SEDL / STP / STP1183-EB / STP25121S

Influence of Two Adjuvants on Rain-Washing Characteristics of Glyphosate Deposits from Trembling Aspen Foliage, Following a Field Spray Application

Leung, JW
Research Assistant, Forest Pest Management Institute, Sault Ste. Marie, Ontario

Webster, GRB
Professor, Pesticide Research LaboratoryThe University of Manitoba, Winnipeg, Manitoba

Pages: 16    Published: Jan 1993

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Abstract

Three end-use mixtures, Vision-W, Vision-Ethomeen-W and Vision-Silwet-W, were prepared from Vision®, a formulation concentrate of glyphosate, without and with Ethomeen® T/25 and Silwet® L-77 adjuvants. The mixtures were sprayed at a dosage rate of 1 kg of glyphosate in 35 L per ha, over young trembling aspen trees selected in a one-year-old cut-over site in northern Ontario, Canada, using the Herbi® spinning disc atomizer. Samples of foliage were collected at 1.0 h after glyphosate treatment to determine the initial deposits of glyphosate. At 36 h after treatment, the trees were subjected to a simulated rainfall of 5 mm using a Solo® backpack sprayer. Foliar samples were collected prior to and after rainfall, to determine the rain-washing characteristics of the residual deposits.

The Herbi atomizer provided large droplets of the three end-use mixtures with a volume median diameter of about 300 to 350 μm. Foliar deposition was almost quantitative because 95% of the applied glyphosate was deposited initially on foliage. The average amount of glyphosate washed-off in the rainfall was 55% for Vision-W, 40% for Vision-Ethomeen-W and 36% for Vision-Silwet-W. The data thus indicated a reduction of 15% and 19% in the amount of glyphosate washed off from foliage, when Ethomeen and Silwet adjuvants were present in the end-use mixtures.