The worst damage occurs to sensitive species planted near heavily salted roads with high traffic, especially when they lie downhill or have poor drainage. Other problems can produce the same symptoms, so examine the whole plant and site. Lower salt levels slow tree growth and vigor by interfering with nutrient availability and uptake in the soil.
Higher levels cause young plant tissues to dry out and die.
In both cases, the chloride ion is the active agent. Severe damage on evergreens comes primarily from spray taken up by the needles. For deciduous trees, research suggests significant damage also comes from salt being taken up by the roots and by soil structural collapse. Plant salt-tolerant species such as ashes, ginkgo, hawthorns, honeylocust, London plane, Norway maple, Red oak, Austrian, pitch, or Japanese black pines, or Sargent cherry. Reduce salt application rates, lower the throwing distance, and apply before roads freeze.