Absorption and translocation of Roundup Ultra^® (glyphosate) in Roundup Ready^® cotton (Gossypium hirsutum L.) was evaluated utilizing previously developed and validated laboratory techniques to apply radiolabeled glyphosate as a spray. These techniques closely simulate and account for numerous factors which greatly impact the amount of glyphosate that ultimately reaches specific sites in the cotton plant after field applications with commercial equipment.

A post-direct application to the stem was compared to an "over-the-top" application to the leaf surface by directing equivalent volumes of radiolabeled spray solution to a 2.5 inch segment of stem between the soil surface and the cotyledon node and to the first (oldest) leaf of a 8-9 leaf Roundup Ready^® cotton. The leaf surface application intercepted and retained 5 times as much of the spray volume that exited the spray nozzle as the stem application. Consequently, the leaf surface application absorbed and mobilized 4 times as much glyphosate as the stem application. Less than 0.1% of the total glyphosate intercepted accumulated in the developing squares from either the leaf or stem.