Some insects eat almost anything green while others are very specific about the plants they infest. Elm leaf miners fall into the latter group since they only chew on members of the genus, Ulmus.

The term "leaf miner" describes a tiny insect that burrows between the upper and lower layers of a leaf. Generally, an adult, flying form lands on the leaf and lays and egg just beneath the surface tissue. The egg hatches and a worm-like larvae begins to feed between the layers.

As the larvae grows, the "mine" becomes larger and the surrounding plant tissue dies and turns a translucent brownish color. Eventually, if held up to the light, you can see the larvae and its tiny, pellet shaped droppings inside the mine.

Eventually, the larvae makes a transformation into a fly adult form. This over winters and comes back in the spring to lay its eggs on the new leaves to start the whole process again.

In reality, leaf miners are not a serious or life threatening insect. They do reduce the area of the leaf that is available for photosynthesis but most trees can adjust to this by adding more leaves. Severe infestations may cause a slight loss of vigor which, in addition to other stresses such as soil compaction, drought, etc., may be detrimental to the tree over time. I have observed elms that are severely infested every year for decades which  do not appear to suffer much.

The other side of the situation is aesthetics. If you have a small Camperdown elm (Ulmus glabra 'Camperdownii') next to your sidewalk and its leaves look brownish later in the summer, it can be quite unattractive. This is one situation in which treatment may be justified.

Since leaf miners do their feeding inside the leaf tissue, they may be difficult to control once they get inside. Most commonly systemic insecticides are used to control serious infestations of leaf miners. However, properly timed surface sprays can also be effective.

Check with your local Extension Service for current recommendations for control of elm leaf miner.

Note: We have provided some general information and observations on this topic aimed at the home gardener. Before you take any serious action in your landscape, check with your state's land grant university's Cooperative Extension Service for the most current, appropriate, localized recommendations.

Types of Insects

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