Western Colorado Insects

Trees and Forestry

Elm Flea Weevil

Newly established pest of elms throughout Colorado. Larvae are leafminers early in the growning season. Adults make shot holes in leaves.

For more info. click here. Elm Flea Weevil

Walnut Decline

Walnut trees along the Front Range of Colorado, Espanola Valley of NM and the Willamette Valley of OR are dying from a syndrome we are calling walnut decline. It is also known as the Thousand Cankers Disease of Walnut. The decline apears to be associated with the Walnut twig beetle, Pityophthorus juglandis, which may transmit a fungal disease, Geosmithia sp. A second disease, Fusarium solani, is also implicated in the decline, but it is apparently not transmitted by the twig beetles.

We are interested in determining if Walnut decline is present on the West Slope of Colorado. If you know of declining walnut trees, especially trees with top death, please email or call your local Extension office.

Powerpoint (pdf) overview of Walnut Decline (2 Mb) from Dr Ned Tisserat


Walnut Decline Pest Alert (pdf)

The Red Hand of Death

Bark beetles are certainly an issue in western Colorado. Mountain pine beetle and spruce beetle have killed tens of millions of lodgepole and ponderosa pines and spruce trees throughout the area in the past couple of years. Clear cutting has been a controversial method of forest management, in part because of the unsightly scars they make on the forests in the short term. This dramatic picture was taken in 2006 in Grand County CO. The red (dead) areas are unmanaged lodgepole pine forests killed by mountain pine beetle. The green areas are healthy, vigorously growing forests that were clear cut in the mid 1950's. The lesson to be learned from this research conducted by the USDA Rocky Mountain Research Station is that forests are constantly changing. What may appear as a mature forest at one time will not always be that way. Clear cuts may appear unsightly shortly after they are done, but they may well be the green forests of the future. .

The Red Hand of Death (pdf)

Linden Loopers

Linden loopers defoliate several species of hardwood trees and shrubs. Outbreaks have occurred in several counties of western CO in 2007 and 2007.

TRA fact sheet (shtml)

Ash Borer

Ash borers are serious pests of ornamental ash trees, especially in western Colorado's urban settings. This publication is an overview of its biology and management.
Utah State Fact Sheet 36 (pdf)

TRA Fact Sheet (shtml)

Ash Borer Adult

Pinyon Ips

Pinyon Ips bark beetle devastated western Colorado between 2003 and 2005. This is an overview of its biology and management for home and small acreage owners.

TRA Pinyon Pine Mortality (shtml)
TRA Pinyon Pine Mortality (pdf)

TRA Pinyon Ips Prevention & Control (shtml)
TRA Pinyon Ips Prevention & Control (pdf)

TRA Protecting Pinyon Trees in Construction Sites (shtml)
TRA Protecting Pinyon Trees in Construction Sites (pdf)

TRA Thinning the Pinon-Juniper Forest to Improve Pest Resistance (shtml)

TRA Thinning the Pinon-Juniper Forest to Improve Pest Resistance (pdf)

Twig Beetle

Twig beetles can be serious pests of pinyon and other pines in both forest and landscape settings. There is little information available on their biology and control. This publication addresses their status in western Colorado.

TRA Article on Twig Beetles (pdf)

Mountain Pine Beetle

The 2006 Colorado State Forest Service Report on the Health of Colorado's Forests is an in-depth look at the mountain pine beetle situation in the state. It is the best information on the subject to date.

2006 CSFS Report on the Health of Colorado's Forests (2.5Mb pdf)
Aspen Scale

A relatively unknown scale insect is attacking Populus trees in several towns in western Colorado. We are calling it the "Aspen scale". It has been found on aspen and cottonwood trees. The scale feeds on the bark of the trees and can become so thick that the true bark is completely covered with insects. Infestations are known from Aspen and Durango and are undoubtly present in other towns. If you have seen this insect in other areas, please let Bob Hammon know about it.

TRA Aspen Scale (shtml)

This page was updated on January 31, 2015