Damage seen in ponderosa pines

What’s causing damage to ponderosa pine trees across eastern Wyoming? Along the eastern border, high levels of damage are visible, varying from partial yellowing of the needles to tree mortality.

According to a press release from State Forestry, the answer is not yet known, but the issue is being investigated with the assistance of the U.S. Forest Service and UW Extension.

At this time, two factors appear to explain some of the effects being seen. The first is winter damage caused by the drying out of needles and the fluctuation and timing of cold temperatures; the second is twig bark beetles.

“At the beginning of last October 2019, Wyoming experienced abnormally high fluctuations between daytime high and nighttime low temperatures. This combined with a late spring freeze in early April of this year likely damaged branch tips and more susceptible areas of the trees,” says the press release.

“In May of this year, high amounts of winter desiccation were observed. Signs of winter desiccation are needles yellowing from the tips back, often on the windward side of the tree. Winter desiccation is caused by the trees losing water due to warmer temperatures or high winds and not having access to adequate moisture in the soil.”

Increased evidence of twig beetles has also been found throughout the summer in ponderosa pine trees affected by winter damage.

“Twig beetles are a variety of small native bark beetle species that primarily affect small diameter branches in stressed or weakened trees. Twig beetles bore into the bark effectively girdling (killing) the ends of the branches,” says the press release.

“The result is a complete reddish yellowing color in affected areas similar to other bark beetle species in ponderosa pine. This can appear as spotted discoloring throughout the tree.”