Coca (Erythroxylum coca) Control is Affected by Glyphosate Formulations and Adjuvants

The aerial spray program for the eradication of coca in Colombia uses Glyphos, a local formulation of glyphosate tank-mixed with an adjuvant product, Cosmo-Flux. There are some potential risks to amphibians from direct overspraying of shallow waters. In order to evaluate potential alternative mixtures, a field experiment was conducted at the Center of National Training of Police Operations in Tolima province, Colombia. Plants of coca were established with irrigation and grown to 75 cm tall. A randomized split-plot design experiment was laid out and sprayed with a range of glyphosate formulations and different adjuvants using an experimental ground sprayer. Assessments were made of plant vigor, height, and above-ground standing crop (fresh weight) 3 wk after application. Resprouting of plants was assessed at 9 wk after treatment. Unformulated glyphosate applied as the product Rodeo gave poorer control of coca than two formulated products, Roundup Biactive (from Europe) and Colombian Glyphos. In general, these products performed well without added adjuvants, giving control similar to that of the eradication mixture with Cosmo-Flux. There was some evidence that addition of the adjuvant Silwet L-77 and to a lesser extent Mixture B (from the United Kingdom) gave more rapid herbicide symptoms. There were also indications that glyphosate rates of less than 3.69 kg acid equivalents (a.e.)/ha could give control in the range of 95%. Depending on the environmental risk requirements, the experiment indicates that, should other spray mixtures be required, there are potential alternatives. These would require extensive field testing to cover different environmental conditions, different coca varieties, and particularly aerial application, prior to a recommendation. Should the glyphosate product require changing, Roundup Biactive may be considered. Should the adjuvant require changing, then on the basis of this research, Silwet L-77 and Mixture B would be good candidates for further evaluation.