Issue 12, October 12, 2020
White Pine Decline
The University of Illinois Plant Clinic frequently receives white pine samples with symptoms described as, “Dying trees with thinning, yellowing and browning needles.” These samples are always somewhat frustrating because they usually lack any pathogens to explain the symptoms. Incubated needles and branches rarely produce any diagnostic clues. The lack of pathogen(s) leads us to attribute the symptoms to white pine decline, a condition caused by an environmental or abiotic stress.
What does white pine decline look like? In some instances, a single tree may be the only one affected out of a group. Trees have yellowish-green or browning needles that drop prematurely, resulting in an overall thinned canopy. Bark on branches and smaller limbs appears shriveled or wrinkled and will sometimes exude sap. The U of I Plant Clinic rarely gets the opportunity to view landscape plants' root systems, especially large trees. Those who have had a chance to examine roots have reported that white pine decline affected trees have sparse root systems with few fine, white roots compared to healthy trees.
White pine decline is believed to result from environmental and site stress, especially for trees planted outside the species’ requirements. White pine performs best on moist, sandy loam soils. Though considered an adaptable species, they seem to grow with intermittent success in Illinois. Many of the symptomatic trees were growing on sites with heavy clay soils, often with high soil pH. An overall trend toward wetter spring climate may also be a contributing factor. Excessive rains saturate soils resulting in a lack of oxygen and impaired root development. Further damage occurs when the tree’s root system is unable to tolerate extended dry spells.
The decline is difficult to reverse once it begins. Fortunately, affected trees do not pose a threat to surrounding trees, and immediate removal is not necessary. Watering during dry periods can help, along with mulching with 3–4 inches of a natural mulch over the root system. Fertilizing with an acidic fertilizer specifically packaged for pines or acid-loving plants may also help. However, prevention is by far the best way to manage white pine decline. Locate white pines on sites well suited to the species.
Photo 1. Eastern white pine (Pinus strobus) with yellowing needles and thin canopy.
Photo 2. Eastern white pine with yellowing and browning needles attributed to white pine decline.
Photo 3. Shriveled and winkled bark on eastern white pine affected by white pine decline.
Author:
Travis Cleveland