PHOTO: Jessica Walliser
Jessica Walliser
September 6, 2018

Swiss chard is a favorite garden crop of my family and many others. It’s a highly productive, nutritious and easy-to-grow green. Swiss chard, however, is not a crop without pest troubles. Leafminers in Swiss chard can become problematic, leaving damaged leaves behind. Here’s more on identifying this pest and managing it without using synthetic chemicals.


Identifying Leafminers in Swiss Chard

Like many insect pests, leafminers are easiest to identify by their damage. While the tiny adult flies are very difficult to spot and identify, the squiggly lines their larvae leave behind are hard to miss.

Female adult leafminers in Swiss chard lay eggs on the leaves. Once the eggs hatch, the larvae travel between the layers of leaf tissues, tunneling out and consuming the tissue inside. This creates distinctive “trails” on the leaves that are hard to miss. If you spot these shiny crooked lines on your Swiss chard, you know leafminers are present.

Are Leafminers Worth My Concern?

Thankfully, a leafminer infestation typically won’t outright kill a chard plant, but it can affect the visual appeal of this vegetable and limit your harvest. Many gardeners control this pest simply by cutting away any leaves with signs of leafminer damage and tossing them into the garbage. Larger farms with big plantings of Swiss chard might need to take other measures.

Controlling Leafminers in Swiss Chard Organically

If the population of leafminers on your chard crop is prolific and causing substantial damage that’s cutting into your bottom line, it’s time to take additional measures. One of the easiest ways to limit damage from these insects is to protect the plants with a layer of floating row cover. This lightweight translucent fabric is placed over the plant tops and forms a protective barrier over the plants and prevents the adult leafminers from accessing the plants. Put the row cover in place soon after planting. And, since Swiss chard doesn’t require pollination prior to harvest, the cover can be left in place all season long.

Another option is to plant a partner plant between the rows of chard that naturally increases the population of predatory insects that feed on leafminers. The primary predator of leafminer larvae are parasitic wasps. Since this pest is between the leaf tissue, most predatory insects can’t get to it. But, parasitic wasps can easily lay their eggs inside the leafminer while it’s still between the leaves. Sweet alyssum, dill and fennel are three great plants to interplant with Swiss chard to reduce leafminers organically.

One final way to manage leafminers in Swiss chard is to plow fields in the late autumn. This brings newly overwintering leafminer pupae to the surface and exposes them to predators such as birds and ground beetles. It also makes them more vulnerable to freezing out during the winter.

Whether or not you take action against leafminers in your Swiss chard patch is up to you. At my house, we simply pick off infested chard leaves and toss them out. In some cases, we even just cut out the damaged leaf portion and then eat the rest. Thankfully, chard is prolific enough that we always have more than enough to share.


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