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Autumn yellowing of conifer needles a normal process

By Ryan Lockwood
Special to The SUN

Although thousands of evergreen trees in the foothills of southwest Colorado are beginning to display dying yellow or orange needles, many are simply going through a natural shedding process — and are not infested by bark beetles or tree disease.

“We’re starting to see the natural fall needle drop that occurs every year, which can be more pronounced during drought years like this one,” said Kent Grant, district forester for the Colorado State Forest Service Durango District.

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, then a reddish-brown color before dropping off.

In the CSFS Durango District, which serves Archuleta, Dolores, La Plata, Montezuma and San Juan counties, Grant says most of the inquiries they receive 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 or early September and can be noticeable through fall and into early winter.

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 247-5250 or visit csfs.colostate.edu.

This story was posted on September 12, 2013.