Articles in this issue:
This past summer and fall, numerous blue spruces (Picea pungens) around the county began showing very noticeable signs of browning out. The main culprit of spruce browning is prolonged stress brought on by several years of below average precipitation. More about that later. But first, let's look into blue spruce and why they are so prevalent and problematic in the El Paso County landscape.
Types of Spruce
Problems
Problem Prevention
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Types of Spruce First, all blue spruce are actually Colorado spruce, but not all Colorado spruces are blue. In any population of seedling Colorado Spruce, a number will display foliage of various shades of bluish-green while the majority will be dull green. The most vivid blue of these have been selected by nurserymen and perpetuated by grafting over the years to give us some of our most popular cultivated varieties including 'Fat Albert', 'Hoopseii', and 'Koster'. These include dwarf and semi dwarf varieties as well. As stated, the vast majority of Colorado spruces have dull green foliage but these are seldom planted in the landscape because they lack the pizzazz of the blue forms. (continued on top of right column of this section) |
(Continued from bottom of left column of this section). The blue forms have been tagged taxonomically as Picea pungens forma glauca but this designation does not make them genetically different from the green 'blue' spruce. Confused? Do not be. Just remember that true blue blue spruce which is a Colorado spruce is the norm in the landscape but the exception in the wild. Does that clear it up? Colorado spruce occurs naturally in the southwestern U.S. from southern Wyoming along the Rockies in Utah, Colorado, and New Mexico at elevations ranging from 7,200 to 10,500 feet. They seldom occur in large stands, mostly scattered along streams in the foothills becoming more prevalent on cool, North-facing slopes in the higher mountains. This preferred habitat is what causes problems for us in the landscape. |
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Problems While Colorado spruce are very tolerant of dry air, they are not tolerant of dry soil. They prefer evenly moist, not waterlogged soil in sunny to light shaded sites. They will tolerate heat and wind as long as the soil is moist. Much of El Paso County is too low in elevation and lacks the protected, consistently moist soil sites that spruce prefers. They do reasonably well in an irrigated lawn area but they can still experience problems. Why is blue spruce such a common part of the planted landscape? It is the Colorado state tree! It is readily available at nurseries and garden centers and has been for many years. It is the perceived "perfect" conifer with its dense, pyramidal habit, and powder blue foliage. Its compact initial size and appearance, coupled with unique blue foliage, make it the perfect specimen plant for the newly installed landscape. Unfortunately, within 20 years it often towers over all but the tallest building and its dense spreading root system tends to choke out anything that dares to grow near. Insect and disease-wise, Colorado spruce is subject to a host of problems. Spruce Ips beetle is becoming a serious problem on older specimens around Colorado Springs, especially in the Broadmoor area. According to Dave Leatherman, Colorado State Forest Service Entomologist, recent prolonged drought stress and the creation of freshly-cut wood favorable for breeding resulting from forest owner efforts to reduce fire hazard have greatly contributed to the buildup of Ips beetle populations in Colorado. Ips beetles are 1/8 to 3/8 inch long, reddish-brown to black beetles. As adults bore into trees and begin to tunnel, a yellowish or reddish brown boring dust is produced that accumulates in bark crevices or around the base of the tree. After larvae hatch and begin tunneling, affected parts of the tree will discolor and die. Symptoms may be limited to parts of the tree, such as branches or tops. An infestation of Ips beetles does not necessarily indicate the whole tree may die. However, over time attacks may progress as later generations "fill" the tree and ultimately the host may die. (continued on top of right column of this section) |
(Continued from bottom of left column of this section)According to Leatherman, problems with Ips beetles attacking Colorado spruce will probably increase over the next year as more and more trees in the landscape succumb to drought stress. Small round holes in the bark of infested trees indicate the beetles have completed development in that part of the tree and adults have exited. The presence of bore holes peppering the bark mean the beetles have moved to another portion of the same tree or other trees nearby. Another common pest problem on spruce in El Paso County is white pine weevil. The female weevil feeds on the cambium near or on the main leader. After eggs are laid, the larvae hatch, feed, and pupate in the cambium near the tree top and generally the leader is destroyed in the process. White pine weevil generally attacks young spruce up to 20 feet in height. Tussock moth is a very destructive insect whose larvae in sufficient numbers can defoliate a spruce from the top downward. In all but the most severe infestations, the buds will survive and the tree can recover somewhat from the assault if tree vigor is maintained. Spruce spider mites can infest trees and cause mottling and browning of the foliage in mid-summer. Cooley Spruce bud gall adelgid is another annoyance that causes unsightly "cone" galls on the ends of branches but does little to harm the long term health of the tree. Generally, spider mites and bud gall adelgid do not cause long-term damage unless populations are extremely high. Again, the continuing drought in Colorado has been the major precipitating factor contributing to problems with Colorado spruce. As conifers in Colorado go, blue spruce is a water hog! Even old established trees 50-60 feet tall with extensive root systems are succumbing. Basically, with subsoil moisture almost non-existent, any spruce not in a regularly irrigated site may begin to show browning and die-back. Drought stress is characterized by browning from the outside needles inward and from the top downward on spruce, but remember that browning may also be attributed to damage by the various pests mentioned above. |
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Problem Prevention How can we prevent many of these significant trees from succumbing to drought and the opportunistic pests that attack stressed trees? Again this winter with little precipitation, it is imperative to irrigate the root zone of spruce and other large trees. The root zone extends 2 to 4 times the height of the tree and watering must penetrate 10-16 inches deep outside the drip line to be effective. Remember, managing trees to be as vigorous as possible is the best defense against drought and pest problems. Some tender loving care now and diligent scouting for potential pest problems may be enough to keep the old beloved giants going another season. Also, remember that management of spruce pests varies for each species. Contact the El Paso County Cooperative Extension office (636-8921) for further information on the best course of action to take. |
News release from the Colorado Department of Agriculture:
On January 1, Colorado nurseries can no longer sell plants that are listed as noxious weeds to in-state customers. The new nursery regulations prohibit the sale of an additional 19 species, which include Russian olive, a popular ornamental tree.
"It was important for us to make these changes, so our Noxious Weed List and Nursery Regulations support one another," said Eric Lane, State Weed Coordinator at the Colorado Department of Agriculture. "We want to decrease the chances of noxious weeds having an impact on our riparian communities across the state."
There are roughly 8,000 acres of Russian olive established in watersheds throughout the state, a figure which does not include ornamental or other plantings such as windbreaks. Specific areas that have problems with Russian olive include river drainages such as the South Platte River and Colorado, Uncompaghre, Gunnison and White Rivers, especially at the lower elevations.
"Since these regulations are supported by the industry, we believe the impact will be minimal to our nurseries as well as consumers," said Lane. "Companies can continue selling these products out of state, and consumers have various substitutes that they can choose from, such as silver buffaloberry, which is almost identical in appearance to Russian olive and is native to the area."
In Colorado, more than 1,700 companies, nurseries and individuals are registered to sell nursery stock. For more information on the new nursery regulations, contact the Colorado Department of Agriculture at (303) 239-4182.
We hope you enjoyed this edition of the Growing Points Newsletter!Larry Vickerman Extension Agent Horticulture
Colorado State University
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