Relating Eriochloa villosa emergence to interference in Zea mays

Critical period experiments were conducted in 1997 near Milton, WI, and in 1998 near Edgerton, WI, in which Eriochloa villosa (Thunb.) Kunth emergence was characterized and related to Zea mays L. yield loss and weed seed prod uction. Ar Milton, 2.7% of the spring seedbank emerged, and at Edgerton, 14 .5% of the spring seedbank emerged. Peak time off. villosa emergence occurr ed early in the season at both locations, accounting for 84% of the total s eason emergence at Milton by 37 d after planting and 90% of the total seaso n emergence at Edgerton by 27 d after planting. A secondary peak in emergen ce occurred at each site, accounting for 14% of the total season emergence at Milton between 38 and 52 d after planting and 8% of the total season eme rgence at Edgerton between 28 and 43 d after planting. Following the second ary peak in emergence at each site, approximately 2% of the total season em ergence occurred. Zea mays grain yield was reduced when E. villosa interfer ed with Z. mays past the V11 stage at Milton and the V3 stage at Edgerton. Zea mays yield reductions at Edgerton were greater, occurred under shorter periods of weed interference, and were associated with greater E. villosa b iomass than yield reductions at Milton. Eriochloa villosa that emerged afte r the V2 Z. mays stage at Milton and the V3 stage at Edgerton did not cause crop yield loss; however, these plants produced seed at 143 and 63% of the initial spring seedbanks, respectively.