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Birch Leafminer Diagnostic Guide

Fenusa pusilla

Native to Europe, the birch leafminer, Fenusa pusilla, first appeared in Connecticut in 1923. This pest is known to feed on most species of birch trees, although susceptibility varies. The birch leafminer feeds on the tissue between the upper and lower surfaces of newly emerging leaves producing large dead blotches and eventual leaf loss. Severe infestations can lead to damage of nearly every leaf by mid-summer. Continued leaf loss year after year can lead to a weakened tree, decline, and greater susceptibility to secondary insect and disease pests including bronze birch borer.

Trees at Risk

Birch leafminer feeds in the leaves of most birches including paper birch, gray birch, erman birch, Asian white birch, monarch birch and European white birch.

Paper Birch

River Birch

Cherry Birch

Yellow Birch

Signs of Damage

  • Irregular blotches on the leaves throughout the canopy.
  • Entire leaves may turn brown, paper-like, and eventually drop off.
  • The whole tree looks scorched or blighted from a distance with foliage at the top turning brown first.
  • Individual damaged leaves may be scattered throughout canopy.
  • Complete defoliation is possible.
Birch Leafminer Signs

Brian Kunkel, University of Delaware, Bugwood.org

Physical Appearance

  • The adult is a four winged black fly-like insect about 1/4” long (3mm).
  • The larva is flat, white, and 1/2” long (6mm) at maturity and can be easily seen when holding the leaves up to the light.
  • The larvae feeds between the layers of the leaf.
Birch Leafminer Signs

Whitney Cranshaw, Colorado State University, Bugwood.org

Birch Leafminer Signs

Ronald S. Kelley, Vermont Department of Forests, Parks and Recreation, Bugwood.org

Life Cycle

  • Mature larvae over-winter in debris in the soil.
  • Adults emerge and mate as the leaves begin expansion in the spring.
  • The female adults insert their eggs in soft, newly developing foliage.
  • The eggs hatch 7-10 days later into larvae and feed for 2-3 weeks before dropping to the ground to enter the soil and pupate.
  • A second generation of adults appears 15-20 days later to start the cycle over again. There can be multiple generations depending on geography.

Treatment Strategy

First generation feeding by birch leafminer larvae occurs early in the growing season. Proper application timing is essential for optimal management of this insect. Soil applications of Xytect™ should be applied in late summer or early fall prior to the growing season to ensure the Xytect™ has ample time to translocate within the crown in sufficient product levels to control the larvae. Early spring Transtect™ soil applications provide acceptable same-season control if they are properly timed.

  • Soil Application using Xytect 2F

    Dosage: 6mL/inch DBH
    Timing: Late summer to early fall for next year protection
    Re-Treatment: Annual
    Xytect 2F
    Xytect 2F
    $69.60
  • Soil Application using Transtect

    Dosage: 1 packet treats 5-17 inches of DBH
    Timing: Apply in early spring as soil begins to thaw
    Re-Treatment: Annual
    Transtect
    Transtect
    $326.00
  • Soil Application using Xytect 75WSP 22 packets

    Dosage: 1 packet treats 24 inches of DBH
    Timing: Late summer to early fall for next year protection
    Re-Treatment: Annual
    Xytect 75WSP 22 packets
    Xytect 75WSP 22 packets
    $148.00
  • Tree Injection using Xytect 10%

    Dosage: 1 ml/inch DBH for trees 2 to 10 inches DBH
    Timing: Early spring – summer, ideally 1-3 weeks before pests are actively feeding
    Re-Treatment: Annual
    Xytect 10%
    Xytect 10%
    $453.96
  • Tree Injection using Xytect 10%

    Dosage: 1.5 ml/inch DBH for trees 10 to 36 inches DBH
    Timing: Early spring – summer, ideally 1-3 weeks before pests are actively feeding
    Re-Treatment: Annual
    Xytect 10%
    Xytect 10%
    $453.96
  • Tree Injection using Xytect 10%

    Dosage: 2 ml/inch DBH for trees 36 inches DBH and above
    Timing: Early spring – summer, ideally 1-3 weeks before pests are actively feeding
    Re-Treatment: Annual
    Xytect 10%
    Xytect 10%
    $453.96
  • Tree Injection using Xytect 10%

    Dosage: For heavier infestation and/or more resistant insects, use 1.5 ml or 2 ml rates on trees having a DBH of 2 inches and above.
    Timing: Early spring – summer, ideally 1-3 weeks before pests are actively feeding
    Re-Treatment: Annual
    Xytect 10%
    Xytect 10%
    $453.96
  • Soil Application using Lepitect

    Dosage: 1 packet/25 – 50 gallons water
    Timing: Apply 1 – 3 weeks before larvae emerge. Emergence begins around GDD 189; Spirea X vanhouttei blooms; Viburnum opulus blooms; Robinia pseudoacacia blooms.
    Re-Treatment: Repeat 30 days after first application to control 2nd generation larvae
    Lepitect
    Lepitect
    $59.20
  • Soil Application using Orthene TT&O WSP

    Dosage: 1/3 lb (5.3oz) in 100 gallons water
    Timing: Apply to control young larvae. GDD 189; Spirea X vanhouttei blooms; Viburnum opulus blooms; Robinia pseudoacacia blooms.
    Re-Treatment: Repeat 14-21 days after first application to control 2nd generation larvae
    Orthene TT&O WSP
    Orthene TT&O WSP
    $15.20

Treatment Expectations

The first generation must be controlled, making spring applications challenging. Xytect™ soil applications are applied in fall to kill adult and larval leafminer the following spring. Transtect™ soil applications applied immediately after soils thaw in the spring can provide adequate control. However, the efficacy of Transtect™ may be diminished in years with shortened springs due to abrupt soil thaw.

A Diagnostic Guide is designed to help you identify a pest issue and management solutions. Always refer to product label for all rates and approved uses. Some images courtesy forestryimages.org. Use of the images does not imply endorsement of treatments by forestryimages.org

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