What is going on with my blue spruce?

Asked July 20, 2014, 5:32 PM EDT

My very large, 35+ year old blue spruce is having bottom branches die. There is a light coating of something on some of the branches and on the trunk. Please see the photos I've attached. Any thoughts on what I can do for the tree greatly appreciated.

Arapahoe County Colorado

1 Response

The fungal disease, Rhizospaera needlecast, can cause the inner needles to die off, leaving only green tips on branches. Over time, this can cause branch death. If examined closely, the brown needles will have tiny black dots, which are evidence of the fungus. Application of a fungicide in early spring just as the needles are emerging helps prevent infection. This disease is usually worse where air circulation is poor. Opening up for better air flow may also help reduce disease incidence. There is more information on this at this link: http://nac.unl.edu/documents/diseasetrees/chap56.pdf

Cytospora canker is another fungal disease that attacks spruces. This disease is most severe on Norway and Colorado spruce and is most common on more established, older trees. Cytospora canker is usually characterized by the dying back of individual branches, usually starting with the oldest branches lower on the tree. As the disease progresses, higher branches will show damage. The brown needles may remain on the branches or fall off. Look for a hard, white residue on the lower branches that resembles bird droppings. This is resin from infected branches higher on the tree dripping down. On those higher branches, you also may find sunken, oozing cankers that are dripping the resin.

The cytospora canker fungus can be caused by splashing water, wind-driven rain, pruning and likely by insects. The fungus generally becomes established through wounds in the bark.

The fungus shows up when the tree is stressed. That makes the disease more prevalent on trees of low vigor, which can be caused by low fertility, insect damage, shallow roots, drought, planting a tree in an improper site and mechanical injury. Cytospora canker occurs most often in trees that are drought stressed.

Trees can live many years with cytospora canker, although it does make them much less attractive. Infected branches cannot be saved and should be pruned off. Prune when the weather is dry or when the tree is dormant in winter so the fungus spores do not spread through dampness. Always disinfect tools with Lysol or a bleach solution between cuts to reduce the chance of spreading the disease.

There are no chemical controls for cytospora canker, so maintenance practices that reduce stress and improve vigor are important. Prevent drought stress by watering when conditions are dry, mulch 2-3" around the base of the tree if the soil under the tree is bare. Always water in the winter when there is no snow cover. Prune out infected branches this winter, and fertilize the tree in spring.

Additional information is available at these links: