Influence of surfactant‐humectant adjuvants on physical properties, droplet size, and efficacy of glufosinate formulations

Abstract

Glufosinate efficacy is inconsistent among weed species and under environmental conditions that favor rapid droplet drying. Surfactant‐humectant adjuvants could maximize glufosinate efficacy by increasing wetting and penetration into the leaf surface while decreasing evaporation rate (ER). However, there is a lack of information in the literature about the interaction of surfactant‐humectants adjuvants with glufosinate. The objective of this study was to investigate the influence of surfactant‐humectant adjuvants on the physical properties, droplet size, and efficacy of two glufosinate formulations. Laboratory, greenhouse, and field studies were conducted at the Pesticide Application Technology Laboratory of the University of Nebraska‐Lincoln. Treatment design was a 2 × 5 factorial with two glufosinate formulations combined with five adjuvant treatments plus an untreated control. Density and viscosity of glufosinate solutions mostly increased with the addition of adjuvants. However, the influence of the adjuvants on dynamic surface tension (dST), static contact angle (sCA), and evaporation rate (ER) varied by glufosinate formulation, adjuvant, and relative humidity (RH). Under greenhouse conditions, an improvement in efficacy by adding adjuvants was mainly observed for Interline solutions. The addition of adjuvants to Interline solutions increased biomass reduction up to 19 and 35% for common lambsquarters (Chenopodium album L.) and kochia [Bassia scoparia (L.) A. J. Scott], respectively. Also, some of the adjuvants presented null or antagonistic influence on herbicide efficacy. No increase in control, biomass reduction, and mortality of horseweed (Erigeron canadensis L.) and Palmer amaranth (Amaranthus palmeri S. Watson) was observed with the use of adjuvants under field conditions. Herbicide‐adjuvant‐plant‐environment interaction is complex. Thus, the use of surfactant‐humectant adjuvants may not increase herbicide efficacy.

Biological, surface, and wetting behavior of bio‐surfactants tank‐mixed with trifloxysulfuron‐sodium on Sorghum halepense

“…Moreover, there is a positive relationship between the retention of spray droplets and the concentration of surfactant 48 . Therefore, the surfactants can increase spray retention on the leaf surface, causing an improved herbicide efficacy 21 . Second, the reduction in the surface tension of the spray solution due to the addition of surfactants reduces the contact angle of the droplet with the leaf surface (Table 1).…”

“…48 Therefore, the surfactants can increase spray retention on the leaf surface, causing an improved herbicide efficacy. 21 Second, the reduction in the surface tension of the spray solution due to the addition of surfactants reduces the contact angle of the droplet with the leaf surface (Table 1). This expands the wetted area of the leaf (Table 1), improving herbicide absorption and, subsequently, its efficacy.…”

“…Third, the crystalline wax in cuticles, mainly observed in grassy species, 18,19 is considered a barrier to herbicide absorption 20 . With a synthetic surfactant, it is well‐established that these problems are overcome when a suitable surfactant type and concentration are chosen to add to the spray solution 21–23 . So far, numerous bio‐surfactants have been discovered, 11 but only the compatibility of rhamnolipid has been checked with glyphosate.…”