Irene Shonle, Director CSU Extension in Gilpin County. Many people have noticed that significant numbers of evergreen trees this spring and summer have been showing an alarming amount of red needles. This is visible on a landscape scale, and is most prevalent on north-facing slopes, all the way from Coal Creek Canyon up towards Allenspark.
While Douglas firs seem to be hit the hardest (with some trees dying altogether), lodgepole, spruce and even some Ponderosa showed symptoms. For the most part, the dead needles seem to be the older needles on the interior of the tree, and most trees showed green growing candles on the exterior of the branches. As summer has progressed, the red needles have begun to drop off, and the green branches have elongated, so it doesn’t look quite as alarming as it did earlier in the season.
A group of us including myself, Allen Owen and other staff from the Colorado State Forest Service, and staff from Boulder County toured the trees in the area to assess the situation. We studied the trees in various locations we sent samples up to the CSU pathology lab. On all samples, there was no vascular staining indicating a canker or wilt problem associated with the trees. There was no evidence of needle cast disease, nor any signs of insect damage.
All species, but particularly the Douglas fir and the Spruce, showed growth increments that were increasingly reduced over the last couple of years, particularly in comparison to previous years’s growth.
The most likely cause is the lack of winter moisture or moisture at the time the trees were trying to put on new growth. If you remember back to March, it was very warm (I was sitting outside in short sleeves!), and unusually dry. Winter also brought many high wind events at times when there was no snow cover, and that can suck moisture out of the trees. We also missed most of our summer monsoonal rains last year, and this all added up to be a big stress on the trees.
The trees are surviving for now, but they will be more susceptible to future drought, insects or disease, so time will tell as to their ultimate fate.
The CSU Gilpin County Extension Office is located at the Exhibit Barn, 230 Norton Drive, Black Hawk, CO 80422, 303-582-9106, www.gilpin.extension.colostate.edu. Colorado State University Extension provides unbiased, research-based information about, horticulture, natural resources, and 4-H youth development. Colorado State University Extension is dedicated to serving all people on an equal and nondiscriminatory basis.