Emergence characteristics of four annual weed species

Emergence characteristics, including initial time of emergence, magnitude o f emergence, and mean time of emergence, of Amaranthus rudis Sauer, Setaria faberi Herrm., Eriochloa villosa (Thunb.) Kunth, and Abutilon theophrasti Medik. were studied in central Iowa during the first 3 yr following burial of seed collected and buried in the fall of 1994 or 1995. Although the init ial emergence date varied among years, the emergence sequence among species was consistent. Eriochloa villosa and A. theophrasti were the first specie s to emerge, with initial emergence occurring between April 28 and May 10. Initial emergence dates for these species were the same, except for 1995 wh en A. theophrasti emerged 4 d prior to E. villosa. Amaranthus rudis was the last species to emerge, with initial emergence ranging from 5 to 25 d afte r A. theophrasti. First-year emergence in 1995 was 8% for A. theophrasti, 7 % for A. rudis, 41% For E. villosa, and 33% for S. faberi, based on the num ber of buried seed. Proportional emergence during the first year following burial in 1996 was similar to 1995 for A. theophrasti and S. faberi, but gr eater emergence was observed in 1996 for E. villosa and A. rudis. During th e 3 yr of both studies, cumulative emergence of the two grass species (43 t o 71%) was higher than for the broadleaf species (13 to 35%). A high percen tage of the total annual emergence of E. villosa occurred within the first 2 wk of initial emergence, whereas a high percentage of A. rudis emergence occurred late in its emergence period. Emergence characteristics of the fou r species were consistent among years and seed sources. Nomenclature: Amaranthus rudis Sauer AMATA, common waterhemp; Setaria faber i Herrm. SETFA, giant foxtail; Abutilon theophrasti Medik. ABUTH, velvetlea f; Eriochloa villosa (Thunb.) Kunth ERBVI, woolly cupgrass.