Determining the Rate of Mortality for Salt Cedar by Size and Age Class Resulting from Repeated Defoliation by the Biocontrol Agent _Diorhabda elongata deserticola_ to Increase Water Salvage along Rivers in the Western United States
* How quickly will the leaf beetle, _Diorhabda elongata deserticola_, kill various sized and aged salt cedar and how will the understory vegetation (grasses, shrubs, and forbs) respond in turn?
It is important to quantify how many defoliations must occur to kill various sized and aged salt cedar in order for biocontrol to be widely accepted and used as a salt cedar control method to increase water salvage. This research quantifies the effects of Diorhabda on vegetation using the *quantitative monitoring protocols* established by the Salt Cedar Biocontrol Consortium. Two data sets per summer have been collected from 2000-2004 and the data reside in an Access database. Although the leaf beetle was released in May 2001, substantial defoliation only began in late summer 2003. Response of understory vegetation is equally important in order to determine the extent of vegetation restoration that may or may not be required. These data also quantify the changes in weedy understory species, a control issue.
Need and Benefit
Various studies have demonstrated that salt cedar, commonly found along western streams, rivers, and reservoirs, uses between three and seven acre-feet of water per year. Biological control appears to be a sustainable, effective method for controlling salt cedar. The salt cedar biocontrol agent, _Diorhabda elongata deserticola_, as been released at eight controlled sites in the Western United States since May 2001. Populations adequate to defoliate individual salt cedars have only been in existence since August 2003. The extent and numbers of defoliations required to kill salt cedar will depend on the age, size, and overall health of individual salt cedars. Although existing research has demonstrated repeated defoliations must occur in order to kill salt cedar, demonstrated salt cedar mortality has not yet occurred at any of the eight orginal biocontrol sites. Several more years of streamlined qualitative and quantitative monitoring are necessary to determine the correlation between numbers of defoliations and resulting mortality of various sized and aged salt cedar. This mortality information is critical to encourage the widespread acceptance and use of biocontrol for salt cedar management and for increasing water availability. This information does not currently exist anywhere in the world.
This research will also quantify how quickly the remaining native grasses, forbs, and shrubs will recover once salt cedar is being controlled and will quantify the increase or decrease of other weedy groundcover species. This information is of great value as native vegetation recovery is the most desirable, least expensive vegetation restoration method and should be encouraged at every opportunity.
Bureau of Reclamation Review
The following documents were reviewed by experts in fields relating to this project's study and findings. The results were determined to be achieved using valid means.
Saltcedar Biocontrol at Pueblo, Colorado: Vegetation Monitoring Final Report (interim, PDF,
By Denise Hosler and Rebecca Siegle
Report completed on May 16, 2013