Experiments were conducted to determine the response of purple nutsedge tuber sprouting to diurnally alternating temperature. These experiments compared the response to alternating and constant temperatures and determined the effect of the amplitude of alternation and time of exposure to the maximum temperature. Tuber sprouting was more rapid and complete with alternating temperatures than with constant temperatures. Increasing temperature fluctuation from 0 to 6 C for 12 h daily linearly increased total tuber sprouting. As little as 30 min exposure to high temperature per day provided nearly the same level of sprouting as a 12 h alternating temperature cycle. This phenomenon should be considered when conducting studies to describe tuber temperature responses or when predicting tuber sprouting and emergence.

Sprouting percentage was estimated for purple nutsedge tubers in the field from daily fluctuating soil temperatures. Tuber sprouting under alternating temperatures ranging from 20 to 45 C for 14 d responded quadratically to alternations of high and low temperature. A response surface regression of the cumulative sprouting percentage accounted for 88% of the variation. The cumulative sprouting percentage curves were sigmoidal, and the Richards function satisfactorily regressed the characteristics of the curves. A simulation model was developed for the cumulative sprouting percentage by estimating sprouting from daily high and low temperatures and accumulating daily increments of tuber sprouting. Five weeks of soil solarization with clear polyethylene film at Waimanalo, Hawaii raised the mean soil temperature at 15-cm depth by 5.8 C in spring and by 7.2 C in summer. Solarization also increased the mean daily temperature difference from 1.5 to 3.7 C in spring and from 2.3 to 3.8 C in summer. Solarization increased the final sprouting percentage in the field from 74 to 97% in spring and from 97 to 100% in summer. The simulation model estimated the final field sprouting of tubers within 95% confidence intervals of the observed means.

The effect of constant or various fluctuating temperature regimes and single or multiple tubers in rhizome chains on tuber sprouting of six purple nutsedge ecotypes was determined. After 24 d at constant 20 C, budbreak of tubers detached from the rhizome chain (single tubers) ranged from 11 to 85% among ecotypes. When dormant tubers were exposed to a single 0.5- to 12-h, 35 C pulse followed by constant 20 C, budbreak increased for all ecotypes; daily 0.5-h, 35 C pulses from a 20 C base temperature for three to seven cycles did not significantly increase budbreak more than these did for a single cycle. Shoot length increased linearly for all ecotypes as the number of 0.5-h, 35 C pulse cycles increased, although the magnitude of shoot elongation varied with ecotype. At a 20 and 30 C (12:12 h) daily alternating temperature regime, 98% of single tubers from a Kamuela, HI, ecotype produced actively growing shoots (active tubers), whereas only 32 to 60% of tubers in two- to six-tuber chains were active. The rhizome chain effect on budbreak was minor because ≥ 90% of the tubers in rhizome chains had budbreak. Using a range of constant and alternating temperatures on single tubers and four-tuber chains, similar results were observed for all six ecotypes as for the Kamuela ecotype. Although alternating temperature increased active tubers for both single tubers and tubers in chains, it did not overcome apical dominance among tubers in rhizome chains in suppressing active tubers. The budbreak and shoot elongation stimulation by alternating temperatures and high-temperature pulses appear to be common physiological responses to all purple nutsedge ecotypes examined in this study.

The influence of green kyllinga and white kyllinga on common bermudagrass growth was compared by planting one to three green or white kyllinga rhizomes with two bermudagrass stolons. White kyllinga reduced bermudagrass shoot fresh weight to 56% of the control, but green kyllinga did not reduce bermudagrass shoot fresh weight significantly. Increased planting densities of both kyllinga species linearly increased kyllinga shoot fresh weight and decreased bermudagrass shoot fresh weight similarly. White kyllinga produced more leaf fresh weight, leaf area, and roots and rhizomes than green kyllinga, which produced more shoots and inflorescences.

A modified power function, y = (A + B·x)–C, was developed for determining the relationship between plant growth and growth retardant treatment. This function accounts for the plant response characteristics by incorporating three coefficients: A, growth level of the nontreated plants; B, the degree of growth reduction; and C, the smallest effective dose of the growth inhibitor. The function accounted for 97% of the variation in purple nutsedge (Cyperus rotundus L.) leaf length as a function of the amount of a growth retardant applied. The procedure resulted in a smaller error sum of squares than several common nonlinear functions because of its greater shape flexibility.