VERNAL SEEDLING EMERGENCE MODEL FOR COMMON LAMBSQUARTERS (CHENOPODIUM-ALBUM)

Knowledge of timing and extent of weed emergence before and immediatel y after crop seedbed preparation is needed to decrease need for prepla nt herbicides and increase efficacy of postemergence weed control in c rops with either mechanical or chemical methods. Such knowledge is imp ortant for weeds that infest most crops over a wide area. For these re asons a mechanistic seedling emergence model based solely on soil temp erature was developed for common lambsquarters. The model was validate d using four sets of field data collected in 1988, 1990, and 1991 near Morris, MN. Agreement of predicted and observed emergence values acro ss all site-years was 0.95 and the coefficient of determination (R2) w as 0.98 (P < 0.001). Agreement for individual site-years was 0.96, 1.0 8, 1.08, and 0.98 and associated R2 values were 0.99, 0.99, 0.99, and 0.98 (P < 0.001 for each site-year), indicating close agreement betwee n predicted and actual emergence values.