Phytotoxicity

Phytotoxicity is caused by misuse or misapplication of chemicals on plants. Symptoms on broadleaved shrubs include leaf spotting, scorch or dead tissue and can be confused with insect or mite damage, diseases, other abiotic problems such as nutrient deficiencies, or environmental conditions. Injury symptoms on evergreens may include needle spotting or banding, tip browning, or curling of new growth. Needles of injured plants may turn yellow, followed by needle browning. 

Insect injury and frost damage predispose plants to chemical damage. Stressed plants are more prone to phytotoxicity damage. High temperatures, in general, will increase the likely hood of injury from pesticides (insecticides and fungicides especially soaps, oils and sulfur compounds). High temperatures and humidity can increase the chance of injury from sulfur-containing pesticides. Cool damp weather may increase the chance of injury by copper fungicides. Phytotoxicity may also result when incompatible chemicals, such as oil and carboxamide compounds, are applied at the same time.

Damage may also occur due to wind drift onto nontarget or sensitive plants.  A pattern of damage to nontargeted plants may be visible over a wide area such as adjacent yards. Spray applications should be applied during calm, dry and cool conditions. Most pesticides are best applied below 85 F. Always check label directions for cautions for sensitive plants. Also, check label cautions about combinations of pesticides.

Phytotoxicity symptoms on leaves

Phytotoxicity from incompatible chemicals,
such as oil and carboximide compounds, applied at the same time


Symptoms on shrub

Phytotoxicity on blue spruce from horticultural oil

Phytotoxicity on pine