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Leaf Miners: How to Get Rid of Leaf Miners | The Old Farmer's Almanac

Leaf Miners

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How to Get Rid of Leaf Miners

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Pale blotches on your spinach? Wandering trails of not-so-green lines on your squash leaves? These are telltale signs that you’ve got leaf miners! Here’s how to identify, get rid of, and prevent leaf miners on your plants.

What Are Leaf Miners?

Leaf miners are a category of pest that includes insects from several different orders. One of the orders, Hymenoptera, has over 130,000 named species. A group of insects that spans several orders is quite broad!

Basically, there are many different types of insects that can be leaf miners. While the adults vary widely in size and form, the larval stages do the mining, and they all look similar to the unaided eye. 

Leaf miners are so named because they eat or mine the stuff between the leaf’s top and bottom surfaces. They eat all the cells and plant matter in the middle layers. As they do so, they crawl along, leaving behind them a pale or even translucent trail of damage within the leaf. 

The color change is from the chlorophyll containing cells inside the leaf being eaten. When you eat the peanut butter out of the jar, you are removing the good stuff inside, and leaving the outside—the jar. This is what leaf miners are doing. Many larvae feeding together may cause blotches.  

The good news is that leaf miners do not usually affect plant growth much and are not a big cause for concern. However, they can be a problem on vegetables grown for their edible leaves, like spinach, lettuce, or swiss chard. The damage is unsightly, and you probably don’t want to eat what the miners left behind. 

Leaf miners commonly attack the plants we grow in our gardens, like lettuce, kale, cucumbers, tomatoes, potatoes, beans, peas, eggplants, peppers, celery, onions, melons, and squash. They also attack trees and shrubs.

Lifecycle of Leaf Miners

The adult form of leaf miners varies greatly, ranging from moths to sawflies. However, the overall lifecycle is similar. Leaf miners overwinter in the soil as pupae. They emerge as adults in spring and find a suitable leaf for egg laying. 

The eggs are either deposited within the leaf or on the leaf’s surface. Once hatched, the larva eats the insides of the leaf for 2-3 weeks before dropping to the ground to become a pupae. In warm weather, several generations can happen during one growing season. 

Leaf miners can cause significant damage for gardeners and growers who market their crops. The visual damage caused by tunneling insects drastically reduces the value of the produce. Leaf miner damage on live plants like mums can make the plant unsellable, too.

Identification

Leaf miners are hard to spot, and the adults are often unnoticed. They are just another fly or moth in the garden. What you can notice is the signs of feeding larvae. 

Leaf miner damage. Photo by Thiti Sukapan/Shutterstock

Wandering trails of lighter-colored areas or scars that seem to be missing their green color are tell-tale signs of leaf miners. Sometimes, depending on the species, eggs may also be seen on the underside of the leaf. Some leaf miner damage looks more like stippling. Here’s a quick read from the University of Wisconsin Extension on spotting leaf miners and the damage they can do. 

Look for these signs:

  • Tiny pale dots on otherwise green leaves. 
  • Lazy, curving trails of lighter color that wander about the leaf.
  • Blotches of missing color, almost like a variegated leaf on a houseplant.
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Control and Prevention

Luckily, if you catch a leaf miner problem early enough, it can usually be controlled without too many leaves being affected. 

How to Prevent Leaf Miners

Cultural controls and prevention are the cornerstones of any integrated pest management system. With leaf miners, there are a few things we can do.

  • Watch the first true leaves in spring. These are a likely target for the initial leaf miner generation that overwintered in the soil. Promptly remove any suspected damage and be ready to take other actions below.
     
  • Rotate your plants each year. This is particularly important if you noticed leaf miner damage to your leafy greens last year. These insects overwinter in the soil, so give them a more challenging time finding your new tasty greens. Learn more about crop rotation.
     
  • Mix things up. If you have a more extensive garden, try planting in diverse patterns instead of mini-monocultures. Utilize companion planting and break up those big patches of spinach or tomatoes into several smaller ones.
     
  • Keep the garden weed-free, especially in the fall. We all want a weed-free garden. But some weeds like lambsquarters, nightshade, and pigweed are commonly used by leaf miners as food in the fall when other sources have gone dormant. Keeping weeds out of your garden can help reduce the next generation of leaf miners in spring.
     
  • Stop using broad-spectrum pesticides. In most cases, natural predators will hold leaf miners to low population numbers. General insecticides kill off the predatory insects that would feed on the larvae, pupae, and adults, allowing the population to explode. Leave it on the shelf. Better yet, take it to your community’s next hazardous materials collection event. 

How to Get Rid of Leaf Miners

Leaf miners don’t usually affect plant growth much, but that doesn’t mean that you want them around. If you have spotted their signature damage and want to get rid of them, you have a few options. 

Get Pickin’

Lower population levels of leaf miners are easily controlled by simple removal of the affected leaves. The larvae do their damage but are stuck inside that leaf until they are done eating and are ready to pupate. They can’t run away. Interrupt their dinner by simply removing the leaf and disposing of it. Don’t compost it, or you may have leaf miners in your compost that did not get killed by the heat of the pile. 

You can even find the “head” end of the trail and simply smush the larva with your fingers while it is still inside the leaf. 

Cover Your Plants

Row covers can be effective at preventing adult insects from laying their eggs. Use row covers to control leaf miners on leafy greens and other plants in areas where there was no previous leaf miner damage the year before.

Remember, leaf miner larva will drop off the leaf and pupate in the soil directly under the plant. If you had leaf miners there before, they may emerge as adults and would already be under your row covers. 

Wasps to the Rescue

Using beneficial insects is like fighting fire with fire. Why go to all the work and trouble to fight garden pests when you can have an army do it for you? If you have a minor problem, biologics might be on the expensive side to handle your situation, although still a neat way to deal with the issue. But introducing predatory insects can be a game changer if you are a market gardener, have a big home garden, or have a greenhouse. 

Several options are available. Specifically, Diglyphus isaea is a wasp showing promise as an effective leaf miner control and can be purchased online. The predatory wasp larvae feed on the leaf miner larvae. Check out this guide by the University of Florida about Diglyphus spp. controlling leaf miners.

About The Author

Andy Wilcox

Andy Wilcox is a flower farmer and master gardener with a passion for soil health, small producers, forestry, and horticulture. Read More from Andy Wilcox

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