The addition of surfactant (trimethylnonylpolyethoxyethanol) at 0.5% (v/v) of the spray solution caused a twofold increase in the deposit of clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) applied at 0.14 or 0.28 kg ae/ha on greenhouse-grown honey mesquite (Prosopis glandulosaTorr. # PRCJG) and increased transport into the plants compared to clopyralid applied alone. Application of equal rates of benazolin [4-chloro-2-oxo-3(2H)-benzothiazoleacetic acid] with clopyralid at 0.28 + 0.28 kg/ha enhanced transport of clopyralid into honey mesquite. Spray deposit, absorption, and translocation of clopyralid was unaffected by addition of 0.5% (v/v) of d'limonene (4-isopropenyl-1-methyl-cyclohexane). Greater spray deposit of clopyralid on plant surfaces after addition of surfactant was associated with reduced liquid surface tension and greater percentage of spray volume in small droplets (<204-μm diam).
The effects of droplet size and spray volume (spray-mixture application rate) on honey mesquite (Prosopis glandulosa Torr.) mortality were evaluated using 0.55 to 0.58 kg ae (acid equivalent) ha-' clopyralid (3,6 dichloro-2-pyridinecarboxylic acid). A factorial combination of 3 spray volumes (19,37, and 75 liters ha-') and droplet sizes of 325 f 25, 475 f 25, and 625 f 25 pm nominal D,, (volume median diameter) were replicated 3 times at both Andrews and Big Lake, Tex., during June 1989. The experiment was repeated in 1990 at Big Lake and Campbellton, Tex., without the 75 liters ha-' spray volume. Honey mesquite mortality and canopy reduction 16 months after application were significantly less on the 625 I.rm droplet treatments in 2 of 4 experiments, when compared to plots treated with smaller droplet sizes. Mortality increased with larger spray volumes, particularly with 625 pm droplets. Relative mortality data from the 4 experiments clearly demonstrated that larger droplet sizes require larger spray volumes for greatest efficacy.
Low pressure and reduced pressure fan and reduced pressure hollow cone nozzles were compared to conventional fan and hollow cone nozzles to determine their potential for reducing spray drift. Other comparisons included two different spray pressures for a low pressure fan nozzle, low and reduced pressure fan nozzles versus air-aspirating foam nozzles, low pressure versus reduced pressure fan nozzles, and reduced pressure hollow cone nozzles versus reduced pressure fan nozzles. Spray recoveries within 36 m downwind of the spray release point were significantly greater for the low pressure and reduced pressure fan and reduced pressure hollow cone nozzles than for the conventional fan and hollow cone nozzles. An air-aspirating nozzle producing spray without foaming adjuvant resulted in significantly greater spray recovery than a low pressure fan nozzle. The recovery from a reduced pressure fan nozzle having a rated flow of 12.6 cm3/s was significantly greater than that from a low pressure fan nozzle.
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