Pests: Leaf Miners

Leaf miner damage on our tomato

Sometime ago we noticed some strange markings on some of our tomato and cucumber leaves.  They were silvery and looked like trails made by a drunk animal. We looked around for signs of additional damage but we didn't find any. Since the plants did not seem to be suffering any ill effects from it we let them be. However, our curiosity remained. In search for answers we went to the bible, The Bountiful Container by McGee & Stuckey's (highly recommended). It mentioned that silver trails are usually a sign of slugs. We searched and searched but we never found a single slug.

Yesterday, I went to one of my favorite garden blogs (and quite possibly the inspiration for this blog), Life on the Balcony,  and right there on the main page was the answer to our question: Leaf Miners. The larvae of some insects burrow themselves in leaves and eat the soft layers inside. The white or silvery trail left is the mine or path being made by the growing larvae. Be warned that the mine is filled with frass (insect poop). So eat greens, such as lettuce or spinach, that show any signs of leaf miners at your own risk.

Killing leaf miners is not easy since they are protected by the leaf itself. Therefore, any spray pesticide (which I don't recommend anyways) will be ineffective. In this case control through other means is necessary. Removing affected leaves is recommended, however, not necessary unless you are eating the leaves (think spinach or lettuce). Nature, in its awesome wisdom, has provided a means of controlling leaf miners; parasitic wasps that preys on this larvae. If you are lucky to have some of these in your garden you may not even have to do anything.

Have you had leaf miners in your garden? If so, let us know what you've used to control them.