Yellow flag iris invasion in South America: is biological control needed?

GERVAZONI, PAULA; SOSA, ALEJANDRO; COETZEE, JULIE; ORCASBERRO, GIANINA; FRANCESCHINI, CELESTE

Simposio; XVI International Symposium on Biological Control of Weeds; 2023

Iris pseudacorus L. is an invasive alien species, introduced from Europe to many other countries in the world, being classified as highly invasive in many of them. This species not only causes significant ecological damage, diminishing native flora and structurally modifying ecosystems, but can also invade urban and rural areas, generating big economic losses. Currently, there is an international alliance between countries from the native and introduced range aimed at testing the feasibility of classical biological control against this weed with the European candidate Aphthoha nonstriata. In South America, I. pseudacorus has been already detected and catalogued as invasive with mandatory control in Argentina and Uruguay, and recorded as naturalized in Chile. The first record was made 92 years ago in Argentina, and recent studies showed that it is present throughout a diversity of habitats, ecoregions, water conditions, and latitudes. Furthermore, studies of potential distribution predicted that the invasion could continue to expand in the territory. In Uruguay, numerous coastal sites are invaded, including protected areas, and recently, projects for researching and controlling this plant have been activated. Despite of the invasion, there are still no assessments of potential bio-controllers in these invaded countries, and little was known about the feasibility of management strategies. Through citizen science, field exploration, literature review, and interviews with park rangers, we studied the invasion and management alternatives against this weed with emphasis on biological control. We discovered a much higher level of invasion than previously recorded in Argentina, indicating the need to apply control. Different methods of mechanical removal and substitution are being applied in Argentina and Uruguay, and although they resulted positive for small infestations, they demand periodic effort, and resulted not feasible for large invasions. Although generalist herbivorous species have been detected feeding on the plant, our results suggest an absence of species with biocontrol potential for I. pseudacorus in Argentina. This information emphasizes the need to continue testing the feasibility of applying classical biocontrol with specific candidates from the native range of the plant that demonstrate specificity for I. pseudacorus, as well as the need to activate early prevention systems to avoid new introductions in susceptible areas