Yellow-Cedar Shoot Blight

Kabatina thujae Schneider & Arx

Host(s) in Alaska:

yellow-cedar (Callitropsis nootkatensis)

Habitat(s): terminal and lateral shoots of yellow-cedar (occassionally cones)

Current Status & Distribution in Alaska (2023 Update)

Yellow-cedar shoot blight was more common and severe than usual in 2023. Seventeen disease locations were recorded during ground detection surveys near Juneau, Sitka and on Mitkof, Zarembo, Annette, and Prince of Wales Islands. High disease incidence was detected in a common garden planting of yellow-cedar north of Juneau adjacent to the Héen Latinee Experimental Forest, where more than one-quarter of yellow-cedar trees displayed disease symptoms. Though disease incidence was high, severity was variable, and trees are expected to recover assuming disease pressure eases under less favorable weather conditions. The common garden trial provides an opportunity to evaluate the heritability of disease susceptibility and tolerance.

Lateral shoots and leaders of yellow-cedar seedlings and saplings typically die from this disease in early spring, though most trees recover. Long-term tree structure is not thought to be compromised by leader infections. This disease is widespread throughout the range of yellow-cedar in Southeast Alaska, but less is known about its prevalence among Prince William Sound populations (see Detection Map).

In 2018, we received samples of yellow-cedar cones infected with a fungal pathogen on Prince of Wales Island near Naukati. Dr. Jane Stewart at Colorado State University identified Kabatina thujae as the causal pathogen. Although this fungus commonly causes shoot blight, damage to cones had not been previously documented in Alaska. 

Fungal databases, such as the Global Biodiversity Information Facility, report that this pathogen has also been documented in France, Great Britain, the Netherlands, and New Zealand. This database excludes British Columbia and Alaska as locations with this disease.

Historic Activity

Yellow-cedar shoot blight is frequently noted in young-growth stands of Southeast Alaska that contain yellow-cedar. The disease is also observed in British Columbia. Prior to 2013, the identity of the causal pathogen in Alaska was not known (it was tentatively called Apostrasseria sp.). Elevated disease activity in Southeast Alaska was noted in 2008, 2014 and 2015.

Symptoms, Biology & Impacts

Terminal and lateral shoots on seedlings and saplings become infected and die during late winter or early spring. Symptoms of this disease are sometimes confused with spring frost damage. Dieback may extend 4 to 10 inches from the tip of the shoot. Sometimes entire seedlings up to 2 feet tall are killed. The long-term tree structure of taller saplings is not thought to be compromised by leader infections.

In 2013, some infections were observed on deer-browsed shoots. Dr. Jeffery Stone at Oregon State University and University of Oregon confirmed the identity of the causal fungus as Kabatine thujae from collections made in 2013. This pathogen is known to damage natural and ornamental yellow-cedar saplings in British Columbia. More work is needed to determine if this is the only shoot blight pathogen that causes widespread damage to yellow-cedar young-growth in Southeast Alaska.

Survey Method

Disease severity and distribution information primarily comes from informal ground observations from Forest Health Protection staff and land managers.

Detection Map

Links

Global Biodiversity Information Facility Database- Kabatina thujae

A Climate Adaptation Strategy for Conservation and Management of Yellow-cedar in Alaska (p.74)
 

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

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