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. Low levels of salt 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.
Severe damage on evergreens comes primarily from spray taken up by the needles. For deciduous trees, it is caused primarily by salt being taken up by the roots. Reduce salt application rates, lower the throwing distance, and apply before roads freeze. Use a less harmful product such as CMA or Iceban, and mix in inert materials like sand. Raise the planting site, or block off the trees from the road with a barrier.