Severe attacks of birch leaf miner predispose trees to bronze birch borer infestation. The insect shows up in mid May but timing can vary with the season. The first of two generations per year is the most damaging. Birch leaf miner can be controlled with sprays of Orthene or Diazinon applied when the mines first show up. The most serious pest of landscape birches is bronze birch borer.
Stressed tree are most susceptible to borer attacks.
The insect bores in the sapwood, beginning in the top third of the tree, causing death of the tree crown. The tunnels are slightly raised and faintly rust colored. Emergence holes in the trunk are shaped like capital D's. Keep the trees healthy by controlling other insects, fertilizing, and watering as needed. Chemical control is applied to the trunk and main branches.