From the Viette's Views Gardening Blog
"A lot of the needles on my pine tree are turning brown and falling off. What’s going on? Should I be worried? Is my tree dying?"
The keyword here is “fall”. Everyone is used to the deciduous trees coloring up and dropping their leaves in the fall but many are not aware that pines and many other evergreens also go through a natural “leaf” drop at this time of the year.
The difference is that evergreens don’t drop all of their “leaves” at one time like deciduous trees and shrubs do so it normally goes unnoticed. Every year all evergreens, including the broadleaf evergreens, shed at least some of their older foliage. When this leaf or needle drop occurs and how much is shed depends upon the species.
Since we aren’t accustomed to thinking of fall needle drop as being a normal occurrence for pines and other evergreens, many people automatically assume that they have an insect or disease problem when this happens. They’re quite relieved to find out that it’s normal.
Pines as a group shed their oldest needles in the fall. Most pines keep their needles for 3 to 5 years spreading out the needle drop over that period. White pines, on the other hand, hold their needles for only one year. Because of this, in certain years, the needle drop on white pines can be rather dramatic and this can be a bit alarming to a homeowner.
It’s because, since they only hold their needles for one year, variations in growth rate from one year to the next can have an effect on the percentage of needles that are shed in a given fall. When you look carefully at white pine branches in the fall, you should see that the needles at the ends of the branches (the current year’s growth) are healthy and green and that the one year old needles behind them towards the interior of the tree are the ones that are yellowing and turning brown. Eventually these will be shed.
When environmental conditions favor good, strong spring growth, the lush, new foliage will usually hide the shedding needles behind it. In these years, the natural needle drop in the fall is less obvious.
However, if new growth in the spring is slowed due to drought for instance, this growth will be shorter and will produce fewer needles than the previous year’s growth (assuming a normal growing season in that year). This sometimes means that a higher percentage of the needles on the tree are one year old needles and when these needles begin to turn yellow and brown in the fall, it becomes much more noticeable (especially if there was a good growing season the year before).
This was the situation for us in 2012. During the time when new growth was forming on the white pines, our temperatures were above normal but rainfall was well below normal. This resulted in reduced spring growth and consequently, more needles were shed that fall than were retained on the tree. Interesting!