Mechanistic Aspects and Effects of Selected Tank-Mix Partners on Herbicidal Activity of a Novel Fatty Acid Ester

Abstract

Only a limited number of contact herbicides exist in agricultural production. Although systemic herbicides are also more efficient for suboptimum spray coverage with long-lasting weed control, contact herbicides provide several advantages. For example, there is no translocation to fruits, roots, and other crop parts and neither have residual activity nor minor risk for spray drift damage. Synthetic products in their use often imply toxicological or other drawbacks. Whereas, natural fatty acids, particularly pelargonic acid (PA), have contact activity and are safer for home and garden use. We recently described a methyl capped polyethylene glycol ester of pelargonic acid (PA-MPEG) as a novel contact herbicide. Both PA-MPEG and PA are applied at high rates per hectare to achieve excellent weed control. We herein report about potential additives to increase PA-MPEG efficacy. Herbicidal active, 1-decanol, and the non-phytotoxic alkylated seed oil-based adjuvant, HastenTM, improved performance by achieving better results than the PA benchmark. Both PA-MPEG and PA appear to mainly act by the disintegration of bio-membranes besides having effects on transpiration. The main suggested effect is desiccation due to cutting the water continuum at the site of evaporation in the intercellular spaces. The synergistic action of the adjuvant HastenTM and its practical uses are also discussed.

Contact herbicidal activity optimization of methyl capped polyethylene glycol ester of pelargonic acid

“…The maximum burndown effect was observed 2 days after application (Coleman and Penner 2008) with no significant differences in weed control even after 7 days, like in previous studies (Campos et al 2021(Campos et al , 2022. The efficacy of a single application of PA-MPEG at 12.8 kg ae ha −1 in a spray volume of 500 L ha −1 was higher than 80%, which could provide long-lasting weed control.…”

“…Cuticular transpiration rate does not have a vital role in PA-MPEG efficacy (Campos et al 2022), and stomatal transpiration measurement after application of the high rates of PA and PA-MPEG does not give a clear response. As mentioned above, the saturated atmosphere could reduce the transpiration by a decreased gradient of water potential and PA-MPEG and PA also via shortage in supply (flow) of water via cell walls.…”

“…For PA herbicides, the label recommendation is to apply during sunny days, but Dayan and Watson (2011) and Lederer et al (2004) reported that PA action was not light dependent. We think that light could also have a direct effect as transpiration, which is at least tenfold higher with open stomata, and imbalanced water loss is the main MoA of PA-MPEG and PA (Campos et al 2022). Weed control at constant light and relative humidity (55%) increased with temperature for both the monocot and dicot weed species (Fig.…”

“…It has been found in previous single droplet studies that locally high concentrations at the axil and similarly also on the leaf petiole or stem, respectively, showed higher damage (de Ruiter et al 1999) and caused the death of the leaf organ, even with low direct damage of the leaf blade (data not shown). We recently suggested that the effect of PA-MPEG and PA might be related to the interruption of capillary water flow in the apoplast in the presence of high amounts of the surfactant or acid and lipids from membrane disintegration (Campos et al 2022). Another effect could be a higher fraction of stomatal penetration into the leaf of the two weeds that are both amphistomatic.…”

“…The mechanism of action of PA is related to effective foliar uptake via the cuticle and erosion of surface waxes, and a moderate increase in cuticular transpiration can sometimes be observed (Ciriminna et al 2019). The main mode of action (MoA) is related to the release of lipids after membranes disintegration (Fukuda et al 2004;Lederer et al 2004), and it was recently suggested that tissue desiccation and ultimately leaf death are related to an interruption of water cohesion in the cell walls (Campos et al 2022) and thus the soil-plant-atmosphere continuum.…”