All yield data were further analyzed separately for each year as
therewas an interaction between years and treatment levels for the
beginning and the end of the CPWC (Fig. 2, Table 4). The duration of
weed-infested or weed-free period influenced the relative yield of
corn, regardless of corn types (Fig. 2). Corn yields in both years were
reduced significantly with increasing periods of weed interference.
Yields from the season-long weed-free plots ranged from 7.8 to
9.3 t ha1 in field corn, 2.7e3.9 t ha1 in popcorn, and
7.6e10.2 t ha1 in sweet corn compared with much lower yields of
2.2e4.6 t ha1 in field corn, 0.59e2.0 t ha1 in popcorn, and
3.6e5.5 t ha1 in sweet corn in the season-long weedy plots.