The exotic shrub red sesbania is an increasingly problematic weed in riparian and wetland ecosystems of California. Current control methods focus on manual removal, followed by herbicide application. Although this method effectively removes mature stands, the control is temporary because the presence of a large seed bank results in rapid germination and growth of new seedlings. We measured the density of seed banks beneath stands of varying densities and evaluated the potential of tarping and inundation for control of red sesbania seed banks. As expected, the abundance of viable red sesbania seeds in the soil was significantly greater beneath high-density stands than it was beneath low-density stands. Results for inundation and tarping experiments were mixed. Sustained inundation significantly decreased survivorship of germinated seeds compared with the control, as well as causing a statistically significant reduction in germination. Seven months after tarping, during the fall/winter growing season, there was no significant effect on red sesbania seedling abundance, stump resprout abundance, or height. Germination in the laboratory was significantly reduced by extended exposure to temperatures of 60 C, although lower temperatures did not reduce germination. Red sesbania appears to be resilient to tarping as a control method, at least in the settings studied.
Nomenclature: Red sesbania, Sesbania punicea (Cav.) Benth. SEBPU.
Management Implications: Inundation was the more-successful seed-bank control treatment studied because 2 mo of sustained inundation reduced Sesbania punicea seedling survivorship and caused a minor reduction in germination. However, this treatment did not eliminate the seed bank. It is possible that the surviving seeds and seedlings of S. punicea would be able to reestablish populations in inundated areas; thus, follow-up control methods may still be required. Whether the required duration of treatment is realistic in the field will depend upon the flood regime at potential sites and other management objectives, such as recreation and provision of wildlife habitat. Inundation would likely be most effective when S. punicea seedlings are small.
Tarping during the fall/winter growing season was not an effective control method for S. punicea. However, solarization (the practice of applying clear plastic film to maximize solar heating of the soil) could potentially be effective during hotter periods. Solarization during periods of average daily high temperatures warmer than 35 C could potentially achieve the 60 C soil temperatures we found were needed to reduce germination. Implementation of solarization is labor intensive, materials are expensive, and plastic sheeting must be monitored for holes, and patching performed if sheeting is damaged. Land managers will have to evaluate the labor costs of solarization compared with conventional biomass removal and herbicide treatments. Long-term control of S. punicea will be difficult because of its dense seed banks. Although complete eradication is unlikely, targeting small, isolated populations in the upstream portion of watersheds using conventional treatments may be the most-effective approach for minimizing downstream impacts.
