A.
It sounds like your Colorado blue spruce (Picea pungens 'Glauca') is
suffering from cytospora canker. This fungal disease affects spruces
(Picea spp.), hemlocks (Tsuga spp.), firs (Abies spp.) and larches (Larix
spp.). Unfortunately, it is most severe on Norway (Picea abies) and
Colorado spruces.
Cytospora canker is characterized by the dieback of individual
branches, usually starting lower on the tree where the branches are
the oldest. On rare occasions, the entire top of the tree may die
first. However, branch dieback starting at the bottom and working
its way up the tree is most common. On close inspection, you may
find a hard, white residue on the lower branches that resembles bird
droppings. This is actually resin from infected branches higher on
the tree, dripping down onto the lower branches. You may also be
able to find the sunken, oozing cankers on branches above those with
resin on them.
Advanced case of Cytospora
canker on a Colorado spruce
The fungus that
causes cytospora canker lives on the bark of trees and causes no
problem until the tree is stressed. It can readily infect wounds
from pruning cuts and mechanical damage to branches, but trees do
not usually begin to show symptoms until they are ten to fifteen
years old. Cytospora canker on Colorado and Norway spruce trees is
overwhelmingly associated with drought stress. There are no chemical
controls for cytospora canker. Protecting susceptible trees from
drought stress by supplying additional water during dry weather and
pruning infected branches can slow the spread of the disease.
Irrigation reduces drought stress, and pruning dead and dying
branches out when the tree is dormant removes some of the
disease-causing spores. Disinfect your pruners or limb loppers with
rubbing alcohol between cuts to reduce the chance of spreading the
disease. Trees can live for many years with cytospora canker,
although it does make them much less attractive.
We often have a period of hot, dry weather in the summer, so it is
important that the trees are sited where they have sufficient soil
to meet their moisture requirements when they are mature. Most
spruce trees grow to a height of 50 to 70 feet. Their feeder roots -
the fine, hair-like roots responsible for absorbing water and
nutrients - extend out from the tree two to three times the diameter
of the spread of its branches. There must be a sufficient volume of
soil to supply their water and nutrient needs to minimize
drought-related problems such as cytospora canker.
MORE
Good tree care
Trimming trees
Sandy's
Tree Tips
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