Simulated herbicide spray retention on floating aquatic plants as affected by carrier volume and adjuvant type

Abstract

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.

Simulated herbicide spray retention of commonly managed invasive emergent aquatic macrophytes

“…All experiments used rhodamine WT (RWT) dye (Rhodamine WT Liquid; Keystone Aniline Corp., Chicago, IL) to approximate herbicide deposition. Doing this cost considerably less money than quantifying herbicides analytically (Mudge et al 2021; Sperry et al 2022). Use of RWT to follow trace aqueous herbicide movement has been used in a variety of field environments for decades (e.g., Fox et al 1991, 1993, 2002).…”

“…Data were processed to account for differences in water volumes and pretreatment dye readings. The percentage of the applied spray solution that reached the water column was calculated following the methods described by Sperry et al (2022) and Mudge et al (2021) using the following formula: …”

Sethoxydim performance on torpedograss (Panicum repens) and sand cordgrass (Spartina bakeri) as affected by carrier volume and rate

“…Foliar aquatic herbicide applications are largely made via airboat using high carrier volumes (average 935 L ha −1 ) (Haller 2020). However, spray retention on the target plant can be low when using high carrier volumes (Sperry et al 2022), and recent research suggests that reducing carrier volume to 187 L ha −1 increases efficacy of glyphosate, diquat, and 2,4-D on the aquatic plant water hyacinth [ Eichhornia crassipes (Mart.) Solms] (Sperry and Ferrell 2021).…”

Low carrier volume herbicide trials and UAAS support management efforts of giant salvinia (Salvinia molesta): a case study

“…Limitations of high carrier volumes (e.g., 935 L ha −1 ) include reduced spray retention at low floating plant densities, thus resulting in spray loss to the water column (Mudge et al 2021), and reduced herbicide concentration per spray droplet (Knoche 1994). In general, herbicide applications made with lower carrier volumes are preferred because of time savings when filling spray tanks (Nelson et al 2007), public perception (Sperry and Ferrell 2021), increased spray retention on plant targets (Sperry et al 2022), and the increased performance of some herbicides on floating plant species (Nelson et al 2007; Sperry and Ferrell 2021; Van et al 1986). In a mesocosm study, Sartain and Mudge (2018a) evaluated winter herbicide applications on S. molesta and T. distichum using a carrier volume representative of an aerial application (94 L ha −1 ).…”

“…While this foliar application strategy has been successful with numerous herbicides and plant targets (Sperry and Ferrell 2021), there are associated hindrances that make “high” spray-volume applications undesirable for current management tactics. Research has established carrier volume directly affects spray deposition, herbicide activity, and ultimately aquatic plant control (Moreira et al 1999; Nelson et al 2007; Sperry and Ferrell 2021; Sperry et al 2022; Van et al 1986; Willard et al 1998). Limitations of high carrier volumes (e.g., 935 L ha– 1 ) include reduced spray retention at low floating plant densities, thus resulting in spray loss to the water column (Mudge et al 2021), and reduced herbicide concentration per spray droplet (Knoche 1994).…”