Simulation of control strategies for decision-making regarding Digitaria sanguinalis in glyphosate-resistant soybeans

Abstract

Cien. Inv. Agr. 39(2): 299-308. A bioeconomic model was developed for decision-making regarding large crabgrass (Digitaria sanguinalis) control in glyphosate-resistant soybeans in the Rolling Pampas of Argentina. The model was used to evaluate the economic returns of four different glyphosate-based strategies for weed control. In the absence of herbicide application (T1), the soil seed bank increases to an equilibrium density of 12,079 seeds m -2 in three years. A single herbicide application during the early stages of the crop (T2), which was intended to be highly effective in the control of an early weed cohort, allows a late, unaffected cohort to produce sufficient seeds to maintain population densities in the soil seed bank. A single, delayed herbicide application (T3), which was intended to control both early and late cohorts, results in a soil seed bank increase up to an equilibrium density similar to that achieved without treatment. Two sequential herbicide applications per year (T4), targeting the two cohorts, leads to a soil seed bank density after 10 years of 107 seeds m -2 . Model predictions indicate that in the absence of control measures, a 93% reduction in soybean yield was predicted due to weed interference. The lowest reduction in crop yield (27%) was predicted using strategy T4, which is the most common control measure used by local farmers. This strategy clearly outperforms the other options tested, leading to lower D. sanguinalis seed bank densities and higher soybean yields and economic returns compared to those obtained using the alternative strategies.

A novel EPSPS Pro‐106‐His mutation confers the first case of glyphosate resistance in Digitaria sanguinalis

“…Considering that glyphosate is the main agronomic tool used to control D. sanguinalis under no‐tillage systems in glyphosate‐tolerant soybean and corn crops, 8 glyphosate resistance evolution in D. sanguinalis emerges as a challenge for farmers in the Rolling Pampas agricultural region. Nevertheless, other herbicides have been shown to be effective in controlling Dgs R plants in different crops, as no evidence of multiple herbicide resistance was found (data not shown).…”

“…In extensive cropping areas from Argentina, D. sanguinalis is one of the most common weeds of soybean, sunflower, maize and sorghum crops and is likewise well adapted to both cultivated and no‐tillage systems 2,6,7 . This species shows an extended period of seedling emergence with several overlapping cohorts during spring and summer, and a high vegetative growth rate and fecundity 8,9 …”

“…2,6,7 This species shows an extended period of seedling emergence with several overlapping cohorts during spring and summer, and a high vegetative growth rate and fecundity. 8,9 Chemical control of D. sanguinalis with glyphosate, Acetyl-CoA carboxylase (ACCase), acetolactate synthase (ALS) or very-longchain fatty acid (VLCFA) herbicides has been challenged as a result of the long emergence period, which enables seedling cohorts to escape from herbicide action. 9 Based on poor control at recommended glyphosate doses, a D. sanguinalis population was identified as a putative glyphosate-resistant biotype.…”

Demographics of glyphosate-resistant and susceptible Italian ryegrass populations from Paraná

“…Several studies have reported different survival rates between cohorts. For instance, C. bonariensis, survival rate ranges from 0.44 to 0.13; Salsoa australis from 0.75 to 0 and Digitaria sanguinalis from 0.2 to 0.003 (Borger, et al, 2009;Oreja et al, 2012;Zambrano-Navea et al, 2018). The difference in survival can be explained by the different establishment times.…”

Digitaria sanguinalis seed dormancy release and seedling emergence are affected by crop canopy and stubble

“…(large crabgrass) is a troublesome annual weed present in most summer crops around the world (Mohler & Callaway, 1995;Monks & Schulteis, 1998;Sarker et al, 2002;Aguyoh & Masiunas, 2003;Bhowmik, 2003;Fu & Ashley, 2006). In Argentinean soyabean fields, high densities of this weed can cause high yield losses (above 90%; Oreja et al, 2012). Despite the good chemical control that can be obtained with glyphosate (around 98%;Culpepper et al, 2001;Van Gessel et al, 2001;Norsworthy, 2004), over the last 20 years, this species has shown very high constancy values in the Argentinean Pampas (Puricelli & Tuesca, 2005;de la Fuente et al, 2006;Scursoni & Satorre, 2010).…”