So you’ve spotted some maze-like squiggly lines in your precious spinach leaves. Or maybe your crops are covered in annoying flies. Bad news: you could have an infestation of leaf miners.
Leaf miner infestations can happen in greenhouses, veggie gardens, and ornamental areas around your property. On top of that, they can show up in almost any region of the U.S. In other words – no one is safe.
The damage caused by leaf miners isn’t just unsightly, it can stunt or kill plants, so you need to understand how to treat these pests. Ready to learn how? Keep reading!
What Are Leaf miners?
The term leaf miners is a catch-all that describes the larvae of three insect species: Lepidoptera, Diptera, and Hymenoptera. These larvae live inside plant leaves, feeding and growing until they reach maturity.
Basically, leaf miners are the larval – or maggot – stage of several insect families.
The first thing you might notice is distinct, discolored lines on foliage since these pests live inside leaves. That pattern of lines is a feeding tunnel created by the leaf miners as they chew through plants.
If you pay close attention to the patterns, you can identify the specific leaf miner variety that’s attacking your plants. You can also narrow down the leaf miner type by watching which plants are targeted.
Identification of Leaf miners
Host plants for leaf miners can include beans, blackberries, tomatoes, cucumbers, potatoes, lettuce, cabbage, peppers, citrus trees, aspens trees, shrubs, and a variety of ornamental flowers. As you can tell, they don’t pick one particular type of plant, which makes it harder to track these insects.
The larvae look like worm-like maggots that can be pale yellow, dark brown, or light green.
Adults measure 1/10 inch long and are typically black or grey flies with yellow stripes and transparent wings. They look similar to small house flies. They lay their eggs on the underside of leaves.
There are two common types of leaf miners, though keep in mind that there are several other varities out there:
Spinach Leaf miners
This species is a type of blotch leaf miner that creates irregular round-shaped mines. The mines are long and narrow at first, then become an irregular shaped patch.
There are a few ways to pinpoint spinach leaf miner larvae:
- They don’t have legs or head.
- The larvae are whitish and look like little carrots.
- They create tunnels between the two leaf surfaces.
- Once matured, the adult flies are hairy, measure ¼ inch long, and are between grey and brown.
Vegetable Leaf miners
Vegetable leaf miners feed on different plants than spinach leaf miners. This variety prefers beans, eggplants, squash, tomatoes, cucumbers, peas, and other edible plants.
Aside from looking at the plants they infect, here are some different ways to identify this species.
- The larvae look like snakes that leave behind winding mines.
- The larvae don’t have legs or a head and are yellow-green with a cylindrical shape.
- This species is smaller than spinach leaf miners, only measuring around 1/15 inch in length. The adult flies are yellow and black.
The Life Cycle of Leaf miners
Understanding the lifecycle of leaf miners is essential to controlling them. It all starts when mature larvae overwinter in the soil under the plants. Then, as the spring temperatures warm up the ground, the larvae mature to their pupal stage. By late April, they’re young adults.
At that point. they’re ready to start laying eggs in your garden. Mated females use a needle-like ovipositor to lay up to 250 eggs under the surface of the leaf epidermis. It can be hard to spot the eggs under the surface; they appear as small raised bumps in the leaf.
The eggs hatch within ten days, and the larvae start to eat their way through the leaf tissue. This is when they leave behind the wavy lines that are visible on the surface.
Larvae take only 2-3 weeks to mature. When they’re ready to pupate, they ditch the leaf and drop to the soil, digging 1-2 inches into the ground. Then, 15 days later, they emerge as an adult fly.
You can have several generations of leaf miners in one single year, so it’s clear how quickly a leaf miner infestation can start.
How to Identify a Leaf miner Infestation
It’s fairly easy to identify the damage caused by a leaf miner infestation because these pests feed on parts of the plants with tissue containing the lowest levels of cellulose and tannins.
They leave behind a distinct trail of maze-lime damage on plants. Typically, the damage is only cosmetic, and the plants continue to live a healthy life.
That’s not to say that leaf miners can’t kill a plant; they absolutely can! Unchecked damage can cause excessive leaf drop and other severe effects. The feeding tunnels created on the foliage can become pathways for diseases or fungal spores.
How to Prevent a Leaf Miner Infestation
As with any pest, prevention is the key to success. It’s easier to prevent an infestation rather than to stop one. Your best bet is to use multiple methods to avoid leaf miners from invading your garden.
Here are some suggestions.
Till Your Soil in the Fall
Leaf miners like to hide in the soil during winter and emerge as the temperatures warm. Till your garden after harvesting your crops in the fall to destroy the pupae and reduce the chance that adult flies will invade nearby plants.
Plant Trap Crops
Planting trap crops is a sneaky-yet-genius way to attract pests to crops you don’t mind sacrificing in order to save the ones you want. Leaf miners particularly enjoy lamb’s quarters, columbine, and velvetleaf. Plant these to prevent leaf miners from bothering plants that you want to keep whole and healthy.
Monitor Your Garden Closely
Monitor your garden closely and watch for any evidence that leaf miners are trying to make it their home. Catching issues early lets you take care of them faster and with less effort.
Keep Your Plants Healthy
If you have healthy plants, leaf miners won’t harm them as much. Use organic fertilizers and adequate watering techniques to ensure your garden is as healthy as possible. Add compost and other soil amendments to create a solid foundation for your plants.
Try Floating Row Covers
Floating row covers can help stop the adult flies from laying their eggs on the leaves. Floating covers are inexpensive and easy to install over your garden beds.
Hang Sticky Traps
One simple trick that you can try is hanging sticky traps in your garden. The traps attract and trap the adult pests before they can lay their eggs.
How to Stop a Leaf Miner Infestation
So your prevention methods failed, or you never had the chance to stop leaf miners from invading. Now you have leaf miners making a meal out of the foliage in your garden.
What can you do to stop leaf miners in your garden beds?
Manually Remove Eggs
If you’re lucky enough to spot the eggs, manually remove them from your garden. The more eggs that you remove, the fewer pests you’ll have to deal with when they hatch.
Introduce Diglyphus Isaea
Diglyphus isaea is a beneficial wasp that parasitizes leaf miner larvae. It kills them before they can mature. D. isaea is the natural enemy of leaf miners, and they’ll make a meal of these pests in your garden.
To reap all of the benefits of this wasp, you need to release them early in the season before the leaf miner population reaches large numbers.
Be aware that if you spray pesticides in your garden, it will kill these beneficial bugs.
Break Out the Spinosad Pesticide
Notice large numbers of leaf miners destroying your foliage? It’s time to take action, and only a few sprays work well against these pests.
I’ve found that Spinosad works well in the fight against leaf miner infestations. You can apply it to all plant surfaces. Once these pests ingest the pesticide, it stops them from feeding and they die in 24-48 hours. You need to apply it 2-3 times per growing season to keep the population at bay entirely.
Spray Neem Oil
I’m a huge fan of neem oil; I’ve used it effectively against many different pests in my garden beds.
Neem oil can be applied as a spray (either pre-diluted or concentrated) to stop the growth and development of pests. It acts as a repellent and has antifeedant properties.
You can use neem oil, which contains azadirachtin, to eradicate a population of leaf miners.
The reason I use neem oil is that it’s non-toxic to honey bees and other beneficial insects. You need these in your garden for proper pollination and using traditional pesticides can kill them as well.
Kicking a Leaf Miner Infestation
The key to getting rid of a leaf miner infestation is to prevent it before it starts, but gardening doesn’t always work that way. Instead, if you find yourself with leaf miners invading your garden, opt for natural methods such as introducing beneficial insects and use neem oil to eradicate them.