Description of the Project

Mesquite encroachment in the Altar Valley, 30 miles southwest of Tucson, has reduced historic grasslands and vegetation cover, causing increased erosion, soil loss, and high rates of sediment pollution downstream. The Altar Valley Conservation Alliance (AVCA) used the aerially applied herbicide, Sendero Plus Premix, to reduce mesquite densities on 2,000 acres of rangeland to promote the return of desert grassland, improve soil conservation, and reduce sediment discharge.

The goal is to reduce the density of mesquite on 2000 acres to a target level of 20% from current levels of approximately 50%-80% cover. The treated area will serve as a pilot test area for future treatments. Sendero is a foliar herbicide that enters mesquite through the leaves while becoming inactive on contact with soil, leaving no residual impacts on vegetation, livestock, or groundwater.

Crop Production Services, a licensed herbicide applicator, aerially applied the herbicide in June 2019, when conditions for Sendero treatment were effective (42-63 days after bud break on the mesquite, < 20% humidity, < 90° F air temperatures, > 75° F soil temperature at 12 inches, and < 7 mph wind speeds) sometime during May or June 2019.

There are limited but immediate impacts on annual forbs and several other species, including false mesquite (Calliandra eriophylla), but these species have been shown to not be killed and return with the immediately following monsoon storms and completely return by the following year. AVCA will work with the U.S. Fish and Wildlife Service (USFWS) to ensure that any Endangered Species Act compliances are met while working in endangered Pima pineapple cactus (Coryphantha scheeri var. robustispina) habitat.

Prior to treatment, AVCA, cooperating landowners, and / or contractors,  obtained the following permits and clearances:
• Arizona State Land Department Land Treatment permit for State Trust land by the lessees
• Arizona Department of Agriculture Permit (form 1080)
• Clearance from US Air Force for use of drones or helicopters in Military Operating Area (MOA)
• SHPO clearance (done via ADEQ program)

Monitoring mesquite densities in the fall pre- (2018), post- (2019), and one-year post-treatment (2020) will be conducted remotely by Quiet Creek Corporation and on the ground by AVCA.  Quiet Creek is a remote sensing and geospatial analysis contractor who will use repeat aerial photography along with National Agricultural Imagery Program data to create a Normalized Difference Vegetation Index (NDVI) orthomosaic.  AVCA staff and volunteers will conduct transects and photography points to observe cover of vegetation, soil, and live mesquite canopy. The ground-based data will be applied to the Rangeland Ecosystem Health Model to analyze the effects of the treatment on soil stability.