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The effect of Sta-Put® and Silwet® L-7607 on physical properties (viscosity, surface tension and volatility), droplet spreading and drying rates, and foliar uptake and translocation of glyphosate was studied using white birch seedlings and branch tips. Three end-use mixtures were prepared using Vision®, one in water alone and the other two with 0.05% of the adjuvants in water. Physical properties were measured to examine their roles on droplet spreading and drying rates. Foliar uptake was investigated to study the effect of droplet spreading and drying rates on foliar retention; and translocation was studied to examine the role of the two polymers on bioavailability of glyphosate.
The adjuvants did not contribute to marked differences in the viscosities or volatilities of the three end-use mixtures, although the surface tensions were altered to some extent. Silwet caused a marked increase in the droplet spread areas, along with a simultaneous decrease in the droplet drying time. Staput did not alter any of these parameters. No simple relationship could be found between surface tensions of the mixtures and droplet spreading or drying rates. Both adjuvants contributed to an increase in the foliar uptake of glyphosate, but Silwet caused a much greater increase than Sta-Put, thus suggesting a relationship between droplet spreading and foliar uptake. Nevertheless, there was no significant difference in the amount of glyphosate translocated between the three end-use mixtures, thus indicating no evidence of reduced bioavailability because of the presence of the two polymers at the concentration levels used in the study.
Glyphosate, herbicide end-use mixtures, polymeric adjuvants, physical properties, droplet spreading, droplet drying, foliar uptake, herbicide translocation
Research Scientist and Project Leader for Pesticide Formulations Project, Forestry Canada, Forest Pest Management Institute, Sault Ste. Marie, Ontario