Deb Babcock's gardening column appears Mondays in Steamboat Today.
Find more gardening columns here.
Master Gardeners and staff at the Routt County Cooperative Extension Office are available to help local homeowners identify beetle problems and suggest treatment options. Call 879-0825 to make arrangements for an on-site visit. A list of Licensed Applicators is also at the Extension office.
Drive most anywhere in the mountains of Colorado, including in the nearby Routt National Forest and Zirkel Wilderness area, and you'll note more and more dead evergreens.
All the evergreens, including spruce, pine and fir, have beetles that naturally attack them. These beetles normally attack dead or weakened trees, but occasionally, the beetles become an epidemic and attack healthy trees. That's what's going on now with spruces and pines. Trees at the greatest risk of attack are those that have a main trunk greater than 5 inches in diameter.
Spruce trees are being attacked by the spruce beetle, and pines are being attacked by the mountain pine beetle. Each beetle attacks their specific species of tree and doesn't cross tree hosts. The scale of the MPB infestation is unprecedented and estimated to have covered more than 1.5 million acres in Colorado since 1996. In Routt County alone, 134,080 acres of new infestations of MPB were reported for 2007.
Beetles bore into a tree and essentially strangle it to death by cutting off its nutrient and water circulation systems. Spruce beetles bore into the tree in early summer and MPBs bore into the trees in late summer. The trees still will be green until the following summer when they will begin to fade, and the needles will turn red.
You can tell if a tree is infected by looking for globs of sticky goo coming out of the trunk. It is a sign of the tree's attempt to expel the insect. These globs are called pitch tubes. Once a tree has been infested or "hit" by beetles, it rarely successfully expels the beetle. A green, healthy-looking spruce or pine with numerous pitch tubes is considered dead or dying. Younger trees occasionally successfully repel beetles.
While it's not feasible to protect the millions of trees in the forest and wilderness area, you can do something about the trees in your yard. You can spray them with an insecticide prior to beetle entry. The insecticide kills the beetles as they try to enter the tree. The CSU Extension Office recommends the use of carbaryl (marketed under the label of Sevin®), or permethrin (marketed under many names). Spruce trees need to be preventatively sprayed no later than the end of May, and pine trees need to be sprayed no later than July 4. You'll probably need a professional to reach the upper trunk. Plus, this application is messy with insecticide dripping on you. A professional, licensed sprayer is usually best. If you choose to do the spraying yourself, be sure to follow label directions and treat the main trunk all the way around, spraying up until the trunk is less than 6 inches in diameter.
If your trees already are infected, no research has shown that an insecticide application is effective in saving it. There were some experimental applications being made to infected trees last year, and we will see if it's possible to save an infected tree later in 2008.
Spraying isn't foolproof either, and 2 percent to 5 percent of trees still could die because of a number of factors including missing parts of the main trunk, spraying too late, rain that washes off the spray, improper application of the insecticide and problems with mixing, dosage and expired shelf-life of stored insecticide.
CJ Mucklow, director of the Routt County Cooperative Extension Office, contributed to this article.
Deb Babcock is a local Master Gardener through the Cooperative Extension Office in Routt County. Questions? at 879-0825 or email to: firstname.lastname@example.org