Colorado blue spruce's silvery green color and perfectly placed boughs make it one of the most sought-after conifers in the industry. It was first discovered growing in the meadows and by the streams in the Rocky Mountains.
Despite the internet boasting this tree is easy to grow it requires extra attention for Illinois gardeners. Blue spruce require moist but well-drained, nutrient-rich soils and thrive in full sun but may succumb to some environmental stressors. There are major diseases that attack this tree, when it is stressed, leaving homeowners dumbfounded.
Some of the major stress issues are incorrect planting, root disturbance, Illinois climate and soil pH.
Root Disturbance: Most trees develop their root systems in the top 12 inches of the soil three times as wide as the canopy. When roots are disturbed or compaction occurs, they die out and the tree evens itself out by killing off some of the canopy and becoming stressed.
Illinois Climate: Shallow roots cause them to not do well in hot and dry climates. They require supplemental water in times of drought. It is important to water this conifer in good before winter comes as this prevents them from drying out in the winter sun and wind. As the tree gets older they can become more adaptable to drought. This tree benefits greatly from a ring of mulch around the base. This tree is not tolerant of floods and may suffer during our wet springs.
Soil pH: Colorado blue spruces prefer mildly acidic soils (pH 5.5 to 7.0). They grow more slowly if the pH is too high or if they are planted in heavy clay soils. In their native habitat their needles would fall to the ground to decompose and therefore make the soil more acidic. If trees are stressed, fertilizer application can be applied in spring and early fall.
Here are the most common diseases for stressed Colorado blue spruces:
Rhizophaera Needle Cast: Symptoms often appear in mid to late summer as purpling of the needles followed by leaf drop. The symptoms move from the bottom of the tree to the top. However, this disease has already been present for more than a year. The disease overwinters on living or dead tissue. Protective sprays in the spring can protect new growth. This should be done at least two years in a row and all fallen needles should be cleaned up before winter.
Stigmina: This disease exhibits symptoms similar to Rhizophaera. They must be distinguished by looking at the fruiting bodies on the back of the needle. Stigmina looks like small spiders and Rhizophaera looks like perfectly round globes. There is no chemical control other than limiting stress of the tree.
Cytospora Canker: Symptoms are dying needles and branches on lower limbs and oozing sap from cankers on branches and trunk of the tree. The newest needles are killed off first when the canker girdles the stem, leaving dry brittle twigs behind. There is no chemical control, but symptomatic branches can be pruned out when the conditions are not wet. Cytospora canker is the No. 1 killer of blue spruces 15 years or older.