Greenhouse experiments were conducted in 1989 at Stoneville, MS to evaluate the efficacy of fluridone and MSMA applied at 0.3 and 1.0 kg ai ha-1, respectively, either alone or in combination and with or without 0.1 M ammonium sulfate on purple nutsedge. The herbicides were applied at 19 L ha-1 in an oil-water, invert emulsion (low-volume) and at 187 L ha-1 in water with a nonionic surfactant (0.25% v/v) (high-volume). Purple nutsedge control with both herbicides alone or in combination was greater with the low-volume than with the high-volume application. Addition of MSMA to fluridone, or of ammonium sulfate to fluridone plus MSMA did not enhance purple nutsedge control over fluridone alone applied in low volume. The addition of ammonium sulfate to fluridone alone applied in low volume reduced purple nutsedge control.

Greenhouse studies were conducted to determine the influence of plant density and spray volume on the retention, spray deposition, efficacy, and translocation of the amine salt of triclopyr in purple loosestrife. More spray solution was retained on leaves at 935 Lha−1 than at 94 Lha−1 at populations of 0, 4, or 8 nontarget neighbors. Spray coverage decreased with decreasing height within the plant canopy when spray cards were placed in the top, middle, and soil surface adjacent to the central target plant. Within a population, spray card coverage generally increased as spray volume increased. Regrowth from the crown was affected by spray volume, and uniform spray coverage of the plant was required for adequate control of vegetative regrowth and was achieved with spray volumes of 374 and 935 L ha−1 spray volume. Regrowth of purple loosestrife was greater at 94 Lha−1 at all three plant populations indicating that less herbicide penetrated the canopy to reach the basal portion of the plant. A laboratory experiment was conducted to investigate the translocation of radiolabelled triclopyr to roots and crowns of purple loosestrife. Only 0.3 to 1.4% of absorbed 14C-labelled material was translocated to roots and crowns. Low spray volumes and dense stands of purple loosestrife would likely result in poor control because inadequate amounts of triclopyr reach the basal portion of the plant and translocate to vegetative propagules.

The importance of spray retention to the biocontrol of green foxtail with Pyricularia setariae was characterized using airbrush and broadcast sprayers at variable application volumes. Spray retention was determined by measuring amounts of a tracer dye solution on treated plants using fluorescence spectrophotometry. Depending on the droplet size, broadcast spraying at 1,000 to 2,000 L/ha produced a level of retention equivalent to that of airbrush spraying until runoff. The trend of P. setariae spore retention on green foxtail was similar to that of liquid retention. Broadcasting P. setariae at volumes producing equivalent spray retention to that of airbrush inoculation resulted in a similar level of weed control under greenhouse conditions. Reducing broadcast volume from 2,000 to 250 L/ha lowered biocontrol efficacy only slightly, when the concentration of P. setariae was increased proportionally to keep the applied fungal dose the same. A nozzle with a fine droplet spectrum (volume median diameter [VMD] 207 μm) had a significantly greater retention efficiency than a coarse spray (VMD 325 μm), but this retention difference was not translated into consistent enhancement of biocontrol efficacy. Higher retention increases may be necessary for more substantial improvement in biocontrol of green foxtail by P. setariae.

The influence of three simulated dew levels and 150, 300, and 450 L/ha spray volume on glyphosate control of oat plants was determined from pot experiments. Results showed that the effect of dew level on glyphosate efficacy was related to application volume. Glyphosate efficacy at the low and medium application volume (150 and 300 L/ha) was not affected by dew level. However, glyphosate efficacy decreased when applied at the high spray volume (450 L/ha), regardless of dew level. However, high dew level reduced efficacy only when glyphosate was applied at 450 L/ha.