A field study was conducted in 2015 and 2016 to compare particle drift of glyphosate using a fluorescent tracer dye applied with hooded and open sprayers at four spray qualities (Fine [F], Medium [M], Very-Coarse [VC], and Ultra-Coarse [UC]). F and M spray qualities exhibited up to 86% and 56% less drift, respectively, out to 31 m downwind with the hooded sprayer than with the open sprayer. Conversely, VC and UC spray qualities were not affected by sprayer type out to 31 m downwind. From 43 to 104 m downwind, hooded sprayer applications exhibited approximately 50% less drift than open sprayer applications, regardless of spray quality. From 43 to 89 m downwind, F spray qualities, regardless of sprayer type, exhibited higher drift than all other spray qualities. These data indicate that hooded sprayers considerably reduce drift of all spray qualities at short distances downwind. Additionally, at longer distances downwind, both larger spray qualities and sprayer hoods reduced drift independently.

Two experiments were conducted in 2013 and 2014 in Florida to evaluate the effects of protoporphyrinogen oxidase (PPO)-inhibiting herbicides and single versus sequential applications on Palmer amaranth control and peanut injury. Protoporphyrinogen oxidase-inhibiting herbicides are among the last available herbicides for the POST control of acetolactate synthase (ALS)-resistant Palmer amaranth in peanut. Lactofen (219 g ai ha -1 ) applied 5 d after the initial application provided the highest level of Palmer amaranth control 7 and 14 d after initial application (DAIT). Delaying sequential applications of lactofen to 15 d resulted in the highest level of Palmer amaranth control 21 and 28 DAIT. Similar to Palmer amaranth control, foliar injury to peanut was often highest from lactofen applications, and by 28 DAIT lactofen treatments were the only treatments that caused foliar injury. Although no statistical difference was observed between yields of plots treated with acifluorfen (280 g ai ha -1 ), bentazon (560 g ai ha -1 ), 2,4-DB (280 g ae ha) alone or in combination with each other, plots treated with sequential applications of lactofen 5 or 15 DAIT produced the lowest yields. Sequential applications of lactofen applied 15 DAIT controlled Palmer amaranth more effectively than any other treatment but also caused the highest level of peanut injury. The use of sequential applications of lactofen was the most effective method for control of Palmer amaranth in this study, but did reduce peanut yield. Nomenclature: acifluorfen; bentazon; lactofen; 2,4-DB; Palmer amaranth, Amaranthus palmeri S. Wats.; peanut, Arachis hypogaea L. Key words: ALS-resistant Palmer amaranth, sequential applications, crop injury.En 2013 y 2014 se realizaron dos experimentos en Florida para evaluar los efectos de los herbicidas inhibidores de protoporphyrinogen oxidase (PPO) y aplicaciones sencillas versus secuenciales sobre el control de Amaranthus palmeri y el daño al maní. Los herbicidas inhibidores de protoporphyrinogen oxidase están entre los últimos herbicidas disponibles para el control POST de A. palmeri resistente a herbicidas inhibidores de acetolactate synthase (ALS) en maní. Lactofen (219 g ai ha −1 ) aplicado 5 d después de la aplicación inicial (DAIT) brindó el mayor nivel de control de A. palmeri 7 y 14 DAIT. El retrasar las aplicaciones secuenciales de lactofen a 15 d resultó en el mayor nivel de control de A. palmeri 21 a 28 DAIT. Similarmente al control de A. palmeri, el daño foliar en el maní fue frecuentemente más alto con aplicaciones de lactofen, y a 28 DAIT los tratamientos con lactofen fueron los únicos que causaron daño foliar. Aunque no se observaron diferencias estadísticas entre los rendimientos de las parcelas tratadas con acifluorfen (280 g ai ha ) solos o en combinaciones entre ellos, las parcelas tratadas con aplicaciones secuenciales de lactofen 5 ó 15 DAIT produjeron los menores rendimientos. Las aplicaciones secuenciales de lactofen aplicado 15 DAIT controlaron A. palmeri más efectivamente que cualquier otro...

Field experiments were conducted in 2012 and 2013 across four locations for a total of 6 site-years in the midsouthern United States to determine the effect of growth stage at exposure on soybean sensitivity to sublethal rates of dicamba (8.8 g ae ha−1) and 2,4-D (140 g ae ha−1). Regression analysis revealed that soybean was most susceptible to injury from 2,4-D when exposed between 413 and 1,391 accumulated growing degree days (GDD) from planting, approximately between V1 and R2 growth stages. In terms of terminal plant height, soybean was most susceptible to 2,4-D between 448 and 1,719 GDD, or from V1 to R4. However, maximum susceptibility to 2,4-D was only between 624 and 1,001 GDD or from V3 to V5 for yield loss. As expected, soybean was sensitive to dicamba for longer spans of time, ranging from 0 to 1,162 GDD for visible injury or from emergence to R2. Likewise, soybean height was most affected when dicamba exposure occurred between 847 and 1,276 GDD or from V4 to R2. Regarding grain yield, soybean was most susceptible to dicamba between 820 and 1,339 GDD or from V4 to R2. Consequently, these data indicate that soybean response to 2,4-D and dicamba can be variable within vegetative or reproductive growth stages; therefore, specific growth stage at the time of exposure should be considered when evaluating injury from off-target movement. In addition, application of dicamba near susceptible soybean within the V4 to R2 growth stages should be avoided because this is the time of maximum susceptibility. Research regarding soybean sensitivity to 2,4-D and dicamba should focus on multiple exposure times and also avoid generalizing growth stages to vegetative or reproductive.

Mesocosm studies were conducted in 2020 to evaluate the effects of carrier volume and application method on waterhyacinth response to 2,4-D, glyphosate, and diquat. Carrier volumes of 935, 467, and 187 L ha-1 were applied using either a conventional stream, conventional cone, adjustable cone, or a drizzle stream spray pattern. Reducing carrier volume from 935 L ha-1 reduced spray coverage up to 60% depending on application method. However, reducing carrier volume did not diminish efficacy of any herbicide or application method. Alternatively, waterhyacinth control from 2,4-D increased 10 to 26% when applied using 187 L ha-1 compared to 935 L ha-1. Likewise, waterhyacinth biomass was reduced 91% when 2,4-D was applied using 935 L ha-1; however, treatment applied at 187 L ha-1 resulted in 99% biomass reduction. In general, 2,4-D resulted in roughly 10% greater control when conventional or adjustable cone applications were used compared to either stream applications. Waterhyacinth control 7 days after treatment (DAT) from diquat increased with decreasing carrier volumes; however, treatment effects in diquat experiments were not detected at other evaluation intervals. Glyphosate efficacy was highly influenced by carrier volume as waterhyacinth control increased up to 61% when applied using 187 L ha-1 compared to 935 L ha-1. Moreover, waterhyacinth biomass reduction increased from 55% in 935 L ha-1 treatment to 97% in 187 L ha-1 treatments. Glyphosate application methods consisting of conventional stream or conventional cone sprayers resulted in slightly increased waterhyacinth control by 28 DAT; however, no differences among application methods were observed in waterhyacinth biomass data. These data support further evaluations of alternative application techniques for waterhyacinth control under field conditions as well as other herbicides and aquatic plant species.

Foliar delivery of herbicides is a common means for plant management in aquatic environments. Though this technique is decades old, little is known about vegetative spray retention relative to this application method. A more complete understanding of maximizing herbicide retention could lead to improved plant management while simultaneously decreasing pesticide load in aquatic environments. Therefore, outdoor mesocosm experiments were conducted in 2020 to evaluate the effect of adjuvant type on foliar spray retention in waterhyacinth. Additionally, the effect of carrier volume on spray retention in waterhyacinth, waterlettuce, and giant salvinia was documented. Spray deposition did not differ among the nine adjuvants tested; however, spray retention was reduced 6 to 11% when an adjuvant was excluded from the spray solution. The effect of carrier volume on spray retention in waterhyacinth, waterlettuce, and giant salvinia was also investigated. Decreases in spray retention was most sensitive to increased carrier volume in waterhyacinth, followed by giant salvinia and waterlettuce. Among species, spray retention potential, as determined by intercept estimates, was greatest in waterlettuce and giant salvinia regardless of carrier volume. Asymptotes estimates for waterhyacinth, waterlettuce, and giant salvinia were 33, 46, and 79% spray retention, respectively. In other words, spray retention was the lowest and remained relatively constant at these values for the high carrier volumes tested (935 and 1870 L ha−1), which were likely due to the presence of pubescence on leaves and flatter leaf architecture represented by waterlettuce and giant salvinia compared to the glabrous vertical leaves of waterhyacinth. Future research will evaluate these concepts under field conditions.