Plant injury (phytotoxicity) may occur when chemicals are employed to protect plants from pests, fertilize plants, regulate plant growth, etc. Phytotoxicity can occur when:

• a material is properly applied directly to the plant during adverse environmental conditions.
• a material is applied improperly.
• a spray, dust, or vapor drifts from the target crop to a sensitive crop.
• runoff carries a chemical to a sensitive crop.
• persistent residues accumulate in the soil or on the plant.

Symptoms

• Poor germination, especially if a soil drench was used
• Death of seedlings
• Death of rapidly growing succulent tissues
• Stunting or delayed plant development
• Misshapen or distorted plants, fruits, or leaves
• Russeting or bronzing of leaves or fruit
• Yellow or dead spots or flecks on leaves
• Yellow or dead leaf tips or leaf margins
• Yellow or dead areas between the veins of the leaves

Other Clues

• No signs of plant pathogenic organisms.
• Injured leaf tissue is sharply defined with little or no color gradation from dead areas into healthy areas.
• Dead spots are of uniform color and may go entirely through the leaf.
• Cropping history indicates that the previous crop or a nearby crop was treated with a chemical to which the injured crop is sensitive.
• Injury occurs over a relatively short period and does not spread from plant to plant.
• Only tissue of a certain age may show damage (only young leaves).
• Plants on ends of rows or ends of benches are the primary ones affected.

Factors That Influence Phytotoxicity

• Chemical: Certain crops are very sensitive to certain chemicals. Be certain the crop to be treated is listed on the chemical label. Some chemicals are persistent. Repeated applications result in accumulation of the chemical to a toxic level.
• Formulation: Dusts and wettable powders are generally less phytotoxic than emulsifiable concentrates (EC).
• Additives (adjuvants) such as spreaders, stickers, and wetting agents may cause injury.
• Concentrations: The use of a chemical concentration higher than label recommendation or its use more frequently than the label recommends is likely to cause plant injury and is illegal.
• Method of application: Always use the method recommended by the label. Apply the chemical thoroughly and evenly. Spray dripped on the ends of rows or benches when slowing down to begin the next sweep and excessive overlapping results in some plants receiving to much chemical. High pressure sprays may force chemical into sensitive tissues.
• Growing conditions:
  • Temperatures during and after treatments should be moderate. High temperatures favor chlorinated hydrocarbon and sulfur toxicity. Low temperatures favor oil, carbamate, and organophosphate toxicity.
  • Humidity or plant wetness. Wet foliage at the time of application or prolonged wetness of foliage after spraying can result in injury.
• Growth stage of plants: Seedlings and fast-growing, succulent plants are usually sensitive to chemical treatment.
• Mixing incompatible chemicals: This can occur when two materials are deliberately applied as a mix or if a material is applied too soon after a previous material was used.