PestMedium Severity

Leaf Miners

Fenusa pusilla (birch), F. ulmi (elm), various species

Small sawfly larvae that tunnel within leaf tissues, creating distinctive brown blotches or blisters on leaves. While healthy trees can withstand infestations, repeated attacks over several years can significantly weaken trees, making them vulnerable to secondary pests and diseases.

Peak Season: Adult emergence: Spring when leaves half-developedEgg laying: On newly unfolded leavesLarval development: 10-15 days per generationMultiple generations: 2-4 cycles per yearPeak damage: Mid to late summerOverwintering: Final generation remains in soil until spring
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Leaf miner damage showing characteristic mining patterns and browning in leaves

Identification & Symptoms

What to Look For

Brown blotches or blisters on leaves from larval tunneling
Trees becoming uniformly brown, especially crown tops
Small, white, flattened larvae visible within mines
Black fecal matter visible in mines when held to light
Small exit holes where larvae have dropped to ground

Potential Damage

Reduction in photosynthetic leaf area
Tree weakening from repeated annual infestations
Increased susceptibility to borers and fungal pathogens
Aesthetic damage from brown, blotched foliage
Potential tree mortality after several years of severe infestation

Lifecycle

Adults emerge from soil in spring when leaves are half-developed. Females lay eggs in young leaf tissue. Larvae develop in 10-15 days, creating mines that often unite into large blotches. Mature larvae drop to ground, pupate in soil, and emerge for additional generations. 2-4 life cycles per year with final generation overwintering in soil.

Professional Treatment Approach

1

Imicide applications targeting adult emergence in spring

2

Systemic Imisol treatments for season-long protection

3

Time treatments with leaf development and adult emergence

4

Multiple applications may be needed for successive generations

5

Monitor for adult activity around unfolded leaves

Recommended Mauget Products

Imicide

Professional-grade treatment specifically effective against leaf miners.

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Imisol

Professional-grade treatment specifically effective against leaf miners.

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