Source: Penn State Extension, D. Lingenfelter
Herbicides are commonly used in Pennsylvania to control unwanted weeds and vegetation and are a valuable tool when used correctly. Sometimes herbicides move off-target for various reasons and can injure or kill desirable crops or other plants. When this happens it is critical to take action quickly to determine the potential cause. Certain herbicides such as the plant growth regulators (PGR) can be more prone to drift and will be the focus of this article. But keep in mind, if any kind of herbicide drift is suspected, it can be useful to report it immediately. Below are some key points to consider if you suspect herbicide has drifted onto your property.
Plant Growth Regulator Herbicides
Most broadleaf plants (e.g., grapes, vegetables, fruit crops, ornamentals, certain trees, non-tolerant soybeans, tobacco, etc.) are extremely sensitive to PGR herbicides. PGR herbicides include phenoxy, benzoic and pyridine classes of compounds. The most common PGR herbicides used are those containing 2, 4–D or dicamba. But others, which have been documented as causing injury include: picloram (e.g., Tordon), triclopyr (e.g., Garlon), and clopyralid (e.g. Stinger). All of the PGR herbicides should be considered to have the potential to cause injury to non-target sensitive plants as a result of spray drift. PGR herbicides are commonly applied to lawns, turf, pasture, agronomic crops (e.g., corn, cereals, sorghum) and noncropland (e.g., roadsides, rights-of-way). There are a wide variety of PGR herbicides and many are included in prepackaged mixes.
Plant Growth Regulator Herbicides - How they work
Auxins are plant hormones which regulate growth and development in the plant and are in the highest concentrations in the growing tips. PGR herbicides mimic the action of these plant growth hormones. The herbicide molecules bind to auxin receptors and abnormal growth results due to disruption in the hormonal balance of the plant. These herbicides are systemic and translocate from absorption sites (i.e., leaves or roots) to areas of rapid growth. The youngest terminal growth is most severely affected. (See example images of typical plant injury on back page.)
I Suspect Herbicide Drift…Now What?
The Pennsylvania Department of Agriculture (PDA), Bureau of Plant Industry regulates pesticides (herbicides, insecticides, fungicides, etc.), pesticide applications, and pesticide applicators. If you believe that a pesticide has drifted and adversely affected plants on your property and you want to initiate an investigation, please don’t wait to call PDA! Some pesticides break down quickly in sunlight or are metabolized rapidly by vegetation. The sooner PDA can collect samples after the pesticide application, the better the chances to find the pesticide through laboratory analysis.
To report a pesticide drift incident, contact your Regional PDA Office and ask for “Plant Industry”. (Or contact your local Penn State Extension office for additional help.)
Steps of a typical pesticide investigation process to determine if drift has occurred:
- A complaint is filed with PDA.
- An inspector will contact the complainant to gather facts about the incident.
- The inspector may take environmental samples and send them to the PDA lab for pesticide analysis.
- The inspector will contact the applicator to do a records inspection.
- Regulatory action will be taken against the applicator if pesticide drift can be proved.
- The case will be closed once the action is settled, or if no violation is found.
Other things to consider about the situation:
- Take notes to document the date and growth stage of the affected plants when the symptoms first appeared.
- Take good quality (high resolution) photographs of injury symptoms at least weekly until symptoms subside.
- Identify area affected; flag both affected and unaffected plants for future reference.
- For grapes growers, see reference websites below for additional information.
Pennsylvania Department of Agriculture
Bureau of Plant Industry
Herbicide Drift and Drift Related Damage
Preventing Herbicide Drift and Injury to Grapes
Questions and Answers about Vineyard Injury from Herbicide Drift
Leaf Index and Severity Rating & Leaf Index Report (Washington State University)