This article is the second in a series reviewing unique or updated label requirements for key herbicides. Instructions printed on your herbicide label supersede this information.
Paraquat is the active ingredient in the herbicide Gramaxone SL 2.0 and others. It kills plants by destroying the membranes around the cells. The same processes occur in human cells. The lungs are especially sensitive, but the chemical characteristics of paraquat make inhalation unlikely. The greatest risk is accidental swallowing. The oral LD50 (lethal dose for 50% of the population) for humans is 3-5 mg/kg, which is roughly equal to 0.4 fluid ounces (1/200th cup) of paraquat for a 200-pound person.
Because of the acute oral toxicity, herbicides that contain paraquat are labeled with the ‘Danger’ signal word, which indicates that this herbicide should be handled with great care. Manufacturers of paraquat-containing herbicides add odorants to the formulated product to alert handlers of its presence. For 2020, paraquat packaging has been updated so that it reduces handler exposure and only allows transfer to application equipment. As with all herbicides, personal protective equipment should be worn when using paraquat-containing herbicides. Unlike other products, the required PPEs (personal protective equipment) are different for applicators and mixers/loaders and are summarized in Table 1.
Table 1. Summary of required PPEs for paraquat applicators and mixers/loaders.
The label has also been updated as of fall 2019 to increase the safety for using the product. First, only certified applicators may handle paraquat. Second, all handlers are required to take paraquat safety training. The certificate of training will not be required for purchase, but should be carried by the handler/applicator.
The recent changes are part of a 2016 EPA decision in response to deaths caused by accidentally swallowing paraquat that was transferred to a drink bottle. The required training emphasizes the importance of storing paraquat in the original, labeled container. Training is available at https://www.epa.gov/pesticide-worker-safety/paraquat-dichloride-training-certified-applicators.
There is the potential for some confusion because there are both old and new containers of Gramaxone available. According to Syngenta officials, handlers will be bound by the requirements of the label on the container they are using.
It may be tempting to think that it would be better not to use paraquat; but it is an important tool for managing weeds, especially those that are resistant to glyphosate and other herbicides. When handled carefully, paraquat is an effective weed management tool that would be difficult to replace in terms of effectiveness on hard-to-control species like pigweeds (Figure 1).
Additional information about the new paraquat regulations can be found at https://www.epa.gov/pesticide-worker-safety/paraquat-dichloride-training-certified-applicators.
Figure 1. Paraquat provides excellent control of large pigweeds in noncropland. Photo by Sarah Lancaster, K-State Research and Extension.
Sarah Lancaster, Extension Weed Science Specialist