Leafminer larvae attack many vegetables and ornamentals. Male and female flies pierce leaves and suck sap. Female lays eggs between the leaf layers. When the larva hatches, it uses its mouth parts to rupture plant cells, weaving trails through the leaf. These trails are called mines.
Category
Insect
Signs/Symptoms
When populations are high, stippling occurs. This is caused by females puncturing the leaves with their ovipositor to feed and lay eggs. Can be serious. Most of the damage is caused by the larval mines that detract from the aesthetic value of the crop.
Where
Damage on leaves.
When
Flies emerge in spring, usually late April to early May and lay their eggs between the leaf layers. Several generations can occur in one year.
Prevent
Remove old plants at the end of the growing season.
Keep area weed free.
Inspect new seedlings before planting.
Plant only in areas where you have not had a leaf miner infestation.
Attract the predators of leaf miners to your garden by planting attractant plants.
Prune and destroy any affected leaves on infected plants.
Manage
Once the pupae emerge, they can live and overwinter in grasses and other host plants, including a favorite habitat plant — lamb’s quarters.
Natural enemies of the tiny one-quarter inch black and yellow flies include hummingbirds and parasitic wasps. In the soil, the pupae of leaf miners are attacked by beneficial nematodes. The best way to attract beneficial insects to your garden is to plant attractant plants, especially California natives such as ceanothus and buckwheat.
For several reasons, it is better not to apply insecticides to control leaf miners. The chemicals will kill off the leaf miners’ natural predators. Leaf miners have developed a resistance to chemicals containing pyrethroids, organophosphates and carbamates; as a result, you may find an increased size in the population of leaf miners.
