Hygroscopic salts support the stomatal penetration of glyphosate and influence its biological efficacy. Issue 3 (9th May 2014)

• Record Type: Journal Article
• Authors: Basi, Sabin; Burkhardt, Juergen; Noga, Georg; Hunsche, Mauricio
• Is Part Of: Weed biology and management. Volume 14:Issue 3(2014)
• Page Start: 186
• Page End: 197
• Publication Date: 2014-05-09
• Subjects: Weeds -- Periodicals; Weeds -- Control -- Periodicals; 632.5
• DOI: 10.1111/wbm.12046
• Languages: English
• ISSNs: 1444-6162

Abstract

<abstract abstract-type="main"> <title> <x xml:space="preserve">Abstract</x> </title> <p>The objective of this study was to better understand the role of chaotropic and kosmotropic salts in stomatal uptake, a process that occurs in parallel with cuticular penetration and affects the bioefficacy of glyphosate. In Trial 1, salt solutions of kosmotropic (NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub> and chaotropic NaClO<sub>3</sub>, with or without the organosilicone surfactant, Break‐Thru® S233 (BT), and with or without glyphosate, were prepared. In Trial 2, sodium salts with a kosmotropic‐to‐chaotropic nature (Na<sub>2</sub>SO<sub>4</sub>, NaCl, NaNO<sub>3</sub> or NaClO<sub>3</sub>) and BT were prepared with or without glyphosate. At very high concentrations, the salts of a kosmotropic nature induced a slight decrease in the surface tension, whereas those of a chaotropic nature triggered a significant decrease in the surface tension. Solution droplets were deposited onto the leaves of <italic>Viola arvensis</italic> and <italic>Chenopodium album</italic>. The dried deposits were analyzed with an environmental scanning electron microscope. The salts formed structures linking the exterior to the interior of the stomata in the crystalline ([NH<sub>4</sub>]<sub>2</sub>SO<sub>4</sub>) or amorphous (NaClO<sub>3</sub>) form. However, the low surface tension alone did not appear to be the unique driving force for stomatal uptake. With glyphosate, amorphous globular structures of glyphosate salt were formed in the Na<sub>2</sub>SO<sub>4</sub> (kosmotropic) solution. Differently, the salts of a rather chaotropic nature (NaNO<sub>3</sub> or NaClO<sub>3</sub>) formed a colloidal matrix. In general, salt residues were observed over the periclinal cell walls and inside the stomatal chamber. Neither (NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub> nor Na<sub>2</sub>SO<sub>4</sub> had a significant impact on glyphosate bioefficacy. However, the chaotropic salt, NaNO<sub>3</sub>, enhanced the bioefficacy of glyphosate the most, with a performance that was comparable to that of the solution glyphosate + organosilicone surfactant.</p> </abstract>