Quantifying field weeds emergence pattern of weeds in rapeseed (Brassica napus L.) under weather conditions of Khuzestan, Iran

In order to quantifying emergence pattern of rapeseed weeds, this experiment was conducted in 40 plots (40 quadrates at Agricultural Sciences and Natural Resources University of Khuzestan, and 30 fields of Bavi (30 quadrates), Ahvaz, Iran, in 2016-2017 growing seasons was monitored, counted and recorded weekly. Three different emergence pattern of nine weed species were identified, Prickly lettuce (Lactuca serriola L.) and Wild mustard (Sinapis arvensis L) were identified as early-emerging species. Also salt sandspurry (Spergularia marina L.) and furrowed melilot (Melilotus sulcatus), were categorized as late- emerging species. However, five species including; mallow (Malva spp), rigid ryegrass (Lolium rigidum), sea beet (Beta vulgaris subsp. maritima), milk thistle (Silybum marianum L) and nettle-leaved goosefoot (Chenopodium murale L) were identified as medium-emerging species. Estimation of GDD50 (time required to reach 50% emergence) showed that the minimum (323.62 ℃d)) and maximum (608.93 ℃d) growing degree day required by Lactuca serriola and Spergularia marina (L.), respectively. Whereas, 10% emergence of Spergularia marina and Melilotus sulcatus required 362.42 ℃d and 426.37 ℃d, respectively. The results of weeds emergence pattern in rapeseed crop showed that the soil herbicides with longer half-life should be applied, and the application of post emergence herbicides and agronomic practices such as plant density and competitive ability of rapeseed cultivars are necessary components in integrated weed management.