Q. My children planted a Colorado blue spruce about 25 years ago when they were small. Now it seems to be dying. Several lower branches have died and more branches seem to be affected. I have a sentimental attachment to this tree and would hate to lose it. Can you tell me what is wrong and what I can do to save it?

A. It sounds like cytospora canker, a fungal disease that affects spruces (Picea spp.), hemlocks (Tsuga spp.), larches (Larix spp.) and firs (Abies spp.) but is most severe on Colorado (Picea pungens) and Norway (P. abies) spruces.

It is characterized by the die back of individual branches, usually starting low on the tree, where the branches are oldest. On rare occasions, the top of the tree may die first. 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. You may also find sunken, oozing cankers on the higher branches.

The fungus that causes cytospora canker lives on the bark and causes no problem until the tree is stressed. It can infect wounds from pruning cuts and mechanical damage to branches, but trees do not usually begin to show symptoms until they are 10 to 15 years old. Cytospora canker on Colorado and Norway spruces is overwhelmingly associated with drought stress.

There is no chemical control. Protecting susceptible trees from drought stress by supplying additional water during dry weather and pruning infected branches can slow the spread of disease. Disinfect your pruners or limb loppers with a 70-percent alcohol solution between cuts to reduce the chance of spreading the disease. Trees can live for years with cytospora canker, but it does make them less attractive.

It is important that trees are sited where they have sufficient soil to meet their moisture requirements when they are mature. Most spruce trees grow from 50 to 70 feet tall. 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 water and nutrient needs to minimize drought-related problems such as cytospora canker.