Studies were conducted to evaluate absorption and translocation of ¹⁴C-glyphosate in glyphosate-resistant (GR) cotton. Both commercial GR cotton events [glyphosate-resistant event 1, marketed as Roundup Ready®, released 1997 (GRE1), and glyphosate-resistant event 2, marketed as Roundup Ready Flex®, released 2006 (GRE2)] were evaluated at the four-leaf and eight-leaf growth stages. Plants were harvested at 1, 3, 5, and 7 d after treatment (DAT). Glyphosate absorption, as a percentage of applied, increased over time with 29 and 36% absorption at 7 DAT in four-leaf GRE1 and GRE2 cotton, respectively. In eight-leaf cotton, glyphosate absorption (33% at 7 DAT) was not different between events. Glyphosate translocation patterns were not different between events or harvest timings and exhibited a source–sink relation. Observed translocation differences between cotton growth stages were probably due to reduced glyphosate export from the treated leaf of eight-leaf cotton. An additional study compared absorption and translocation of ¹⁴C-glyphosate and ¹⁴C-sucrose in 5- and 10-leaf GRE2 cotton. Averaged over trials, ¹⁴C compounds, and growth stages, cotton absorbed 28% of the applied dose at 14 DAT. On the basis of the percentage of ¹⁴C exported out of the treated leaf, glyphosate and sucrose translocation patterns were similar, indicating that glyphosate may be used as a photoassimilate model in GRE2 cotton.

Nomenclature: Glyphosate; cotton, Gossypium hirsutum L.