Magnesium Chloride Toxicity in Trees Fact Sheet No. 7.425 Gardening Series|Trees and Shrubs by B.A. Goodrich and W.R. Jacobi*

MgCl2 Uses for Road Quick Facts Treatments • Magnesium chloride Along highways and city streets, liquid (MgCl ) is a salt compound magnesium chloride (MgCl ) deicing 2 2 composed of Mg+2 and solutions are applied during snow events, Cl- ions. as preventative deicers, and as anti-icing treatments. Granulated MgCl is also 2 • Magnesium chloride (MgCl2) commonly applied to sidewalks, driveways, is used as a dust suppressant and walkways in smaller quantities. Liquid and road stabilizer on non- MgCl2 solutions are applied to non-paved paved roads and as a deicing roads during spring and summer months product on paved roads and for dust suppression and road stabilization, Figure 1: Marginal burn on roadside aspen leaves. sidewalks. especially in arid regions. • MgCl based products can toward the middle of the leaf in deciduous 2 MgCl Toxicity: Biology species and towards the base of the needle in move from treated roads 2 conifers. Early leaf loss can also occur. into adjacent soils through Chloride (Cl-) and magnesium (Mg+2) are Necrosis is usually more severe on older precipitation. both essential nutrients important for normal conifer needles (i.e., those nearest the trunk). plant growth. Too much of either nutrient • Trees take up soil magnesium Sometimes newly flushed, or current season, may harm a plant, although foliar chloride needles are unaffected and remain green and chloride through roots concentrations are more strongly related throughout the summer and fall. Deciduous and accumulate them in with foliar damage than magnesium. High species may not exhibit symptoms for leaves. concentrations of MgCl ions in the soil may 2 several months after flushing new leaves. In be toxic or change water relationships such • To avoid chloride toxicity in some cases, foliar damage may appear on that the plant cannot easily accumulate water roadside trees, use non- branches in a spiral pattern in the tree crown and nutrients. Once inside the plant, chloride chloride based products to (Figure 3). moves through the water-conducting system Some symptoms associated with exposure treat for dust suppression and and accumulates at the margins of leaves or to deicing salt spray, aerosols, or road dust deicing purposes. needles, where dieback occurs first. Leaves differ from root absorption. The side of the are weakened or killed, which can lead to the tree facing the road may exhibit more damage death of the tree. and needles may have surface deposits of

salt crystals or dust. Trees exposed to MgCl2 Symptoms of Chloride aerosols are often, but not always, in soils with high MgCl concentrations and thus Toxicity 2 may show a range of symptoms. Chloride toxicity in woody plants initially develops as a marginal necrosis on deciduous leaves (Figure 1) or a tip burn or necrosis Abiotic Disorders Similar on conifer needles (Figure 2). Generally, the to Chloride Toxicity higher the foliar chloride concentrations, Drought effects, dehydration, winter burn, the more extensive the necrosis becomes. and some herbicide damage also appear as ©Colorado State University In prolonged exposures, necrosis moves tip or marginal burning on trees. Water stress Extension. 7/08. Revised 12/14. and dehydration may exacerbate chloride www.ext.colostate.edu *B.A. Goodrich, department of bioagricultural sciences toxicity and cause even more extensive and pest management; and W.R. Jacobi, Colorado State damage. There is no known method to fully University Extension specialist and professor, department separate the symptoms of chloride toxicity of bioagricultural sciences and pest management. 7/08 Additional Resources

• CSU fact sheet 2.932, Environmental Disorders of Woody Plants

• CSU fact sheet 0.503, Managing Saline Soils

• CSU fact sheet 0.520, Selecting an Analytical Laboratory

• CSU fact sheet 0.521, Diagnosing Saline and Sodic Soil Problems

• CSU fact sheet 7.227, Growing Turf on Salt-Affected Sites

• Cranshaw, W., Leatherman, D., Jacobi, W.R., Tisserat, N. 2014. Colorado State University Figure 2: Tip burn on conifer foliage. Low severity of tip burn (left). High severity of tip burn (right). Extension. Insects and Diseases of Woody Plants in Colorado. with water stress. Follow the diagnosis 2. Are herbicides applied along the Bulletin 506A. 322 pp. questions below and collect foliar samples road or the walkway? to determine chloride content. Some patterns of damage on herbicide- • Goodrich, B. A., R. D. Koski and affected leaves include cupping and W. R. Jacobi. 2009. Condition of deformation of leaf shape in addition to Diagnosis Soils and Vegetation Along Roads marginal necrosis. Treated with Magnesium Chloride Eliminating other major biotic (insects, 3. Is the road treated with MgCl ? 2 for Dust Suppression. Water Air diseases) or abiotic (herbicide) damages to If the road is or has been treated with Soil Poll. 198:165-188. trees is the first diagnostic step, although MgCl2 products, it may have washed into these issues may also occur on trees already surrounding soils. A splash and aerosol • Sinclair, W. A. and H. H. Lyon. stressed by chloride toxicity. The next major zone also occurs along treated paved roads 2005. Diseases of Trees and factors useful in determining whether a and contributes to foliar accumulation of Shrubs: Second Edition. tree is exposed to chloride are position and MgCl2. At very high soil concentrations, Comstock Publishing Associates, distance from the road, position in drainage MgCl damage may appear on trees after 2 Cornell University Press. or culvert areas, and eventually measuring two years of treatment. Ithaca, NY. chloride concentration in foliage. • Swift, C.E. 2007. An analysis Diagnostic Questions: of plant problems related to 1. Does foliar damage occur only Magnesium Chloride use for along the road or are many trees in the summer dust control on gravel area affected? roads in a mountain community in Eliminate other potential causes by Colorado. looking at the distribution of symptoms in the area. If many non-roadside trees in • Trahan, N.A. and C.M. Peterson. the area have similar symptoms this may 2007. Factors Impacting the be drought, winter burn, or needlecast Health of Roadside Vegetation. fungi causing tip necrosis or a band of Colorado Department of necrosis in the center of the needle. Check Transportation Research for insect frass and galleries on the stem, Branch Final Report No. CDOT- galls and cankers on stems and branches, DTD-R-2005-12. 223 pp. or potential root disease and other biotic agents that might be causing stress to the tree. CSU Extension Bulletin 506A: Insects and Diseases of Woody Plants in Colorado lists common biotic damage agents, signs, and symptoms for many species of woody Figure 3: Necrotic foliage “spiral” on roadside plants. lodgepole pine crown. Table 1. Foliar chloride concentrations (ppm) in seven common Colorado roadside tree species.1,2 Roadside Field Trees Shadehouse Trees Species Background Severe Foliar Damage3 Severe Foliar Damage4 Complete Foliar Damage5 lodepole pine < 1,000 4,000 9,000 17,000 aspen < 2,500 20,000 28,000 40,000 Engelmann spruce < 1,000 6,500 — — subalpine fir < 2,000 5,000 — — ponderosa pine < 1,500 7,500 8,000 22,000 Douglas-fir < 800 — 10,000 17,000 limber pine < 700 — — — 1Concentrations in parts per million (ppm) (1 ppm = 1 mg/kg = 0.0001% dry weight) 2Concentration data from: Goodrich 2008 and ongoing shadehouse trials at CSU (non-published data). Dashes (-) indicate concentrations are not known. 3Concentrations necessary to cause ~50% crown damage in roadside field trees* 4Concentrations necessary to cause ~50% crown damage in shadehouse trial trees* 5Concentrations necessary to cause 100% crown damage in shadehouse trial trees* *Experimental shadehouse trees are well-watered and not exposed to drought stress like roadside field trees growing in ambient conditions.

4. Is the tree downhill from the road? two-year-old needles (from conifers) or the soil with water can remove MgCl2

While trees uphill of MgCl2 may current leaves (from deciduous trees) ions from the upper soil profiles (see exhibit damage, the majority of foliar exhibiting tip burn from at least three fact sheet 0.503, Managing Saline Soils). damage occurs on trees downhill from the different branches. Avoid collecting Tree roots are extensive and may not road edge. needles or leaves from shaded or the benefit as much as agricultural crops 5. How far is the tree from the lowest branches. Avoid leaves that are from soil flushing. road edge? not fully developed. Store samples in a • Use non-chloride based products on On straight segments of non-paved cloth or paper bag (not plastic). roads that run through forested areas, roads most damage symptoms occur within • Lightly rinse foliage with distilled water or on roads with sharp curves and

20 feet from the road. Along MgCl2 treated prior to analysis to eliminate dust or steep slopes. highways, a splash zone may extend 300 aerially deposited salts. If foliage has • Lowering application rates of MgCl2 feet due to snowplowing, traffic, and the crystallized salt deposits, chloride may still cause damage to sensitive resulting aerial spray. concentrations will be extremely high conifers. Even the lowest application 6. Is the tree in an area where a culvert and not indicative of foliar cellular rates may become concentrated in discharges water from the road? content. If aerial spray or dust is roadside ditches and move off the In areas where culverts discharge water suspected as causing needle symptoms, road via culvert systems and into from the road and areas adjacent to sharply the water leachate (water used to rinse drainage areas. banked roads, water and MgCl2 ions are the foliage) can also be collected and • Do not apply dust suppression products concentrated and diverted into drainage tested for chloride content or electrical to non-paved roads immediately before areas. High concentrations of MgCl2 ions conductivity (EC: estimates the amount or during rain. in soil and plant tissue have been measured of total dissolved salts in a solution). • Select and use more tolerant up to 300 feet from non-paved roads in • If possible, ship samples the same day. If trees if tolerance has been drainage areas. No research is available same day shipping is not possible store experimentally proven. on MgCl2 movement through culvert and samples in a dry area or oven on low • Reduce exposure to deicing salts by drainage areas along highways treated for heat (less than 100 degrees F). minimizing the splash zone and aerial deicing purposes. • Close and seal the shipping container drift of deicing particulates (straw, to avoid contamination. Mail samples fencing, other structures). directly to the laboratory of your • The effectiveness of washing Recommendations for choice for analysis (see fact sheet 0.520, accumulated surface depositions from Sample Collection Selecting an Analytical Laboratory for a needles is not known, but it may help • Chloride concentrations in leaves, list of laboratory recommendations). maintain healthy needles. Additional rather than the soil, are a better • Compare results of chemical analysis leaching to move salt through the soil is indicator of potential damage to with the information in Table 1 to needed after needles are washed. roadside trees. determine if the tree is exposed to • Collect foliar samples towards the end chloride salts. of summer or beginning of fall along non-paved roads. Collect samples in Management Colorado State University, U.S. Department of spring if trees are along roads treated for Agriculture and Colorado counties cooperating. deicing purposes in the winter. • No chemical treatments can reclaim CSU Extension programs are available to all without discrimination. No endorsement of products mentioned • Collect at least 30 grams (a handful or saline soils (high in soluble salts), is intended nor is criticism implied of products not half a small paper lunch bag full) of although proper drainage and flushing mentioned.