The potential of Melaleuca quinquenervia (Cav.) S.T. Blake to reinvade cleared areas was evaluated over a 13-yr period that included two wildfires and the introduction of biological control agents. The first wildfire occurred in 1998 and was followed by a mean of 591.5 recruited seedlings m−2. Recruits from that fire were cleared 7 yr later in July 2005 for a second experiment to evaluate seedling recruitment into cleared areas. Seed rain, seedling recruitment and mortality, and sapling growth rates were measured in four plots located around individual large reproductive trees. A second natural wildfire in 2007 burned through those plots, leading to increases in seed rain followed by a pulse in recruitment of 21.04 seedlings m−2, 96.5% fewer than after the 1998 fire. Recruits in half of the plots around each tree were then treated with regular applications of an insecticide to restrict herbivory by biological control agents, while herbivory was not restricted in the other half. There was no difference in seedling mortality between treatments 1,083 d post-fire (2007) with 96.6% seedling mortality in the unrestricted herbivory treatment and 89.4% mortality in the restricted herbivory treatment. Recruits subjected to the restricted herbivory treatment grew taller than those in the unrestricted herbivory treatment, 101.3 cm versus 37.4 cm. Many of the recruits were attacked by the biological control agents, which slowed their growth. Although solitary M. quinquenervia trees retain some capacity to reinvade areas under specific circumstances, there was a downward trend in their overall invasiveness at this site, with progressively smaller recruitment cohorts due to biological control agents. Land managers should prioritize removing large reproductive trees over treating recently recruited populations, which can be left for many years for the biological control agents to suppress before any additional treatment would be needed.

Invasive species negatively impact vegetation communities. Invasive European common reed [Phragmites australis (Cav.) Trin. ex Steud. ssp. australis] is rapidly spreading throughout North American wetlands. As such, the suppression of P. australis populations is a goal of many managers, as its removal should provide an opportunity to restore native vegetation communities. In Ontario, managers applied a glyphosate-based herbicide to more than 400 ha of P. australis in ecologically significant coastal marshes, representing the first time this tool was used over standing water to suppress an invasive species in Canada. Using a before–after–control–impact monitoring design, we evaluated the efficacy of glyphosate-based herbicide at removing P. australis along a water-depth gradient and assessed the recovery of the vegetation community for 2 yr after treatment in relation to reference conditions. We found that herbicide suppressed more than 99% of P. australis 1 yr after treatment and worked effectively along the entire water-depth gradient (10 to 48 cm). However, the post-treatment vegetation community remains distinctive from reference marsh 2 yr after treatment. In many plots where P. australis was removed, nonnative European frog-bit (Hydrocharis morsus-ranae L.) is now dominant, likely aided by high lake-water levels.

Strong competitive ability of introduced plant species has been frequently stated as a key factor promoting successful invasion. The dynamics of invasive species may depend on their abilities to compete for resources and exploit disturbances relative to native species. This study compares the growth performance of the invasive blackberry (Rubus niveus Thunb.) with four of the most common woody native species of the Scalesia forest in the Galapagos Islands. Using a series of greenhouse and field studies, the growth rate and biomass production of native species alone and in competition with R. niveus was compared under different water and light stress conditions. Rubus niveus showed a faster growth rate and biomass production than the native species as well as a broad tolerance to light and water stress conditions. Competitive ability was also assessed by looking at the seedbank and regeneration processes after herbicide control in the field. Although the number of R. niveus seedlings that germinated from the soil samples was considerably larger than that of native species, recruitment of the invasive on the experimental plots was limited. Overall, R. niveus showed superior competitive ability over native species with comparable growth forms, suggesting a possible mechanism that enables R. niveus to successfully invade a wide range of habitats in the Galapagos Islands. Implementing an integrated management strategy including biological control, seedbank reduction, and active revegetation, should improve the efficiency of R. niveus management, enabling the restoration of degraded vegetation in the Galapagos.

Mesocosm studies were conducted in 2020 to evaluate the effects of carrier volume and application method on waterhyacinth [Eichhornia crassipes (Mart.) Solms] response to 2,4-D, glyphosate, and diquat. Carrier volumes of 935, 467, and 187 L ha−1 were applied using either a conventional stream, conventional cone, adjustable cone, or a drizzle-stream spray pattern. Reducing carrier volume from 935 L ha−1 reduced spray coverage up to 60%, depending on application method. However, reducing carrier volume did not diminish efficacy of any herbicide or application method. Alternatively, E. crassipes control from 2,4-D increased 10% to 26% when applied using 187 L ha−1 compared with 935 L ha−1. Likewise, E. crassipes biomass was reduced 91% when 2,4-D was applied using 935 L ha−1; however, treatment applied at 187 L ha−1 resulted in 99% biomass reduction. In general, 2,4-D resulted in roughly 10% greater control when conventional or adjustable cone applications were used compared with either stream applications. Eichhornia crassipes control at 7 d after treatment (DAT) from diquat increased with decreasing carrier volumes; however, treatment effects in diquat experiments were not detected at other evaluation intervals. Glyphosate efficacy was highly influenced by carrier volume, as E. crassipes control increased up to 61% when applied using 187 L ha−1 compared with 935 L ha−1. Moreover, E. crassipes biomass reduction increased from 55% in the 935 L ha−1 treatment to 97% in the 187 L ha−1 treatments. Glyphosate application methods consisting of conventional stream or conventional cone sprayers resulted in slightly increased E. crassipes control by 28 DAT; however, no differences among application methods were observed in E. crassipes biomass data. These data support further evaluations of alternative application techniques for E. crassipes control under field conditions and for other herbicides and aquatic plant species.

Waterhyacinth [Eichhornia crassipes (Mart.) Solms] has been the focus of national legislation efforts and has been listed as noxious, invasive, potentially invasive, or prohibited by at least seven U.S. states. Auxinic herbicides are one of the most effective control methods labeled for use in aquatic sites. In the United States, florpyrauxifen-benzyl, a synthetic auxin, was recently (2018) registered for use in aquatic sites, but limited information has been published on efficacy, especially differences between the two formulations. Therefore, the purpose of this work was to evaluate two formulations of florpyrauxifen-benzyl—suspension concentrate (SC) and emulsifiable concentrate (EC)—at three rates each (14.8, 29.5, and 58.9 g ai ha−1) for control of E. crassipes under outdoor and greenhouse conditions. All rates of each florpyrauxifen-benzyl formulation reduced E. crassipes biomass by 90% to 100% when compared with nontreated plants at 5 wk after treatment. Based on plant recovery in the outdoor trial, there was some evidence that the lowest rate (14.8 g ai ha−1) of florpyrauxifen-benzyl SC and EC may not be as efficacious at reducing E. crassipes biomass as the SC and EC formulations when applied at 29.5 and 58.9 g ai ha−1. Future work should evaluate the florpyrauxifen-benzyl rates tested in this research against E. crassipes in field trials and/or an operational setting to confirm findings.