Yellowing conifer needles, like those shown here, are perfectly normal in Colorado in the Autumn
Yellowing conifer needles, like those shown here, are perfectly normal in Colorado in the Autumn

COLORADO – Although thousands of evergreen trees in Colorado are beginning to display dying yellow or brown needles, most are simply going through a natural shedding process – and are not infested by bark beetles or tree disease.

Colorado evergreens 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, then a reddish-orange or brown color before dropping off.

Most inquiries related to the phenomenon relate to ponderosa and lodgepole pine. However, other local conifer trees, such as spruce and fir, also will experience needle drop in the fall.

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 fine sawdust at the base of the tree and popcorn-shaped masses of resin on the trunk.

This fall needle drop is frequently mislabeled as “needle cast,” but the term actually refers to a fungal disease of spruce and fir trees.

For more information about tree and forest health, contact the your local CSFS District.