We have a field of canaan and fraiser fir trees that seem to be dying. It started off with the potted trees last year (sold as potted and taken out to plant into loamy clay soil, pH approx. 5.8). The trees turned yellow, then red and about 100 of 500 died. They had been planted for 2 full years before they started turning yellow. had been irrigated by groundwater (well) all summer previously. This year about 1/3 are turning yellow and now our bareroot trees that had been planted 2 months AFTER the potted trees (different nursery) are starting to turn yellow too. I am concerned they are all going to die as some are starting to drop needles and parts are turning red. Digging up the dead trees shows grubs (1 grub in a 3" wide by 10" deep hole) in roughly 1/4 of the holes, soil does not seem to be a factor as some holes are sandier and some are heavy clay, and some are a lovely loamy topsoil. All trees are planted on the same field. I did find a few 'webs" and wondering if Spider mites are a cause? No sprays or herbicides are used and trees were not fertilized recently.