A recently completed study quantified the long-term effect of mesquite top-killing and root-killing herbicides (see Ansley et al. 2004). We found that the root-killing herbicide had a treatment life of over 20 years if herbaceous production was the criteria used to evaluate treatment longevity.
Use this link to see how mesquite appeared at 10 and 20 years after a root-killing and a top-killing herbicide treatment. We used a life-sized artificial cow made of plywood and a 3 meter tall pole to provide scale. The cow is the same distance away from the camera in each image. The root-kill treatment is not void of mesquite because recruitment of new plants is continuous. However, these plots are much more open even at 20 years post treatment, than are the 10 year old top-kill plots.
Use this link to view all herbicide publications
Spraying mesquite
photo by J. Ansley