Cedar leafminer

Overview

• Native to North America.
• Cedar leafminer complex is a group of insects that feed on cedar foliage, causing a yellowing of the leaves.
• The group includes:
  • brown cedar leafminer (Coleotechnites thujaella)
  • cedar leafminer (Argyresthia aureoargentella)
  • cedar leafminer (Argyresthia canadensis)
  • arborvitae leafminer (Argyresthia thuiella)

Host species

Cedar leafminers feed on eastern white cedar (Thuja occidentalis).

Characteristics and life cycle

• Four closely related species feed within the leaves, hollowing out the leaflets.
• Damage can be seen early in the season and can be confused with winter browning.
• Adults are small white moths which emerge during June and July.
• Eggs are laid in July and August and larvae over-winter in leaflets.
• It is not uncommon to find all four species in a single location.
• Repeated attacks over several years can cause twig death and sometimes stem death.

Symptoms and damage

• Leaflets gradually become discoloured, from yellowish to brown in colour.
• Twigs become bare in the autumn as damaged leaflets fall off.
• Damaged leaflets can be held up to a light and tiny caterpillars can be seen feeding in the tunnels.

Control measures

Ornamental trees may become infested. Twigs can be pruned during the winter to prevent spread.