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Browning and Dropping Evergreen Needles
Martha Maletta, Home Horticultural Consultant
Dated - October 20, 2003
No one is surprised when leaves of deciduous trees and shrubs turn various colors and drop. But when it happens to evergreens, people may take notice. Every fall we talk with residents wondering why their evergreens (especially white pines and arborvitae) are yellowing, browning, and dropping needles. They generally assume that the trees are dying, but, after discussing the symptoms, they can usually be reassured that they are seeing the natural leaf drop.
Evergreens, both needle and broadleaf, stay green all year because they don’t lose all their leaves at one time, not because they never lose leaves. Depending on species, leaf life ranges from one to six years. Each year some of the oldest (inside) leaves are shed. Hollies drop leaves in spring, most other evergreens drop leaves in fall.
Laurel, American holly, white pine and arborvitae lose their one year old foliage (what grew last year). This drop can be very noticeable, especially on new transplants and during years when the current seasons growth has not been as vigorous as that of the previous season.
Spruce, fir, hemlock, yew, Douglas fir and most other pines hold needles for 2-5 years and the normal drop may not even be noticeable. Most broadleaf evergreens, excepting laurel and some hollies, lose older leaves gradually so the drop is not dramatic.
If you observe yellowing on evergreens during the fall, look the situation over carefully. You are most likely seeing natural leaf drop if the yellowing: appeared suddenly and is affecting the oldest foliage (inside the plant); occurs on all the plants of that species at about the same time; is pretty uniform throughout the plant; occurs as a distinct zone on each branch or twig. If the new foliage is affected or the yellowing is only apparent on part of the plant there is something else going on. A closer look may be warranted.
Douglas-fir owners should keep an eye out for yellow mottling of this year’s needles that shows up now or through winter and into spring. (Yellow blotches eventually turn reddish-brown.) This is a symptom of rhabdocline needlecast, a fungus disease that is a serious problem, and we had perfect spring weather for infection this year. If the disease is confirmed, preventive fungicides can be applied next year to protect the new growth. Needlecast of spruce and pine may also cause blotchy yellowing of one or two year old needles in the fall.
Needle yellowing may indicate an infestation of spider mites or other sucking pests, some more obvious than others. Hemlock wooly adelgid is quite noticeable as tiny, cottony puffs at the base of needles. Mites or their eggs are most visible through a microscope or magnifying lens. Needle yellowing may be due to nutrient deficiencies, environmental stress, adverse site conditions such as poor drainage, air pollution and many other causes.
For help in sorting out evergreen symptoms that don’t fit the description of normal leaf drop, contact the Rutgers Master Gardener Helpline at 908-788-1735 or in person at the Extension Center in the Rt. 31 County Complex on Gauntt Place. The winter schedule, November 1 through March 31, is: Monday, Tuesday, and Thursday 10 a.m.-12 noon.
As I’ve been noting, it’s
been a good year for plant diseases with one interesting exception. The powdery
mildew that I battle annually on phlox and beebalm did not show up until very
recently. Infection by these fungus diseases is actually inhibited by rainy
weather. They thrive not when plant leaves are actually wet but when the leaf
environment is very humid. Greenhouse conditions (high humidity), crowded
plantings (poor air movement) and warm, dry days with cool nights (typical
in late summer and fall and indoors in winter) promote powdery mildews. This
late in the season there is no value in treating garden plants. The best solution
for houseplants is to avoid conditions that contribute to powdery mildew.