A Summary of Studies Comparing Nozzle Types, Application Volumes, and Spray Pressures on Postemergence Weed Control Robert E. Wolf and Dallas E. Peterson, Kansas State University, Manhattan, KS Introduction Multiple field studies were conducted in Kansas, USA over several years to measure herbicide efficacy comparing various nozzle types (extended range flat-fans, turbo flat-fans, air induction/venturi flat-fans, variable rate flat-fans), application volumes (47, 94, and 187 L/ha), and spray pressures (ranging from 137 to 483 kPa) (Figure 1). Orifice sizes were selected to deliver desired application volumes at given pressures when application speeds were 9.6 km/h. Various plant species representing broadleaf and grass type weeds were treated with glyphosate and paraquat at sublethal herbicide rates to accentuate efficacy differences. Typically, ammonium sulfate at 2% w/w was added to the glyphosate treatments and NIS at 0.25% v/v was added to the paraquat treatments. Most applications occurred in hot/dry conditions. Figure 1. Nozzle types used in field studies. Discussion Findings from multiple field studies are reported for each experiment. Graph # 1 — In early oat control the TT was significantly better at 47 and slightly better at 187 L/ha. The AI exhibited significantly less control than the TT but not the XR at these volumes. Graph # 2 — In early oats the TT was significantly better than the AI with glyphosate, but only slightly better than the XR. The TT was also significantly better than the XR with paraquat, but was similar to slightly better than the AI. Graph # 3 — Using glyphosate in early oats, 47 L/ha was significantly better than 94 L/ha and 94 L/ha was significantly better than 187 L/ha. With paraquat 47 L/ha and 94 L/ha were significantly better for control than 187 L/ha. Graph # 4 — In early oats the TT and the AI were slightly better than the XR at 47 L/ha. The TT was slightly better than the AI and significantly better than the XR at 94 L/ha. The TT was significantly better than the AI and XR at 187 L/ha. Figure 2. Test species used in field studies. Table 1. Treatments by year (graph number). 2000 (1,2,3) 2000 (4,5) 2001 (6) 2002 (7,8) 2005 (9,10) 2006 (11,12) Nozzle Types* XR, TT, AI XR, TT, AI, DR TT, AM, AI, ULD TT, AM, ULD, TTI TT, AM, ULD, TTI, VT L/Ha 47, 94, 187 47, 94 94 kPa 276 173, 242, 345 207, 345, 483 276, 483 Species controlled Oats (15cm) Oats (15, 50 cm) Velvetleaf Common Sunflower Sorghum Corn Large Crabgrass Ivyleaf Morningglory Herbicides Glyphosate Paraquat * Nozzle manufacturers: XR, TT, AI, TTI – Spraying Systems; DR – Wilger; AM – Greenleaf; ULD – Hypro; VT - VariTarget Results Graph #2 a b d c c d Graph #3 LSD Nozzle = 7 a a a b a a b a b Graph #4 LSD = 4 b a b b a a Graph #5 Graph #1 Graph #6 Velvetleaf Sunflower Sorghum Corn b a a a Graph #7 Graph #8 Graph #9 ab bc a c b bc b c bc c c b Graph #10 LSD = 11 Graph #11 LSD = 7 LSD = 8 LSD = 9 ab a ab ab b a a b ab ab a a b ab b a a a a b Graph #12 Graph # 5 — In late oats the TT was significantly better than the XR and AI at 47 L/ha. The AI was significantly better than the XR and slightly better than the TT at 94 L/ha. The TT was significantly better than the XR and slightly better than the AI at 187 L. Graph # 6 — In early oats there were no significant differences at either volume. Using the XR and lower pressure (173 kPa) was slightly better at both volumes comparing all nozzle and pressure treatments. Graph # 7 — Venturi nozzles had slightly better control for all species tested. Only the velvetleaf control was significant with the TT measuring the poorest control of the nozzles compared. The broadleaf species were controlled better than the grass species. Graph # 8 — No differences were measured when comparing pressures for all species. Broadleaf species were better controlled than the grass species. Graph # 9 — With glyphosate no significant differences were found when comparing nozzle/pressure treatments on sorghum, corn, and common sunflower. For all species the velvetleaf control was the poorest. The TTI at 483 kPa was significantly better than the AM at 276 kPa. Graph # 10 — With paraquat significant differences were measured when comparing nozzle/pressure for each species. Broadleaf species control was much better than grass control. The ULD at 483 kPa had significantly higher control in velvetleaf and was slightly higher in common sunflower control. In the grass species significant differences were measured but with mixed results. Graph # 11 — When comparing nozzle types at 276 kPa significant differences were measured across all species. In large crabgrass control the TT was significantly less effective than the AM, ULD, and VT. For ivyleaf morningglory the AM had the best level of control and overall ivyleaf morningglory control was much lower than the other species. The TT and AM both resulted in slightly better control of velvetleaf. In sorghum the VT was significantly lower than all the other nozzle comparisons. In corn and common sunflower the ULD had the best control. Common sunflower control was the highest in all the species tested. In most all comparisons the VT exhibited the poorest control. Graph # 12 — When comparing nozzle types at 483 kPa significant differences were measured in four of the six species tested. Ivyleaf morningglory exhibited the lowest amount of control and common sunflower the best. In all these comparisons the AM and the TT performed well. The VT tended to have the poorest control. Control between the high and low pressure comparisons was similar for all species. Summary Summarized results indicate that weed control is not sacrificed while minimizing water requirements utilizing low spray volumes using venturi and chamber style nozzles that produce much larger droplet sizes with potentially less coverage than conventional flat-fan spray nozzles. It was also found that using higher pressure for air induction venturi-style nozzles improved coverage and efficacy potential while still minimizing drift potential when compared to conventional nozzles at lower pressures. Results also reflect improved efficacy with venturi style nozzles in the presence of higher temperature and lower humidity. This result is possibly due to the increased evaporation potential from the smaller droplet sizes associated with conventional nozzle types. There was very little measured difference in how the two herbicides responded to the different nozzle types and application variables. From these studies it is recommended that applicators should consider using drift reduction nozzle technology to make applications when conditions are conducive to spray drift. However, to achieve the best results it is recommended that venturi nozzle types be used at higher pressures to generate a droplet size consistent with improved coverage and minimized drift. Results may differ with application parameters outside the scope of this research.