Birch leafminer is the larval stage of a small “fly-like” wasp, Fenusa pusilla. The larvae feed between the epidermal layers of a leaf and are protected from predators and parasites by the leaf. Once damage is obvious, it is usually too late to treat as the larvae leave the mine to pupate. Control measures need to be systemic or be timed to coincide with early larval feeding before damage becomes apparent.
Treatments for birch leafminer are effective, and will also protect the tree from bronze birch borer. Which product to use is determined by the time of year treatment will be applied.
Minor infestation of leafminer does not affect the health of the tree or the appearance. Major infestations will cause the whole tree to look brown and compromise its ability to make sugars in the leaves which can compromise health.
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How Is It Spread?
• Pupae overwinter in a cocoon 1-2 inches under the soil
• Adults emerge in spring (March-May)
• Mated females lay eggs in leaf (April-May)
• Larvae produce a blotch mine (April-June)
• Larvae form a pupation chamber in the soil (May-June)
All birch species (Betula)
• Large blotch mines in the leaves
• Damage is scattered throughout the tree
o Mines will turn brown
o Leaves will look wilted
• High populations can damage the entire canopy
• Repeated defoliation by leaf miner will decrease tree health
• Leaf miner defoliation is directly correlated to Bronze birch borer attack
Drought; bronze birch borer.
Spring or fall
Risk Of Spreading