Megathyrsus maximus is nonnative in the neotropics, with a tall form that is commonly used as a forage grass and a smaller-statured form that is considered invasive in south Texas, USA. Biological control researchers are challenged to find an agent that will attack the short form, but not the desirable tall form in other parts of the neotropics. We conducted molecular analyses on 155 Megathyrsus maximus samples from its native range in Africa and compared them with U.S. short-form samples to help determine the geographic origins of its invasion. We found eight distinct genotypes in 34 short-form samples from Texas and Florida, USA. The highest genetic similarity of invasive samples was with plants from South Africa, while highest matches for the desirable tall form were from Kenya, Uganda, Ivory Coast, and Zambia. Ongoing biological control agent exploration and research has found agents from Kenya that are associated with an M. maximus genotype not well matched to the invasive short form, thus leading to a lack of rearing success. Two eriophyoid mite agents from the genetic match locality in South Africa have been evaluated but are not sufficiently host specific, as they develop on both the short and tall forms. Additional exploration is needed at the genetic match populations in South Africa to discover and evaluate potential biological control agents for the invasive form of M. maximus.

Downy brome (Bromus tectorum L.) is a highly invasive winter annual grass that can fill open niches in native plant communities. Prescribed burning is often used to control B. tectorum and can be combined with herbicide treatments to extend the duration of control and promote the native plant community. Several herbicides have been evaluated in conjunction with burning for B. tectorum control, although the herbicide indaziflam has not. In September 2017, two B. tectorum–infested sites were burned in Colorado foothill shrublands. In March 2018, indaziflam was applied alone or in combination with glyphosate, rimsulfuron, or imazapic. These treatments were compared with imazapic plus glyphosate as a standard. All treatments were made within burned and non-burned areas in a crossed-nested design. Bromus tectorum cover and the desirable plant community responses were evaluated 1 and 2 yr after treatment (YAT). In non-burned areas, all indaziflam treatments reduced B. tectorum cover compared with the control. In contrast, reductions from the imazapic treatments did not persist after the first year. Most post-burn treatments further decreased B. tectorum cover compared with the non-burned treatments. The most effective treatments (indaziflam 44 and 73 g ai ha^–1 + imazapic 123 g ae ha^–1) provided similar levels of control (<1% B. tectorum cover at 2 YAT), with or without burning. Desirable plant cover, richness, and diversity were not negatively impacted by burning or herbicide treatments. Plant diversity and species richness increased at Site 2 when burning was followed by indaziflam treatments. This study indicates that B. tectorum control using indaziflam can be enhanced when applied after burning, and the combinations with imazapic or rimsulfuron provide a wider application window compared with the combination with glyphosate.

Invasive woody perennials pose an immense threat to the diversity and function of many ecosystems, including forests in the eastern United States. While herbicide treatments have proven effective in controlling many plant invasions, there is considerable interest in the refinement of herbicide prescriptions to improve efficacy and prevent non-target damage. Adjuvants are widely utilized to improve herbicide efficacy, but research on novel adjuvants is often lacking. Furthermore, adjuvant research has generally focused on enhancement of foliar herbicide absorption, and few studies focus on adjuvant utility for other herbicide delivery techniques such as cut stump treatments. We evaluated 2XL—a cocktail of cellulase enzymes derived from fungi—as a potential herbicide adjuvant for use with glyphosate applied in a cut stump treatment due to its ability to degrade a key component of cell walls. We conducted a field experiment using the cut stump method of treatment (cut surface treated with herbicide) on a problematic invasive shrub, Amur honeysuckle [Lonicera maackii (Rupr.) Herder]. We tested combinations of three concentrations of 2XL with five concentrations of glyphosate and hypothesized that low concentrations of glyphosate combined with 2XL would be as effective in limiting the resprouting of L. maackii as higher concentrations of glyphosate without the enzymes. Our results indicated that 2XL did not improve glyphosate efficacy for reducing the number of resprouting stems or the length of the longest resprouting stem within the same or following year as treatment. Limited data indicated the combination of 2XL and glyphosate applied at 30 g L^–1 slightly increased resprouting in the year following treatment. While 2XL did not improve glyphosate efficacy, our results showed effective control of L. maackii at the lowest concentration of glyphosate tested (30 g L^–1), suggesting that concentrations lower than those typically applied may be effective in controlling L. maackii within parameters similar to those tested here.

Invasive plant species (IPS) management in national parks is a complex problem often characterized by the involvement of various organizations with different responsibilities, legal mandates, and jurisdictions. These institutional arrangements shape the structure, function, and decision-making behaviors of organizations and influence management effectiveness. Drawing on institutional theory, this study analyzed institutional arrangements and how these influenced IPS management in Vietnam's national parks. Data were collected between May and July 2017 using in-depth interviews with 39 key informants with responsibility for IPS management at different institutional levels (national, provincial, and local national parks). Results demonstrated that IPS management in Vietnam's national parks was characterized by centralized management with overlaps and gaps in vertical institutional relationships that limited the effectiveness of horizontal relationships. These characteristics resulted in a lack of clear guiding regulations and limited resources that restricted decision making and hindered implementation at the local national park level. The study highlights the need for a common set of principles across agencies, governed by an overarching body to promote constructive relationships across the vertical and horizontal institutional dimensions of IPS management.

Sulphur cinquefoil (Potentilla recta L.) is an invasive plant of concern within grasslands in western North America. To better understand the role of native plant communities and soil seedbank in P. recta invasion within grasslands, we conducted two greenhouse studies to examine (1) P. recta growth response when grown with and without fertilizer in established native plant communities of varying functional groups (grasses, forbs, or grasses and forbs), and (2) the prevalence of P. recta and other species in the soil seedbank at varying soil depths (0 to 5 cm, 5 to 10 cm, 10 to 15 cm) of grasslands invaded by P. recta in southeastern British Columbia, Canada. The growth response of P. recta did not differ between the native plant communities. However, P. recta above- and belowground biomass declined as native plant aboveground biomass increased, suggesting a productive plant community may be important to suppress P. recta. Fertilizer did not affect the growth response of P. recta or native plants, suggesting nutrients may not have been a dominant limiting factor under greenhouse conditions. Nine species were identified in the soil seedbank. Seven were nonnative, which included P. recta, and native species represented less than 2% of the seedbank. Of the average number of emerged nonnative seedlings, more than 20% were P. recta. The number of emerged P. recta seedlings was 69% lower at 10- to 15-cm compared with 0- to 5-cm soil depth, although the successful germination of P. recta at greater soil depths suggests viable P. recta seeds are persisting in the seedbank. Active revegetation may be an important strategy to mitigate P. recta reinvasion or secondary invasion by other invasive species from the soil seedbank.