Evaluation of the efficacy of glyphosate plus urea phosphate in the greenhouse and the field.

Background: Glyphosate is a non-selective, foliar-applied, systemic herbicide that kills weeds by inhibiting the synthesis of 5-enolpyruvylshikimate-3-phosphate synthase. Urea phosphate (UPP), made by the reaction of urea with phosphoric acid, was applied as an adjuvant for glyphosate in this study. Experiments in the greenhouse and the field were conducted to determine the effects of UPP by comparing the efficacies of glyphosate plus UPP, glyphosate plus 1-aminomethanamide dihydrogen tetraoxosulfate (AMADS) and Roundup.

Results: The optimum concentration of UPP in glyphosate solution was 2.0% when UPP was used as an adjuvant. The ED50 values for glyphosate-UPP were 291.7 and 462.4 g AI ha(-1) in the greenhouse and the field respectively, while the values for Roundup were 448.2 and 519.6 g AI ha(-1). The ED50 values at 2 weeks after treatment (WAT) and 3 WAT were lowered when UPP was used as an adjuvant in the greenhouse and field study, and the glyphosate+UPP was absorbed over a 2 week period. UPP may increase the efficacy by causing severe cuticle disruption or accelerating the initial herbicide absorption. The result also showed that UPP could reduce the binding behaviour of Ca2+ to glyphosate.

Conclusion: The application of UPP as an adjuvant could increase the efficacy of glyphosate and make it possible to achieve effective control of weeds with glyphosate at lower dose. Moreover, UPP showed less causticity to spraying tools and presented less of a health hazard. Therefore, UPP is accepted as being a new, effective and environmentally benign adjuvant for glyphosate.