Crop yield loss in relation to weed time of emergence and removal: analysis of the variability with mixed infestations

Contrasting data have been reported for the variability of yield loss in relation to weed time of emergence and removal. Three data sets relating to maize (northern Italy), soybean (Ontario - Canada) and durum wheat (southern Italy), have been used to analyse the variability of duration of tolerated competition and weed free period curves across reasonably homogeneous areas. The pattern of these relationships appears to depend more on crop characteristics than on the composition of the weed infestation. If these results are confirmed, it will be possible to predict yield loss caused by mixed weed infestation with any time of emergence and/or removal.