How To Get Rid Of Leaf Miners On Weed Plants

Want to learn how to get rid of leaf miners from your marijuana plants?

While plenty of insects are capable of creating weed crop issues, none are so insidious as leaf miners. These bugs are among the most troublesome problems growers face. If you’re dealing with this issue, don’t despair, help is at hand.

Read on for a breakdown of this pest, its lifecycle, what it looks like, and how it operates. You’ll also learn what to look for and how to remove leaf miners from your plants.

Let’s jump in!

What are leaf miners?

Leaf miners is a collective term given to the offspring of several species of bugs on weed plants, usually beetles, moths, wasps, or sawflies. The offending insects lay eggs on the underside of leaves, where growers easily miss them.

As opposed to other garden menaces, leaf miners on cannabis munch your crops from the inside out. Once their eggs hatch, the larvae emerge and burrow into the interior of your foliage, leaving behind a literal trail of destruction.

The reason these little pests work like this is twofold. Firstly, by burrowing into the weed leaves, they’re protected from other predators that would otherwise snap them up for a quick snack. Secondly, the soft, juicy internal tissues are easier to consume for the growing larvae.

An invasion of these bugs can damage crops and negatively impact their growth and yield. Before learning how to prevent leaf miners, it’s essential to understand the enemy you’re dealing with.

What is the life cycle of a leaf miner?

Although leaf miners comprise several species, their life cycles are much the same. These pernicious pests go through four stages of growth: egg, larva, pupa, and adult insect.

What do leaf miners look like? The eggs hang on the bottom of your leaves until they hatch. They’re usually found in small clusters of 2–5 eggs and look like grains of tiny rice.

When they hatch into larvae, their first order of business is to bore a hole into the leaf for safety and sustenance. Once inside, they’re safe from predators and free to gorge on your precious plants.

Should the larvae survive this stage, they start preparing an area where they can pupate. They exit their tunnels and wrap part of a leaf around themselves, again for protection from predators.

If the pupae remain undisturbed and uneaten, an adult insect eventually emerges, and the cycle starts over. 

Continue reading for tips on identifying, preventing, and removing them if all else fails.

How to identify leaf miners on cannabis?

Now that you know what leaf miners are, it’s time to move on to identifying and eliminating these bothersome pests.

The easiest way to identify these bugs is by signs of their damage. As these tiny larvae work their way through the foliage of your plants, they leave behind evidence of their work.

White lines appear in the wake of the leaf miner. These light-colored, winding trails across the leaves may cause you to think you have slugs or worms on your weed plants. A closer inspection reveals these marks are on the leaves’ interior, not the surface.

How can I prevent cannabis leaf miner invasions?

Like with most infestations, the best offense is a good defense. Implementing preventative measures is always preferable to dealing with an existing problem.

Here are a few ways to keep your crops free of cannabis leaf miners:

Floating row covers

Installing floating row covers is an excellent way to protect your plants from bugs of all sorts. It’s helpful that they’re cheap and easy to install.

Row covers are made of a delicate fabric mesh and placed over your crops. They allow light, heat, and air to pass while blocking access to insects and other predators. They’re suitable for raising indoor weed seeds or for outdoor use.

Once you’ve installed your row covers, check them regularly for any access points that may open up over time. Monitoring them is especially important for outdoor growers. Strong wind may cause them to shift, creating an opening for the pests.

Regular observation

By paying close attention to your plants, it’s possible to avoid the problem entirely. Spend some time each day thoroughly inspecting your crops for any signs of damage or infestation.

Remove the affected leaves immediately if you spot any eggs or telltale signs of trouble. Always destroy the infected material to prevent the problem from spreading further.

Maintain a good growing environment

Maintaining a suitable growing environment is just as important as providing adequate lights and the correct nutrients for weed. On top of promoting healthy growth, environmental conditions play a part in fending off leaf miners in cannabis.

These insects need temperatures above 77°F to lay their eggs. Cooler conditions shouldn’t give you any issues with these destructive little buggers.

How to get rid of leaf miners on cannabis plants

Prevention methods are less practical if you’re already dealing with marijuana pests. If you want to know how to get rid of leaf miners, here are six effective ways of exterminating these bothersome bugs:

Neem oil

Neem oil, extracted from the fruit of the neem tree, is a widely used fungicide and pesticide. Unlike other indiscriminate pesticides, it doesn’t kill beneficial insects such as ladybirds, earthworms, and lacewings.

The best way to use neem oil for cannabis is to apply it to the leaves with a mister. To create your foliar spray, fill your mister with a liter of water. Add a teaspoon of oil and a few drops of dish soap to facilitate emulsification.

Apply the mixture once or twice a week to your crops, paying particular attention to the underside of the leaves. A few applications should clear up the problem. Along with killing the miners, neem oil also eliminates other pests such as worms in your weed plants.

Unlike synthetic pesticides, neem oil has a low toxicity rating, but you should still avoid applying it to your buds. Stop spraying your plants 3–4 weeks before harvest to avoid any unpleasant tastes or smells.

Sticky traps

Sticky traps won’t get rid of existing larvae on your crops, but they’re very effective at preventing further infestations. They come in bright colors, causing fatal attraction for adult egg-laying insects.

Place the sticky traps around the base of your plants, and consider hanging some more amongst the leaves. This method is best suited for indoor setups; those raising outdoor cannabis seeds may find the adhesive washes off when exposed to rain.

Spinosad

Spinosad is a pesticide safe for animals, humans, and plants. As it’s all-natural, it’s suitable for growing organic cannabis. Made from fermented soil-borne bacteria, Spinosad kills leaf miners on contact or through ingestion.

As with neem oil, it’s best applied as a foliar spray. Apply an even misting to your plants, focusing on any leaves showing telltale signs of the cannabis worms. Spinosad solution remains effective for just one day, so mix a new batch for each application.

Remove affected leaves

Discarding affected foliage is a self-explanatory method of leaf miner treatment. If you spot their distinctive trails on the blades, act quickly and remove the offending leaf. While pulling foliage may slow growth, it’s much better than allowing the infestation to spread.

Always destroy or burn any leaves you remove to prevent the problem from spreading further.

Beneficial insect predators

If you’re wondering how to treat leaf miners without pesticides, introducing predators into the food chain does wonders. Your best insect ally in this fight is Diglyphus isaea. This parasitic wasp gobbles up any larvae or worms it finds.

For those who aren’t big fans of wasps, here’s a short list of some alternatives:

• Whitefly lady beetles 
• Green lacewings
• Nematodes
• Insidious flower bugs
• Praying mantises
• Ladybugs
• Rove beetles

Squish the bugs

This method of learning how to stop leaf miners entails bringing the fight to them. It’s you versus them; time for a bug hunt.

If the infestation spreads to the bulk of your plants, removing all of the leaves isn’t an option. Instead, examine the leaves closely for the leaf miner larvae. When you find one, press your thumb and forefinger together over the spot with the larvae to eradicate them.

Bug-free buds

Keep your crops free of pests with our expert tips and harvest a haul of juicy buds.

The best yields come from quality cannabis seeds with proven genetics, so head to our store and pick up a pack today.

About the author: Derek LaRose

Also known as Kronic from The Cannabis Kronicles, Derek LaRose is a young ambitious cultivator and a staple educator for indoor cultivation.