2007 Annual Report 1a.Objectives (from AD-416) The objectives of this cooperative research are to. 1)understand the water use of Arundo donax in riparian areas of the Rio Grande Basin;. 2)determine in pre-release quarantine studies the potential impact of the candidate biological control agents on water use by A. donax; and . 3)use this information to select the agents with the greatest potential to decrease water use of A. donax in the Rio Grande Basin. 1b.Approach (from AD-416) Field and laboratory populations of A. donax will be studied to determine the water use by this invasive weed of the Rio Grande Basin. This research will be coupled with greenhouse studies of A. donax inside the quarantine containment facilities to determine the impact of the candidate biological control agents on water use. This ecohydrology research will include plant collection and processing, leaf gas exchange measurements, plot surveys and delineation, installing and maintaining groundwater wells. The work will be conducted at the USDA-ARS APHIS biological control quarantine facility on Moore Air Base in Edinburg, TX, and various field sites in the lower Rio Grande Valley and Brazos Valley. 3.Progress Report This report serves to document research conducted under a Sepcific Cooperative Agreement between ARS and Texas A&M University, Dept. of Rangeland Ecology. This research is integrated with objectives in the parent CRIS 6204-22000-019-00D, Biologically Based Management of Field and Greenhouse Crops. Invasive exotic plant species and other noxious weeds pose a huge and increasing threat to agriculture and native ecosystems throughout North America. In our region, which includes the Rio Grande River watershed, invasive weeds degrade the riparian environment and consume water resources in an arid region impacted by recurrent drought. Arundo donax L. is one of the most serious and widespread invasive weeds in the watershed, and a biological control program is needed because available chemical and mechanical control methods are not applicable over such a large area. The introduction of natural enemies from the origin of the A. donax (Mediterranean Europe) could be an effective solution, but these agents must be rigorously evaluated for both safety and efficacy. This project was initiated in FY 2007 to determine if the water use of A. donax is reduced following herbivory by the biological control agents. The research is being conducted in the greenhouse of the quarantine greenhouse facilities in TX where the candidate biological control agents are being screened prior to field release. Light conditions for A. donax were determined for the greenhouses and subsequently used to perform the experiments under highly controlled conditions. The studies have focused on leaf scale evapotranspiration of A. donax under attack by the stem-galling wasp Tetramesa romana. Future studies will compare water use with and without the Arundo scale, Rhizaspidotus donacis, and in combination with T. romana. Field studies were also initiated along the Rio Grande River where A. donax is highly invasive. High rainfall during the summer months of 2007 have prevented the accurate measurement of water use by A. donax, but no differences were observed within clones along a transect to the river. These field experiments will be repeated in 2008 on the Rio Grande and Brazos Rivers. The ADODR is in regular contact via email with cooperator.