Chlorine Toxicity

Excess Chlorine

• Scorched leaves may be the result of chlorine toxicity.
• Chlorine is a micronutrient, essential to plant growth. However, too much chlorine can accumulate in leaf tissue, resulting in leaves with a scorched or burned appearance.
• Trees with scorched leaves have brown or dead tissue on the tips, margins, or between the veins of the leaf. Leaf tissue may appear bleached, instead of scorched.
• Leaves may be smaller than usual. They may yellow and drop early.
• Chlorine toxicity can result from air pollution, in the form of chlorine gas, or from excess chloride in the soil.

How do plants become exposed to chloride?

• Chlorine (Cl) converts to chloride (Cl-) in the soil and is absorbed by plants in this form.
• Excess chloride can build up in the soil from swimming pool runoff, irrigation water, or excess soil salts (sodium chloride).
• Chloride toxicity is most common in irrigated, dry regions, seacoast areas, and near roads frequently treated with salt in the wintertime. 
• Damage to plants from chlorine gas is less common than damage from other air pollutants, such as sulfur dioxide, fluoride, and ozone.
• Chlorine gas is a by-product in the manufacture or incineration of glass, plastics, paints, and stains. It is released from refineries or as a result of chemical spills.
• Reducing air pollution at its source is the best solution to reduce damage to plants and people. Careful watering practices can reduce air pollution damage to plants.
• Soil should be dry during periods of exposure to air pollutants, followed by thorough watering after exposure.
• Wetting the leaves of sensitive plants may help to reduce damage during periods of poor air quality.
• Trees sensitive to chlorine are ash, boxelder, Siberian crabapple, dogwood, horse-chestnut, silver maple, sugar maple, pin oak, sweet gum, and yellow-wood.

Management 

• Chloride levels can be reduced with the use of gypsum. Incorporate gypsum into the soil at a rate of about 50 lbs. per 1000 square feet, in loam soils. Less gypsum is needed in sandy soils, more in heavy clay soils.
• Water thoroughly to leach toxic levels of chlorine from the soil. 

Rev. 2020