Effect of carrier volume and application method on waterhyacinth (Eichhornia crassipes) response to 2,4-D, glyphosate, and diquat

Abstract

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.

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

“…The data in this study suggest that aerial applications would promote greater spray retention and reduced spray loss relative to a standard highvolume hand-gun application. Furthermore, there is evidence of decreased carrier volumes resulting in increased efficacy of systemic herbicides in some aquatic species (Sperry and Ferrell 2021; Van et al 1986). It has been speculated that those herbicides in aquatics that possess in-water activity require a fraction of the intended herbicide rate to be absorbed by below-water structures; however, this theory has not been directly tested (Sperry and Ferrell 2021).…”

“…Furthermore, there is evidence of decreased carrier volumes resulting in increased efficacy of systemic herbicides in some aquatic species (Sperry and Ferrell 2021; Van et al 1986). It has been speculated that those herbicides in aquatics that possess in-water activity require a fraction of the intended herbicide rate to be absorbed by below-water structures; however, this theory has not been directly tested (Sperry and Ferrell 2021). For other herbicides that do not exhibit in-water activity, such as glyphosate or imazapyr (UF 2018), it is assumed that any spray solution that is not retained on above-water plant material does not contribute to plant uptake through the water column and, ultimately, to death.…”

“…This is likely due to concentrated herbicide spray solutions at lower carrier volumes, whereas more carrier (i.e., water) dilutes the herbicide and potentially increases runoff of spray solution. Previous research on carrier volume effects on herbicide efficacy for aquatic plant species has shown that decreased carrier volumes can increase efficacy, depending on the target species and herbicide being used (Van et al 1986;Willard et al 1998;Nelson et al 2007;Sperry and Ferrell 2021). Additionally, Van et al (1986) reported that glyphosate applications to waterhyacinth exhibited 33% greater spray retention at a carrier volume of 467 L ha −1 compared to 935 L ha −1 .…”

“…Because increased herbicide efficacy is one of the primary goals of aquatic weed management, factors like adjuvant type and carrier volume manipulation should be investigated to determine the role of these factors in improving control of floating and emergent species. Efficacy has been determined using various carrier volume trials on multiple aquatic plants ( Van et al 1986;Willard et al 1998;Nelson et al 2007;Sperry and Ferrell 2021), but to minimize spray deposition into the water column, further evaluations are required on specific growth habits of various floating plants. Therefore the objectives of these studies were to investigate (1) the effect of adjuvant type on spray retention in waterhyacinth and (2) the influence of carrier volume spray retention in waterhyacinth, waterlettuce, and giant salvinia.…”

Simulated Herbicide Spray Retention on Floating Aquatic Plants as Affected by Carrier Volume and Adjuvant Type

“…This is likely due to concentrated herbicide spray solutions at lower carrier volumes, whereas more carrier (i.e., water) dilutes the herbicide and potentially increases runoff of spray solution. Previous research on carrier volume effects on herbicide efficacy for aquatic plant species has shown that decreased carrier volumes can increase efficacy, depending on the target species and herbicide being used (Van et al 1986;Willard et al 1998;Nelsonetal.2007;Sperry and Ferrell 2021). Additionally, Van et al (1986) reported that glyphosate applications to waterhyacinth exhibited 33% greater spray retention at a carrier volume of 467 L ha −1 compared to 935 L ha −1 .…”