Studies were conducted to determine the extent of full and partitioned interference of two nutsedge species with tomato. For full interference, the crop and the weed were transplanted in the same container. For belowground interference, tomato and either weed species were grown in the same container, but the canopies were separated. For aboveground interference, tomato and nutsedges were grown in separate containers placed adjacently, whereas for the no-interference treatment, tomato and nutsedge plants were grown in individual containers. Full interference by yellow nutsedge was more detrimental to tomato shoot dry weight accumulation (34% reduction) than was full interference by purple nutsedge (28% reduction). Belowground interference by purple nutsedge reduced tomato shoot dry weight (18%) more than did aboveground interference (9%). Yellow nutsedge interference above- or belowground reduced tomato shoot dry weight to a similar extent (19%). The belowground interference of both nutsedges with tomato resulted in deficient concentrations of nitrate in the sap of tomato (> 18% reduction). The growth of purple nutsedge was influenced more strongly by tomato shading than by belowground interference from the crop, whereas yellow nutsedge growth was equally affected by tomato above- and belowground. According to these results, shoot dry weight accumulation in tomato was affected to the same extent by belowground interference from purple and yellow nutsedge, and the higher effect of full interference by yellow nutsedge may be attributed to increased aboveground competition between tomato and yellow nutsedge.

Nomenclature: Purple nutsedge, Cyperus rotundus L. CYPRO; yellow nutsedge, Cyperus esculentus L. CYPES; tomato, Lycopersicon esculentum Mill. ‘Solimar’.