As I came walking in the front door yesterday I noticed the tell-tale white trails of leafminer on the leaves of a petunia plant. Lethal? No. Unsightly? Yes.
There are lots of different types of leafminers, and each feeds on a different type of plant. Citrus leafminer, azalea leafminer, and other shrubs are very commonly effected by this pest. You can see examples of leafminer on other types of plants in this University of Florida publication. Each leaves the very telltale signs of infestation: the silvery-white circuitous paths that weave around the leaf. This is the pathway of a small larvae (kind of like a teeny, tiny worm) that has hatched within the leaf and is eating his way through, leaving that little pathway behind. The adult has laid the egg within the leaf, so it is actually impossible to spray anything that will reach this pest because it is protected by the layers of the leaf.
How do you control leafminer? Well, there is very little you can do. I’ve read where one organic method of control is to follow the silver trail to the end point and then squish the leaf so as to kill the small larvae inside. I will be honest: not happening here. Who has time for that? There is a parasitic wasp that will help control leafminer and these are naturally occurring. If you are very concerned you can purchase these wasps, called Diglyphus isaea, from reputable nurseries. These leaf miner natural enemies will make a meal of the leaf miners in your garden.
The good news is that although leaf miner damage can be unsightly, the damage is on a relatively small portion of the leaf. The best way to combat this pest is to have healthy plants to begin with! If you consider that any green space on a leaf is photosynthesizing and collecting energy for the plant, then even a leaf with these silver trails still has a lot of work going on. Unless it drives you absolutely nuts, I recommend leaving these leaves so that they can continue to work for the plant.