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On-Going Studies

The following is a sampling of on-going buffelgrass research. As these studies are completed, the information learned will be used to improve management and control in Southern Arizona.

Project Title: Buffelgrass (Pennisetum ciliare) Herbicide Trials

Researcher(s): Brock Habitat Restoration and Invasive Plant Management
Contact: John Brock, PO Box 25939; Tempe, Arizona; (480) 980-4802;

Abstract: Buffelgrass, a difficult to control invasive species found in Southern Arizona, can be killed with "Roundup" herbicide when it is applied to green foliage. However, effectiveness of other commercially available herbicides is not well documented. Buffelgrass growing on fallow agricultural land in Avra Valley about 13 miles south of Marana, AZ (now owned and managed by Tucson Water), was treated with several herbicides at a variety of application rates on August 20, 2008. Herbicides in this study were selected for their potential to control grasses and for the possibility of the chemical to control reinfestation of the plots by germinating seedlings. These plots will be monitored for buffelgrass control for at least 2 years to evaluate mortality of the initial stands and to assess reinvasion of the site from either new seeds or seeds in the on-site seed bank.

Project Title: Herbicide Efficacy at Different Buffelgrass Phenological Stages

Researcher(s): D. Backer, Saguaro National Park

Contact: Dana Backer, 3693 Old Spanish Trail, Tucson, Arizona; (520) 733-5153

Abstract: This project will assess the effectiveness of herbicides on established plants during three buffelgrass phenological stages. Because timing of herbicide application is important, herbicide mixtures consisting of different concentrations of active ingredient will be applied alone and in combination with adjuvants at each phenological stage. Three phenological stages identified include (1) first sign of green growth on new plants, (2) basal growth or regrowth of already established plants, and (3) early dormancy (<50% green biomass). A minimum of 50 plants per formulation type and phenological stage will be treated. Within 3-4 days of herbicide application, then every week throughout the remainder of the growing season, and again the following growing season, plants will be monitored for necrosis, resprouts, secondary branch growth, inflorescence emergence, and mortality. In the following growing season mortality, re-growth and the location of growth will be recorded. Seeds from all treated plants will be collected; the number of seeds collected will depend on whether seeds are produced on plants that are treated prior to flowering. Seed fascicles (defined in Ward 2006) will be grown out in germination plates to determine percent germination.

Project Title: Effectiveness and Application Time of Soil Residue Herbicide (Imazapic) on Buffelgrass Germination

Researcher(s): D. Backer, Saguaro National Park

Contact: Dana Backer, 3693 Old Spanish Trail, Tucson, Arizona; (520) 733-5153

Abstract: In order to determine whether a soil-residual herbicide is effective on buffelgrass and to test for native species tolerance, Plateau® will be applied as a pre-emergent to bare soil in areas previously infested with buffelgrass (cover >50%). Because precipitation, irrigation or tilling is needed to activate the herbicide and the viability of longevity for the product to be effective is dependent on soil type, soil microbes, temperature, sunlight, and other environmental conditions, the pre-emergent will be applied at four different times prior to the predicted start of the summer rains. Time of application includes 3 months (April), 2 months (May), and 1 month (June) prior to the average start of the monsoon for Tucson (July 3) and during the monsoon event (July). Following herbicide application, the number of buffelgrass and native plants that emerge will be monitored. Since the majority of desert species, particularly annuals, germinate during the cool season, mortality of existing native species will be observed.

Project Title: Seed Viability Following Herbicide Application

Researcher(s): D. Backer, Saguaro National Park

Contact: Dana Backer, 3693 Old Spanish Trail, Tucson, Arizona; (520) 733-5153

Abstract: The purpose of this study is to determine whether buffelgrass fascicles that developed on plants just prior to or just following treatment with a 3% formulation of glyphosate can germinate. Fascicles were collected in August and September of 2007 from a variety of plants on the south slope of Tanque Verde Ridge of Saguaro National Park. Four sets of ten fascicles per treatment date (5 different dates) were collected for a total of 120 fascicles. Fascicles will be tested at 6 months and 12 months post treatment.

Project Title: Using Remote Sensing to Map and Manage Buffelgrass Infestations in the Tucson and Santa Catalina Mountains

Researcher(s): University of Arizona (A. Olsson, S. Marsh) and Saguaro National Park (Daniels, D. Swann, and D. Backer)

Contact: Dana Backer, 3693 Old Spanish Trail, Tucson, Arizona; (520) 733-5153

Abstract: The use of ASTER satellite imagery in mapping buffelgrass infestations at a landscape, multi-jurisdictional level will be evaluated. ASTER imagery includes 6 shortwave infrared bands that can be used to help distinguish fractional parts of photosynthetic and non-photosynthetic vegetation. By spectrally unmixing pixels before and after the summer monsoon season, the unique signature of buffelgrass may be deduced. Using these techniques, the feasibility of mapping buffelgrass at a landscape level using the ASTER imagery will be determined. If this method proves successful at this scale, it should be possible to use this imagery through time so that agencies can monitor changes in the distribution and patch size of this species in specific areas. In addition, this landscape approach to mapping buffelgrass will help standardize buffelgrass data collection along with allowing multiple land management agencies to focus on data gaps in existing geodatabases which have traditionally relied solely on field collection methods.

Project Title: Impacts on Sonoran Desert Vegetation from Fires in Buffelgrass

Researcher(s): University of Arizona (C. McDonald, G. McPherson) and Saguaro National Park (P. Grissom)

Contact: Perry Grissom, 3693 Old Spanish Trail, Tucson, Arizona; (520) 733-5153

Abstract: The primary objective of this research is to learn more about fire impacts in buffelgrass-invaded native plant communities. Specifically, we hope to conduct experimental burning and measure properties of fire behavior in areas with significant amounts of buffelgrass. We will measure rate of fire spread, flame length, above-ground temperatures, and other parameters. We will also evaluate ecological impacts to native vegetation. We will measure or estimate survival of above-ground vegetation, seeds and seed banks, and biological soils. We will also sample fuel loading prior to experimental fires in the experimental burned area, as well as in unburned areas in Saguaro National Park so that we can develop models to predict fire impacts in buffelgrass-dominated areas of the park. Results will also provide important information about fire behavior for fire suppression personnel.