Co-penetration of Actives and Adjuvants and Its Significance for the Matched Pair Liaison

Abstract

Most formulants and adjuvants are low molecular weight solutes and can principally be sorbed in the surface lipids and deeper layers of the cuticle. This can have huge impact on the sorption potential of actives and their mobility in the rate limiting barrier of the cuticle. Factors like volatility, photostability, plant compatibility, selectivity, salt compatibility, rainfastness, speed of action, weed control, residual efficacy, the possibility of product combinations etc. depend often primarily on the relative absorption and penetration of active and adjuvant and their interaction. However, many factors affect the manifestation of these effects in practice like separation of active and adjuvant from the respective dispersion during evaporation, unmatched speed of penetration, or precipitation of active or adjuvant, respectively. Typically, adjuvants have several functions and -ignoring wetting effects in this contribution -they can act in the dry spray deposit as much as in the cuticle, for example they can solubilize actives in the former and mobilize them in the latter. For best results a timely and rate fit is needed, robust enough to withstand practical variability. Important commercial formulations show a perfect match of active(s) and adjuvant penetration or non-penetration, respectively. Examples on interactions among formulation or spray ingredients will be shown for a model compound and leaf cuticle system. On the

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

“…Other active substances are weak organic acids or form such acids from pre-drug esters that move both basipetally and acropetally through the plant (mobility in the phloem) [ 2 ]. In many cases, systemic soil-applied herbicides are only xylem mobile after root or hypocotyl uptake, and/or when sufficiently volatile to also distribute in the gas phase of soils [ 2 , 3 ]. Selective weed control by such systemic herbicides is based on several complex and sophisticated plant-herbicide interactions, such as herbicide-tolerant transgenic crops, combinations with safeners, timing of applications or tolerance by a higher biomass, or the quick growth compensation of damaged assimilation areas [ 1 , 2 , 4 , 5 , 6 ].…”

What makes a molecule a pre‐ or a post‐herbicide – how valuable are physicochemical parameters for their design?

“…Different methods were employed to understand the uptake process including osmotic measurements, studies on the impact of pH, staining with cationic and anionic dyes, radiolabeled tracer studies and here also measurement of the size selectivity of penetration 3,29,30,32,33 . Independent of the method, the ‘cut‐off’ size of these pores is below 1.5 nm.…”

“…Uptake of pre‐emergence herbicides into different dicot plant stages (designed by Aponte and Baur 3 ). …”

Impact of glyphosate formulations and adjuvants: effects on leaf interaction, metabolism, and control of sourgrass

“…In Brazil, many glyphosate formulations are commercially available, which differ in salt composition, active ingredient (AI) concentrations, and physicochemical nature. In addition, additives/ adjuvants are incorporated into formulations as inert ingredients (in-can adjuvants), fulfilling functions related to the stability of the formulations, the compatibility of the mix, and bio performance improvement (BAUR & APoNTE et al, 2014).…”

“…Surfactants with low ethylene oxide (Eo) content are known to readily penetration through the cuticle and facilitate IA uptake through the lipophilic pathways of this membrane (SToCK et al, 1992;SHI et al, 2005). Adjuvants with a high Eo content increase the permeability of hydrophilic solutes (LIU, 2004;BAUR & APoNTE 2014), mainly due to their humectant activity (ASMUS et al, 2016).…”