Mortality of bitternut and shagbark hickory has been observed in Wisconsin
since the late 1980's. This is similar to occurrences in the 1960's. The recent
tree mortality has been associated with affacks by the hickory bark beetle,
Scolytus quadrispinosus Say, and a newly discovered fungus in the genus
Ceratocystis (tentatively C. caryae). The fungus can be isolated from
sunken bark cankers and discolored wood associated with beetle attacks. In
field and greenhouse studies done at the University of Wisconsin, the fungus
was found to be highly virulent to bitternut and shagbark hickory, pecan,
butternut and black walnut.
|Photo 1: Varying stages of mortality in bitternut
hickory. Declining (yellow leaves), recently dead (brown leaves), and trees
dead for an extended time (no leaves).
||Photo 2: Egg and larval galleries of the hickory
bark beetle found under the bark of infested hickories. The dark discoloration
is the Ceratocystis sp. fungus.
Recent reports indicate hickory mortality is
apparently widespread across the eastern United States. It has not been
determined if this mortality is always associated with the hickory bark beetle
or with the Ceratocystis sp. fungus. You can help us delineate the
extent of the problem by reporting any hickory mortality.
||Photo 3: Fungal development deep into the wood on a
cross-section of shagbark hickory about one year after bark beetle attack.
||Dr. Eugene Smalley
Department of Plant Pathology
University of Wisconsin-Madison
Madison, WI 53706
Please send reports of dying hickory to:
Manfred Mielke and
Forest Health Protection
St. Paul, MN