Performance of post-emergence herbicides for grass weed control in soybeans

Abstract

Two field experiments were conducted during 1984/85 at Estação Experimental Agronômica of Universidade Federal do Rio Grande do Sul, in Guaíba, RS, Brazil, using soybeans, cv. BR4 , seeded at the beginning and at the end of November for experiments 1 and 2, respectively. The objectives were to evaluate the activity of four herbicides on crop and grass weeds, as a function of application rate and time, as well as to quantify weed competition effects on soybean that was mainly infested with crabgrass [Digitaria ciliaris (Reta.) Koel.]. In application at 14 days alter soybean emergence, all herbicides presented higli efficiency in both rates tested. However, in latter applications (28 and 42 days), grass activity of the herbicides was quite dependent on environmental conditions, mainly soil moisture, and on weed growth stage. Haloxyfop was the compound least affected by these variables, whereas fluazilop was the most affected. The grass weed competition decreased sobybean grain yield by 31 and 50% for experiments 1 and 2, respectively