Fluoride toxicity in plants irrigated with city water
Sensitive plants irrigated with city water can develop fluoride toxicity that results in tip burn.
Many municipalities inject fluoride into the water to prevent tooth decay of its residents. However, plants that are irrigated with city water containing fluoride can develop fluoride toxicity (Photo 1). In addition to city water, other sources of fluoride include single superphosphates in the fertilizer and to some extent, perlite.
The symptoms of fluoride toxicity in plants are necrotic regions, especially at the tips and along margins of leaves (Photo 2). Some plants that are more susceptible to fluoride toxicity are monocots, including spider plant, lilies, spikes and dracaena. Furthermore, some of these crops also have long cropping times and therefore will be irrigated with fluorinated water by growers for months, increasing the risk of developing fluoride toxicity.
There are a few things that a grower can do to prevent fluoride toxicity. First, if possible, only use well-water or rainwater to irrigate susceptible crops. For growers irrigating with city water containing fluoride only, be sure your fertilizer is free of fluoride or superphosphates. If the crop will tolerate it and not develop nutrient deficiencies, try to maintain of pH of 6.0 to 6.8 to reduce the availability of fluoride in the growing media. Also, increase the calcium available to the plant to help counteract the effects of fluoride.
For a long-term solution, growers could install a reverse osmosis water filtration system to prevent fluoride toxicity. Another option is to collect and store rainwater and use that alone or to dilute the city water to irrigate susceptible crops.
Once plants develop necrotic spots on their leaves, the damage is irreversible. The grower could trim off affected leaves or affected necrotic regions after the damage has been done, but that can take a lot of labor. Also, Michigan State University Extension recommends growers monitor the soluble salts in the soil and leach the plants if the salts are high. Growers should not over-water or over-fertilize crops susceptible to fluoride toxicity.
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