Officials with the Idaho Department of Lands (IDL) are puzzled over a seemingly new disease affecting ponderosa pines (Pinus ponderosa) in the region. They are discouraging culling trees with discolored needles until they can determine the underlying cause of the disease; this may mean waiting until June when the ponderosa pines produce new needles. According to Tom Eckberg, an IDL forest health specialist, “It has no rhyme or reason and doesn’t fit the pattern of typical diseases.”
So far, it seems the disease is limited to populations growing at lower elevations, trees in the mountains are not displaying the reddish-browning of needles similar to those in and around Moscow, ID. The first damage of its kind was identified mid-December 2014 in Clearwater County. Further damage was soon discovers in Coeur D’Alene, Hauser, Boise and Hathdrum. Damage appears on growth from the last season and is only present on a couple of trees in a stand, while surrounding trees remain unaffected.
Eckberg continues, “We have ruled out bark beetles, salt damage, herbicide damage and common needles. From a distance, the damage can resemble what happens as a result of bark beetle, but if you look closer there are significant differences.” He maintains that cutting down affected trees and leaving wood will only attract pests. A theory being explored as explanation for the state of the area’s ponderosa pines postulates that the trees are affected by winter-related injury caused by a series of severe cold snaps which occurred in late fall of last year.
Fluctuating extreme temperatures may have caused some freezing injuries. When soil freezes and dry wind blows needles cannot get adequate moisture. This may cause winter burn-like symptoms on some needles while leaving others completely green. Eckberg wants homeowners to avoid cutting down affected trees before they have a chance to produce new needles this year, which would help them confirm causation for the symptoms. Also, since symptoms are only appearing on a single species, experts would like to observe normal sprouting in order to rule out other possibilities.