CONTROL OF HONEY MESQUITE WITH CLOPYRALID, TRICLOPYR, OR CLOPYRALID-TRICLOPYR MIXTURES

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 butoxyethlyl 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:triclopy mixtures at total rates of 0.07, 0.14, and 0.28 kg ae/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.