Not to Worry about Trees Browning
Autumn Yellowing of Conifer Needles a Normal Process
DURANGO, Colo. – Sept. 7, 2017 – Although thousands of evergreen trees in the foothills of southwest Colorado are beginning to display dying yellow or orange needles, most are simply going through a natural shedding process – and are not infested by bark beetles or tree disease.
Colorado evergreens commonly shed their older, interior needles as part of an annual growth cycle. Needles on the lower portion of the crowns or closest to the trunk are most commonly shed, but trees stressed due to drought or root damage may shed more needles to keep the tree in balance with its root system.
Soon-to-be shed needles typically turn yellow first, progressing to a reddish-brown color before dropping off. Trees can have varying levels of needle shed, even within the same property or general area.
In the CSFS Durango District, which serves Archuleta, Dolores, La Plata, Montezuma and San Juan counties, most of the inquiries received about the phenomenon relate to ponderosa pine, but other conifer species commonly exhibit fall needle drop as well. Needle drop is generally observed starting in late August and can be noticeable through the month of October.
Evergreen trees that shed fall needles have a different appearance than trees infested by bark beetles. The needles on a beetle-infested tree typically change color throughout the entire tree, initially starting with an off-shade of green and turning to reddish-orange by the following summer. In addition to changing needle color, bark beetle-infested trees will show other signs of attack, such as popcorn-shaped pitch tubes on the trunk, boring dust resembling fine sawdust collecting in bark crevices and at the base of the tree, and regular woodpecker activity.
Seasonal discoloration and loss of pine needles frequently is called “needle cast,” but the term actually refers to several fungal diseases affecting conifers.
For more information about tree and forest health, contact the CSFS Durango District at 970-247-5250 or visit csfs.colostate.edu.
The Colorado State Forest Service (CSFS) is a service and outreach agency of the Warner College of Natural Resources at Colorado State University and provides staffing for the Division of Forestry within the Colorado Department of Natural Resources. The CSFS provides technical forestry assistance, wildfire mitigation expertise and outreach and education to help landowners and communities achieve their forest management goals. The CSFS Durango District serves Archuleta, Dolores, La Plata, Montezuma and San Juan counties.