Response of glyphosate-resistant cotton to various rates of topically applied glyphosate was investigated in growth chamber experiments to determine the relationship between glyphosate rate and boll abscission. Glyphosate at 0, 0.56, 1.12, or 2.24 kg ai/ha was applied to all exposed foliage at the 12-leaf growth stage. Immediately after this treatment, ¹⁴C-glyphosate was applied to the three uppermost fully expanded leaves at 0, 37, 74, or 148 kBq per leaf for the 0, 0.56, 1.12, or 2.24 kg/ha treatment, respectively. After glyphosate application, glyphosate accumulated in reproductive tissue, and bolls were abscised. Abscission increased as the amount of glyphosate translocated to fruiting sites increased.

Nomenclature: Glyphosate; cotton, Gossypium hirsutum L., ‘Delta & Pine Land 5690RR’.

Additional index words: Boll abscission; transgenic crops.

Abbreviations: EPSPS, 5-enolpyruvylshikimate-3-phosphate synthase (EC 2.5.1.19); GR, glyphosate resistant; WAT, weeks after treatment.