I have had this fir in my front yard for 15 years and have never seen the needles turn yellow in this manner. We have not made any changes to the trees environment. Is this something that I need to get treated? Would be so sad to see the tree succumb to disease.
Thank you for the photo. I would not be alarmed. If you look closely, you will see that the yellow needles are all towards the interior of the branchlets, meaning that they are older. Conifers shed their older needles as they become shaded out or less productive, i.e. they are no longer pulling their weight in terms of producing energy for the tree. It is a normal process that happens in the fall, and it seems like trees shed their needles like this more in one year than others - although I don't know if anyone has ever identified the reason. Most of the yellow needles will shed with the winter wind and rain. As long as the tips of the branches are green, then the tree will be fine.