Autumn is the time of year when mature white pines annually drop older needles. Unfortunately, this year's wet spring and dry summer have caused problems with many evergreen trees, including white pine. It is important to recognize whether pine needle drop is normal or due to a deeper problem.
All trees and shrubs renew their foliage annually, producing new leaves in the spring of the year and shedding old leaves in the fall. The leaves of deciduous plants such as maples and oaks live for one growing season and then fall off, usually in a blaze of color.
Despite the name, evergreen foliage does not live forever. Actually evergreen foliage lives from one to several years, depending on the species. As new growth emerges in the spring, last year's growth becomes shaded and is no longer the plant's primary food. During fall, this inner or older foliage dies and falls away.
There is really nothing to be concerned about. What is happening is commonly called inner needle drop or third year needle drop.
In some species like white pine and arborvitae, this fall browning takes place rather suddenly. The older needles turn a bright gold-yellow and remain attached for about 7 to 10 days depending on the weather. If we have strong autumn winds and heavy rains, these needles fall quickly. Sometimes, this natural occurrence is hardly noticed. But every few years it is very noticeable, and people become concerned.
This natural foliage drop may be distinguished from cases of severe foliage damage due to disease or stress by its uniform appearance over the whole tree and its common occurrence on neighboring trees of the same kind. It is also confined to the innermost or oldest needles. White pines bear needles in bundles five and the needles remain together when they drop.
Unfortunately, many white pines across Illinois are experiencing "white pine decline" due to a complex combination of stress factors. Inclement weather stresses a tree and can result in poor growth and/or the slow decline of white pines. Symptoms vary but generally include some pattern of needle yellowing or browning, small needle size, stunted growth, sparse foliage, shriveled bark on branches or trunk, sap exudate on branches, and in some cases death of the tree. Often trees with white pine decline do not recover. Watering helps (except in cases of flooding stress), as does the use of natural mulch (such as shredded bark) over the root system.
So how do you know if your white pine needle drop is normal or not? If older, inner needles turn yellow and drop uniformly across the entire tree in the autumn, it is probably normal needle drop. But, if needles turn yellow and drop in other times of the year, include the outer needles, or is sporadically arranged across the tree, it might be something more serious.