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Image by Werner Sevenster

Insect and Bug Guide: Leaf Miner

Updated: 3 days ago


Leaf miner damage on tomato leaves
Leaf miner damage on tomato leaves

LEAF MINER: attacks a large variety of vegetables, ornamental and flowering plants.

Leaf miner larvae and adults are rarely noticed, however seeing the insects doesn't mean you have a leaf miner problem. The way to determine if you have a problem is by watching for symptoms of leaf miner feeding like shown in the picture above. Leaf miners create patches or winding mines in vegetable leaves.


Leafminers overwinter in the soil as pupae and emerge in late May as adults. Females lay eggs on the undersides of host leaves which will hatch in about 2-4 days, and the small maggots feed between the upper and lower surfaces. One leaf may have several maggots. Larvae emerge from feeding mines to pupate on the leaf surface or just below the soil surface. Adults emerge in 10-25 days and begin to lay eggs for another generation. There are at least three generations each year.


Types of Leaf Miners

There are four types of leaf miners. These include the American Serpentine Leaf miner, Spinach Leaf Miner, Vegetable Leaf Miner, and Pea Leaf Miner. They all have very similar life cycles.


Spinach Leaf Miner

beet leafhopper
Spinach Leaf Miner Adult is hairy, about 1/4 inch long and grayish or brownish.

The spinach leafminer (Pegomya hyoscyami) is a type of blotch leafminer that creates irregular round-shaped mines. The mines are long and narrow at first but eventually become an irregularly shaped patch. Its larvae are whitish and carrot shaped. They do not have legs or an obvious head.


Leaf miner feeding has little impact on overall plant growth but can be quite damaging to vegetables grown for edible greens seeing as they feed between the upper and lower surface of leaves. This is what creates the winding tunnels or mines. Mines start out narrow when the larvae first hatches but as the larvae grow the mines become wider. Once the mature larvae exit the leaf, they fall to the ground to pupate.


The spinach leaf miner feeds on:


  • Spinach

  • Swiss chard

  • Tomato

  • Cucumber

  • Celery



Vegetable Leaf Miner

Leaf miner larvae on spinach leaves
Leaf miner larvae on spinach leaves

Like all it's other family members, the vegetable leaf miner makes windy patterns for mines. Their larvae is yellowish green with cylindrical shaped bodies. They too have no legs and no obvious head. The mature adult vegetable leaf miner is a yellow and black fly and is much smaller than spinach leaf miners, only 1/15th long! Even though it is tiny, it is considered one of the three most damaging leaf miners.


They like to eat on the following:

  • beans

  • peas

  • eggplant

  • peppers

  • potato

  • tomato

  • squash

  • watermelon

  • cucumber

  • beets

  • onion

  • lettuce


American Serpentine Leaf miner 

white apple leafhopper
Pupa of the American serpentine leaf miner (Liriomyza trifolii)

The American serpentine leaf miner is prevalent all throughout the Southern United States and attacks many plants. It targets not only vegetables but also ornamental and flowering plants.


Some of the plants they find tasty include:

  • aster

  • baby's breath

  • chrysanthemum

  • dahlia

  • daisy

  • marigold

  • mist flower

  • petunia

  • sunflower

  • zinnia

  • beans

  • cantaloupe

  • carrot

  • celery

  • cucumber

  • eggplant

  • lettuce

  • onion

  • peas

  • potato


Weeds such as nightshade, Bidens, and pilewort are a food source for the American serpentine leaf miner. It is important that you keep these out of and away from your garden.


Pea Leafminer

 Adult Pea Leaf Miner (Liriomyza huidobrensis)
Adult Pea Leaf Miner (Liriomyza huidobrensis)

The pea leaf miner is also yellow and black and is only 0.07 to 0.09 inches long. Like the ones mentioned already, it too has a smorgasbord of crops it likes to attack.


This broad range of tasty crops includes:

  • broccoli

  • cauliflower

  • spinach

  • beets

  • swiss chard

  • melons

  • potato

  • sweet pea

  • garden pea

  • onion

  • garlic

  • peppers

  • tomato

  • baby's breath

  • carnation

  • aster

  • calendula

  • nasturtium


Damaged Caused by Leaf Miners

Beet plant with damage from a leaf miner
Beet plant with damage from a leaf miner

Leaf miners can really mess up your plants by creating mines on the leaves. This isn't so much of big deal if you are not eating the leaves, however they often leave mines on your peas and potato tubers! Plus, the little punctures made by female leaf miner flies when they feed and lay eggs along with the tunnels they dig, can let in bacterial and fungal diseases. It's super important to keep an eye on your crops. That way if you spot any leaf miner damage you can catch any diseases early and deal with them before they become a bigger problem.


Management of Leaf Miners

Leaf miners, while often considered a nuisance in gardens, do not have to pose a significant threat to the health and vitality of your plants. With the right approach, these pests can be effectively managed through a combination of natural predators, biological controls, and mechanical strategies.


The first time we noticed leaf miners was on our green bean leaves. I had never seen those tunnels before, so I had no clue what was causing the damage. Turns out, it was leaf miners. Since then we've mostly relied on biological controls, namely nematodes, to manage them, and now we hardly ever see any signs of leaf miners.


Biological Controls 


  • General predators of leaf miners are parasitic wasps. These have proven to be very effective. You can introduce these into your garden if needed. It is always a good idea to get a native species that is local to your area. Check with your local extension office for information pertaining to native parasitic wasps.


  • Maintain a healthy soil as this boosts the plants immune system allowing the plant to fend off attacks from pests and disease. Having a balance soil food web is critical to having reduced pest load. When the leaves are strong the female leaf miner will have a difficult time penetrating the leaf to feed and lay eggs.


  • Beneficial Sc (Steinernema carpocapsae)* Nematodes have been effective in our garden. Simply apply them as a spray over the plant stem and leaves and as a soil drench.



Yellow and blue insect sticky traps
Yellow and blue insect sticky traps

Mechanical Controls

  • Cover susceptible plants with floating row covers early in the season. Although this will not be effective against larvae pupae that has overwintered in the ground. This is where the beneficial nematodes come in handy. Often combining more than one strategy is effective.


  • If you notice larvae in the tunnels, you can always squish them. If you find eggs you can pick them off or squish them also.


  • The use of sticky traps to catch the Leaf miner fly could be used. Just remember, the sticky trap can catch beneficial insects and bugs too.



Cultural Controls

  • Check your garden daily. This helps to identify things early before they have a chance to get out of hand.


  • Again, make sure that you have healthy soil. This is a fundamental principle. The stonger the health of your plant, the better your plant will be able to fight off attacks. This cannot be stressed enough.


  • Companion planting may deter leaf miners. Plant varieties such as marigolds and nasturtiums may act as a trap crop.


  • Keep weeds out from in and around the garden. Good biology in the soil will help you acheive this naturally. When your soil is balanced with good biology and nutrients, the weeds have no need to grow. Weeds are evidence that something is wrong with your soil. However, in the mean time, while you are building up good healthy soil, it is a really good idea to remove those weeds so that there isn't another food source for leaf miners to be attracted to.


  • Remove infected leaves and throw them away. It is probably not a good idea to put them in your compost.


  • Plant flowers that attract beneficial insects which are natural predators for leaf miners.



Marigolds
Marigolds

It is essential to monitor your garden regularly for signs of leaf miners, such as the distinctive mine tunnels they leave on leaves, so that you can take action promptly and prevent a larger infestation.


Moreover, focusing on soil health is crucial in creating a resilient garden that can withstand pest pressures. Healthy soil is rich in organic matter and teeming with beneficial microorganisms that contribute to plant vigor. By enhancing your soil with compost and mulches you can promote robust plant growth, which makes your plants less susceptible to pest damage. When plants are healthy and thriving, they are better able to fend off pests like leaf miners, and their natural defenses are strengthened.


Ultimately, by prioritizing soil health and fostering a diverse ecosystem filled with natural predators, you can create an environment where leaf miners are kept under control.


Embracing these natural and sustainable gardening practices not only helps manage leaf miners but also contributes to the overall health and productivity of your garden.


Remember, nature has a way of balancing itself, and with a little effort and attention, you can cultivate a thriving garden that minimizes pest problems and enhances your gardening experience.


Happy Gardening!




* CAUTION: Mention of a pesticide or use of a pesticide label is for educational purposes only. Always follow the pesticide label directions attached to the pesticide container you are using. Be sure that the plant you wish to treat is listed on the label of the pesticide you intend to use. And observe the number of days between pesticide application and when you can harvest your crop. Remember, the label is the law.



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