Predicting Seedling Emergence of Flixweed (Descurainia sophia (L.) Webb.) and Hoary cress (Cardaria draba (L.) Desv.) in Rapeseed(Brassica napus) Field in Zanjan Conditionsd

Prediction of weed emergence timing would help to minimize weed–crop competition and reducing herbicide use by facilitating the implementation of more effective weed control strategies through the optimization of the timing of weed control. Therefore, in order to anticipate the of flix weed and hoary cress an experiment was conducted at the Research Farm of University of Zanjan, Zanjan, Iran, in fall planted rapeseed during 2009-2010 to find and develop the best emergence model. The number of, flix weed and hoary cress seedlings was recorded at least weekly and then removed from plots. Emergence for each species was expressed as a cumulative percentage of total emergences. Percentage of cumulative emergence values was compared with thermal time using Logistic,Gompertz and Weibull modified functions. The three models were compared using the Akaike information criterion. The results indicated that Weibull model fits best for both species with 20 to 59 differences in AIC compare with the two other models. Conversely, Logistic model fits worse, with AIC values far higher than Weibull and Gompertz models. The two species showed different patterns of emergence and TT required for 10% emergence in hoary cress was lower than the other, whereas, flix weed reached to 90% emergence faster than hoary cress.