"Dying" Conifers - NOT!
Karen Rane, Plant Disease Diagnostician,
Director, Botany & Plant Pathology, Purdue University
Every year in late summer and fall, the P&PDL receives several
calls about conifers that appear to be dying. Clients complain
that the inner foliage of their pine and spruce trees turns yellow
then brown (Figures 1 and 2). The discolored needles then
drop from the branches. There is no cause for alarm, however – this
condition is normal for conifers at this time of year.
Despite the common name, evergreen foliage
is not “forever
green”. The foliage produced each year has a finite
life-span, which can be 2 to 4 years depending on the host species
and overall health of the tree. The oldest foliage will turn
yellow or brown and die each year. With some species, this is
a gradual change that occurs over several weeks or months. With
others, such as white pine and arborvitae, this change occurs
more rapidly, and is therefore quite noticeable. The environment
may also play a role in how quickly this natural phenomenon occurs.
Trees under stress from adverse environmental factors such as
drought may lose more than one year’s foliage at a time,
or the discoloration may occur more quickly than in healthy trees.
However, as long as the youngest foliage remains green (1 to
3 years’ worth, depending on the tree species), the health
of the tree will not be affected by this needle loss.
Normal fall needle drop should not be confused with needle loss
due to spider mites. These arthropod pests often feed on interior
foliage, and cause stippled or speckled discoloration which eventually
leads to brown needles. If spider mites are responsible for interior
needle loss, you should see the mites or their eggs, webbing
or cast skins when you examine the foliage with a hand lens.
For more information on spider mites, refer to E-42-W,
Spider Mites on Ornamentals (pdf file).