Problem type: Insect
Name of problem: Leaf Miners
Plant name(s): Deciduous trees and shrubs, herbaceous perennials and vegetables
Symptoms / Characteristics:
Leaf miner damage is generally attributed to larval feeding or "mining" of leaf tissue between the upper and lower surfaces. Mining of the leaf tissue may cause desiccation (drying), browning and premature defoliation. In certain cases, the leaves may become thin, papery and translucent and the two leaf surfaces can be peeled apart. When examined closely, black pellets can be seen within the tunnels as a result of faecal deposition.
Adult leaf miners can be moths, beetles, or flies, and the tunnelling patterns of their larvae vary depending on the nature of the insect. For example, an aspen serpentine leaf miner creates winding or meandering tunnels whereas a birch leaf miner creates large blotches. Serpentine miners are also known to attack herbaceous perennials such as columbine. For most deciduous ornamentals, leaf mining has a negative effect on appearance rather than on plant health. However, leaf miners also attack an array of vegetable crops and can have a detrimental effect on yield due to defoliation. They are particularly damaging to vegetable crops in which the leaves are consumed such as beet, spinach and Swiss chard.
Adult leaf miners can also cause severe damage to the foliage. Basswood adult leaf miners are beetles that will begin feeding on the upper leaf surface, skeletonizing the leaf tissue. When infestations are severe, entire leaves may appear skeletonized as the tissues dry up. Dead tissue may remain in place but mined leaved usually dry, shrivel and drop off the branch prematurely. Repeated severe infestations will reduce plant health and growth rate and on occasion, can kill a tree.
Control / Preventions:
Control measures vary, depending on the nature of the leaf mining insect. The birch leaf miner can be controlled by applying a systemic insecticide which works by travelling up through the root system, transporting throughout the plant internally and is eaten by the insect. Contact insecticides will not effectively control leaf miners, as the larvae feed within the leaf interior.
There is no effective control for poplar or aspen leaf miners. Infected leaves should be removed and discarded and pruning may be required in the event of a heavy infestation. Many species of leaf miners overwinter in fallen leaves and soil beneath the host plant. Doing a fall clean up can be beneficial in reducing these overwintering sites. Vegetable leaf miners must be controlled using a combination of cultural practices, including the collection and disposal of infected leaves, as well as the removal of weeds that can act as alternate hosts.
The use of chemicals should be restricted, as leaf miners are particularly prone to developing resistance. Systemic insecticides may be used according to direction, though not recommended for edible crops.