Most Common Pests In Cannabis: Leaf Miners

Author Luke Sumpter
24 February 2023
Leaf miners are any species of bug whose larvae lives inside your cannabis plant, eating away the leaf tissue.
24 February 2023
18 min read
Most Common Pests In Cannabis: Leaf Miners

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  • 1. What are leaf miners?
  • 2. What do leaf miners look like?
  • 3. Where are they found?
  • 4. Leaf miners symptoms
  • 5. What do leaf miners do?
  • 6. How to prevent them?
  • 7. How to deal with them?
  • 8. In conclusion

Leaf miners are larvae that leave a unique type of scar on your cannabis seeds and plant. Because they’re eating away the middle layer of your plant's leaves, they leave a “trail” that can be easily recognizable. Even if you’ve never grown cannabis before, but still have green fingers, you’ll most likely have come across the signs of leaf miners in other commonly cultivated plants, such as radishes and peas. However, leaf miner activity isn’t restricted to outdoor plants—although they are more common in such an environment. These critters can also show up indoors, and often end up there through vectors such as plant material and soil.

Although leaf miner damage might seem severe to the naked eye, these creatures don't usually kill plants. However, the damage they cause to leaves can inhibit photosynthesis over time. This, of course, can result in reduced growth and inferior yields once harvest time swings around. Below, you’re going to find out everything you need to know about leaf miners. You’ll discover what they look like, what the symptoms of infestation are, how to prevent them, and how to deal with them when they make an appearance.

1. What Are Leaf Miners?

Leaf miners are any larvae that start as eggs which are located on the underside of the leaves and as soon as they hatch, these yellowish white worm-like insects go into the leaves of your cannabis plant, eating the plant tissue and leaving a trail behind. Leaf miners are not actually a specific species of bug. It is a term used for the larvae of any bug (moths, flies, and beetles) that lays eggs on your plant’s leaves. 


Most Common Pests In Cannabis: Where Are Leaf Miners Found

Leaf Miners are the larvae of any bug (moths, flies, and beetles).

After the eggs hatch, they will eat their way into your cannabis plant's leaves.

2. What Do Leaf Miners Look Like?

Although they may differ when adults (because they are different bug species) all leaf miners are larvae.


Most Common Pests In Cannabis: What Do Leaf Miners Look Like

What do Leaf Miners look like.

Larvae look like small white or yellow worms, but it can be super hard to see them because they live inside the leaves until they are mature enough to grow wings or legs.

3. Where Are They Found?

Leaf miners are found inside your cannabis leaves. Their eggs are laid on top of the leaves and once they hatch they start eating their way under the second layer of a cannabis leaves “skin”.


Most Common Pests In Cannabis: Leaf Miners Eggs

Eggs of Leaf Miners laid on top of a Cannabis leaf.

And when they become adults, they can stick around and lay even more eggs if you don’t deal with them. 

4. Leaf Miners Symptoms

Although finding a couple of them eating away your leaves isn’t a super serious problem, a big infestation can reduce your plants' ability to grow and may ultimately decrease yields.


Most Common Pests In Cannabis: Leaf Miners on Cannabis plants

Leaf Miners eating their way under the second layer of a cannabis leaves “skin”.

The “trails” left behind can also start yellowing the leaves and if they get too affected, they can turn brown and fall, resulting in a less healthy plant.

5. What Do Leaf Miners Do?

The larvae eat the leaves cells, which means they eat what the plant needs to photosynthesize. These “tunnels” or trails can also be an entry point to diseases and can attract other bugs trying to feed on your plant.

As their name suggests, leaf miners burrow tunnels within leaf tissue. Because most leaves are so thin, this internal damage is easily visible from the outside. The main symptom is essentially a series of white squiggly lines that map out the route that leaf miners have taken through the inside of your plant’s leaves.

6. How To Prevent Them?

There’s no other way to prevent these bugs other than maintaining a good growing environment. If you keep a good temperature, females won’t lay eggs. Because females lay eggs in temperatures higher than 25 Celsius, keeping a lower temperature can effectively prevent these bugs.

7. How To Deal With Them?

It can be really hard to deal with leaf miners because they live inside the leaves and insecticides won’t reach them. What you can do is press your leaves with your fingers to squish the bugs, this is a good way to deal with a low amount of miners while still keeping the leaves on your plants. There are a few other options though. Chemical pesticides will stop the little buggers in their tracks quick smart, but not every grower is willing to use these. They can have an effect on the quality of the flowers and are just not great for the environment in general. Luckily, there are a few less invasive ways to help your ladies out.


Most Common Pests In Cannabis: Symptoms of Leaf Miners

In order to get rid of leaf Miners press your leaves with your fingers to squish the bugs.

Neem oil is a widely used organic pesticide and fungicide and can do wonders when battling the nasty leaf miners. You can find this item stocked at any reputable hydro or garden center. The oil is extracted from the fruit of the neem tree, which is indigenous to India, Sri Lanka, Bangladesh, and Pakistan. One of the huge upsides of using neem oil is that it only attacks the bugs that we want to stay away from our cannabis plants, and not the beneficial ones. Ladybugs, green lacewings, and earthworms are totally unaffected by Neem oil - while a wide range of bugs that we want to stay well clear off hate the stuff.

Neem oil is best applied as a foliar spray. To mix a spray-up, simply add about a teaspoon of Neem oil to about a liter of warm water, and don't forget to add a few drops of insecticidal soap to help the oil emulsify with the water. Then all you have to do is give the plant a good old spray. Remember to focus on the whole plant, and especially the underside of the leaves as this is where eggs are most commonly laid. This application should get rid of leaf miners after just a couple of uses, and it also works as a great preventative tool for other infestation issues. Just remember, Neem oil should not be used in the last 3 weeks of the flowering cycle, and if you are applying during flower then be very careful to not spray the budding sites.

Beneficial predators can help keep the number of pesky pests, like leaf miners, under control all while adding to the biodiversity of your garden. There are a few to keep in mind, but for leaf miner issues the parasitic wasp Diglyphus Isaea is your best friend. They love to feast on leaf miners while still in the larvae stage, and once they have matured to the leaf-eating time of their life cycle. Other beneficial insects that you might think about adding to your cannabis garden are:

  • Praying Mantis
  • Ladybugs
  • Delphastus Catalinae
  • Rove Beetles
  • Nematodes
  • Insidious Flower Bugs
  • Green Lacewings

Sticky traps won't go a long way in reducing the number of leaf miners currently attacking your plants, but they are pretty effective at cutting down the number of adult bugs which helps prevent any new larvae from being spread. They come in a range of bright and vibrant colors which the pests find almost irresistible, and all you have to do is place some around the base of each plant and hang some in and around the canopy.

If you see the infestation is getting out of hand, the only way to remove them effectively is to pluck the leaves out. This will ensure all the bugs eating your plant are removed. Obviously, this can stunt your plant’s growth but not doing anything will be way worse for your cannabis plants.

8. In Conclusion

Leaf miners aren’t that big of a problem in a small number. Of course, they are bad for your plant but won’t be a huge risk unless it’s a serious infestation. If you’re having continuous problems with bugs, we recommend our new Gorilla Cookies Auto. 

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Her high resistance will give you an advantage over any type of bug. Try to always take care of any bugs in the early stages so your plant doesn’t feel it too much.