Last week, I received an interesting e-mail from a member of the public asking me what I thought was plaguing his columbine. Included in his email was a picture of the plant’s leaves that had intricate, almost beautiful, white lines and squiggles throughout the leaves. As soon as I saw the picture, I knew it was damage caused by Columbine leaf miners!

What are leaf miners? Leaf miners are the larvae or maggots of certain species of moths, sawflies, and flies that feed on soft tissue found within a leaf.

What is the life cycle of a leaf miner? There are slight differences depending on the species, but in general most follow a similar life cycle pattern. A female will lay eggs either on or within a leaf. Once the eggs hatch and the larvae emerge, they will begin feeding on the soft tissue within the leaf, between the upper and lower epidermis. The feeding will go on anywhere between 2 to 3 weeks. Once larvae approach the pupation stage, they will chew through the leaf and drop to the soil burrowing an inch or two beneath the surface. Pupae can either overwinter in the soil if it is too cold, or will develop into adults after 15 days or so, and the cycle begins again.

What plants do leaf miners feed on?

Various types of leaf miners feed on various kinds of plants, and can be common pests on columbine, chrysanthemums, birch and other broadleaf trees, and bushes. They can also be a nuisance pest on arborvitae, juniper, and a variety of flowering and vegetable plants.

What does the damage look like? The damage of a leaf miner is usually telltale silvery to white squiggles and lines on a leaf. Eventually, these areas will turn brown. The picture below was submitted by R. MacHarg of his columbine plants.

Can leaf miners kill my plant? Most leaf miners will not kill plants, although the plant will suffer leaf loss. Recurring and severe damage may weaken the plant enough that it will eventually die, but is generally considered an aesthetic problem.

How do I treat for leaf miners? The answer to this can depend on the host plant being treated. In the case of our friend with the columbine plant, there are a couple of steps to take to get rid of or at least minimize pest damage. Encourage a new flush of healthy leaves by cutting all foliage to the ground. Be sure to dispose of the affected leaves and do not put them in your compost. Monitor the new growth, and immediately remove and destroy any leaves showing damage. Additionally, gently spading the soil around the affected plants in the late fall will help expose any pupae to freezing weather over the winter and destroy them. Lastly, neem oil can be applied to plants in the early spring and again every few weeks to repel flying adults and keep them from laying eggs. Once the larvae are in the leaf, however, neem oil will not be effective. Native wild columbine rather than hybrids are generally considered less susceptible to leaf miner damage.

For more information on plant problems, including insect damage, please visit the University of Illinois Extension “Focus on Plant Problems” website at: https://web.extension.illinois.edu/focus/splash.cfm

Do you have some questions for us? Remember you can email us at meo@illinois.edu, or cal

l our University of Illinois County Extension Unit Office at 815.224.0889. Please note that due to the COVID-19 epidemic, offices are closed until further notice.

Happy Gardening!

The Mission of University of Illinois Extension is to provide practical education you can trust to help people, businesses and communities solve problems, develop skills and build a better future. University of Illinois Extension provides equal opportunities in programs and employment. Visit our website at http://extension.illinois.edu/blmp/

Source: Meg Overocker, U of I Extension Program Coordinator and Master Gardener