• 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.
    • Economic evaluation of spotted knapweed [Centaurea maculosa] control using picloram

      Griffith, D.; Lacey, J. R. (Society for Range Management, 1991-01-01)
      Spotted knapweed is the most serious range weed problem in western Montana. Although picloram is often used to control knapweed, the economic feasibility of the practice has not been evaluated. We developed a model to economically evaluate spotted knapweed control on rangeland. Model functions describing the dynamics of the plant community preceding and following treatment were derived from field observations in western Montana. Economic returns per management unit were calculated for 3 scenarios: (1) no treatment, (2) containment, and (3) eradication of spotted knapweed. After tax costs and benefits of treatments were analyzed for a 20-year period and discounted to the present. An economic loss in current dollars of 2.38/ha was incurred under the no treatment strategy when 25% of the management unit was initiaily infested with spotted knapweed and the weed was spreading to new acres and replacing desirable forage. After-tax present value of added AUMs in the eradication strategy was greater than the after-tax present value of added costs, 3.41/ha and l.99/ha, respectively. As site productivity, value of an AUM, and rate of knapweed spread to new acres increased, economic returns increased relative to treatment costs. In contrast, herbicide treatment became least cost-effective as knapweed utilization by livestock increased. Thus, economic feasibility of spotted knapweed control varied with economic and biologic conditions.
    • 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.