Mesquite Treatment and Rangeland Restoration

One of the goals of the grassland restoration project is to return the segment of the San Simon riverbed at the Painted Pony Resort to open grassland, creating a seed reservoir, and this means removing mesquite.  The riverbed was over run with mesquite as a result of unmanaged cattle grazing.  Cattle are a major dispersal agent in the spread of mesquite, eating and passing seeds back onto the landscape where they germinate.  Originally confined to riparian areas, mesquite has spread across the landscape in modern times.  But it is not all bad, mesquite provide forage for cattle and other native browsers, habitat for nesting birds, and most importantly they fix nitrogen in addition to holding the soil.  Mesquite can be stubborn to remove since they produce deep tap roots and mechanically removed mesquite come back quickly requiring further treatment.  A backhoe or other device that will pull the taproot out is required to completely remove the plant and prevent regrowth.  Alternatively, herbicide treatment may be used after initial removal of the above ground portions of the plant.  But tests by others with a number of different herbicides show variable results with both application timing and herbicide compound being important variables.  Because of the variable results with different herbicides a 2 prong approach was chosen for herbicide treatment.  Glyphosate (the active chemical compound found in Roundup) is available off label at 40% concentration.   This is diluted to a final concentration of 2% (found in commercially available formulations) and combined with 2,4-D at a final concentration of 0.2%.  2,4-D is a plant hormone analogue while Glyphosate interrupts amino acid synthesis.  Once absorbed both herbicides work through different mechanisms interrupting plant growth and killing the reoccurring mesquite.  Below are photographs of a mechanically removed mesquite in the riverbed treated with this combination of herbicides.  Although effective some regrowth is noted requiring a second application to finish off the mesquite.

This combination of mechanical removal followed by herbicide treatment is returning the riverbed to an open grassland while maintaining a few large single stemmed mesquites for habitat and leaving mesquite along the margins and on the uplands to provide cover, soil stabilization, and nitrogen fixation this approach shows what may be accomplished with a minimal investment.  

Untreated, 2 weeks after mechanical removal

96 hrs post herbicide treatment

10 days post herbicide treatment, residual new growth will require a second treatment