Gary W. Moorman, Professor of Plant Pathology
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.
- a runoff carries a chemical to a sensitive crop.
- persistent residues accumulate in the soil or on the plant.
- Poor germination, especially if a soil drench was used.
- Death of seedlings.
- Death of rapidly growing succulent tissues
- Stunting or delayed plant development.
- Misshaped or distorted plants, fruits, or leaves.
- Russeting or bronzing of leaves or fruit.
- Dead spots or flecks on leaves.
- Dead leaf tips or leaf margins.
- Dead areas between the veins of the leaves.
- 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 Which 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.
a. Temperatures during and after treatments should be moderate. High temperatures favor chlorinated hydrocarbon and sulfur toxicity. Low temperatures favor oil, carbamate, and organophosphate toxicity.
b. 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.
Various Symptoms Caused By Pesticides
Notice: The user of this information assumes all risks for personal injury or property damage.
Warning! Pesticides are poisonous. Read and follow all directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams or ponds.
Issued in furtherance of Cooperative Extension work, Acts of Congress, May 8 and June 30, 1914, in cooperation with the U. S. Department of Penn State College of Agricultural Sciences research and extension programs are funded in part by Pennsylvania counties, the Commonwealth of Pennsylvania, and the U.S. Department of Agriculture.
Visit Penn State Extension on the web at extension.psu.edu.
Where trade names appear, no discrimination is intended, and no endorsement by Penn State Cooperative Extension is implied.
This publication is available in alternative media on request.
The Pennsylvania State University is committed to the policy that all persons shall have equal access to programs, facilities, admission, and employment without regard to personal characteristics not related to ability, performance, or qualifications as determined by University policy or by state or federal authorities. It is the policy of the University to maintain an academic and work environment free of discrimination, including harassment. The Pennsylvania State University prohibits discrimination and harassment against any person because of age, ancestry, color, disability or handicap, national origin, race, religious creed, sex, sexual orientation, gender identity, or veteran status. Discrimination or harassment against faculty, staff, or students will not be tolerated at The Pennsylvania State University. Direct all inquiries regarding the nondiscrimination policy to the Affirmative Action Director, The Pennsylvania State University, 328 Boucke Building, University Park, PA 16802-5901; Tel 814-865-4700/V, 814-863-1150/TTY.