Interference between Rottboellia cochinchinensis and Zea mays

Field studies conducted over 2 yr in Louisiana determined critical periods of Rottboellia cochinchinensis interference in Zea mays. In a duration of i nterference study, R. cochinchinensis was allowed to compete with Z. mays f or 0 tweed-free, season-long), 2, 4, 6, 8, 10, 12, or 14 (weedy, season-lon g) wk, after which plots were maintained weed-free for the rest of the grow ing season. Rottboellia cochinchinensis biomass at rime of initial removal increased linearly as weeks of interference increased. For 2 wk of interfer ence, R. cochinchinensis biomass was greater in 1993 than 1994, but for 4 w k or more of interference, biomass was greater the second year indicating e nvironmental conditions were more conducive to R. cochinchinensis growth in 1994. Season-long R. cochinchinensis interference reduced Z. mays height b y 18% compared with the weed-free check. For both years, R. cochinchinensis reduced yields 125 kg ha(-1) for each week of interference. In weed-free m aintenance studies, 0, 2, 4, 6, 8, 10, 12, or 14 tweed-free, season-long) w k of weed-free conditions were provided, after which R. cochinchinensis was allowed to repopulate. Zen mays yield was equivalent for the weed-free con trol and plots maintained free of R. cochinchinensis for 2 wk or more. In t he interference studies, season-long R. cochinchinensis interference reduce d Z. mays yield at least 33% compared with the season-long weed-free check.