Salt damage and warranty issues
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
As we noted in an earlier CAT alert (May 2, 2008), last winter was a season of heavy snowfall and therefore, also a year of heavy de-icing salt application. In fact, in many parts of the state salt usage was so heavy that salt was in short supply or completely unavailable by the end of the winter. Along with heavy de-icing salt application comes the potential for plant damage.
Salt damage or potential salt damage can be especially vexing for landscapers that offer plant warranties. Imagine the frustration of a professional landscaper that selects quality plant material, uses proper planting techniques, waters and coaxes the plants through the summer and fall, only to see them damaged by deicing salt. The problem can be especially difficult for landscape installers that provide plant warranties. Plant warranties vary and some exclude problems associated with improper maintenance or damage caused by external agents. Depending on the warranty, salt damage may be excluded. This then raises the question, how do we determine if landscape plants were damaged or killed by salt? Most landscape problems caused by abiotic problems require some detective work and finding a “smoking gun” is more the exception that the rule. With that in mind, here are some clues that point to salt damage as a causal factor.
Damaged plants are near a road, highway, parking lot or sidewalk that is salted during the winter.
Damage decreases with distance from the source. A study of de-icing salt impacts to roadside plants in Massachusetts showed that leaf sodium concentrations dropped by 90 percent from plants adjacent to highways to 30 feet away from the road. Salt drift is also influenced by traffic speed; faster vehicle traffic increases the distance spray will travel.
Damage is greater on the side of trees facing the roadway. The most dramatic causes of de-icing salt damage are caused by acute exposure of above ground portions of plants to aerial drift. Therefore parts of the plant facing the exposure are most damaged.
Damage is greater on salt-sensitive plants. In general, evergreen plants are more sensitive to salt damage than deciduous plants since evergreen leaves are exposed to salt during the winter. Even within evergreens, however, salt sensitivity can vary widely. White pine and red pine are highly sensitive to salt whereas Austrian pine and ponderosa pine are relatively tolerant of salt exposure.
Plant tissues contain elevated levels of sodium or chloride. Healthy plants contain some sodium and chloride. In fact, chloride is an essential nutrient element for plants. However, when either sodium or chloride builds up in plants, especially in leaves, toxicity can occur. The toxicity levels in foliage vary, but foliage browning is often associated with leaf concentrations (percent dry weight) in excess of 0.5 percent for sodium and 1.0 percent for chloride.
Soil salt levels may or may not be elevated. Both sodium and chloride can be leached from soils. As winter snowmelt is followed by spring rain, deicing salts may be leached and therefore may not show up in soil samples collected in late spring when plant damage becomes apparent.
Eliminate other causes. It’s easy to assume that roadside plants that die or are damaged over winter were injured by de-icing salt. It is still important to do a good detective job and look at other causes. How is the soil pH? Soil drainage? Were there any other chemical applications on the site such as herbicides or fertilizers? Are their potential pest problems? Did you install similar plant materials elsewhere? Did they have similar problems? If not, what was different about the sites?