Four greenhouse experiments were conducted to study the effects of plant residues and extracts of yellow nutsedge (Cyperus esculentus L.) plant residues on the growth of corn (Zea mays L.) and soybeans [Glycine max (L.) Merr.]. At equal concentrations, tuber residues reduced the dry weight of corn and soybeans more than foliage residues. As the concentration increased, growth decreased, affecting soybeans more than corn. Soybean growth was significantly reduced by the addition of tuber extracts. At a constant residue concentration, increasing the percentage of sand in the soil mixture reduced the growth of corn and soybeans. Growth inhibition was greatest when tuber residues were in contact with the corn or soybean seed. We conclude that extracts and residues of yellow nutsedge have an allelopathic effect on corn and soybeans under greenhouse conditions.