Everyone knows that deciduous trees, like Aspen and Maples, lose their leaves in the fall. Fewer people learn that evergreen trees also lose their old needles sometime in the late summer or fall. Fall needle drop is alarming and can come on fairly quickly. Typically, needle drop is most prominent on shaded sides or parts of the tree. This can include, but is not limited to, northern sides, the lower branches, and the interior of the tree. Residents of the Wood River Valley have noticed a sudden onset of yellowing needles on the interior of Spruce, Fir, and Pine trees. If evergreen needles turn brown from the interior of the tree, and the outer needles stay green, there is probably no cause for alarm. The age of the needles at which needle drop occurs varies between conifer species, and is generally four to six years for Spruce trees, and less for Pines.
Needle drop is generally associated with the needles of the tree becoming less productive for that tree. Older needles are found on the interior of the tree and less light, and therefore less photosynthesis, is captured by those needles. Needle drop can be pronounced in those trees that are crowded with other trees.
There are various environmental factors other than shade that can contribute to an increase in the amount of needles lost. Long, hot, dry periods can create stress on the trees that may increase the annual loss. Recent transplant can also increase the stress on trees. It is very common for newly transplanted trees that are still in recovery to experience a more dramatic needle drop.
There may be a problem if there is yellowing or dieback on the tips of branches. The Valley has seen insect, disease, and herbicide problems with conifers and dieback of new growth can be an indicator of one or more of these problems. Please don’t hesitate to