stage is hydrogen peroxide.
- But beware it can harm the roots if used to much.
Make sure you dry out the soil, then mix 1 part hydrogen peroxide to 4 parts water and then water your infected cannabis plants.
If it starts to foam, it is killing the larvae.
Sand this another significant step that can be done when transplanting.
Place and inch on the bottom and top of your pots. It acts like shredded glass, and they cannot get inside it impenetrable.
The growing trend in the growing community is the use of “living organisms and bacteria” to help fight pests and insects in the garden.
One of them is nematodes,
Beneficial Nematodes are microscopic roundworms that seek out and kill 200 different insects in soil or growing medium.
That’s 200!. No wondering it is starting to be a trend.
Not only are they great a getting rid of fungus gnats but are also beneficial to kill many other pests.
The great thing about them is they do not bother ladybugs or earthworms. Simply mix with water and water your plants.
Here is short video about using nematodes
Landscape fabric is a great at preventing fungus gnats to invade your soil either through the bottom of your pots or through the top part of the soil.
The fabric comes in different sizes and thickness. you don’t want the fabric to be too thick because you want to allow water to run through it when watering your plants.
The other benefits of landscape fabric is you can make fabric pots out of them if you wish or they can be used outside in your garden and landscaping features so it does not go to waste.
The best way to use landscape fabric is to do the following:
Take your landscape fabric and place your pot upside down on top.
Simply cut the dimensions of your pot around the fabric.
Trying to leave an approximately 2 or 3 inches around the corners and sides of the circle, to ensure there’s enough room to hold the medium inside it.
Place the landscape fabric at the bottom of your pot.
Slowly add your grow medium in and around the fabric until the fabric is pressed against the walls of the pot or container.
After that, fill the rest of your pot up with your growing medium as you need to at least 1 to 2 in of room on the top of the pot or container.
You can now add an additional layer of fabric on top of your grow medium.
So cut a circle around the top part of your pot next cut a line to the center of the circle so this can wrap around the stock.
Next place layer with a small amount of grow medium on top of the fabric or you can use GrowStones gnat gnix if you wish.
This will now ensure that the fungus gnats cannot crawl through the bottom part or through the top part of your pot.
Fungus gnats cannot crawl through the layers of the fabric.
I found this to be an effective way to preventive these nasty fungus gnats from invading your marijuana plants
Natural Organic Remedies
Neem oil can be used on fungus gnats it is an effective solution.
Mix with water and soak the plants after the soil has been dried out for at least two days. The same as hydrogen peroxide.
A bacteria called Bacillus thuringiensis, it’s used by organic farmers to control insects that eat crops.
Also by the World Health Organization to help control mosquitoes.
The bacteria is is an another safe alternative can be used and when growing cannabis.
The bacteria comes in pellet form like:
Just crush up some pellets and place them in your growing medium when transplanting or even on top when an outbreak hits.
It wipes out the fungus gnat larvae and does not harm the roots of the plant.
Diatomaceous Earth is a food supplement that contains silica and is also good at destroying fungus gnats.
It has a whole lot of beneficial properties to humans and pets
- Used to detox the body and kill parasites/worms
- Removes heavy metals scrub the intestinal walls
Nicknamed the “grass of the sea”
Mix Diatomaceous Earth in with your soil for maximum benefits.
For proper handling here is a resource from: The International Diatomite Producers Association (IDPA).
Growstone Gnat Nix is made up of recycled glass this a a excellent solutions for your gnat outbreak.
The Gnat Nix has been tested in Universities and is proven to be an effective top dress on your plants against fungus gnats.
This acts like sand or diatomaceous earth at keeping the gnats inside and the soil to die as the turn to adults.
Also you keep them from laying eggs on the grow medium.
It’s a great addition to prevent fungus gnats on cannabis plants.
Insecticidal Soap is another safe way to get rid of gnats on in your plants. An organic safe solution that will not harm your cannabis plants.
It is also effective against other insects that are common to growing marijuana.
The soap usually comes in a spray form you can spray the top part of your grow medium.
You can spray on the leaves of the plant preferably in vegetative stage.
The ingredient have a fatty acid salts that works against the pest such as fungus gnats.
Its effective against all larvae and nymph stages of the pests life, kills on contact by being absorbed by their bodies killing on the spot.
Can also be a great tool in fighting other invasions of insects in your garden.
If you have on hand some SM-90 spray this can also work in a pinch and is also perfect for another issue in the garden such as powdery mildew.
How I got Rid of Fungus Gnats
The battle plan that I found to be the best for me was to isolate the major problem area, my medical marijuana.
Contained the area.
Find and isolate the plants.
I immediately used the yellow sticky trap paper by the two plants that I noticed them walking and flying around.
Then I sprayed a dose of Insecticidal Soap.
Waited a day.
The fungus gnat tape seemed to be working well and got covered in gnats.
I replaced them once more to let the soil dry out as much as possible not to stress out my plants.
Once dry enough I then made a mixture of Beneficial Nematodes with water.
I then watered my plants and sprayed another dose of Insecticidal Soap just to be safe and replaced the tape one last time.
As an extra measure I placed Gnat Gnix on top of my plants to make sure no nymphs flew out.
Over the course of about a good ten days, the flies all but vanished!
I was able to stop and kill fungus gnats on cannabis.
But the most frustrating came when having to try and find the cause in my house.
I am a green thumb and like to have my houseplants as well.
That took about another week to find and get rid of the rest of the fungus gnat invasion.
Do you have fungus gnats, try some of the solutions I know you can win the war just like I have.
What solution do you use and what works for you let me know in the comments and share.
Grow on my friends.