Forest Health Protection, Southern Region

Importance. - Drift and misapplication of herbicides can often damage nontarget trees. The total extent of such damage remains unknown, but localized, severe damage occurs. All tree species can be damaged by herbicides.

Identifying the Causal Agent. - Identification of the causal chemical is done primarily through symptom expression of the tree and determination of the method and rate of nearby herbicide applications. Symptom expression can be variable for a given chemical and is often unreliable when used as the only diagnostic tool.

Identifying the Injury. - Symptoms of herbicide injury are variable due to chemical mode of action, dosage, duration of exposure, tree species, and environmental conditions. Some herbicides cause growth abnormalities such as cupping or twisting of foliage while others cause foliage yellowing or browning, defoliation, or death. Environmental conditions such as temperature and humidity affect the degree of symptom expression by the host. Since symptom expression is so variable, professional help is desirable in diagnosing the problem.

Control. - Protect trees from unwanted or misapplied herbicides.