Most of the injury we have seen is from wind-driven salt spray. When salt becomes airborne it can affect plants 100 to 150 feet from a highway, depending on the force and direction of winds. Classic symptoms of airborne salt spray appear on the side of the plant facing the road. This year whole plants were affected in many cases, and it seems likely that the higher doses of deicing salt coupled with driving winter winds are responsible. Bud and branch dieback of deciduous plants from salt injury becomes apparent at budbreak, whereas damage on evergreens first appears in late winter, and worsens through the spring.
Needles turn progressively brown from the tips towards the bases.
The current understanding is that salt injury from airborne saltspray is caused primarily by cell and tissue sensitivity to the chloride ion. Salts that accumulate on the stems and buds also cause desiccation of those tissues by drawing water out of them. A lesser problem associated with road salt usage is soil contamination. Salt must have been cheap then, too, because they found it was a handy substance to wipe out agriculture in any uncooperative civilization raising a fuss about being conquered. Rhododendrons and azaleas are particularly sensitive to this kind of injury.