Diseases of the Colorado Blue Spruce
Colorado blue spruce trees are evergreens discovered growing on the sides of the Rocky Mountains in 1862. Their beauty and color quickly made them a favorite tree. Blue spruce is a hardy tree type that has few problems with disease. But when they do become diseased, it decreases their value and reduces their ability to act as a wind break.
Blue spruce trees make beautiful Christmas trees and are used as wind breaks and ornamental landscape. The trees grow well is zones 2-8 if they are planted in a sunny location. Full-grown healthy trees can reach 75 feet in height. Birds and small animals nest in blue spruce's full, branching foliage.
Needle Blight Diseases
Lirula and Rhizosphaera are needle blight diseases occurring in blue spruce trees.
Lirula macrospore fungus infects the trees during the warm summer months. The needles show yellow bands that turn purplish brown about 17 months after infection. Black spore bodies that are smooth in texture develop on the needles about 23 months after infection. Needles become light in color and drop from the tree. Control requires two applications of fungicide for three years after the start of infection.
Rhizosphaera kalkoffi fungus infects trees in late spring through early summer. The needles turn yellow followed by purplish brown in winter following infection. Black fuzzy spore bodies develop along the needles a year after infection. The needles start falling off the trees shortly after spore development. Rhizosphaera is controlled with an application of fungicide twice a year for two years.
Cytospora canker fungus infects blue spruce trees through wounds in the branches. The spores spread by means of rain drops, animals and pruning tools. Once infected, the lower branches of the tree turn brown, which results in needle loss. Infected branches display cankers that are covered with white-blue colored sap. Control of the disease includes limiting the number of wounds while pruning and cleaning tools between each cut. Remove and destroy infected branches over a two-year period to reduce the spread of the fungus.
Dirty and infected pruning tools spread disease to healthy trees. Disinfect the tools between each cut by dipping into alcohol for three minutes. Sterilize tools after use by cleaning with a solution of one part bleach to nine parts water. Reduce environmental damage to trees to decrease the risk of a disease. This includes compacted soil, drought conditions and excessive temperatures.
Prune healthy trees first to prevent spreading disease spores. Inspect new stock for spore bodies before planting to eliminate the introduction of unhealthy trees to healthy trees. Prune during dry seasons to prevent the spread of spores. Space trees when planting to improve air circulation and decrease moisture build up.