Influence of Removal Time and Plant Density of Canarygrass (Phalaris minor) on Wheat Seed Yield

Canarygrass is one of the most important weeds at wheat fields in north of Iran. Considering the effect time of removal on weed- crop interference is critical for the development of accurate crop yield loss models and weed density thresholds. Therefore، field experiments conducted at Mazandaran province، Iran، in 2005 and 2006 to determine the effect of canarygrass density and time of removal on wheat yield. Canarygrass was removed in 4 weeks intervals (mean 170 degree days) from wheat emergence until 24 weeks after that (mean 1097 degree days). Canarygrass density ranged from 0 to 320 plants m. High densities of late removal canarygrass greatly reduced wheat yield (44%). The difference in wheat yield loss between early and late removal of canarygrass was significant (mean 33%). The yield loss caused by individual canarygrass plants at low densities (parameter I) ranged from 0. 30 to 0. 32%. The effect of canarygrass time of removal (parameter C) varied significantly between years. The results of this study emphasize both the need for early removal of canarygrass، as well as the importance of weed emergence time in crop yield loss prediction.