The Dry Creek Red Sesbania Control Program maintenance phase, initiated in 2007, continued in 2010 with two control sweeps of the watershed in July and October. A monitoring visit was conducted in July before the first sweep and in October after the last sweep was complete. The October monitoring visit indicated that less than 1% of the Sesbania population remained. Therefore, the 2010 program met its success criterion. A comparison of 2008, 2009 and 2010 monitoring results and control data is presented. Additionally, maps prepared as part of a statewide Sesbania mapping project, which include Dry Creek locations, are included.
The 2010 treatment year was successful in removing 99% of the germinated Sesbania plants. The contractor also removed all visible Sesbania pods from the floodway, preventing future germination of those seeds. Since the project started in 2004 the focus has been on removal of upstream seed producing Sesbania plants, and given the reduction in seed production each year (i.e., all seed pods removed), the seedbank should continue to decline over time. While results this year are promising, treatments must continue until the population is reduced to low levels. The size of the Dry Creek Sesbania population increased with the heavy rainfall in 2006 due to high water flows bringing seeds from low-flow channel sediments up onto the upper floodplain where they germinated far from the channel. Therefore the level of treatment effort needed in high rainfall years is expected to increase. The comparison of three years of monitoring in Table 3 shows that the number of seedlings of Sesbania germinating per meter remains high, especially in the lower parts of the watershed. It appears from the Agri Chemical information in Table 4 that the amount of herbicide needed to treat plants is decreasing. Since the number of operator hours needed is still high, this may indicate that the number of plants sprayed is lower, because it takes the same amount of time to access the plants given the long river distances included in the treatment area.
Progress was made this year in compiling all the Agri Chemical GIS data into one database. This will be useful in the future as it shows areas within the watershed where the Sesbania infestation is heavier and those areas can be the focus of future control efforts.
Finally, the Dry Creek Sesbania data was added to a state-wide Sesbania map prepared by ICF in summer 2010 (Appendix F). The mapping effort compiled all known Sesbania locations and then re-mapped and collected percent cover information for accessible locations. Dry Creek was shown to be one of the most dense infestations in the state, and appears to be a major source of the seed contribution from the Sacramento area which is expanding downstream into the San Joaquin Delta. Other areas of the state with dense infestations were Churn Creek in Shasta County, Oroville area and downstream into the Feather River, and the San Joaquin River in Fresno County. The Sacramento and Placer County Dry Creek Sesbania management program is the largest in the state and could serve as a model for other areas in need of a regional management strategy.
Contents of Report
- Results and Discussion
Download the 2010 Dry Creek Red Sesbania Control Program Monitoring Report [PDF*, .4 MB]
Note: Appendices have been omitted from the PDF version.