Conifer Aphid has been rife this year and because of the warm wet spring fungal diseases have also... Excessive trimming can also kill conifers, but due to the amount of conifers that are dying this year, its probably another cause that's already been mentioned. To much moisture.. Most of the Conifers started to die off just after the heavy snows last winter. I think the melting snow absolutely saturated the ground and this was the probable cause...