Birch Leaf Miner
Birch Leaf Miner (Fenuma pusilla) was first seen in the United States in 1923. It was introduced from Europe, and has spread throughout North America. It attacks white or paper birch (Betula papyrifera), weeping birch (B. pendula), and wire or grey birch (B. populifolia). The adult black sawfly is 3 mm long, and the females lay their eggs on new leaves. The larvae hatch in 7-10 days and feed on leaf tissue. The larvae are flat and white in color, devloping to 6 mm in length in 10-15 days. The larvae cause brown and translucent patches on the leaf and the leaves fall prematurely or the larva cut a hole in the leaf and drop to the ground where they move into the soil and pupate for approximately 2-3 weeks.
To control the outbreak of the leaf birch minor one can apply a systemic insecticide, such as Cygon 2-E or Lygon, (dimethoate). A soil drench can be made by applying 50mL or full strength Cygon for every 2.5 cm of the tree trunk’s diameter (taken at 4.5 m above the ground). This only has to be done once in May, while the trees are leafing out. One can also paint Cygon to the tree trunk below the first lateral branch. Two applications per year must be made, once when the buds are green and the second application in the last week of june or the first week of July. The width of the band of Cygon should be 2.5 cm of every 2.5 cm of trunk diamter taken at 4.5 m above the ground.
By Dr. Paton and Vicki East