Why is my Evergreen tree not green forever?
The term "evergreen" used to describe conifer (cone-bearing) trees isn't 100% accurate. This is the time of year some "evergreens" begin showing symptoms of seasonal needle loss as conifers do not keep their needles indefinitely. Older, inner needles turn yellow or brown, and drop from the tree after one to several years depending on the tree species. People often mistake this discoloration and loss of needles for an infectious disease problem if they are not aware of this normal process.
Seasonal needle loss is especially striking on bald cypress and larch trees. All of the needles turn brown and fall from these trees. Unfortunate events have occurred in the past, where owners of these trees removed them after incorrectly concluding that the barren trees were dead!
Because we do not have many bald cypress or larch trees in our region, white pine may be the conifer species most dramatically affected here by seasonal needle loss. By November of most years, only one year's needles may remain attached to the tree. Other pines like the Austrian and Scots pines usually retain their needles for three years. Spruce and fir needles also yellow and drop with age, but since these trees retain their needles for several years; needle drop is often not noticeable. The needles on arborvitae and some cedars usually turn brown rather than yellow with age.
These general patterns of needle drop may vary from tree to tree and year to year. Adverse conditions, such as drought and hot temperatures, may cause greater-than-normal loss of needles. The normal pattern of seasonal needle loss is a gradual discoloration and eventual loss of inner needles from the top to the bottom of the trees.
That doesn't mean that all needle loss is seasonal. Fungal diseases, like Rhizosphaera needle cast or Diplodia tip blight often cause browning of the newest (outermost) needles, death of entire branches, or thinning of needles on just the lower branches. These and other diseases are described and pictured in an ISU Extension publication, Pm-1528 "Common Diseases of Conifers in Iowa." As mentioned in the bulletin, applying fungicide sprays in the spring of the year controls infectious needle diseases.
Knowing what is normal for your landscape trees at different times of the year is the first step in diagnosing possible "evergreen" problems.
Stop into our office at 209 Centennial, Suite A, Cherokee, IA to pick up the publication mentioned above "Common Diseases of Conifers in Iowa." We have this publication and some others about conifers. You can also call and talk to us about any concerns you may have about your evergreens. As always we have our Hortline, these experts are available Monday thru Friday from 10 a.m. until noon and 1 p.m. until 4:30 p.m. The phone number is 515-294