Influence of floating plant density on potential herbicide spray loss

Abstract

BACKGROUND Mesocosm experiments were conducted to evaluate the effect of floating plant density on over‐the‐top spray solution loss to the column using a tracer dye. Experiments quantified in‐water rhodamine water tracer (RWT) dye concentration after foliar treatment at 935 L ha−1 to waterhyacinth [Eichhornia crassipes (Mart.) Solms], waterlettuce (Pistia stratiotes L.) and giant salvinia (Salvinia molesta D.S. Mitchell) at 0, 25, 50 and 100% area covered (PAC). RESULTS As expected, spray loss to the water surface decreased with increasing plant density in all species. However, each species exhibited an unique relationship between density and percentage spray loss. The plant material required to result in 50% spray loss (ED50) was 32, 62 and 55 PAC for waterhyacinth, waterlettuce and giant salvinia, respectively. Greater ED50 estimates in waterlettuce and giant salvinia were attributed to plant architecture and leaf orientation compared to waterhyacinth, which grows more vertically and has a greater overall surface area to intercept and retain spray solution. However, when treated at 100 PAC, waterhyacinth and waterlettuce resulted in 20–25% spray loss, whereas giant salvinia resulted in only 10% loss. Consequently, giant salvinia exhibited a near 1:1 relationship between spray loss and PAC (slope = −0.93). CONCLUSION These data suggest that potential herbicide spray loss, as affected by plant density, is largely species‐specific and dependent on leaf morphology and plant architecture. Further research will confirm these findings under field conditions as well as to identify other parameters that might affect spray loss when treating floating and emergent plants. © 2021 Society of Chemical Industry. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Simulated herbicide spray retention of commonly managed invasive emergent aquatic macrophytes

“…Canopy cover and height were strongly correlated with percent spray retention for all broadleaf weeds (Table 3). These results are consistent with those of other studies that suggested canopy height and structure influence spray interception among floating plant species (Mudge et al 2021;Sperry et al 2022).…”

“…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).…”

“…To estimate uniformity in plant growth between replicates of the same species, biomass measurements for rooted species (shoot tissue above the soil level) and water hyacinth (shoot and root tissue) were collected (Table 1). Biomass was harvested at the conclusion of each experiment and was dried to a constant mass in an industrial drying room at 60 C for 48 h. Measurements of percent canopy coverage and canopy height were collected because other studies have found these parameters to affect spray retention (Don Wauchope and Street 1987; Mudge et al 2021). Canopy height was estimated by measuring the height above the water column of five random stems per replicate.…”

“…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: …”

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

“…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). 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).…”