What to do about leaf miners?

By now, you probably know that I don’t think a  garden should be free of pests. In order to have a garden as free from chemicals or pesticides as possible, there has to be both “bad” bugs and “good” bugs. Sadly, the bad bugs usually show up first, and then it takes time for us gardeners to see the beneficial insects arrive to handle the problem. Today I want to chat about leaf miners—technically “bad” bugs—and how I deal with leaf miner treatment in my garden organically.

Recently, I’ve witnessed a couple amazing things in the garden that reaffirms my desire to nurture a space that is organic and a habitat for beneficial insects and pollinators. First, my dahlia seedlings were being attacked by leaf hoppers, until one day I spied a spider living in the seedlings and eating a leafhopper! Spiders actually eat a lot of pesky garden bugs like flies and cabbage caterpillars too. Second, as one of my roses was dealing with an aphid infestation on its buds, imagine my relief to see two ladybug larvae chowing down on the aphids as I watched! Yes, organic gardening can be frustrating at times, but I haven’t lost hope that each year will get easier and more rewarding. It really does take time.

Common Garden Pests

Each season I try to write a blogpost about a current garden pest or problem I’m dealing with. Recently, I updated my post on leaf hoppers because they were voraciously attacking my Spring calendula. Each Fall it’s the notorious cabbage caterpillars and loopers that attack my brassicas. In Summer, I break out my organic powdery mildew treatment to stave off this common fungal disease from tomatoes, squashes, dahlias, and more. Inevitably, each season brings some garden pest or problem—so you’re not alone if you feel this way.

Well, this year I planted out a bed of forty (40!) dahlia flowers grown from seeds. Within just a couple weeks, I started to see a problem with the dahlia leaves. There were definitely little squiggly tunnels on a lot of the foliage— a quintessential sign of leaf miners! Truthfully, of all the problems that dahlias could have, I’m thankful it’s something like leaf miner, where I know the treatment and it’s not typically fatal to your plants. So, as I’m spending some time this week dealing with my leaf miners, I decided this was as good a time as any to share what I do in terms of leaf miner treatment in the garden.

What Are Leaf Miner Bugs?

Now, I’m not an entomologist, but it appears that the category of “leaf miner” can actually refer to any larvae that tunnels through leaves, whether the adult form is a moth or type of fly. Essentially, there are lots of different types of leaf miners out there, such as citrus leaf miner or spinach leaf miner. Thankfully, any kind of leaf miner treatment is basically the same from plant to plant.

Leaf miners tend to like young, new growth. Commonly, you’ll notice new, light green leaves have the tunnels and curled damage from the larvae. As you might suspect, this is not great news for young or small plants that don’t have lots of foliage to spare. Meanwhile, mature and large plants tend to treat leaf miners as a nuisance and aren’t effected at all. Whether or not the leaf miners demand any treatment or attention in your garden will depend on your own assessment of the situation. Most of the time, I don’t do anything!

Here’s the basic breakdown of the life cycle of a leaf miner: first, the adult moth or fly leaf miner lays eggs on your plant. Second, the larvae hatches and slowly eats its way through your foliage. The leaf miner leaves behind a tunnel in your leaves. Now, this last part I didn’t know until I read about citrus miner from UC IPM, but the citrus leaf miner larvae will then turn into a pupae at the edge of the leaf and curl the leaf for protection. This is often why you see curled and deformed leaves on the new growth of your citrus. At this point, their mining “tunnels” are left behind—some say that these empty tunnels can make your plant susceptible to disease—as the pupae turns into the adult moth or fly.

What does leaf miner damage look like?

Let’s quickly identify leaf miner damage. In most cases, you will notice the damage before you ever see the actual insects. For example, you might see curling or deformed leaves like in the picture I’ve included of our lemon tree. In fact, this happens a lot with citrus leaf miner. Typically found on new growth, leaves with severe leaf miner damage will be curled up and crinkled. When you notice this, time for a closer look!

Another type of leaf miner damage are their swerving tunnel tracks on the leaves. These tunnels swerve back and forth like winding roads along the length of the leaf. These trails or tunnels are the result of leaf miners in their larval stage eating through the leaves. The leaf miner larvae are super destructive!

Organic Leaf Miner Treatment & Approach

Because we are backyard organic gardeners, there are really only a few things I do for leaf miners. Please remember that, most of the time, leaf miners are not fatal to a plant. Yes, the results of the damage can be unattractive and cause harm to new growth of young trees and plants, but it’s generally recommended to do nothing at all.

For young plants, who can’t afford to have their new growth all curled up and disfigured, or for severe cases, it’s possible to apply two approaches to leaf miner larvae. First, simply follow the tracks on the leaves and find the larvae at the end. Often, it’s possible to see the larvae inside the tunnel! Gently, use a fingernail to crush the larvae and that’s it! Second, you can remove the damaged leaves if you aren’t able to find the larvae or you simply can’t take the time to individually crush the leaf miners. Remember, dispose of these leaves in the trash, not your compost!

Aside from physical removal, there are an assortment of beneficial, parasitic wasps that will eat various leaf miners. These natural predators lay their eggs in or around the larvae, and will eat the leaf miners when they hatch. Plant lots of small umbel-type flowers, like yarrow or dill or cilantro/carrot flowers, to attract a wide array of beneficial insects (my California ceanothus seems to attract a lot of small beneficial insects too). Truly, the best part about avoiding chemicals (that often kill both bad and good bugs) is that you can encourage a thriving habitat for these beneficials to move in.

Honestly, using insecticidal sprays or treatments to fight off leaf minerts isn’t really effective anyway because they can’t reach into the tunnels to kill the leaf miner larvae. You’re better off squishing, removing, or leaving your plants alone.

Leaf miner Prevention Options

While I’ve never really had to worry too much about these pests, there are some ways you can take a preventative approach to leaf miners. For one, you can use a mesh cover to protect your plants. This approach is meant to keep the adult moth or fly away from your plants so they can’t lay eggs in the leaves.

Another approach uses something I’ve used for other garden pests before—sticky traps! Sometimes, placing yellow sticky traps around your plants can capture the adult leaf miner moths/flies before they can lay eggs on your plants. Personally, I’ve used sticky traps before for leaf hoppers, but it’s not my favorite organic pest control method. Why? Because sticky traps can capture both good and bad bugs. In the end, if you really are having an issue with pests like leaf miners or leaf hoppers, sticky traps are worth a try!

So, as I battle leaf miners on my dahlias, I wish you all luck as well! Every time I write one of these pest control blogposts I do my best to create a little more “calm” in our approach to seeing bugs in the garden. Bugs are everywhere, and it’s like a whole little world right in our backyards. The garden is more magical and productive when we let it buzz and move with life. If you found this helpful, please share it with your garden friends, leave a “hello!” or pin it for later over on Pinterest.