Pacific silver firs are susceptible to several fungal diseased, including Annosus root disease (Heterobasidion annosum). Infected trees may show retarded leader growth, sparse and chlorotic foliage, stem decay, and abortive cones. The most reliable way to detect this disease is by the presence of fruiting bodies in the duff layer at the root collar on the outer bark. Trees become infected by rood contact or by airborne spores falling onto woonds. Other fungal diseases include Indian paint fungus (Echinodontium tinctorium) and laminated root rot (Phellinus weirii). Both can infect stands of trees and result in patches of damaged or dead trees.

Trees weakened by disease or poor growing conditions may become infested with fir-engraver beetle (Scolylus ventralis), silver fir beetle (Pseudohylesinus sericeus), or fir root bark beetle (Pseudohylesinus granulatus). In large numbers, these beetles may kill entire trees before any symptoms are observed. Pacific silver firs are also susceptible to Western spruce budworm (Choristeneura occidentalis), Douglas fir tussock moth (Orygia pseudotsugata) infestation. Applying fertilized and varying the age and density of stands reduces the infestation. Balsam wooly aphids (Adelges piceae) are an extremely devastating pest to this species. Infected trees appear swollen with little growth and usually die from the top down within 2 to 3 years. To prevent further infestation, most trees need to be removed and the site rplanted with such species as western hemlock.