Effect of post-emergence applications of imazapyr and imazapic on the growth and grain yield of AHAS-transgene soybean plants

One of the factors that limit grain yield in soybean crops is weed competition. The objective of the present work was to evaluate the agronomic performance of an AHAS-transgene soybean cultivar (BRS 397; Cultivance®) subjected to different rates of Soyvance® (525 g kg-1 imazapyr, and 175 g kg-1 imazapic). Two field experiments were conducted in the 2015-2016 crop season in two sites with different soil and weather characteristics located in the state of Paraná, Brazil. A completely randomized block design was used, with 11 treatments consisted of different rates of Soyvance®. Phytotoxicity, chlorophyll index, first pod height, plant height, number of pods per plant, 100-seed weight, and grain yield were evaluated. The use of high rates of the herbicide decreased the final height and grain yield of soybean plants in approximately 25% in both locations, but did not affect their 100-seed weight and chlorophyll index. The use of rates of the commercial product higher than that recommended by the manufacturer (100 g ha-1) may affect the agronomic performance of AHAS-transgene soybean plants.