University of Manitoba - Faculty of Agricultural & Food Sciences - Herbicide Damage
Herbicide Damage

Problem type: Environmental

Name of problem: 
Herbicide Damage

Plant name(s): All plants

Symptoms / Characteristics:
Herbicide products have different active ingredients and modes of action, which results in numerous injury symptoms related to herbicide injury. Symptoms can range from leaf distortion, cupping, rolling, yellowing, browning to irregular leaf spots. Stems may bend, twist, crack, develop swellings, or abnormal growth may occur. Flowers can change shape, size and arrangement. Roots can also be affected showing swelling and shortening. Some contact herbicides will cause plant parts to rapidly burn and be killed quickly upon contact with that tissue. Other chemicals work systemically, delaying symptoms until a later time. Soil sterilants are long lasting herbicides that move slowly through the soil profile. Symptoms may not become evident for years following an application and can persist for years afterward.

Plants can be exposed to herbicides in a number of ways. Herbicide drift occurs when liquid applications are made during even the slightest breeze. Wind can carry chemicals onto non-targeted nearby plants causing damage. Herbicides can also be active in the soil and can damage non-target plants. Chemicals can leach (move by water) through the soil or travel with runoff water and enter the root zone of nearby plants that then come in contact with the chemical.

Individuals unfamiliar with the chemical they are applying can lead to disastrous results. The use of the wrong chemical, improperly mixing chemicals or applying chemicals in the wrong manner or at the wrong time can all result in unwanted damage. Using spray equipment that has not been cleaned properly and is contaminated with an herbicide will lead to unwanted results. Landscape materials such as compost, manure, soil or mulch can be contaminated with an herbicide, which can have an affect on susceptible plants.

Control / Preventions:
Read and follow all labels on any chemicals you are using. Use recommended application rates and ensure equipment will provide safe accurate applications. Apply chemicals properly, especially liquid sprays as they can drift easily. Drift can be reduced by lowering spray pressure, spraying close to the ground or targeted area and avoid spraying on windy days. Be careful with water runoff when applying soil active herbicides and avoid the used of soil sterilants as they remain active for long periods of time. Do not use herbicide spray equipment to apply insecticides or fungicides.

Plants affected by herbicides can vary in how they will recover, depending on the general health and vigor of the plant affected, the amount of herbicide it received and the type of herbicide causing the damage. Woody plants that are healthy and have only received a small dose will usually recover. However, larger doses may cause long- term effects and symptoms may persist over a few years.

Plants can be washed off with water following an accidental herbicide spray. This must be done almost immediately, and after 4 or 5 hours, may not provide any control. This does not apply to herbicides that are active in the soil as water may only help the chemical cause greater damage.

Soil contaminated with a long lasting herbicide such as a soil sterilant may need to be completely excavated and replaced with clean soil.

Tree roots may be pruned if they are growing into a soil contaminated area. This can be done by trenching between the tree and affected area. Water availability to the tree can be reduced if root pruning takes place.

Plants can shows signs of herbicide injury for many years and recovery can be very slow. On valuable specimens, it is worth while to wait and see if improvement occurs. To positively identify whether the damage is herbicide injury, a soil analysis or tissue sample test needs to be conducted.