Q. Our children planted a Colorado blue spruce for us 30 years ago when they were in grade school. Now the spruce seems to be slowly dying. Several lower branches have died, and this spring I see more branches that are affected. We have a sentimental attachment to this tree and would like to save the tree. Can you tell me what is wrong with our blue spruce and what we can do to save it?
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.
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.