Phytotoxicity

Phytotoxicity refers to the damage caused by the misapplication of chemicals to plants.

Herbicides are supposed to be toxic to plants, but sometimes beneficial treatments can have a negative effect, too.

Phytotoxicity caused by copper fungicide spray to Chamadorea palm leaves (Scot Nelson) Public Domain

Even the most benign treatments can become phytotoxic if too much is used. Each plant is unique in how they respond to horticultural oils, insecticidal soaps, and other treatments. Read labels thoroughly before you apply a treatment, especially when they contain emulsifiers and solvents. Do your plants a favor and follow the directions.
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Causes of phytotoxicity

Phytotoxicity can occur when you use old chemicals in new ways, new chemicals in the wrong way, or the right chemicals at the wrong time. Some plant species are sensitive to certain chemicals, and some life stages are vulnerable to all treatments. Water-stressed plants are more susceptible to phytotoxicity. 

Signs of phytotoxicity

Plants affected by phytotoxicity may show any of these symptoms:​

• Abnormal growth
• Chlorosis (yellowing) of tips, margins, or entire leaves
• Defoliation (leaf loss)
• Leaf curling, cupping, or crinkling
• Leaf spotting
• Stunted growth of parts or the entire plant

Preventing phototoxicity

You can prevent phytotoxicity with these good practices:

• Apply horticultural oils on days when temperatures are below 90°F
• Do not apply chemicals, oils, or soaps on breezy or windy days
• Prevent herbicide build-up in the soil by precisely following the package directions
• Stand at the recommended distance from a plant when applying treatments
  
• Use the minimum amount of fertilizer after getting a lab-based soil test

Plants affected by phytotoxicity will generally recover, but not always. Provide phytotoxic plants with a little TLC and an extra drink of water. And remove the cause whenever possible.