Selectivity and efficacy of terbuthylazine as an alternative herbicide applied alone or in combination for the control of weeds in wheat

Abstract Herbicides are commonly used for weed control in wheat production due to their effectiveness, speed, and lower cost compared to other management methods. This study aimed to evaluate the selectivity and efficacy of herbicides applied alone or in combination for controlling major weed species infesting wheat in Brazil. Field experiments were conducted in 2022 and 2023 using a randomized complete block design with four replications. Terbuthylazine (500 and 750 g ha −1 ) + adjuvant, carfentrazone-ethyl (120 g ha −1 ), saflufenacil and pyraflufen-ethyl (3.75 and 5 g ha −1 ) + clodinafop-propargyl caused the highest phytotoxicity to wheat. The best wheat physiological performance (internal CO 2 concentration, photosynthesis and transpiration rates, stomatal conductance, water use, and carboxylation efficiencies) was observed with terbuthylazine (750 g ha −1 ), carfentrazone-ethyl (80 g ha −1 ), 2,4-D (670 g ha −1 ), and terbuthylazine + clodinafop-propargyl (750 + 96 g ha −1 ). Terbuthylazine (500 and 750 g ha −1 ) and pyraflufen-ethyl (3.75 and 5 g ha −1 ) combined with clodinafop-propargyl (96 g ha −1 ), provided the most effective control of wild radish and ryegrass and resulted in the highest grain yields. Regarding the grain yield components of wheat (number of plants per meter, number of spikes, spike length, number of filled and sterile grains, hectoliter weight, thousand-grain mass, and grain yield), the weed-free control and the treatment with terbuthylazine + clodinafop-propargyl (750 + 96 g ha⁻¹) showed the best performance. In the absence of weed control, average grain yield losses reached 91%. The herbicides terbuthylazine and pyraflufen-ethyl demonstrated potential for the control of broadleaf weeds such as wild radish, which exhibit resistance to acetolactate synthase inhibitors, and where 2,4-D is less effective under low-temperature conditions. However, further studies using commercial formulations, adjuvants, and varietal tolerance tests are required to validate the use of these herbicides on wheat in Brazil.