What Are Leaf Miners?
Leaf miner is the term used to describe the larvae of several insect species that tunnel through the interior of the leaf as they mature. Leaf miners include a variety of different insects local to our area but are most often small flies. The specific species can often be determined by cross-referencing the tunneling pattern with the type of plant affected and the time of year. Adult leaf miners will lay their eggs under the surface of the leaf and once hatched the larvae will tunnel their way through the interior of the leaf as they feed.
Many of our plants can be affected. Most commonly they can be found on trees like aspen and hawthorn, shrubs like lilacs, and even vegetable plants.
How to Manage Leaf Miners
There are several pesticidal controls available; however, they are not super effective and depend heavily on timing. Since chemical controls can only be applied to the exterior surface of the plant, they are only effective in preventing the eggs from being laid by mature insects. Once the larvae are inside the leaf, chemical controls are no longer effective. This means they have to be applied at exactly the right time and reapplied often since they can easily be washed away with rain or watering.
Luckily, there are species of parasitic wasps, local to our area, that will act as a biological control. Parasitic wasps are harmless to humans but a natural predator of most leaf miners.
The damage caused by leaf miners is mostly aesthetic. If the plant is healthy and large enough, it can handle the reduction of photosynthesis from affected leaves. Unsightly leaves can be removed by hand if wanted.