Should you be worried about those yellowing needles? Seasonal Needle Drop is happening now.
Have you noticed recently that your evergreen tree is, well, not completely green?
If the yellow-orange discoloration recently started with the innermost part of the tree there is probably little reason for concern. This is a natural occurrence in many evergreen trees (Arborvitae and Pine especially) known as Seasonal Needle Drop. These trees naturally drop needles that are several years old – the innermost needles – leaving the new, outermost needles intact. The discolored needles will soon fall off the tree and no longer be noticeable.
That said, Seasonal Needle Drop can sometimes be more intense for trees that were planted within the last year, or if conditions have been dry or droughty. If there has not been a significant rain event in some time, it would be beneficial for the tree or trees to be watered. A one-time thorough soaking at the base of the tree will help the tree stay healthy.
However, if the outermost needles of the tree are exhibiting color change, this would be cause for concern. Discoloration of the outermost needles can be caused by one or several factors including: insect infestation, disease, chemical misapplication and environmental conditions (weather, soil, broken branches caused by animals, etc.).