Arborvitae and white pine needles turn brown or yellow and drop in the autumn of the second year. During this time, older needles should be shed and not the current season's growth. If the new growth is turning yellow or brown, it may be caused by other stresses such as insects or disease. Various environmental stresses can also cause leaf and needle drop of evergreen and deciduous plants. The most common of these is drought or too much soil moisture.
Nitrogen deficiency causes the older leaves of a plant to turn yellow.
Air pollution, insect infestations or disease can all cause similar symptoms. Always check your plants closely to determine the true cause of its leaf or needle drop. Prepared by Nancy Doubrava, HGIC Information Specialist, and Bob Polomski, Extension Consumer Horticulturist, Clemson University. This information is supplied with the understanding that no discrimination is intended and no endorsement by the Clemson University Cooperative Extension Service is implied. All recommendations are for South Carolina conditions and may not apply to other areas.