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Leaf Miner Invasion? How To Eliminate Trailblazing Larvae

Are your plant’s leaves starting to look like they have white or brown squiggles all over them? If so, leaf miner larvae may be hard at work. These tiny larvae chew tunnels through the interior of leaves, creating a complex network of damage that is highly distinctive.

Other than making the leaves of your plants look strange, are leaf miners dangerous to your plants? What are some of the more prevalent versions, and what plants do they impact? We’ll go over all of this and more in this guide to eliminating the leafminer menace!

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Leaf Miner Overview

Leaf miner damage
Leaf miner damage. Source: Ecuador Megadiverso
Common Name(s) Leaf miner, leafminer, citrus leafminer, tomato leafminer, spinach leaf miner, beet leaf miner, and a number of other names related to particular plant species
Scientific Name(s) Hundreds of species names
Family Multiple different families including Lepidoptera, Symphyta, Diptera, Agromyzidae, Douglasiidae, Gracillariidae, Nepticulidae, Tenthredinidae, Tischeriidae, and more
Origin Worldwide
Plants Affected Extremely wide host range of plants, comprising most trees, shrubs, large-leaved ornamentals, and edible plants
Common Remedies Crushing larval form in their trails is most effective killing method. Alternatives include neem oil, bacillus thurigiensis, and spinosad sprays as well as beneficial insects such as beneficial nematodes and parasitic wasps. Prevention using lures, sticky traps, and floating row covers is highly effective.

All About Leaf Miners

Firethorn leaf miner
A closeup of a firethorn leaf miner moth. Source: davidshort

Thousands of different fly or moth larvae are considered to be leaf miners, and each variety has its own favored plant type.

Most of these are from the Lepidoptera (moth), Symphyta (sawfly) or Diptera (fly) families, although there are a few exceptions from other genera. Their life cycles are all quite similar, although there’s some subtle differences here and there.

Let’s look deeper into these insects and learn how they impact our plants.

Leaf Miner Life Cycle

While there are slight differences between species, the basic life cycle is the same for all leaf miner species.

An adult, mated female will lay her eggs on or inside an egg’s surface. If inside, this is done with the female’s ovipositor, which pierces through the leaf’s skin to inject the eggsant . This may create a small raised spot on the leaf’s surface. One female may lay up to 250 eggs.

In ten days or less, the eggs will begin hatching into larvae. This is when they are at their most destructive, as the larvae tunnel through the leaf tissue and feed on it, leaving the telltale trails that leaf miners are associated with.

This feeding phase will go on for 2-3 weeks depending on the particular species. Once the larvae are nearing pupation, they will chew through the skin of the leaf and drop onto the ground below and burrow an inch or two beneath its surface.

At this point, if the weather is too cold for them to survive as adults, the larvae can go dormant and overwinter in the soil beneath the plant. Otherwise, they will form a pupa and begin their final transition to adulthood.

It takes approximately 15 days to transition from pupal form to adult. At that point, the adult moth or fly will dig its way back out of the soil and begin the cycle anew.

Common Habitats Of Leaf Miners

Horse chestnut leaf miner
A horse chestnut leaf miner adult on a leaf. Source: davidshort

Throughout the United States, leaf miners are a fairly common sight, although they aren’t as financially destructive in the northern states. This is mostly because the warmer climate regions house commercial farms which can suffer major issues.

Not only is their range extensive, but their chosen plants are as well. A wide range of plants are subject to leafminer damage, from trees through shrubs. Grasses are not likely to be consumed, but there may be pupa stages beneath grassy soil.

What Do Leaf Miners Eat?

The juicy inner tissues of leaves are subject to leaf miner damage, although they prefer leaf matter that has less cellulose. While they may chew through a leaf’s vein to get to more leaf on the other side, they tend to ignore the veins in favor of sweeter, softer plant tissues.

Particular species of leaf miners have opted to be incredibly selective. The citrus leafminer is an excellent example. This leaf miner on citrus trees may not cause extensive damage to the tree itself, but they leave open pathways for fungal or bacterial growth on the leaves.

For farmers, this damage can cause portions of or entire crops to become unsellable. For instance, spinach leaf miner damage will make the leaves unpalatable and potentially unsafe to consume. Needless to say, that can spell disaster for growers.

However, this pest isn’t limited to edible plants. Oak and aspen leaf miner damage exists, and boxwood leaf miner is common in hedging. A number of flowering plants are susceptible to the damage as well.

While in most cases this leaf miner damage won’t kill the plant unless it’s extremely heavily infested, it can be unsightly and potentially a gateway for fungal or bacterial diseases to get access to the plant. If your plants are healthy, they should survive the leaf miner assault.

How To Get Rid Of Leaf Miners

Old leaf miner damage
Old leaf miner trails which have turned brown and dried out. Source: Dis da fi we

If you, like me, would prefer not to discover that your spinach has been spoiled or your beet greens defaced, you’ll want to find some way of controlling leaf miners. Here’s a short list of ways to keep them from laying waste to your plants!

Organic Leaf Miner Control

One of the most difficult aspects of getting rid of leaf miners is that insecticides often can’t reach the larvae. Protected within the leaf’s confines, it can be a real chore to figure out how to deal with them.

Because of this, spray solutions have limited effect. However, a thorough coating of all plant surfaces with neem oil does have some effect. Not only does neem actively fertilize the plant, the naturally-occuring azdirachtin in the oil can slowly kill off larvae with repeated spraying.

Application of bacillus thurigiensis, also known as BT, can help with some larval issues as well. Available as a powdered form (Garden Dust) or a spray form (Monterey BT), this bacteria will poison leaf miner larvae if they come into contact with it.

In the worst cases of infestation, a spinosad-based product such as Monterey Garden Insect Spray may be of use. Once it has soaked through the leaf surface, the spinosad will poison leafminer larvae inside. However, like all of these, it may take multiple applications to work.

Environmental Leaf Miner Control

Liriomyza leaf miner damage
Damage from a Liriomyza species leaf miner. Source: Eran Finkle

The first step in environmental control is actually the simplest. If you see a leaf which appears to be housing leaf miners, pinch along the trails with your thumb and forefinger. You may be able to kill the larvae inside the leaf that way.

Healthy plants are the least damaged by these little chewing pests, so ensuring your plants are healthy is the best option. Be sure to regularly fertilize your plants. Keep them pruned well, and provide compost or other good soil for them to grow in. Healthy plants are happy ones!

Beneficial insects come into play here as well. Certain species of nematodes will kill pupae in the soil. Adding some beneficial nematodes to your soil will help eliminate those from ever emerging as adults.

A particular species of parasitic wasp, the leafminer parasite (Diglyphus isaea), will find the larvae while they’re in their trails. These tiny wasps lay their eggs inside the leaf miner larvae. As the eggs hatch, the larvae are consumed from within, and they’re harmless to humans!

Preventing Leaf Miners

There are a few different options for preventing the assortment of flies and moths that produce leaf miners from causing future harm.

Using floating row covers such as AgFabric can help prevent adult flies from reaching your plants. If they can’t reach the plant, they can’t lay their eggs. And if they can’t lay their eggs, the leaf miners can’t leave trails!

Yellow sticky traps are also a solution. Simply hang these near or on plants where leaf miner damage is likely to happen. Adult flies and moths will get stuck to them and will die off.

Certain species of leafminer respond well to pheromone traps. Citrus leafminer control can be achieved with the use of these ISCA lures, for instance. The pheromones lure adults to the trap, and they get stuck within and die.

Frequently Asked Questions

Aspen leaf miner damage
Leaf miner damage on an aspen leaf. Source: Blizno

Q: Will diatomaceous earth kill leaf miners?

A: The answer to this is yes, but in very limited quantities. Like sprays, powders like diatomaceous earth are less efficient at eradicating leaf miner larvae because the larvae just don’t come into contact with it.

However, it can be spread dry over the soil surface underneath a plant and dusted onto the plant’s leaf surfaces. Emerging larvae that are preparing to drop into the soil to pupate may come into contact with it that way. The diatomaceous earth won’t harm the soil, just the miners!

To wrap up, while leaf miners aren’t the end of the world, they do cause some rather unsightly damage and can destroy your salad greens. Hopefully you’re now much better armed to take on these little munching menaces! What plants have leaf miners destroyed in your garden? Share your stories in the comments below!

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