Cytospora canker of
spruce is the most common and damaging disease of spruces in the
East. The causal agent, Leucostoma kunzei, attacks black
spruce, Colorado blue spruce, Norway spruce, white spruce, Douglas
fir, balsam fir, eastern hemlock, eastern larch, European larch,
Japanese larch and eastern white pine.
The needles on infected
spruce branches turn brown in spring or early summer. Copious amounts
of white sap exude from cankers on the affected branches and run
down the tree. White patches of dry resin on the trunk are characteristic
of this disease. Brown needles persist throughout much of the growing
season, but drop in winter, leaving bare branches. The infection
tends to move up through the tree, as older branches are more susceptible
than younger ones. This disease affects mature trees, commonly 15-25
years old and 20 to 40 feet high. Symptoms of cytospora canker are
the same on other conifers, with cankers produced on branches and
trunks of balsam fir, Douglas fir, eastern larch and, rarely, hemlock.
Sap production, however, is less noticeable in these conifers.
Removing a thin slice
of bark in the area where healthy and infected tissue meet will
reveal tiny, black fruiting structures. Yellow to orange masses
of spores ooze from these structures in tiny tendrils during rainy
spring and summer weather and are disseminated by splashing water,
wind-driven rain, pruning, and possibly by insects and birds. The
fungus generally becomes established in fresh wounds, and overwinters
on bark and in cankers.
There are no effective
chemicals to control this disease.
Avoid wounding branches.
Early detection and removal of infected branches will
reduce the probability of more extensive disease development.
Prune out infected branches close to the trunk during dry weather or during
winter to reduce disease transmission, disinfecting tools between
cuts. Burn infected branches to prevent the release of spores.
Trees suffering from drought stress and low fertility
are more susceptible to this disease, so provide adequate water
and fertilizer. Water the entire root zone deeply- 1 1/2 times farther
than the branches extend.
Control insects and mites--especially spruce gall adelgids
and spider mites--to prevent spore transmission.
Picea omorika is resistant to this disease.
Avoid planting Colorado blue spruce, as it is extremely susceptible
to cytospora canker.
from the Ohio State University Extension, 1999