It is often difficult, if not impossible to eradicate an invasive species from a given area, no matter the resources at one’s disposal. Here we describe an example of one such successful effort and the approaches used to achieve it. As of 2001, approximately 40% of the island of Tutuila, American Samoa was infested with large stands of the fast growing, N-fixing tree, Falcataria moluccana – known as Albizia in Hawaiʻi and Tamaligi in American Samoa. Research found that when Tamaligi trees are eliminated, native Samoan forest species quickly reestablish and persist. In 2017, field crews from the National Park of American Samoa (NPAS) terminated the last remaining accessible Tamaligi population of 1,500 trees on Tutuila Island. Since the beginning of September of 2014, field crews killed a total of 12,350 mature Tamaligi trees across 19 villages and in the process restored approximately 4,120 acres of native forest. This greatly exceeded the number of Tamaligi killed by NPAS staff and their partners over the previous 13 years (i.e., 7,237 mature trees) since 2001. This dramatic increase in numbers killed came from switching from a manual approach whereby trees were laboriously girdled with machetes to a more efficient method using the highly effective herbicide, Milestone (a.i. aminopyralid). Clearing Tamaligi from these forests has protected important habitats of Samoa’s native flora and fauna and reduced the negative impacts of Tamaligi on watershed-streams and coastal habitats. Strong support of American Samoa’s village community enabled NPAS staff to accomplish the daunting and often dangerous control efforts. American Samoa’s Office of the Governor also supported and helped coordinate efforts with the traditional leadership of the affected villages. The importance of having many conversations with village communities in a respectful, candid and cordial manner cannot be overstated as a means to success. Further, these efforts have employed numerous village youth whose work has produced tangible results. Views of dead Tamaligi populations across landscapes have provided a powerful message to the Island’s communities about the importance of saving Samoa’s rainforests and that it can be accomplished by American Samoa’s people. Job opportunities to improve forest health have provided a source of income to many families, in turn, creating investments back to their villages, and justifying public support for government conservation initiatives.

There are hundreds of exotic, woody species naturalized in Hawaiʻi, with many considered to be problematic, invasive weeds impacting natural areas and forested watersheds. Among conservation groups, the active ingredient triclopyr (TCP) is the most relied upon herbicide selection for woody species control, with a basal bark application of a 25% v/v oil adjuvant blend being the most typical method. Anecdotally, the technique is mostly successful, but without calibrations to report on effective dose, supporting the observation that effective applications are mostly compensated by high doses. Field efficacy trials were initiated in 2011 to determine if other registered active ingredients including: aminopyralid (AMP), imazapyr (IMZ) and glyphosate (GLY), along with aminocyclopyrachlor (ACP); would prove to be more effective in measured doses. Thereby expanding the “palette” of herbicide options and encouraging an optimized approach to pesticide use. These treatments were administered via injection with metered doses of undiluted formulations. Starting in 2011, replicated efficacy trials have been administered to naturalized stands of thirty species, all from different genera. Size was a variable among experimental units with basal diameters ranging 10-30 cm (50th percentile). Dose volumes were consistent within treatment designs and ranged from 2-4 ml per target (50th percentile) across experiments. Performance was measured by recording defoliation over time. The treatments ACP, AMP and IMZ were consistently strong performers (>80% defoliation) effective on 85%, 45% and 61% of treated species, respectively, while GLY and TCP were only effective across 21% and 27% of species, respectively. Median effective doses for ACP, AMP and IMZ were 2.0, 2.3 and 2.2 mg ae cm-2 (acid equivalent applied to area of basal cross section), respectively, while GLY and TCP were effective at 5.7 and 5.3 mg ae cm-2, respectively, with noticeable efficacy reduction at 90% defoliation observed in 90% defoliation typically observed 150-200 DAT. Effective control was determined for 73% of the species tested, with 50% of those species having a single herbicide option superior to the other herbicides and multiple options becoming less frequent among species. Furthermore, all effective options (i.e., ACP, AMP and IMZ) superseded TCP using this low-dose injection technique. The injection technique is proving to be an effective, efficient and more hygienic alternative to woody species control in Hawaiʻi, where performance outcomes are improved with inclusion of a more diverse herbicide inventory.