Their annual loss of needles can be especially alarming on mature white pines, as the number of yellow needles outnumbers the current season’s green growth. Typically, white pines will retain needles for three years, but in autumn, 2-or-3-year-old needles will change color and drop, leaving only the current season’s growth still attached. Austrian and Scots pines usually retain their needles for three years. Red pine drops its needles in the fourth year. Spruce and fir needles also turn yellow and drop, but the change is usually less noticeable because their older needles are thinned progressively, making the process more gradual than in pines.
Arborvitae sheds branchlets rather than needles which usually turn brown as they age, yet remain on the tree for quite some time before falling. Yew needles turn yellow and drop in late spring or early summer of their third year. Check your plants regularly. If the current season’s growth is discolored or wilted, the tree may be suffering from a more serious disease or insect problem and should be diagnosed to determine if control is warranted.
There is no control required. As long as needle drop is restricted to older growth and is not excessive, the “problem” is simply seasonal needle drop, a normal and natural process. Always follow good cultural practices to keep trees healthy.