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 -i-picloram was more effective in klllmg 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)f 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 et al. 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.
Water stress (LWP) was measured in honey mesquite, Prosopis glandu/osa var. glandulosa [Torr.], trees by using the pressure-chamber method to detect negative hydrostatic pressure in the xylem of leaf petioles. The method was sufficiently sensitive to measure shortterm changes of ± 1 bar LWP throughout the diurnal period. Mean differences between sun-exposed and shaded leaves averaged 4.7 bars LWP on a clear day in May. Although the mean LWP for five trees ranged from 15.8 to 18.1 bars LWP, the interaction of exposure and tree was relatively minor in comparison with the large diurnal differences in LWP. Diurnal changes in LWP, often greater than 20 bars, were associated with changes in the evaporative potential of the atmosphere. Total daily water stress CEL) and net daily water stress (~L -~L 0 ) were calculated by integrating the area under a curve formed by the periodic measurements of LWP during the diurnal period. Net daily water stress was more sensitive to changes in environmental variables than other daily summaries. Throughout the range of available soil moisture there was a close relationship between net daily water stress and the integrated evaporative potential on a daily basis.
Triethylamine salts of 4-amino-3,5,6-trichloropicolinic acid (picloram) plus (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) (1:1) sprays were more effective for the control of huisache(Acacia farnesiana(L.) Willd.) than for the control of Macartney rose(Rosa bracteataWendl.) at 13 dates of application in 1969 and 1970. Both species were more controlled effectively with the application rate of 1.12 than 0.56 kg/ha. Most effective control of huisache was obtained June 18, 1970, although other summer treatments in 1970 were effective. The herbicide was, on the average, more effective on huisache and Macartney rose when applied in the evening than morning or midday. Macartney rose was most effectively controlled by treatments applied in September and October of both years. Poorest control of the two species occurred when internal water stress was highest.
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