Giant blue spruce falling to tiny beetle

By Barbara Maynard
Correspondent

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While some local residents have spent the last few years anxiously searching the skies for signs of precipitation, one native is apparently thriving in the drought. A small insect known as the engraver beetle, Ips hunteri, has been munching its way through water-stressed Colorado blue spruce.

The beetle is native to Colorado, but it usually doesn't have a significant impact because healthy trees are able to fight off infestation. The drought, however, has weakened the defenses of blue spruce along the Front Range. In 2002, 42 blue spruce trees were removed from Fort Collins because of ips infestations. Greeley has removed over 300 spruce since 1995.

"Mature trees are affected, which is really unfortunate. They are expensive to remove, and people love their trees," said Dave Lentz, forester with the Larimer County Department of Natural Resources.

Last September spruce ips was added to the Larimer County pest control resolution, which means that the county can require landowners to remove infested trees, or can charge owners for the cost of removal if the owner doesn't take care of the problem. The other pests on the resolution are Dutch elm disease, mountain pine beetle and Douglas-fir beetle.

Engraver beetles damage trees by burrowing into the inner bark of pine and spruce trees, where they mate and lay eggs. When the eggs hatch, the larvae feed on phloem, the tree's sugar transporting tissue. Normally, healthy trees defend themselves against burrowing insects by exuding pitch through the wounds created by the insects. Water stress, however, disables the trees' defenses. Once a tree is infested with the ips beetle, little can be done to save it.

"When the top starts looking brownish, or shows excessive needle loss, which can happen for a number of reasons, that's the time to have somebody come out and take a look," said Dave Leatherman, entomologist with the Colorado State Forest Service.

For a professional diagnosis, homeowners can call a city or county forester, an extension agent, a professional arborist or the Colorado State Forest Service. If the problem is ips, then the tree will almost certainly need to be removed.

Residents looking for preventative measures have a couple of options. "To protect the tree, you have to keep the tree healthy," Lentz said. This means maintaining a regular water regime and avoiding stresses such as construction projects near trees that could disrupt root systems.

Commercial insecticides are also available. "If you know you have a blue spruce that's stressed, preventative spraying is about your only hope to keep ips out of these trees," Leatherman said. "I view that as a necessary evil."

Spraying is best done in the spring, before the first generation of beetles takes flight. "It is best to have treatment done by April, and it should be good for 12 months," Lentz said. He recommended hiring professional arborists for the job because the dense needles and branches of spruce trees make application difficult.

Colorado blue spruce planted along the Front Range are particularly vulnerable to water stress, since this is not their natural habitat. "Where does blue spruce grow in the mountains? Along streams--it's a water loving tree," Leatherman said. "Spruce has the shallowest root system of any of our conifer trees. In times of water shortage, they're going to feel it first when the upper layers of soil start drying out. They just seem very sensitive to change."

In addition, Leatherman pointed out that many of the county's urban spruce trees are aging. "These trees, many of the big blue spruce that we see and love in our cities, are 50-plus years old and are coming into their maturity or over their maturity," he said. While 50 to 100 years old might not be much for a blue spruce living in its native habitat, it could be a ripe old age for a tree planted in the city.

For homeowners looking for new trees to plant, Leatherman suggested that people think twice before planting a water-lover like blue spruce locally. "Maybe it isn't the best choice for an urban setting, maybe there are better trees," he said.

The desert southwest has been hit hard by infestations of related ips species as a result of the drought. "We're losing pinyon pines by the millions in the Four Corners area and the southern Front Range to Ips confusus," Leatherman said. "Ips is not the problem, but ips is what is at crime scene."