Table 322 Diseases and Pests of Trees in Urban Environments
American Thuja shoot moth, Thuja mining moth -
Argyresthia thuiella
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Host species

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Arborvitae (Thuja spp.), false cypress (Chamaecyparis spp.)

Already in autumn there is a continuous browning of the leaf scales beginning at the tips - scales translucent. Shoots are mined and contain larvae, in spring pupae. From June on nearly circular emergence holes mostly at the base of the brown shoot parts

Causal agent
Moth: light grey with brown and grey dots, about 6mm in size; egg deposition in June; young larvae enter leaf scales two weeks later. Larvae: reddish green to brownish green, head black

Possibilities of errors
Related species of the genus Argyresthia (Juniper mining moth*, Cypress mining moth); Kabatina - blight of Thuja*; other dieback fungi ; Didymascella - leaf blight of Cedar*

*on this sample plate, the links are leading only to the german version without pictures

Brown shoots break and cause optical impairment. Repeated heavy attacks may cause death of very young plants

Control with biotechnical insecticides (insect growth regulators) - no environmental impact, safe. Watch for the precise time of application (a few days after the flight period of the moths in June); control of the flight time possible with pheromone traps

. Symptoms Symptoms