Every winter and spring we usually notice that some trees and shrubs along driveways, in parking lots and along major highways in our area look brown and unhealthy. The injury is desiccation from moisture stress to certain species of evergreens, especially White Pine and a malformation of growth like a witch's broom on deciduous species such as Ornamental Crabapple. The cause of the injury is from salt spray that splashes or drifts onto roadside trees following highway de-icing operations during the winter.

In studies conducted by researchers at several universities, it was observed that certain species of plants are very sensitive to the salt spray, whereas other species appear to be tolerant. Examples of salt sensitive evergreen trees include White Pine, Scotch Pine, White Spruce and American Arborvitae while Colorado Spruce and Austrian Pine are very tolerant. Examples of salt sensitive deciduous trees include Redbud, Crabapple, American Sycamore, many oaks species, while Norway Maple, Silver Maple, Green Ash and White Ash are tolerant.

The damage from de-icing salts is most severe in urban areas and appears to be associated with the greater amounts of applied salts and increase density of traffic. The symptoms are most pronounced on sensitive plants close to the highway, but injury can be observed about 250 feet down wind of the traffic. Sensitive plants may exhibit injury to a height of 20 to 25 feet. But when lower branches are protected by snow, they escape injury.

It appears that the tolerant evergreens may be protected from injury due to a thick coating of wax on their needles. For example, Austrian Pine is quite tolerant with its thick coating of wax covering the needles, whereas White Pine with less wax protection is sensitive and damaged.

It is more difficult to characterize the nature of tolerance in deciduous species. Those plants with sticky, pubescent (hairy) or sunken buds appear to be some what more tolerant than those plants with smooth and exposed buds.

Over the next few months in New York and many other northern states, tons of salt will be applied to highways, drives, walks and porches to remove snow and ice.

The slush that results will be plowed, shoveled or brushed onto any convenient site where it will stay until it melts.

A by-product of this practice is the salt that remains. And all too often the salted ice is plowed onto planted areas along the highway, walks or foundation plantings about the home, with dead plants as a net result.

The excess salt or sodium chloride causes soil compaction in heavy clay and toxic levels of chlorine absorbed by the roots that injury the shoots.

The best solution to this problem is to plant the more tolerant species and avoid the sensitive species.

Curt Peterson, Ph.D. landscape specialist, is from Union Springs. He can be reached at curt.peters@hotmail.com