roses with brown petals and spray residue

Rose petals damaged by a pesticide spray. Photo: M. Talabac, UME

Updated: June 7, 2024

What is phytotoxicity?

Plant tissue damage from chemical exposure is called phytotoxicity (phyto relates to plants). It may or may not be an irreversible condition: the severity of plant injury will depend on the type and amount of chemicals involved, and healthy new growth may eventually replace damaged foliage.

What causes phytotoxic damage?

There are several ways chemical exposure can damage plants. Among the most common is drift from a nearby pesticide application or from direct contact with a pesticide. When diagnosing suspected phytotoxicity, knowing the care history of the plant or what recently changed in its environment can help narrow down which factor was likely responsible for the damage.

  • Pesticides (insecticides, miticides, herbicides, and fungicides) can injure plants in certain conditions, even when used as directed. Using home remedy alternatives to registered pesticides are also more likely to cause damage. Common risks for phytotoxicity include application mistakes like:
    • overdosing (using too concentrated of a solution, or making follow-up applications too soon)
    • overlap with other pesticides (interaction between chemicals)
    • treatment of stressed plants, or plant species not listed on the pesticide label
    • treatment in warm or windy weather that evaporates or moves airborne chemical into other areas
  • Salts leach moisture from plant cells and kill them, causing a kind of chemical burn. Salts in this context comprise a range of mineral compounds, and are not limited to sodium chloride (table salt or rock salt). Leaves and roots can be exposed to salt residue from:
    • ice-melting products
    • fertilizer that was applied dry and not brushed or rinsed off of foliage
    • fertilizer which was over-applied
  • Cleaning agents, like those for window glass or for pressure-washing decking, siding, and gutters, can drift onto nearby foliage from spray mist and drips.
  • Gasses and leachates from materials that have become anaerobic (decaying without oxygen), or which generate air pollution, can poison plant tissues.
    • Off-gassing and degradation byproducts of “sour” mulch (ammonia gas, hydrogen sulfide, acid, and alcohol) can scorch foliage in close contact.
    • Exhaust fumes and heat can burn foliage near idle engines or power tools.
    • Ground-level ozone on poor air quality days can injure sensitive plants.

When is phytotoxicity risk higher?

Some plant species or particular cultivars are more sensitive to certain chemicals than others. Conditions that can make any plant more vulnerable to phytotoxic injury include:

  • drought or insufficient soil moisture; wilting foliage
  • slow leaf drying due to wet weather, high humidity, or overcast skies
  • temperatures above about 85℉, particularly for pesticides with active ingredients using oil, soap, and sulfur compounds
  • cool, damp weather during applications of copper-based fungicides
  • pre-existing tissue damage from insect or mite feeding, infection, or frost injury
  • recent application of an incompatible pesticide

What are the symptoms of damage?

Damage to desirable plants can range from minor (temporarily altered growth) to lethal. Common symptoms, while not exclusive to phytotoxicity, include:

  • spots or blotches on leaves or petals that turn yellow, light brown, or darker, often looking bleached, burned, or “scorched”
  • deformed leaves, often twisted, curled, shrunken, or more slender than normal
  • sudden and prolific leaf shedding, especially combined with scorch or a change in color to yellow or near-black
  • scarring on fruits, such as russeting (patches of rough, reddish-brown discoloration) on the skin of tree fruits

Examples of phytotoxicity injury

Damage from power wash spray

Fig leaf damage from the overspray of power washing detergent.

Photo: University of Maryland Extension-HGIC


Soap and insecticide damage

Squash leaf damage from spraying with a soap and pyrethrin-based insecticide.

Photo: J. Traunfeld, UME


Damage from fungicide

Rose leaf damage from a fungicide application.

Photo: M. Talabac, UME


Russeting from fungicide over-use

Russeting on the skin of ‘Golden Delicious’ apple fruits due to over-use of bordeaux mix fungicide.

Off-gassing from sour mulch

Off-gassing from sour mulch bleached the lower perennial foliage that was touching or closest to the mulch.

Photo: University of Maryland Extension - HGIC


Herbicide damage

Herbicide exposure symptoms on a tomato plant, with leaf twisting and a bleached yellowing of the youngest growth. Affected growth does not reach its normal size and shape.

Photo: J. Traunfeld, UME


How do symptoms differ from other causes?

Phytotoxic injury can resemble symptoms of other problems, like plant diseases, insect or mite feeding, or frost damage. Clues can sometimes be used to separate phytotoxic damage from other causes.

For example, observe whether the damage worsens or spreads over time. Phytotoxicity injury will be a limited, one-time occurrence unless the chemical exposure is repeated or ongoing. As a test, pruning can usually remove phytotoxicity symptoms, but will not cure a plant infection if a disease is responsible for symptoms.

  • Leaf spotting from phytotoxicity will not expand or increase in number, unlike spots caused by infections and sap-sucking insects. Diseased leaf spots in particular are also often surrounded by a yellow, red, or brown ring or halo.
  • Leaf distortion like curling, twisting, and stunting from exposure to certain herbicides can continue to appear in new growth if contamination was significant. Otherwise, distortions may disappear from new leaves as growth continues. Any growth produced before herbicide exposure will remain normal. Viral infections, which can create similar symptoms, will spread to new growth and usually become more severe over time, weakening plants.
  • Leaf scorch, where portions of the leaf dry out and become bleached-looking, tends to be evenly damaging anywhere a chemical touches a leaf. In comparison, leaf scorch from drought stress or high heat will generally affect the younger, more sun-exposed leaves first.

Comparisons of leaf symptoms

Virus symptoms

Young pea growth is deformed and mottled due to a virus.

Photo: University of Maryland Extension - HGIC


Herbicide exposure

Oak leaves distorted and shrunken by exposure to herbicide. New growth after a single exposure is returning to normal.

Photo: D. Clement, UME


Fungal disease

Cedar-apple rust fungal infection on crabapple leaves. The infection sites are surrounded by a yellow-orange halo.

Photo: University of Maryland Extension - HGIC


Fungicide spray damage

Apple leaf spotting caused by a fungicide containing captan. The spots are more uniform in size and color.

Photo: University of Georgia Plant Pathology, University of Georgia,


Pesticide injury

Scattered specks of dead tissue from horticultural oil droplets on gerbera daisy.

Photo: University of Maryland Extension - HGIC


Insect feeding damage

Sap-sucking insect damage from a garden fleahopper, concentrated into patches where the insect was feeding.

Photo: Jim Baker, North Carolina State University,


Managing phytotoxicity damage

  • If objectionable, deformed growth or damaged leaves can be trimmed off, though those leaves will eventually fall off on their own.
  • Plants exposed to salts or over-fertilization can be well-watered to dilute residues and prevent ongoing damage.
  • Pesticide residues cannot be extracted from contaminated plants or soil, but they are eventually degraded by environmental conditions (weather and microbe activity) to render them inert.

Existing phytotoxicity injury cannot be cured, but avoiding a repeat of the conditions that made the plant vulnerable will reduce the risk of new damage. To reduce pesticide use, suppress pests with other techniques, such as physical removal, boosting plant vigor, and encouraging beneficial insects.

Additional resources

Plants grown in a home greenhouse with a combustion heater, grown near large quantities of decaying organic matter, or which are growing near sources of exhaust (from any combustion engine) might be exposed to ethylene gas, which can cause phytotoxicity damage.

Author: Miri Talabac, Horticulture Coordinator, HGIC, June 2024

Reviewed by Andrew Ristvey, principal agent & Extension specialist for commercial horticulture, and Kurt Vollmer, Extension specialist in weed management.

Still have a question? Contact us at Ask Extension.