The leaf miner can attack a large range of plants from trees, fruits, vegetables, and even flowers. As the name implies, the leaf miner larvae eat their way through the middle layer of the leaf. This causes a telltale white curling trail. The larva continues to eat for two to three weeks and when ready to pupate it falls out of the leaf. Once it hits the ground, the larvas go down one to two inches into the soil. Here the larva will pupate. Adults will emerge in 15 days as flies. Females mate and deposit their eggs into the middle epidermis layer of the leaf. Several generations of leaf miner will appear in a season.
The first technique is a two part one. The first approach is to check your plants often. If you see signs of the tunnels, squish the tunnels to kill the larva. Leaves that have several tunnels, simply remove the infected leaf and through away. The second part of this approach is to keep your plants healthy. A healthy plant is more likely to recover from the damage compared to one that is under stress due to improper watering, nutritional deficiencies and/or environmental conditions. What this means is to make sure that you only water when needed, feed with an appropriate fertilizer, and/or make sure the growing conditions are right.
The second technique is to cover the ground under plants that have been infected with plastic. This technique works as a control because it blocks the soil from the larva, which prevents them from pupating and turning into adults. This is also very important to do with host plants, such as blackberries, cabbage, and peppers just to name a few. These plants provide shelter for mature larva during the winter months. Covering the soil prevents them from surfacing in the spring.
If you are growing blackberries and/or vegetables, you may want to consider using floating row covers. These cover hover over the plant material keeping the adult female flies from getting to the foliage to lay their eggs. This is especially important if you are growing spinach, which is a favorite of the leaf miner.
Finally, keep in mind that while a small infestation can be controlled by squishing the larva in the leaf, there is a slight problem with this approach. Empty tunnels can become home to pathogenic fungus and/or bacteria, which will compound the problem. The best approach is to prevent the problem when possible and to block the life cycle of the leaf miner.