Problem type: Disease
Name of problem: Cytospora Canker
Plant name(s): Colorado blue spruce, black spruce, white spruce, red spruce and other ornamental spruce
Symptoms / Characteristics:
Dead or dying branches. Needle bundles near the tips of one or more branches fade and turn brown. Branch dieback can occur. Fungus moves from older, lower branches to younger, higher ones. Dark cankers appear on branches and may be sunken. Clear, amber resin exudes from a canker in large amounts and runs down the bark onto lower branches or the ground. The resin then hardens into a white-blue crust, crystallizing to form a hard shiny coat.
Spores are spread by wet weather and splashing water. Spores can be airborne, spreading by wind as well as spread by insects and pruning tools. The fungal spores survive in dead and diseased stems. Infection continually occurs annually destroying branches. Most infections occur in the spring when spores are most abundant and favorable environmental conditions exist.
Cytospora canker is caused by the fungus Cytospora kunzei, which invades trees that are weak and stressed. Damage is usually not observed until trees are at least 10-15 years old. Trees stressed by drought, insects, crowding, nutrient imbalance, pesticides or mechanical injury are open to infection. Spruces introduced to the landscape are more susceptible because they are not growing in their native habitat. Colorado blue spruce shows the most damage where it is grown east of its natural range in the Rocky Mountains.
Control / Preventions:
Immediately remove and destroy diseased branches by pruning at the base of the infected branch back to the main stem. Prune only in dry weather as wet conditions encourage spore dispersal. Sterilize pruning tools between every cut to prevent spread of the fungus (dip in 10% bleach solution or 70% alcohol solution).
Control insects or other disease problems. Proper watering and fertilizing every 3-5 years will promote healthy trees. Mulching can help moderate moisture levels. Adequately space trees and promote air movement in the tree canopy.
Currently there are no chemical control products available. Avoid planting Colorado blue spruce. Minimize any stress to the tree, especially drought and compaction.