Effect of Management Operations on the Thermal Time of Velvetleaf (Abutilon theophrasti Medicus.) Emergence in Soybean (Glycine max L.)

In order to evaluate the effect of different management practices on the emergence time of vevetleaf, a split-split plot experiment was conducted in a completely randomized block design with three replications in Dasht-e-Naz Sari in 2016 and 2017. Two tillage systems (Conventional tillage and no-till), three soyabean seeding rates (200,000; 300,000 and 400,000 seeds ha-1), and three doses of imazethapyr (SL 10%) (0, 50, and 100 g ai ha-1) were considered as experimental factors. The velvetleaf emergence was significantly affected by management practices including tillage system, soybean seeding rate, and imazethapyr dose. No-till system, a density of 400 000 seeds ha-1 and a 100 g a.i. ha-1 imazethapyr dose not only resulted in the lowest velvetleaf seedling density m-2 but also caused the longest delay in the time to reach 50% of seedling emergence, thus resulting in a long lag phase of velvetleaf emergence early in the season. Findings from our study may facilitate the development of effective P. oleracea management strategies.