Glyphosate applied at rates of 0, 0.3, 0.6, 1.1, 2.2, 3.4, 4.5, 6.7, 9.0, and 13.4 kg ai ha−1 was evaluated for the control of greenhouse-grown Erythroxylum novogranatense var. novogranatense and E. coca var. coca plants. Glyphosate reduced live weight of both species, 6 wk after treatment, at rates as low as 0.6 kg ha−1, but was more effective in reducing live weight and regrowth on E. novogranatense than E. coca. Glyphosate at 1.1 kg ha−1 killed 100% of E. novogranatense plants 5 mo after treatment. Glyphosate rates of 2.2 kg ha−1 and higher reduced regrowth of E. coca plants 65 to 100%, independent of leaf age at time of spraying. Control of regrowth persisted for over 17 mo after treatment, with 37% of E. coca plants dying at rates of 13.4 kg ha−1 between 6 mo and 1 yr after treatment. Glyphosate, applied up to 6.7 kg ha−1, had no significant effect on regrowth of E. coca when plants were defoliated 24 h before treatment. Glyphosate at 2.2 kg ha−1 effectively killed E. novogranatense plants and reduced leaf production of E. coca plants.

Absorption and translocation of 14C-glyphosate was studied in greenhouse-grown Erythroxylum coca and E. novogranatense. Autoradiography indicated that translocation patterns were similar for both species and that E. novogranatense absorbed and translocated more glyphosate than E. coca. In both young and mature plants, absorption of leaf-applied 14C-glyphosate increased with increased exposure time, and 288 h after application, absorption was higher in E. novogranatense (79 and 52% of applied, respectively) compared with E. coca (60 and 14% of applied, respectively). Similarly, translocation of 14C-glyphosate increased with time in both species. In mature plants, after 288 h more 14C-glyphosate translocated in E. novogranatense (6.9% of applied) than E. coca (2.5%), but the opposite occurred in young plants. Most of the radioactivity translocated from the treated leaf accumulated in the main stems and roots of both species with little accumulation in tissues above the treated leaf. However, most of the applied radioactivity remained in the treated leaf regardless of growth stage and species. The absorption of 14C-glyphosate in young and mature plants of E. coca was 1.3 and 3.6 times lower, respectively, than in E. novogranatense 288 h after treatment. Differences in absorption and translocation of glyphosate in E. coca and E. novogranatense may partially explain the reported differential response to glyphosate.