Written by: Jake Kubisiak, Certified Arborist IL-1392A
By definition “Ever Green” trees are supposed to retain their foliage throughout the year. However, an increasingly common scenario is the loss of needles and eventual degradation and loss of canopy density. The theme of this article relates to a primary cause of this degradation, Needle Cast Disease.
Colorado Spruce are a popular evergreen species, and with good reason. The thick foliage usually with a blue coloration and minimal issues provides a solid landscape option. However, over the past 10-15 years there seems to have been a huge increase of fungal disease infections leading to increased needle loss and general degradation of these valuable evergreens. Currently I can hardly drive through a mature neighborhood without seeing symptoms of needle cast disease on most of the mature Colorado Spruce. The increase of the incidence of these diseases is unclear. My theory is a combination of severe summer droughts along with prolonged wet and cool spring weather has provided ideal conditions for this disease to occur, and it has increased and spread across the region.
The needles of a Spruce are intended to fall off, eventually. Usually needles are retained for 5-7 years on a healthy tree growing in good sunlight. However, needle cast disease can cause premature loss of needles. This can be so severe that all but the current year’s needles can be shed. This loss is usually most prominent on the north side of the canopy and towards the lower half of the tree where sunlight and humidity may be slightly higher. Eventually the lower 2/3 to 3/4 of the canopy can become thinned and degraded due to needle losses. Individual limbs may die leading to degraded appearing and weakened trees when left untreated.
An arborist should review the individual tree and growing situation for other possible factors. Commonly fungicide treatments are our primary defense for control of this needle loss. The improvement of a weakening tree can take several seasons of consecutive treatments. Treatments primarily provide protection to the newest year’s needle growth. Previous year’s needles may still be shed prematurely even after treatments are started as they were likely previously infected by this disease. Once several years of treated growth has been given time to fill the results improve.
Has your favorite Colorado Spruce started to look more like Charlie Brown’s thin and weakened Christmas Tree? Consider contacting your Wachtel Tree Science Arborist for an evaluation to identify the possible issues and treatment options.