Management of an Invasive Ornamental: Suppression of Ruellia simplex (Mexican Petunia) by Native Species during Initial Establishment from Seed

Active revegetation with select native species may limit reinvasions, yet little is known about the critical stage of initial competition during revegetation with direct seeding efforts. Ruellia simplex (Mexican petunia) is a commonly planted ornamental known for establishing monotypic invasions along floodplains in the southeastern United States. As R. simplex continues to be planted in urban landscapes, propagule pressure to natural areas will persist; therefore techniques for control and management of R. simplex invasions are particularly urgent. We examined the role of initial competition during active revegetation between R. simplex and select native floodplain species: Andropogon glomeratus (bushy bluestem), Juncus effusus (soft rush), Panicum longifolium (redtop panicgrass), and Solidago fistulosa (pinebarren goldenrod). Our competition study consisted of a 2x2x3 experimental replacement design with diffferent hydrologic regimes, native species densities, and native species compositions (J. effusus + R. simplex, S. fistulosa + R. simplex, and a broad mix of native species + R. simplex), in controlled greenhouse conditions. Seedling establishment and survival were collected weekly for 24 weeks. Shoot height was collected biweekly for 24 weeks. Aboveground and belowground biomass were collected at the conclusion of the study at week 24. Solidago fistulosa and A. glomeratus established rapidly, initiating germination in week 2 and reaching maximum establishment in week 4. R. simplex similarly initiated germination in week 2, and reached maximum establishment in week 5. Perhaps as a result of the rapid establishment of these two native species, R. simplex was suppressed by S. fistulosa and the broad mix treatments by a reduction in survival and biomass. Ruellia simplex was not suppressed by J. effusus, which did not establish rapidly. No reduction in R. simplex shoot height was detected when grown with natives. Instead, R. simplex shoot height was affected by hydrologic conditions; shoot height was greater when grown in saturated conditions. Using the results from this study, we are currently conducting a field revegetation study to assess competition in the field and potential revegetation efforts with these native species. By selecting and testing logistically feasible revegetation strategies, we aim to address land managers’ needs and concerns for control and management, while generating restoration approaches for R. simplex invaded lands.