Herbicide programs for hairy fleabane control in Enlist^® soybean systems

Background:  Hairy fleabane (Conyza bonariensis L.) is a difficult weed to control in soybean production systems as it presents resistance to some herbicides; thus, leading to substantial grain yield losses.

Objective:  The objective of this study was to evaluate the efficacy and selectivity of herbicides applied before and after soybean planting on glyphosate-resistant C. bonariensis.

Methods:  Field experiments were conducted over two soybean growing seasons in 2021/22 and 2022/23 near Erechim, Rio Grande do Sul, Brazil. Early weed management treatments included terbuthilazine (1,500 g ha⁻¹), mesotrione+atrazine (120+1,200 g ha⁻¹), metsulfuron-methyl (6 g ha⁻¹), dicamba (720 g ha⁻¹), 2,4-D amine (1,612 g ha⁻¹), flumioxazin (50 g ha⁻¹), diclosulam (35.28 g ha⁻¹) and atrazine+simazine (1,500+1,500 g ha⁻¹) applied 60 days before soybean planting. For pre-plant burndown, diquat + saflufenacil (600+70 g ha⁻¹) were applied three days before soybean planting. For post-emergence weed control, 2,4-D choline+glyphosate (971.28+1232.65 g ha⁻¹) were applied at the V3 to V4 soybean growth stage. The C. bonariensis plants present in the experimental area were resistant to the herbicide glyphosate.

Results:  The best early hairy fleabane control was achieved with mesotrione+atrazine, dicamba, and 2,4-D amine, providing more than 90% efficacy. Diquat+saflufenacil applied pre-plant burndown provided excellent level of control, particularly following dicamba in early management, reaching 100% control. Post-emergence application of 2,4-D choline+glyphosate after early treatments with mesotrione+atrazine or dicamba resulted in 100% control.

Conclusions:  The combination of atrazine + simazine for early management, diquat + saflufenacil for pre-plant burndown, and 2,4-D choline+glyphosate post-emergence effectively controlled hairy fleabane and contributed to higher grain yield.

Keywords:
Conyza bonariensis ; Glycine max ; Weed Management