Spruce Aphid Defoliation of Coastal Alaska Sitka Spruce

Mark Schultz and Ann Lynch

USDA Forest Service Alaskan Region and Rocky Mountain Research Station

Spruce aphid (Elatobium abietinum Walker) defoliation of Sitka spruce in southeast Alaska occurs mostly in the beach fringe. Acreage of defoliated trees has been small until the 1970s when the acreage mapped started to increase significantly and outbreaks increased in duration.  Spruce aphids are adversely affected by low winter temperatures.  Several days below -10 °C will kill over-wintering aphids.  The number of and duration of these cold periods has declined since spruce aphid was introduced into North America. Trees that were once fed upon for a couple of years are now being feed upon for several years.  This has caused tree mortality or contributed to tree mortality in breach-fringe areas where Sitka spruce is the only large tree for nesting eagles.   Treatment options are limited and a study is being done to determine which single tree treatments will best protect the more valuable trees from attack, with the least amount of tree injury.  With protection from spruce aphid feeding, live branches will produce new buds.   Without protection trees usually die from the bottom of the tree crown to the top.  In other places bark beetles might find these weakened trees good breeding material. In southeast Alaska the only tree killing bark beetle, spruce beetle, has been in low population numbers for many years.

corresponding authors:

Mark Schultz
USDA Forest Service, Alaska Region
3301 C Street, Suite 202
Anchorage, AK 99503-3956
907-586-8883
mschultz01@fs.fed.us