Influence of linseed oil ethoxylate adjuvants and rain on biological efficacy of glyphosate, evaluated using Chenopodium album, Abutilon theophrasti and Setaria viridis
M. Hunsche, H. Scherhag, M. Schmitz-Eiberger and G. Noga, Institute of Crop Science and Resource Conservation - Horticultural Sciences, University of Bonn Auf dem Hügel 6, D-53121 Bonn, Germany.
The influence of four linseed oil ethoxylate adjuvants (LSO 10, LSO 0903, LSO 30, LSO 3003) on the rain-induced wash-off and biological efficacy of glyphosate was studied using lambsquarter (Chenopodium album L.), velvetleaf (Abutilon theophrasti Medik.), and green foxtail (Setaria viridis L.). In addition, the adaxial leaf surface of weed species was characterized by means of scanning electron microscopy (SEM) and contact angle (CA) of solution droplets. Micro-roughness of leaf surface was quantitatively characterized by measuring the CA of water/acetone solution droplets; results show, leaves of velvetleaf (CA = 65°) were easily wetted while lambsquarter (CA = 118°) and green foxtail (CA = 118°) were difficult to wet, indicating a pronounced micromorphology. These differences arise from surface characteristics such as cell size, presence or absence of trichomes, glands or wax structures, as visualized by SEM. Evaluation of biological efficacy as a function of treatment solutions (RUM®; unformulated isopropylamine salt (glyphosate IPA) and isopropylamine salt plus adjuvants) and rain intensity (0.5, 5 and 48 mm h-1.) in a bi-factorial experiment for each species showed no significant interaction between the evaluated factors. In lambsquarter, heavy (5 mm h-1) and torrential (48 mm h-1) rain events reduced, while light rain (0.5 mm h-1) raised the biological efficacy to some extent. Further, addition of LSO adjuvants to glyphosate IPA resulted in the same dry matter level as achieved with the commercial formulation RUM®. In velvetleaf, all rain intensities reduced efficacy of the herbicidal treatments significantly. Comparisons showed that all LSOs when added to glyphosate IPA achieved at least the same level as RUM® reference, whereas the best result was obtained by adding LSO 0903. In the case of green foxtail, all rain intensities significantly reduced the efficacy of treatment solutions, whereas highest reduction was observed when plants were exposed to heavy (5 mm h-1) or torrential (48 mm h-1) rain. Comparisons among treatments showed a significantly lower dry matter for glyphosate IPA plus LSO 30, whilst the other LSO ethoxylates had the same dry matter level as unformulated glyphosate IPA.
Plant Protection Quarterly (2007) 22 (1) 17-23.