Eastern White Pine - Modern Disease Threats to a Historically Important Species

Eastern white pine's current status belies its political past and potential future. Once demanded by the King's Royal Navy for its straight tall masts, Pinus strobus inspired the White Pine Acts of 1691 and 1711 and fueled colonial resistance. Surveyors for the "King's Woods" blazed the largest white pines with the "King's Broad Arrow", a series of three hatchet slices. The Pine Tree Riot of 1772, where local townspeople chased and beat the King’s mast surveyors with pine switches may have even inspired the Boston Tea Party.

Widely distributed (10.6% of area), and the tallest of the eastern conifers, some consider white pine the Sequoia of the East. A popular landscape tree used for screening (although it naturally loses its bottom branches over time) and its delicate five needled bundle of fine-textured leaves. White pine provides both important ecosystem benefits and enhances health. One mature white pine can intercept up to 4000 gallons of rainwater per year. Stroking its leaves can activate an immune response of T-cells in the human body.  Due to its susceptibility to drought, air pollution, and salt, sometimes white pine requires special siting and care in an urban environment.

White Pine Decline

White pine decline refers to a complex of environmental and biotic factors negatively influencing both short- and long-term health of the plant. The result is a decline in the overall health of the tree. Environmental factors leading to white pine decline include soil and moisture conditions white pine is not adapted to growing in. Avoid those factors by siting your tree to succeed from the start! Proper soils for best growth includes sandy or loamy noncompacted soils (not clay), a pH between 5.5 and 6.5, and good drainage. Above ground canopy space would accommodate a 50 - 100-foot future height with 20 to 40-foot of spread and plenty of sun. White pine tolerate neither root disturbance, street-side planting requiring heavy winter salt maintenance, nor moisture extremes. Unless a needle cast disease as described below occurs, retain the fallen needles as a natural moisture and pH buffering mulch, or provide up to 3" of mulch up to the drip line for young, planted trees.

White Pine Needle Disease

Browning needles and sparse tufts of new growth often signal the first obvious symptoms of an ailing white pine. Distinguish this from the normal yellow coloration and drop of the oldest needles in the fall. Looking at the needles themselves, you may notice brown tips or entire needle discoloration of a disease complex known as White Pine Needle Disease or WPND.

White pine decline symptoms include shriveling bark, oozing resin, or brown needles. Photo credit: Rosie Lerner, Purdue University

Hot sunny days with air pollution danger warnings can have the gas ozone damaging the needle tips. Needle blight pathogens associated with WPND include the fungi Lecanosticta acicula, Lophophacidium dooksii (brown spot needle blight), Bifusella linearis, and Septorioides strobi. Lesions or banding in older needles that develop into brown and yellow expanding areas can cause death to the distal part of the needle. The extent of damage for affected needles varies. The bases of needles can remain green, and not all needles in a bundle may get infected. Wyka et al. (2017) determined that an increase in precipitation during May to July — the time when white pine needles are elongating — positively correlates with damage from needle blight pathogens. However, as is the case with many conifer needle pathogens, that effect has a one-year delay. This means an initial infection of current-year needles happens in spring/early summer and the needles show symptoms the following year. Trees commonly shed entirely infected needles, with substantial needle drop occurring in June or with rain. Tree crowns begin to look sparse a year after initial infection. Hence, the stress of late spring frosts, drought, and wet spring weather favor needle disease outbreaks.

Septorioides strobi, recently described as a new species, uncharacteristically affects current season's needles. In many cases, troubled trees exist directly adjacent to healthy trees in the landscape.  Most often, needle tips were straw‐colored to brown while the base of the needle remained green and healthy. Chemical management for this organism differs from other needle disease organisms so check with your local County Extension office for recommendations.

The black colored, circular lesions extruding clear spore masses of Septorioides strobi. Photo Credit: Nicholas J. Brazee, Ph.D., UMass 

The Eyelash Fungus

Caliciopsis pinea causes smooth, reddish-brown branch and trunk depressions (cankers) which stream resin. If the canker starts below a branch whorl, the bark appears rough and cracked. With distinctive fruiting, the fungus forms visible curved black colored stalks resembling eyelashes. Pole-sized white pine in dense stands and landscape tree in dense groves or screens are most susceptible. White Pine Bast Scale (Matsucoccus macrocicatrices or WPBS), feeds on fluids of the phloem’s bast cells. By themselves, both organisms cause relatively little harm to white pine. Recently, researchers found that Caliciopsis readily colonizes feeding sites of WPBS and now consider it a potentially serious pest-pathogen complex attacking stressed and weakened trees. Saplings regenerating in the understory become regularly infected and die.

Keeping White Pines Healthy

Management not only includes chemical control, but also measures to increase light and air flow to decrease moisture, removing dead, diseased, or dying branches, and fertilization. White pines have adapted by increasing photosynthetic rates in remaining needles, increasing water-use efficiency, and prioritizing carbon storage over annual growth. Close inspection of affected white pine may reveal undersized shoots and stunted needles. These trees elect to save resources over spending it on new growth to ensure future energy resources, thereby betting on better times. Going into dormancy, trees normally pull nitrogen out of the naturally senescing foliage in the fall, a process known as resorption. When prematurely shed needles drop from WPND, white pines lose foliar nitrogen that fall senescence would have retained. Judicious fertilization may prove to improve vigor the most in a WPND affected white pine.

In addition, forestry practices such as thinning to lower forest density, promote crown vigor, radial growth, and significantly reduce WPND severity. On a landscape scale, thin white pine groves and rows or remove neighboring less desirable plants. Eliminate unnecessary stresses on white pine by avoiding moisture extremes and following proper cultural practices.

Whether it’s three chops of a hatchet or the microscopic fungal spore on a needle that’s causing injury to white pine, one can argue that white pine is resilient. Climate change may induce its range to move farther west to survive, even while it changes its biological processes to withstand stress and biotic attack. The more we understand the environmental and biotic stresses any tree species faces, the more we can make the choices that ensure its survival in the landscape and forest.

Sources

Beale, J. and N. Gauthier. 2015. When White Pines Turn Brown... Plant Pathology Factsheet PPFS-OR-W-22. University of Kentucky College of Agriculture, Food and Environment. 4 pp.

Brazee, N.J. 2021. Dieback of Eastern White Pine (Pinus strobus): Pathogens, Pests, and a Changing Climate. University of Massachusetts at Amherst Center for Agriculture, Food, and the Environment.

Gandhi, K. J. K., Livingston, W. H., Munck, I.A. Eds. 2018. Resilience and Health of Eastern White Pines under Novel and Historical Factors. Forest Ecology and Management. Vol. 423. 1-120 pp.

Li Q, Kobayashi M, Wakayama Y, Inagaki H, Katsumata M, Hirata Y, Hirata K, Shimizu T, Kawada T, Park BJ, Ohira T, Kagawa T, Miyazaki Y.  2009. Effect of phytoncide from trees on human natural killer cell function. Int J Immunopathol Pharmacol. 22(4):951-959.

Rogers, S.A. 2013. The Tree that Sparked the Revolutionary War: Eastern White Pine’s Colonial History. Northeastern Lumber Manufacturers Association (NELMA).

Wyka, S.A, Smith C., Munck, I.A., Rock, B.N., Ziniti, B. L, Broders, K. 2017. Emergence of White Pine Needle Damage (WPND) in the northeastern U.S. is associated with changes in pathogen pressure in response to climate change. Global Change Biology, Vol. 23, Issue 1, pp 394-405.