Forest & Grassland Health

Cedar Leaf Blight

Didymascella thujina (Durand) Maire (= Keithia thujina Durand)

Host(s) in Alaska:

Western redcedar (Thuja plicata)

Habitat(s): foliage

Photos

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Cedar leaf blight

Cedar leaf blight damage to western redcedar. 

Cedar leaf blight on western redcedar.

Cedar leaf blight damage to western redcedar. 

Cedar leaf blight on western redcedar.

Cedar leaf blight damage to western redcedar. 

 

Cedar leaf blight

Cedar leaf blight damage to western redcedar. 

 

 

Current Status & Distribution in Alaska (2018 Update)

Cedar leaf blight is a foliage disease of western redcedar that can cause mortality of seedlings and reduced growth of mature trees in low-elevation coastal environments. In British Columbia, this disease is considered one of the most important diseases of western redcedar. In Southeast Alaska, where the disease is known to occur throughought the range of western redcedar, this will be a disease to watch for as climate warms; warmer, wet conditions are conducive to disease development. Disease-climate models produced for British Columbia (Gray et al. 2013) could be extended to Alaska to predict potential change in disease occurrence. In 2018, severe disease on individual redcedars was noted near Anita Bay on Etolin Island. 

Symptoms, Biology & Impacts

Infected one-year-old foliage becomes bleached or reddish-brown. Fruiting structures develop on the upper surface of cedar foliage in June and gradually darken. Following sporulation, fruiting structures often fall from foliage, leaving circular pits or holes. Twigs with heavily infected foliage may be shed in fall. 

This disease is very common on western redcedar in the forest and in ornamental settings, but seldom causes mortality of western recedar trees. Reduced growth may result when foliage is killed. Seedlings and saplings are the most vulnerable to heavy damage and can be killed. Disease tends to be most severe in lower tree crowns, and at sites with high humidity and high tree density. Fungicides are sometimes applied in nurseries or to ornamental trees to control disease.

Survey Method

Cedar leaf blight damage is observed through ground surveys. Systematic surveys have not been conducted to evaluate disease extent or severity in Alaska.

Distribution

Cedar leaf blight occurs throughout the range of western redcedar in Alaska. The northern extent of western redcedar is near Kake on Kupreanof Island in the central Panhandle. The disease is found elsewhere in the Pacific Northwest where the host occurs, especially in low-elevation, coastal environments.

Links to Resources & Publications

Gray, L.K., Russell, J.H., Yanchuk, A.D. and B.J. Hawkins. 2013. Predicting the risk of cedar leaf blight (Diymascella thujina) in British Columbia under future climate change. Agricultural and Forest Meteorology 180: 152-163. Available here.

 

Content prepared by Robin Mulvey, Forest Health Protection, robin.mulvey@usda.gov.

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