Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/13/2006
Publication Date: 12/1/2006
Citation: Belles, D., Shaner, D.L., Westra, P., Brunk, G. 2006. Comparison Of Efficacy, Absorption And Translocation Of An Isopropyl Amine Salt And An Acid Formulation Of Glyphosate In Velvetleaf (Abutilon Theophrasti). Pest Management Science. Interpretive Summary: Glyphosate is the most widely used post-emergent herbicides in the world. The herbicidal activity of glyphosate is highly dependent on the formulation. The goal of these formulations is to provide potent and consistent activity. A study was done to compare the herbicidal activity of two different formulation of glyphosate on Abutilon theophrasti, a major weed in corn and soybeans. The activity of the acid formulation of glyphosate was approximately 4-fold more active compared to the isopropylamine formulation under greenhouse conditions. Studies with radiolabelled formulations showed that the increased activity of the acid formulation was due to more rapid uptake and translocation. These results suggest that the additives in the acid formulation of glyphosate could reduce the amount of chemical needed for weed control.
Technical Abstract: Growth analysis, absorption and translocation studies were conducted to compare an acid formulation of glyphosate with an isopropyl amine formulation and to determine patterns of the two glyphosate formulations absorption and translocation. Four to six leaf velvetleaf were treated with 0, 210, 280, 420, 560 and 840 g ae ha-1 of the acid and isopropyl amine formulations. The acid formulation at each application rate reduced velvetleaf biomass more than the isopropyl amine formulation. The GR50 value for the acid formulation was 4 times lower than the GR50 calculated for the isopropyl amine formulation based on a log-logistic regression analysis of velvetleaf dry weight. Absorption of 14C glyphosate into leaves of 4 to 6 leaf velvetleaf was 3.6 times greater (19 vs. 5%) after 6 h when applied as the acid formulation compared to isopropyl amine formulation. Translocation out of the treated leaf was also greater with the acid formulation but the differences were not as large as those for absorption. After 24 h, 1.4 times more 14C glyphosate applied in the acid formulation had translocated out of the treated leaf compared to the isopropyl amine formulation. The greater efficacy of the acid formulation of glyphosate over the isopropyl amine formulation on velvetleaf is probably due to the greater rate of absorption of the herbicide and increased translocation.