Phytotoxicity in Plants: Causes, Symptoms, and Prevention

Phytotoxicity—plant injury caused by chemicals—can occur during pest control, fertilization, growth regulation, or other treatments. Understanding why it happens helps you avoid costly damage.

When Phytotoxicity Occurs

• A correctly applied material contacts the plant during adverse environmental conditions.
• A material is applied incorrectly (wrong rate, timing, or method).
• Spray drift, dust, or vapor reaches a sensitive non-target crop.
• Runoff carries chemicals to sensitive plants.
• Persistent residues accumulate in soil or on foliage.

Typical Symptoms

• Poor germination (especially after soil drenches)
• Seedling death
• Death of rapidly growing, succulent tissues
• Stunted or delayed development
• Misshapen or distorted leaves, fruits, or plants
• Russeting or bronzing of foliage or fruit
• Dead spots or flecks on leaves
• Dead leaf tips or margins
• Dead areas between leaf veins

Clues That Point to Chemical Injury

• No signs of pathogens (fungi, bacteria, viruses).
• Injured tissue is sharply defined with little color gradation into healthy tissue.
• Dead spots are uniform in color and may penetrate the entire leaf.
• Recent chemical application to the current crop, a previous crop, or a nearby crop known to affect the injured species.
• Damage appears over a short period and does not spread from plant to plant.
• Only tissue of a certain age shows injury (e.g., only young leaves).
• Plants at row ends or bench edges are primarily affected.

Factors Influencing Phytotoxicity

Chemical Sensitivity

Certain crops are highly sensitive to specific chemicals. Always verify the crop is on the label. Some chemicals persist; repeated applications can accumulate to toxic levels.

Formulation

Dusts and wettable powders are generally less phytotoxic than emulsifiable concentrates (EC).

Additives (Adjuvants)

Spreaders, stickers, and wetting agents can sometimes cause injury.

Concentration and Frequency

Exceeding label rates or application intervals is likely to cause injury and is illegal.

Application Method

• Use the label-recommended method; apply thoroughly and evenly.
• Overlapping passes or slowing at row ends deposits excess chemical.
• High-pressure sprays can force chemicals into sensitive tissues.

Growing Conditions

• Temperature: High temperatures favor chlorinated hydrocarbon and sulfur toxicity; low temperatures favor oil, carbamate, and organophosphate toxicity.
• Humidity/Leaf Wetness: Wet foliage at application or prolonged wetness afterward increases injury risk.

Plant Growth Stage

Seedlings and fast-growing, succulent plants are usually more sensitive.

Incompatible Chemical Mixtures

Mixing incompatible products (either intentionally or by applying one too soon after another) can cause phytotoxicity.