Weed control efficacy of herbicide mixtures and digital assessment methods during pre-planting burndown in soybean

Abstract

Farmers use herbicide mixtures to increase the efficacy and spectrum of weed control during the pre-planting burndown stage of soybean. The efficacy of herbicides should be rigorously assessed, and digital tools have great potential for application during pre-planting weed management. This study aimed to evaluate the efficacy of weed control using herbicide mixtures and to test digital tools that analyze spectral responses as a means to assess efficacy. Two field experiments were set up, and the herbicides tested included diquat + carfentrazone-ethyl, glyphosate + 2,4-D, glyphosate + ammonium glufosinate, glyphosate + carfentrazone-ethyl, and glyphosate + clethodim. The main weed species identified were Urochloa plantaginea, Commelina benghalensis, Nicandra physalodes, Ipomoea triloba, Portulaca oleracea, Cyperus rotundus, Eleusine indica, and Alternanthera tenella. Efficacy for each species was assessed using a 0–100% scale for visual injury (VI). Each plot was evaluated using five methods: VI, Visible Atmospherically Resistant Index (VARI), Canopeo App, manual Greenseeker, and evaluation of images on a computer screen. The alternative methods were compared to the VI scores using Pearson correlation analysis. It was observed that, in general, the herbicides were less effective in controlling E. indica, C. benghalensis, I. triloba, and A. tenella. Control scores greater than 80% were recorded for U. plantaginea, N. physalodes, and P. oleracea. Alternative methods can be used as additives or substitutes for herbicide efficacy assessments. Greenseeker generally showed a strong correlation with VI, and the efficacy of fast-acting products was more easily detected using alternative methods.