Evaluation of Some Adjuvants for Improving Glyphosate Efficacy

Glyphosate is the most common non-selective post-emergence herbicide used under diverse conditions. The efficacy of foliar applied herbicides is greatly influenced by adjuvants, but not all adjuvants have a synergistic effect. Greenhouse experiments were conducted using weed species of Echinochola crus-galli, Panicum maximum, Bidens pilosa, and Abutilon theophrasti to evaluate glyphosate efficacy by tank mixing with 0.5 % of Blaze®, Condition®, Improve®, and Induce®. Glyphosate at 0, 0.14, 0.28, and 0.56 kg ae/ha alone and with adjuvants was sprayed at the 4 leaf stage of weeds. Surface tension and contact angle were measured under lab conditions.

Adjuvants increased the activity of glyphosate by 15–29 % compared to glyphosate alone. Among the weed species, higher mortality was observed in P. maximum and B. pilosa followed by E. crus-galli and lowest in A. theophrasti. On mortality of grass and broadleaf weed species, significant differences were observed by tank mixing glyphosate with different adjuvants. Lowest Contact Angle (CA) and Surface Tension (ST) were recorded when glyphosate (Rodeo®, with no surfactant) was mixed with Improve and Blaze surfactants, which was significantly lower than glyphosate formulation pre-mixed with surfactant (Roundup UltraMax®). In the case of Condition, the relative decrease in CA was less than ST when added to glyphosate, compared to Improve and Blaze. Lower ST and CA of glyphosate tank mixed with Improve and Blaze correlated with improved weed mortality in the activity study.