PPDL Picture of the Week
November 2, 2020
"Dying" Conifers – NOT!
Karen Rane, Plant Disease Diagnostician
Photos by: Gail Ruhl
Every year in late summer and fall, the PPDL 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.