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.