Effect of management operations on spotted spurge (Euphorbia maculata L.) emergence time in soybean

Spotted spurge is a summer annual weed in row crops that can reduce their yield. Thus, in order to evaluate the effect of different management practices on the emergence time of spotted spurge, 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 soybean densities (200,000; 300,000 and 400,000 seeds ha-1), and three doses of imazethapyr (0, 50, and 100 g ai ha-1) were considered as experimental factors. The spotted spurge emergence was significantly affected by management practices including tillage system, soybean seeding rate, and imazethapyr dose. Conventional tillage, 400,000 seeds ha-1 of soybean and a 100 g a.i. ha-1 imazethapyr resulted not only the lowest spotted spurge seedling density m-2 but also caused the longest delay in the time to reach 50% of seedling emergence (T50), thus resulting in a long lag phase of spotted spurge emergence early in the season. This condition provided more time for soybeans to establish better and improve their competitive ability, which resulted in higher soybean yield per unit area at the end of the growing season in these treatments. The results of our study could help to develop effective management strategies for this species.