Purple nutsedge is considered to be the worst weed in the tropical and subtropical regions of the world. Although the plant is a low grower it has very strong competitive abilities. The influence of initial tuber size and cold treatment on tuber sprouting, accumulation of plant biomass and new tubers formation was studied. Tubers sprouted continuously over 30 to 50 d with significantly lower sprouting ability of small tubers (0.1 to 0.2 g). Short cold treatment (4 C for 4 d) significantly stimulated sprouting process. The early sprouting of cold treated tubers led to increased number of shoots and inflorescences and therefore more intensive biomass accumulation, as well as more intensive formation of new tubers. The increase in total biomass accumulation raises the reproductive and spreading potential of the weed.

Native to temperate South America, deeproot sedge has naturalized throughout the southeastern United States. Often forming dense, homogenous stands, deeproot sedge has become widespread, invasive, and potentially harmful ecologically throughout the coastal prairie ecoregion of Texas. Possessing characteristics (rapid growth, generalized habitat requirements) of other weedy congeners (purple nutsedge and yellow nutsedge), its relatively recent expansion highlights the critical need to develop effective control techniques and strategies for this species throughout this endangered ecoregion. Research was performed to delineate total nonstructural carbohydrate (TNC) trends in deeproot sedge rhizomes for development of a phenologically based schedule for herbicide applications and mechanical treatments. Overall, TNC levels were greatest in May to August and lowest from October to January, regardless of study area. Apparently, deeproot sedge exerts little energy into seed production because TNC levels were continually replenished throughout the growing season. As such, foliar-herbicide application throughout the growing season should achieve total plant kill. Conversely, deeproot sedge rhizome TNC levels never fell below 30%, even during winter, which indicates that winter mechanical treatments or winter prescribed fires will not be effective because substantial rhizome reserves are present to support resprouting during the next growing season. Beyond a priori prevention, sequential herbicide applications combined with integrated, sequential, prescribed fire and herbicide treatments will be needed for long-term deeproot sedge control throughout its geographic range.

Herbicides are the basis for conventional management of purple nutsedge, one of the world's most troublesome weeds. However, as concern rises over their environmental impact, farmers are being required to reduce herbicide usage. Herbicide efficacy is strongly affected by weed growth stage and density at application, and when herbicides are applied under optimal conditions, low rates can provide maximal control efficacy (CE). Therefore, this study aimed to determine the time window for control of purple nutsedge using a low rate of herbicide, based on an effective degree days (EDDs) model, at low (one tuber) and high (10 tubers) densities. Two experiments were performed under field conditions, in the summers of 2009 and 2010. Rate of 3.75 g a.i. ha−1 trifloxysulfuron was applied once on each of five individual application dates. The growth of both treated and untreated plots was evaluated by means of leaf cover area (LCA) and biomass, which were then used to establish the time window for control. Results showed differences in both growth parameters between low and high tuber densities. The high-density patches reached LCA and fresh biomass values of 1,367 g and 1.12 m2, respectively, compared to 604 g and 0.69 m2, respectively, in the lower density patches. The favorable control periods based on biomass and LCA for the lower density patches were set to later dates than those for the higher density patches, 626 EDD compared to 483 EDD for biomass, and 786 EDD compared to 502 EDD for LCA, respectively. Although differences between the biomass- and LCA-based favorable control periods were observed at both tuber densities, the computed linear relations between the two growth parameters enabled adjusting them and setting the appropriate control period.