Effects of soil temperature and tuber depth on Cyperus spp. control

Studies were conducted to determine lethal temperatures for Cyperus esculen tus and Cyperus rotundus tubers using diurnal oscillations in soil temperat ure with maxima of 40, 45, 50, and 55 C and a minimum of 26 C. Growth of Cy perus spp. plants was Easter at 40 C than at a constant temperature of 26 C . The 45 C treatment delayed Cyperus spp. emergence but was not lethal to t ubers. Tuber mortality was 100% for both Cyperus spp. with the 50 and 55 C temperature regimes. Soil solarization with thermal-infrared-retentive (TIR ) films resulted in higher soil temperatures than with a 30-mu m low-densit y polyethylene (LDPE) clear film. With TIR films, greater proportions of em erged C. rotundus plants were killed by foliar scorching, and 6 wk of soil solarization was more effective at reducing C. rotundus density than with t he LDPE film. Four weeks after film removal, the lowest level of control wa s obtained with the LDPE film. For C. rotundus tubers planted 5 and 10 cm d eep, 62% control was obtained with the LDPE film, and it decreased to 32% w ith a 15-cm planting depth. The best residual control was 95 and 92% with t he 75-and 100-mu m TIR films, respectively. With the TIR films, there was n o significant change in C. rotundus control with planting depth.