Bioassays with a floating aquatic plant (Lemna minor) for effects of sprayed and dissolved glyphosate

Axenically grown duckweed cultures were exposed to glyphosate herbicide either by dissolving formulated Roundup in the culture media or by spraying the cultures in a laboratory spray chamber and allowing them to stand for 6, 12 and 24 h. Plant growth, as measured by the increased number of fronds occurring over a 2-week period following treatment, or increased wet or dry weights, after the final count, was relatively insensitive to glyphosate in water. The plants were killed by spray application of glyphosate, indicating that deposit contact might be more hazardous to emergent aquatic vegetation than water pollution.