• Blue grama response to Zn source and rates

      White, E. M. (Society for Range Management, 1991-01-01)
      Surface-applied zinc (Zn) in range with claypan soils could increase herbage production, but the Zn concentration could become toxic to the crown and roots of blue grama (Bouteloua grucilis). Metallic Zn, ZnCl2, and Zn chelate were applied in the greenhouse to the soil surface of pots with blue grama to determine the rate that would be toxic and the effect of Zn source on toxicity and herbage Zn content. Metallic Zn (dust, 30- and 40-mesh) was not toxic at rates below 0.40 g Zn kg soil-1, but Zn chelate was toxic and ZnCl2 at the 0.40 g Zn rate was toxic initially. After 2 years growth, salt was leached and herbage yields were not significantly different for different sources. Herbage Zn increased with increasing application up to about 0.9 g Zn kg-1. ZnCI2, applied to plants that were not Zn deficient, decreased growth; and half the plants died at rates of 2 g Zn kg soil-1. Herbage from the 2-gm rate had 7.4 g Zn kg-1. DTPA-extracted soil Zn increased with increasing applications but not at the same rate for different sources. Metallic Zn or ZnCl2, if applied at reasonable rates, is a satisfactory Zn source, but high rates of Zn chelate cause soil dispersion initially and should not be used on soil that disperses readily.
    • Control of honey mesquite with clopyralid, triclopyr, or clopyralid:triclopyr mixtures

      Bovey, R. W.; Whisenant, S. G. (Society for Range Management, 1991-01-01)
      Greenhouse and field experiments were conducted to evaluate clopyralid formulations and triclopyr ester alone and in mixtures with clopyralid for control of honey mesquite. In the greenhouse, mixtures of the butoxyethyl ester of triclopyr enhanced the activity of the 2-ethylhexyl ester, the monoethanolamine salt and the free acid of clopyralid when applied in 1:1, 1:2 or 1:4 clopyralid:triclopyr mixtures at total rates of 0.07, 0.14, and 0.28 kg se/ha. The activity of triclopyr was not enhanced by addition of clopyralid. In the field, mixtures of the 1-decyl ester of clopyralid + the butoxyethyl ester of triclopyr were usually more effective than either herbicide applied alone. Addition of 0.14 kg/ha of triclopyr to clopyralid applied at 0.28 kg/ha markedly increased canopy reduction and mortality by at least 47% compared to either herbicide applied alone. Basal pours of diesel oil alone at 0.9 L/tree were usually as effective as diesel oil fortified with esters of clopyralid, 2,4,5-T or triclopyr at 4.8 or 9.6 g/L. Basal sprays of diesel oil + esters of clopyralid, 2,4,5-T or triclopyr in concentrations of 4.8 or 9.6 g/L applied at 0.5 L/tree caused high mortality of honey mesquite trees similar to basal pours. Triclopyr or clopyralid at 4.8 g/L were less effective in diesel oil:water carrier (1:4 or 1:3), respectively, than in diesel oil carrier.
    • Late season control of honey mesquite with clopyralid

      Jacoby, P. W.; Ansley, R. J.; Meadors, C. H. (Society for Range Management, 1991-01-01)
      Herbicides were applied aerially to honey mesquite (Prosopis glandulosa Torr.) in the Rolling Plains and Edwards Plateau land resource areas of Texas to evaluate efficacy during late season applications. Although other herbicides gave higher levels of above ground mortality, clopyralid caused higher whole plant mortality throughout the growing season than 2,4,5-T + picloram, both of which were ineffective when applied in September. Mixtures of clopyralid + picloram also were less effective when applied during later periods in the growing season, suggestiong picloram added little or even reduced the efficacy of clopyralid for late season control of honey mesquite. Triclopyr alone or in combination with picloram was ineffective in controlling honey mesquite in the fall. Clopyralid in the fall was most effective when applied at rates of 0.56 kg ha-1 or more. Dosage response of honey mesquite in late season applications (late August to October) was practically identical to that found for applications made in June and July, which indicates that clopyralid provides constant levels of mortality throughout the growing season. This research supports the practice of extending the season of applications with clopyralid into the fall. Applications in the fall might allow more rangeland to be treated for honey mesquite reduction and also reduce risks associated with drift damage to crops during their most susceptible periods of growth in early to mid-summer.