Leaf Miners

Columbine leaf with leaf miner damage

This morning as I was watering my flowers, I found the leaf pictured at right, with the tell-tale pale scribbly line of a leaf-miner. Leaf miners are the larval stage of many different types of insects, which burrow and feed between the outer layers of the leaf. They eat the green interior tissue, leaving trails covered by a papery lighter-colored outer layer. These insects may be beetles, flies, or moths. Depending on the variety of insect, the tunnels may be meandering ones, such as those I find on my columbines, or large blotches. Such insects specialize in the plant they use as host during their larval stage; whether specific types of trees, shrubs, vegetables, or flowers.

The tunneling action of these insects is seldom a major problem for a healthy plant, but may slow growth, and certainly doesn't look good. Normally, there are enough natural controls for these insects to keep them from becoming a major issue. Parasitic wasps are natural enemies of leaf miners, and will help control them unless killed off by broad-spectrum insecticides.

Also, some weeds such as plantain and chickweed serve as host plants for these insects, so keeping the weeds out of your yard helps prevent an infestation.  

Spraying tends to be ineffective on leaf miners, since they are protected by being inside the leaf. I generally just pick off infected leaves and destroy them. Don't drop these leaves on the ground, as the larvae can then finish their life cycle and continue to attack your plants. By promptly removing any affected leaves, you can prevent future generations of these pests.

Spending time in your garden regularly lets you spot problems like this early, when it's easiest to keep them under control.