See:
Fir, True (Abies spp.) - Drought Injury
Notes: Leyland cypress in the landscape is susceptible to drought problems at planting. Care in the first several years is often recom-mended to get them established. Since they are often planted as dense hedgerows they may become stressed from competition and intra-tree shading as they mature and experience drought. This can result in branch flagging and may be attacked by cedar bark beetles. Cedar bark beetles do not appear to be primary killers, but indicators of tree stress, especially drought.