Weed species respond to the cumulative effect of multiple practices employed within weed management systems. However, this response is rarely studied at the system level, and the relationships between weed communities and management systems in crops are not well understood. We used multivariate analyses to assess relationships among tomato management systems and weed species identified through on-farm sampling of 59 fields. Giant foxtail, common lambsquarters, prickly sida, and carpetweed were common in all systems. Eastern black nightshade was common in the conventional processing and mixed fresh-market systems but largely absent from the organic system. Barnyardgrass and goosegrass were common in the organic fresh-market system but not in the other systems. Canonical correspondence analysis identified distinct associations between specific species and the management systems. Common purslane was strongly associated with the rain-fed, mixed fresh-market system, and barnyardgrass, goosegrass, yellow nutsedge, and green foxtail were associated with the irrigated, organic fresh-market system. Indicator species analysis identified five species that were significant indicators of the organic, fresh-market system and one species that was a significant indicator of the rain-fed, mixed fresh-market system. Weed populations persist or increase when a set of species-specific environmental conditions are met. The association of weed species in this study with particular systems supports the hypothesis that weed communities are strongly affected by management systems.
Nomenclature: Barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG; carpetweed, Mollugo verticillata L. MOLVE; common lambsquarters, Chenopodium album L. CHEAL; common purslane, Portulaca oleracea L. POROL; eastern black nightshade, Solanum ptycanthum Dun. SOLPT; giant foxtail, Setaria faberi Herrm. SETFA; goosegrass, Eleusine indica (L.) Gaertn. ELEIN; green foxtail, Setaria viridis (L.) Beauv. SETVI; prickly sida, Sida spinosa L.; yellow nutsedge, Cyperus esculentus L. CYPES; tomato, Solanum lycopersicum L.
