Herbicide applications often do not reach their full potential because only a small amount of the active ingredients reaches the intended targets. Selecting the appropriate application parameters and equipment can allow for improved efficacy. The objective of this research was to evaluate the effect of droplet size on efficacy of six commonly used herbicides. Atrazine (1.12 kg ai ha−1), cloransulam-methyl (0.18 g ai ha−1), dicamba (0.14 kg ae ha−1), glufosinate (0.59 kg ai ha−1), saflufenacil (12.48 g ai ha−1), and 2,4-D (0.20 kg ae ha−1) were applied to seven plant species using an XR11003 nozzle at 138, 276, and 414 kPa and a AI11003 nozzle at 207, 345, and 483 kPa. Each herbicide, nozzle, and pressure combination was evaluated for droplet size spectra. Treatments were applied at 131 L ha−1to common lambsquarters, common sunflower, shattercane, soybean, tomato, velvetleaf, and volunteer corn. Control from 2,4-D was observed to increase approximately 12% on average for all species except common lambsquarters as droplet size increased from medium to very coarse (Dv0.5303 to 462 μm;Dv0.5is droplet size such that 50% of spray volume is contained in droplets of equal or smaller size). Control with atrazine was near 95% for common lambsquarters, common sunflower, and soybean. Atrazine provided the greatest shattercane control using a medium (Dv0.5325 μm) droplet, whereas the same droplet size provided the lowest tomato control. Control of common lambsquarters, shattercane, and tomato with cloransulam-methyl increased 79% when decreasing droplet size from extremely coarse to fine (Dv0.5637 to 228 μm). Dicamba control of common lambsquarters increased 17% using a medium droplet compared with a fine droplet (Dv0.5279 to 204 μm). Dry weight of common sunflower and soybean was reduced 21% using dicamba when using a very coarse spray compared with a fine spray classification (Dv0.5491 to 204 μm). Common lambsquarters control using glufosinate increased 18% using a fine spray classification (Dv0.5186 μm) compared with medium (Dv0.5250 μm) and both very coarse droplet sizes (Dv0.5470 and 516 μm). Conversely, tomato and velvetleaf control with glufosinate was maximized using a very coarse (Dv0.5470 and 516 μm) or extremely coarse droplet (Dv0.5628 μm) with increases of 11 and 25% compared with a fine spray (Dv0.5186 μm). Saflufenacil control of volunteer corn was 38% greater using extremely coarse droplets (Dv0.5622 μm) than fine, medium, and very coarse spray classifications (Dv0.5257 to 514 μm). Overall, spray classifications for the herbicides evaluated play an important role in herbicide efficacy and should be tailored to the herbicide being used and the targeted weed species.

PPO-inhibiting herbicides in combination with glyphosate for postemergence applications is a common approach to manage glyphosate- and ALS-inhibitor-resistant weeds. PPO-inhibitors can reduce glyphosate translocation when applied in tank-mixtures, but adjuvants may be used to overcome this effect. Additionally, optimal droplet size may be affected by tank-mixtures of different herbicides and it can be crucial to herbicide efficacy. Field and greenhouse studies were conducted to investigate the impact of nozzle selection and adjuvants on weed control and interactions when applying PPO-inhibitors (fomesafen or lactofen) alone or in tank-mixture with glyphosate to five weed species using six nozzle types. Ultra-coarse droplets were just as effective as medium droplets regardless of the spray solution, but have a lower likelihood of off-target movement. Tank-mixtures applied were consistently antagonistic to common lambsquarters, horseweed, and Palmer amaranth. Only fomesafen was antagonistic to kochia whereas synergistic interactions were observed when glyphosate plus lactofen were applied in combination with COC, DRA + COC, or NIS. Separate applications are advisable with herbicide- and weed-specific situations to avoid antagonism, which is necessary to achieve optimum weed control and maintain the effectiveness of PPO-inhibitors. Future research should continue to look at these important interactions across a wide range of weed species.

Concern about pesticide drift has increased dramatically in recent years. An emphasis on increasing spray droplet size to mitigate off-target particle movement has occurred in response to this concern. Venturi nozzles were designed to create coarser droplets by entraining air within the spray solution in the nozzle body. In field applications, dirt, fertilizer, and other debris can plug air-inclusion ports. The objective of our research was to identify the impact of plugged air-inclusion ports on the droplet-size distribution of multiple venturi nozzles. The study was conducted using the low-speed wind tunnel at the Pesticide Application Technology Laboratory in North Platte, NE. Droplet-size distributions for five venturi nozzles and two orifice sizes (Air Induction [AI11004 and AI11006], Air Induction Extended Range [AIXR11004 and AIXR11006], Turbo TeeJet Induction [TTI11004 and TTI11006], Turbo Drop [TDXL11004 and TDXL11006], and Ultra Lo-Drift [ULD12004 and ULD12006]) were measured in combination with plugged or unobstructed air-inclusion ports, providing 28 total treatments. Measurements were made using a Sympatec HELOS-VARIO/KR laser diffraction system while testing water sprayed at 276 kPa. Similar patterns in droplet-size distribution within nozzles were observed across orifice sizes. When air-inclusion ports were plugged, the Dv0.1, Dv0.5, and Dv0.9 decreased for the AI and TDXL nozzles, remained relatively unchanged for the AIXR and ULD nozzles, and increased for the TTI nozzle. In addition, the percentage of fines less than 150 µm increased for the AI and TDXL nozzles, remained relatively unchanged for the AIXR and ULD nozzles, and decreased for the TTI nozzle when air-inclusion ports were plugged. This research helps to better understand the drift mitigation implications if debris were to plug venturi nozzle air-inclusion ports.

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The objectives of this study were to (a) investigate the spray drift potential of dicamba (3,6‐dichloro‐2‐methoxybenzoic acid) formulations with different nozzles in a low‐speed wind tunnel and (b) evaluate the effects of sublethal rates of dicamba‐containing formulations on non–dicamba‐tolerant (DT) soybean [Glycine max (L.) Merr.] cultivars. The dicamba formulations used were diglycolamine (DGA), N,N‐Bis‐(3‐aminopropyl)methylamine, and diglycolamine with VaporGrip (DGAvg). The wind tunnel drift study was conducted with these three dicamba formulations, two nozzle types (AIXR110015 and TTI110015), and five downwind distances from the nozzle (1, 2, 4, 8, and 12 m). The dicamba rate was 560 g ae ha−1, simulating a 140 L ha−1 carrier volume. The soybean exposure study was conducted in two experimental runs with three sublethal dicamba rates (0.112, 0.56, and 5.6 g ae ha−1), the three dicamba formulations aforementioned, and five non‐DT soybean cultivars (Asgrow A3253, Asgrow AG2636, Credenz CZ2601LL, DynaGro 39RY25, and Hoegemeyer 2511NRR). Applications were made using a spray chamber with a single AI9502EVS even nozzle that delivered 140 L ha−1. During applications, soybean plants were at three‐leaf growth stage. Dicamba formulations had different drift deposition across the AIXR and TTI nozzles. The soybean cultivars had different levels of sensitivity to dicamba and depended on rate vs. formulation interaction. The DGA caused greater biomass reduction on soybean cultivars compared with DGAvg, especially for Credenz CZ2601LL, which was one of the most dicamba‐sensitive cultivars along with Hoegemeyer 2511NRR. Additional care must be taken to mitigate off‐target movement from dicamba applications with these cultivars nearby.