Phototoxicity in Plants: Chemical Sensitivity and Human Risks

Phototoxicity—adverse reactions to chemicals—can stem from pesticides, herbicides, fungicides, or the plant's own defenses. Responses range from leaf discoloration to death. Some plants are phototoxic to humans.

Plant Phototoxicity (Chemical Sensitivity)

Occurs in chemically sensitive plants, during hot-weather tank mixing, with adjuvants/solvents, or on stressed plants. Ferns, palms, English ivy, poinsettias are highly sensitive.

Specific Sensitivities:

• Stone fruits: copper (Bordeaux mix) causes russeting, stunted leaves
• Cucurbits: copper issues
• Fruit trees: zinc sulfate defoliation
• Roses, ornamentals, cucurbits: sulfur burns
• Improperly mixed/applied insecticides/herbicides: wide damage range

Plants Phototoxic to Humans

Defensive chemicals cause topical reactions:

• Wild parsnip: Contact + sun = severe burns
• Mayapple: All parts poisonous
• Common garden plants with mild phototoxicity: dill, celery, carrots, coriander, angelica, rue, parsley, anise, fennel, lovage (wear gloves, wash after handling)

Treatment & Prevention

Human exposure: Wash area; apply cortisone or baking soda paste.

Plants: Rinse off; damage often done. Remove affected stems. Provide excellent care for recovery. Prevent: apply chemicals on cool, cloudy days; use less toxic options (baking soda, phosphate salts, horticultural oils/soaps, beneficial insects).