Mesotrione use for selective post-emergence control of glyphosate-resistant Conyza spp. in black oats

Background: Achieving satisfactory weed control levels in black oat (Avena strigosa) fields is often difficult, owing to the limited number of registered herbicide molecules. Objective: To determine novel options for selective, post-emergence chemical weed control in this crop. Methods: Eight herbicide treatments were sprayed in the field onto black oat plants at the tillering stage to evaluate crop safety and control of Conyza spp. and Gamochaeta americana, two major weeds of Brazilian black oats. A separate trial was conducted to further assess herbicide safety in a controlled-environment setting, and mesotrione selectivity was then re-evaluated separately in the greenhouse during the following growing season. Crop phytotoxicity was determined using biomass production both in the field and in greenhouse trials. Results: Mesotrione, bentazon, 2,4-D, and a 2,4-D+bentazon tank-mix produced light symptoms of crop phytotoxicity, from which plants quickly recovered. Conyza spp. control was achieved via applications of mesotrione (192 g a.i. ha(-1)), metsulfuron-methyl (3.9 g a.i. ha(-1)), and a 2,4-D + bentazon tank-mix (502.5 g a.e. ha(-1) + 720 g a.i. ha(-1), respectively), whereas proper G. americana control was only achieved via applications of either mesotrione or metsulfuron-methyl. Biomass accumulation by black oat plants in the greenhouse was similar across mesotrione-treated and untreated plants. Conclusions: Mesotrione could become an option for selective, postemergence weed control in black oat fields, aiding in the fight against multiple herbicide-resistant Conyza spp. populations which are widespread across major black oat-growing areas in Brazil.

Automated summary

This study aimed to determine novel options for selective, post-emergence chemical weed control in black oat fields. Through field and greenhouse trials, it was found that mesotrione could be an effective selective herbicide for black oat fields. Some herbicide treatments caused light crop phytotoxicity symptoms, but plants quickly recovered.