Weed Control J 2021; 20: e202100747

Research Article

Biological and economic efficiency of glyphosate-containing herbicide mixtures for pre-plant burndown control of Conyza spp.

DOI: 10.7824/wcj.2021;20:00747

Abstract

Background

Pre-plant burndown using herbicides is a key practice in no-till cropping systems which has been complicated by the evolution of glyphosate-resistant (R) weed populations in Brazil.

Objective

To evaluate pre-plant burndown weed control efficacy of glyphosate-containing tank mixtures such that novel, cost-effective control options can be determined.

Methods

Glyphosate was sprayed alone or tank-mixed with 2,4-D, flumioxazin, saflufenacil, or ammonium-glufosinate onto nutsedge (Cyperus spp.), arrowleaf sida (Sida rhombifolia L.), and glyphosate-R Conyza spp. populations. Treatments ranged from one (glyphosate only) to up to four active ingredients (a.i.) in the mixture and included an untreated check. Experimental units (15 m2 plots) were replicated four times and arranged as complete blocks. Weed control efficacy was visually assessed 7-42 days after spraying (DAS) using a 0-100% grading scale and was later combined with treatment costs to evaluate economic feasibility.

Results

Glyphosate controlled nutsedge and arrowleaf sida effectively, scoring the lowest cost per control unit, but mixtures were required for satisfactory (>80%) glyphosate-R Conyza spp. control. Mixing glyphosate and 2,4-D resulted in 78% control at 42DAS while incurring the lowest price per control unit. However, a glyphosate+ ammonium-glufosinate tank- mix was the only two-way mixture to match control results of three- or four -way mixtures, resulting in 98% control.

Conclusions

Mixtures are required for proper glyphosate-R Conyza spp. control. Despite an increase in overall costs, tank-mixing herbicides with different modes of action should not be completely disregarded, especially in a scenario where resistance can develop under recurrent selection pressure.