Research Studies Support Aquatic Labeling of Aminopyralid

Aminopyralid is the active ingredient in several herbicides used for invasive plant control. It is currently registered in products such as Milestone® herbicide, or mixed with other active ingredients such as triclopyr or 2,4-D (for example, Capstone® herbicide, PasturAll® herbicide, GrazonNext® HL herbicide). 

The current labels for these products allow treatment of invasive plants growing on many sites including those near water, such as non-irrigation ditch banks, seasonally dry wetlands (flood plains, deltas, marshes, swamps, or bogs), and transitional areas between upland and lowland sites. Although aminopyralid-containing herbicides can be used to the water’s edge, the herbicide label does not allow for applications directly to water. 

An aquatic registration would expand the utility of aminopyralid-containing herbicides by allowing control of invasive or other weedy plants along shorelines, and on banks of ponds or moving water sites. The new label would not include control of submersed aquatic plants; however it will expand uses to sites currently covered under the National Pollutant Discharge Elimination System permit requirements. 

Field research trials were initiated in ponds and flowing water systems to gather data to support the addition of aquatic uses to aminopyralid product labels. Research was designed to establish food tolerances for fish, shellfish and crustaceans, and define herbicide dissipation in water and sediment over time. 


Figure 1: Pond study site at the US Army Corps of Engineers Aquatic Plant Control Research Center. Photo by Arcadis U.S., Inc.

Studies were conducted in Texas and Indiana on ponds that ranged in size from 0.4 to 0.7 surface acres, and averaged about five feet deep (Figure 1). Milestone herbicide at 7 fluid ounces per acre (fl oz/A) was applied on the pond banks, with over-spray into adjacent water. Applications were made on June 24, 2010 in Texas, and July 7, 2010 in Indiana. Water and sediment samples were collected prior to application and periodically over 120 days following application (Table 1). Dissipation of aminopyralid was calculated from residues in water and sediment samples. 

Caged organisms including catfish, bluegill sunfish, and fresh water clams were collected prior to and following application. Analysis provided data on the amount of aminopyralid in the tissue of aquatic organisms, and whether residues were at levels that would harm animals consuming the organisms. 

Results of the pond study indicated that there was rapid dissipation of aminopyralid with more than 99 percent of the applied herbicide dissipating within 120 days following treatment. No residue was measured accumulating in water, sediment or aquatic organisms.


Figure 2: Diagram of herbicide application and sampling in flowing water dissipation sites. Photo by Arcadis U.S., Inc.

Dissipation studies in a flowing water system were established near Blodget, Oregon and in Lake County, Florida. Milestone® herbicide at 7 fl oz/A was applied along the stream bank and over adjacent water on April 20, 2011 in Oregon and June 22, 2011 in Florida. The treated area was 225 feet long and 15 feet wide, encompassing 12 feet of soil/vegetation on the stream bank, and 3 feet beyond the edge of the stream bank (over vegetation in water and/or directly over water) (Figure 2 and 3). Absorbent pads were used to observe the herbicide application pattern (Figure 4). The total number of water, soil, and sediment samples that were collected and analyzed is shown in Table 1. 

Figure 3: Herbicide application at the Oregon flowing water research site. Total width of the application pattern was 15 feet, with 12 feet over soil/vegetation and 3 feet past the edge of stream bank (over vegetation in water and/or directly over water). Photo by Vanelle Peterson.

Figure 4: Application pattern using Hypro XT010 boomless nozzle for the flowing water studies. Photo by Vanelle Peterson.

Results of the flowing water dissipation studies (120-day study period) indicate that dilution was the major route of dissipation in the Oregon research site. Dissipation to non-quantifiable levels within the treated plot was reached in less than two hours following application. At the Florida research site, degradation was the major route of dissipation. Transport of aminopyralid from the treated area was significantly slower in Florida compared to the Oregon location; however, dissipation to non-quantifiable levels was similar (a few hours following application). Sporadic detections of the herbicide were found 1,175 feet downstream at 37 minutes following application in Oregon, and 335 feet downstream from the application area at 2 hours and 13 minutes following application in Florida. 


Data collected in the pond and flowing water field research trials were used in registration submissions to the Environmental Protection Agency in November 2012 to support aquatic uses for Milestone herbicide, GrazonNext ® HL herbicide, Capstone® herbicide, and PasturAll® herbicide. Registration will support use of these products for invasive or other weedy plant control on shorelines, and stream or river banks. Following approval, labels are NOT expected to have restrictions on recreational or livestock use of water after applications. Use will NOT be permitted on the inside banks of irrigation ditches or for submersed aquatic plant control. Precautions and restrictions on use of water treated with Milestone for irrigation will likely be included on the new label. Registration is anticipated for the 2014 use season. Although the cost of these studies is substantial ($300,000 for the pond studies and $200,000 for flowing water studies), it shows Dow AgroSciences commitment to supporting responsible use of aminopyralid-containing products for invasive plant management.

®Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow. Milestone is not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. PasturAll is not available for sale, distribution or use in the state of New York.

Always read and follow label directions.