Changes in Vegetation and Grazing Capacity following Honey Mesquite Control

Abstract

Honey mesquite kill and suppression, vegetation response, and changes in grazing use and capacity were evaluated following brush control in north-central Texas. Tree grubbing was most effective for eliminating honey mesquite, but because of soil and plant damage the treatment did not increase grazing capacity or improve range condition compared to nontreated rangeland. Aerial application of 2,4,5-T + picloram was more effective in killing and defoliating honey mesquite than 2,4,5-T alone, but both treatments significantly increased forage production. The 2,4,5-T + picloram and 2,4,5-T sprays provided a 7 to 16% increase in grazing capacity over a 4-year period on light and heavy honey mesquite infested pastures, respectively. Nearly 6 million hectares in the Rolling Plains of Texas are infested with woody plants of low forage value (Smith and Rechenthin 1969). Honey mesquite (Prosopis glandulosa Torr. var. glandulosa)l is the most abundant woody invader having increased in density over the past century with drought, overgrazing, and the cessation of natural fires (Fisher 1948, Bogoush 1951, Rechenthin and Smith 1967). Chemical and mechanical control of honey mesquite has been used extensively throughout the Rolling Plains with the objective of reducing the size and number of plants and to promote secondary succession (Fisher 1977, Scifres 1980). Thirty years of experience have shown that total eradication of honey mesquite is neither practical nor feasible. Several methods for controlling honey mesquite have been developed, however, and are widely used to maintain and increase forage production. Foliar applications of herbicides, such as 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), and 2,4,5-T plus 4-amino-3,5,6 trichloropicolinic acid (picloram), usually root-kill only 25 to 40% of the honey mesquite plants (Fisher et al. 1972). Plants not killed by the herbicides develop new stems from previously defoliated branches or from the root crown (Younget al. 1948, Scifres etal. 1974). Prolific sprouting from the root crown can result in a multi-stemmed, shrubby growth requiring retreatment in 4 to 7 years (Scifres and Hoffman 1974). Grass response following spraying is most significant under the honey mesquite canopy and over a period of years expands into interspace areas between the plants (Brock et al. 1979). Tree grubbing with a low energy crawler tractor equipped with a sharp, U-shaped blade attached to the front can eliminate over 90% of the honey mesquite by cutting roots 15 to 30 cm below the soil surface (McDaniel et al. 1978). Grasses growing beneath the canopy are often uprooted with the grubbed honey mesquite leaving a pit of bare exposed soil. Grubbing honey mesquite usually induces a lower seral stage of succession because of the disturbance of soil under the canopy area. The authors are assistant professor, Range Improvement Task Force, Department of Animal and Range Sciences, New Mexico State University, Las Cruces; assistant professor, Division of Agriculture, Arizona State University, Tempe; and principal application scientist-range science, EROS Data Center, Sioux Falls, South Dakota. The paper is published with approval of the Director, Texas Agr. Sta., as TA16819. Research reported in this paper was funded in part by a grant from the E. Paul and Helen Buck Waggoner Foundation, Inc. Manuscript received March 10, 1981. 'Scientific names follow Gould, F.W. 1975. Spraying honey mesquite is expected to give maximum increases in grazing capacity the first 3 years, whereas mechanical control may not yield a return until after 3 or 4 years (Workman et al. 1965, Dahl et al. 1978, Wiedeman et al. 1977). Following interviews with range trained personnel, Whitson and Scifres (1980) reported an annual rate of return from aerial applications of 2,4,5-T on honey mesquite in the Rolling Plains to be from 12.7 to 16.9% over a 20-year planning horizon. Five to 9 years are required to recover the initial investment of aerial application of 2,4,5-T on deep soils, and 12 to 13 years are required on shallow soils. Tree dozed or grubbed areas seeded to a native mixture of adapted species require nearly three times the number of years to yield a return on the original investment compared to spraying 2,4,5-T. The choice of which method to use for honey mesquite control is more complex than the treatment's ability to kill the plant or yield the greatest economic return. Environmental and management variables enter into the decision-making process making the choice of no single specific practice uniformly superior for every situation (Whitson and Scifres 1980). A brush control method which provides a favorable vegetation response and which allows an increase in red meat production is likely to be the preferred practice. The objective of this research was to evaluate changes in vegetation and grazing capacity following several different brush control techniques on light and heavy infested honey mesquite rangeland.