We constructed a mechanistic model of purple nutsedge tuber population dynamics to provide a theoretical framework for the integrated management of this weed. The model relies on a transition matrix with 10 age classes to simulate fluctuations in the tuber population. Parameters of the transition matrix are given by functions of density, age, and cumulated incident photosynthetically active radiation (PAR) underneath crop canopies. Sensitivity ratios based on a 10% reduction in parameter values indicated that the parameters of the birthrate function were most sensitive. Simulations showed that in the absence of weed control, cumulated incident PAR was by far the strongest determinant of population size; intraspecific interference was the strongest determinant of the rate of population increase. When weed control was introduced, the simulation suggested that 95% control would be required to eliminate this weed. The analysis of simulation results led to the formulation of five research hypotheses of practical relevance to the management of purple nutsedge. New insights gained by testing these hypotheses should lead to practical recommendations as well as a better understanding of the relationships between management practices and fluctuations in purple nutsedge populations.

Knowledge of weed biology is essential for development of both economically and environmentally acceptable weed management systems. Weed biology relates to plant attributes such as morphology, seed dormancy and germination, physiology of growth, competitive ability, and reproductive biology. Concepts of population biology such as seedbank dynamics for annuals and root reserves, dormancy, and longevity of vegetative propagules for perennials can be used to predict weed infestations better and to evaluate sustainable management strategies. Integrated approaches that give priority to depletion of root reserves or seedbanks through interfering with dormancy or germination requirements have great potential to enhance weed management strategies in the future.

A series of greenhouse studies examined the effectiveness of PRE- and POST-applied sulfentrazone in controlling purple and yellow nutsedge as influenced by selective tissue exposure. In addition, 14C-sulfentrazone was utilized to contrast absorption and translocation resulting from these exposures. Consistent control with preemergence applications to germinating tubers was obtained with a combined root and shoot zone exposure. Yellow nutsedge was more susceptible than purple nutsedge. Performance of the separate root and shoot zone exposure was soil pH- and nutsedge-species dependent. POST-foliar applications to established nutsedge were more effective when sulfentrazone was allowed to contact the soil surface. 14C-sulfentrazone was readily absorbed by the roots and translocated to the foliage of both species in hydroponic culture.

Greenhouse studies in 1995 and 1996 examined the response of yellow and purple nutsedge to inoculation with increasing densities of southern root-knot nematodes. Yellow and purple nutsedge root and shoot weight, numbers of leaves and tubers produced, and tuber weight were unaffected across 17 nematode inoculum densities that ranged from 0 to 20,000 eggs per 15-cm pot, four times the maximum nematode density recorded under field conditions in New Mexico. Hence, yellow and purple nutsedge do not exhibit a classic threshold response to root-knot nematodes. Moreover, the results suggest that the relationship between these nematodes and perennial nutsedges is an example of a positive biological interaction. The relationship between root-knot nematodes and purple nutsedge appears to be one of commensalism, because while the nematodes reproduced effectively, purple nutsedge reproduction was not related to final nematode populations. The relationship between yellow nutsedge and root-knot nematodes appears to be a mutually beneficial one, because yellow nutsedge tuber number and weight and root weight increased as final nematode populations increased. However, while both nutsedges were unaffected in the absence of the association, root-knot nematodes cannot survive without a host plant.

Replacement series experiments were conducted under greenhouse conditions to evaluate effects of population densities and proportions on the intraspecific and interspecific interference of either purple nutsedge or yellow nutsedge with tomato cv. Sunny, under nonlimiting conditions of water and nutrients. When grown with either nutsedge species for 40 d, tomato dry weight per plant increased and dry weight per plant of nutsedge decreased as their relative proportions decreased in mixture. Relative yield analysis indicated tomato is a stronger competitor than either nutsedge species. Both nutsedges appeared to be weak interspecific competitors but strong intraspecific competitors. Attenuated light on a purple nutsedge canopy showed that tomato additions can reduce light received by the weed compared to pure nutsedge stands.

Greenhouse studies were conducted to determine purple and yellow nutsedge response to selective placement of a 5-cm layer of pyrithiobac sodium-treated soil above, below, or above and below nutsedge tubers. Pyrithiobac sodium at 36 or 72 g ae ha−1 applied postemergence as foliar, soil, or foliar and soil treatments also was evaluated. Pyrithiobac sodium applied above, below, or above and below nutsedge tubers reduced yellow and purple nutsedge shoot number, shoot regrowth, and root-tuber dry weight at least 90%. Foliar-only treatment of pyrithiobac sodium was less effective at reducing emerged purple and yellow nutsedge numbers than application to soil only or to foliage and soil. Best reduction in yellow and purple nutsedge growth with pyrithiobac sodium was obtained with soil-incorporated treatments.

Soil solarization is a process of soil disinfestation that involves solar heating of moist soil covered with transparent polyethylene film. This nonchemical approach to controlling soil-borne pests is being investigated as an alternative to methyl bromide fumigation. Summer solarization controlled annual weed species and suppressed purple nutsedge. Although some nutsedge tubers sprouted despite the solarization treatment, the resulting shoots were almost always trapped under the clear solarization film. Conversely, in rows that were mulched with black film, nutsedge rhizomes punctured the film so that leaf expansion occurred above the film. In controlled pot experiments conducted in darkness, yellow nutsedge rhizomes readily penetrated 19- and 30-μm clear films as effectively as opaque films. Thicker clear films and bubble film reduced nutsedge penetration. In the greenhouse and laboratory, nutsedge penetration of transparent polyethylene film was inversely related to irradiance levels when the film was in direct contact with the soil. However, when there was a 5- to 10-mm space between the soil and the film, the lowest irradiance level (30 μmol m−2 s−1) was as effective as 320 μmol m−2 s−1 in reducing penetration by purple nutsedge. The film penetration by nutsedge rhizomes appears to be linked to a light-dependent morphological change from rhizome growth to leaf development, which occurs before film penetration with clear mulch and after film penetration with opaque mulch. The alternate sprouting and foliar scorching of nutsedge shoots trapped under clear films could potentially be exploited to deplete nutsedge tubers that occur at soil depths that do not develop lethal temperatures under soil solarization.

Greenhouse and field experiments were conducted to determine the effects of nitrogen (N) supply and purple nutsedge population densities on the yield of radish. In the greenhouse studies, additive series with purple nutsedge densities of 0, 50, 100, 200 or 350 plants m−2 were established. Nitrogen rates of 0, 110, 220, or 330 kg ha−1 were provided to the potting medium. A significant density by N interaction was found for radish fresh weight. Within a given nutsedge density, radish yield decreased as N rate increased. In field studies, additive series of 0, 50, 100, 150, or 200 nutsedge plants m−2 were established the same day radish was sown. Nitrogen rates were 100 or 200 kg ha−1. Marketable radish yield losses and nutsedge shoot dry weight and height were determined 30 d after seeding the crop. Nutsedge densities and N rates interactively influenced radish root yield. Radish yield loss reached 100% at nutsedge densities of 75 and 125 plants m−2 at 200 and 100 kg N ha−1, respectively. Purple nutsedge produced larger shoot biomass as N increased from 100 to 200 kg ha−1. Results of both greenhouse and field studies showed that as N increased, the negative effect of the weed on the crop was enhanced.

Three years of field trials have been carried out in Zaragoza, Spain, using different biodegradable mulch materials in processing tomatoes. The aim was to evaluate weed control with several biodegradable mulches as alternatives to black polyethylene (PE) mulch. The treatments were rice straw, barley straw, maize harvest residue, absinth wormwood plants, black biodegradable plastic, brown kraft paper, PE, herbicide, manual weeding, and unweeded control. Assessments focused on weeds and on crop yield. A laboratory study showed that 1 kg/m2 of organic mulch was sufficient to cover the soil for rice, barley straw, and maize harvest residue. The most abundant weed species in the field were purple nutsedge, common purslane, common lambsquarters, and large crabgrass and a change in weed composition was observed between treatments and years. Most weed species were controlled by the mulching materials except that purple nutsedge was controlled only by paper mulch. The other species were well controlled by PE and biodegradable plastic and also by some of the organic mulch treatments. Best weed control and lowest weed biomass were achieved by paper followed by PE and biodegradable plastic. The best organic mulch was rice straw and the worst weed control was from absinth wormwood. Tomato yield was highest for PE followed by paper, manual weeding, biodegradable plastic, and rice straw and was clearly related to weed control. Paper, biodegradable plastic, and rice straw are potential substitutes for PE and herbicides.

A field microplot experiment was conducted in 1996 and 1997 to determine the influence of root-knot nematodes on intra- and interspecific interactions between chile pepper (chile) and spurred anoda and between chile and yellow or purple nutsedge (or both) using a substitution design. An additional objective was to determine the influence of London rocket, a winter annual and host plant for root-knot nematodes, on the inter- and intraspecific interactions between chile and spurred anoda. Twelve plant combinations were planted into paired 76-cm-diam microplots at a density of 24 plants per microplot each year. Each pair of microplots had one root-knot nematode–infested and one uninfested plot. One randomly selected plant pair or triplet from each plot was destructively sampled in June, July, August, and September each year. Data included leaf area, plant dry weights (leaf, stem, root or root plus rhizome, chile fruit, and nutsedge tuber), and nematode egg production from the belowground biomass of the different plant species within a 2,355-cm3 sampled soil volume. Chile hosted the highest population of root-knot nematodes, followed by spurred anoda, purple nutsedge, and yellow nutsedge. Few root-knot nematode eggs were recovered from London rocket before incorporation into the microplots each spring. Root-knot nematode populations were higher in 1997 and, as a result, more interactions between nematodes and plant combinations were observed for chile. Spurred anoda and root-knot nematodes reduced chile shoot and root weights to levels not significantly different from zero in 1997. Yellow and purple nutsedge shoots, except for those from the original tuber, were removed throughout the season, and these species interfered less with chile. Spurred anoda was not affected by interspecific interference. Few interactions were observed between the spurred anoda plant combinations and root-knot nematodes. In June 1996, low populations of root-knot nematodes (< 4,000 eggs per gram of root) stimulated spurred anoda growth, but higher populations in June 1997 (> 30,000 eggs per gram of root) reduced spurred anoda growth. Prior presence of London rocket had little consistent influence on spurred anoda or chile. Yellow and purple nutsedge growth variables were affected by interference from chile and the other nutsedge species. Tuber number and tuber weight were higher when plants were infected with root-knot nematodes, particularly early in the season. The enhanced tuber production may increase early-season interference from nutsedge species under production conditions. The results suggest that the presence of root-knot nematodes influences plant interference, but the effect is species specific. Annual plants are affected differently compared with perennial nutsedges, possibly because of the continuous association between the perennials and the parasite.

Dormancy is a critical factor for the survival and persistence of weedy species. Contemporary approaches can be used to identify genes that regulate dormancy directly or indirectly to elucidate key mechanisms, signals, and pathways. Several domesticated plant species have been used as model systems to mark quantitative trait loci (QTL) that affect dormancy in seeds and vegetative propagules directly. A few weedy species have also been used to mark QTL and to determine dormancy genes using microarray analysis. Given the number of serious weeds worldwide and the role that dormancy plays in their persistence, developing fundamental knowledge on dormancy is an important step toward developing new strategies for weed management. This paper describes current research and outlines some weeds that might be candidates for dormancy investigations using molecular genetic and genomics approaches. An underlying theme in the selection of weeds for dormancy investigations is their relation to crop species and the ability to adapt existing resources to investigate dormancy in weedy plants.

A field experiment was conducted in Okinawa, Japan from 2005 to 2007 to evaluate the effect of purple nutsedge and other weeds on turmeric growth and yield and determine the effective weed-control period to minimize crop interference. Treatments consisted of all weeds removed at 70, 115, and 160 d sequentially after planting (DAP), all weeds except purple nutsedge removed at these three dates, plus weedy and weed-free controls. Purple nutsedge density increased until 115 DAP when grown alone with turmeric and thereafter decreased markedly, whereas it increased only until 70 DAP when grown with other weeds. Weed reinfestation in turmeric that was sequentially weeded was high until 115 DAP, but thereafter was negligible. In the weedy control, the weed infestation was severe until 160 DAP. Plant height and leaf and tiller number per plant of turmeric increased rapidly from 70 to 160 DAP. Season-long weed infestation significantly reduced shoot biomass and rhizome yield of turmeric, but both were similarly high among treatments of weed-free turmeric, all weed removal, and removal of all weeds except purple nutsedge. Purple nutsedge (> 3,000 plants/m2) did not significantly reduce turmeric yield, whereas the combined weed species reduced yield by greater than 40%. Thus, crop interference by purple nutsedge was not high, and other weeds could be removed during 70 to 160 DAP for reduced labor requirements and higher yield of turmeric.

Experiments were conducted at the Upper Coastal Plain Research Station near Rocky Mount and at the Peanut Belt Research Station near Lewiston-Woodville in 2002 and 2003. Peanut injury was minimal (< 5%) with all soil-applied programs. S-Metolachlor PRE alone or in mixture with sulfentrazone, diclosulam, or flumioxazin controlled annual grasses similarly (66 to 87%). The addition of imazapic plus 2,4-DB POST increased annual grass control (> 93%). Sulfentrazone or diclosulam in mixture with S-metolachlor were the best PRE options, with 94% and 92% control of yellow and purple nutsedge, respectively, with flumioxazin being least effective at 70%. Diclosulam and flumioxazin in mixture with S-metolachlor were the best PRE options, with 99% and 93%, respectively for common ragweed control, whereas sulfentrazone was the least effective at 65%. S-Metolachlor in mixture with sulfentrazone, diclosulam, or flumioxazin PRE were similar (87 to 90%) for common lambsquarters control. S-Metolachlor in mixture with sulfentrazone, diclosulam, or flumioxazin provided similar levels of entireleaf, ivyleaf, pitted, and tall morningglory control (87, 86, and 87%, respectively) and better than S-metolachlor alone at 64%. Flumioxazin in mixture with S-metolachlor was the best PRE option for control of Palmer amaranth at 96%, whereas diclosulam with S-metolachlor was the best PRE option for control of eclipta at 100%. The prepackaged mixture of acifluorfen and bentazon plus 2,4-DB POST and imazapic plus 2,4-DB POST were similar for all morningglory species (> 96%) and Palmer amaranth control (93 and 97%, respectively). Peanut treated with S-metolachlor plus diclosulam PRE numerically yielded the highest at 3,210 kg/ha, but were statistically equivalent to S-metolachlor plus flumioxazin PRE at 3,040 kg/ha. Peanut treated with imazapic plus 2,4-DB POST yielded the most at 3,400 kg/ha, while peanut treated with a prepackaged mixture of acifluorfen and bentazon plus 2,4-DB POST yielded less (3,070 kg/ha).

Purple and yellow nutsedge are the most troublesome weeds of vegetable crops in the southeast United States. Elimination of methyl bromide use will require alternative management programs to suppress nutsedge growth and interference in vegetables. Polyethylene mulch is an effective barrier for most weeds; however, nutsedges can proliferate in beds covered with polyethylene mulch. The influence of polyethylene mulch on shoot production and lateral expansion patterns of single tubers of purple nutsedge and yellow nutsedge over time was evaluated in field studies. Purple nutsedge patch size was similar in the black mulch treatment and nonmulched control after 8 and 16 wk after planting (WAP). By the end of the growing season, purple nutsedge patch size in the black mulch treatment was nearly twice that in the nonmulched control. At 32 WAP, there were 1,550 shoots in the 16.1 m2 patch in the black mulch treatment and 790 shoots in the 8.1 m2 patch in the nonmulched control. In contrast, yellow nutsedge growth was suppressed in the black mulch treatment, relative to the nonmulched control. Compared with the black mulch treatment at 16 and 24 WAP, the nonmulched control produced nearly three times as many yellow nutsedge shoots (140 shoots at 16 WAP and 210 shoots at 24 WAP) and patches that were twice the size (0.10 m2 at 16 WAP and 0.18 m2 at 24 WAP). These data indicate that there are significant differences in the growth habits of the two nutsedges species in mulched vegetable systems. The differences in response to black mulch will likely lead to purple nutsedge becoming a greater problem, relative to yellow nutsedge, in vegetable systems. The rapid expansion of a single purple nutsedge shoot to form a patch that is 22.1 m2 and containing 3,440 shoots at 60 WAP illustrates the importance of managing this species.

Purple nutsedge is among the most troublesome weeds of vegetables in the Southeast US and a substantial impediment in the search for methyl bromide alternatives. Greater understanding of the environmental cues that regulate tuber sprouting may assist in improved nutsedge management. Experiments were conducted to evaluate the effect of diurnal temperature variation on sprouting of purple nutsedge tubers. Two temperature regimes were evaluated: the first averaged 28 C, with daily fluctuations ranging from 0 to 19.5 C; the second temperature regime averaged 16 C, with daily fluctuations ranging from 0 to 18.5 C. When average temperature was 28 C, cumulative tuber sprouting ranged from 88 to 92%, with no detectable differences among diurnal fluctuations. The high average temperature in the first study may have negated any type of enforced sprouting suppression. However, when average temperature was lowered to 16 C (simulating early spring diurnal fluctuations under polyethylene mulch), there was a positive linear correlation between maximum tuber sprouting and temperature variation. With an average temperature of 16 C, the absence of temperature variation resulted in 52% purple nutsedge sprouting, while 87% sprouting occurred when daily temperature varied 18.5 C at the same average temperature. The use of various types of mulching material can affect average soil temperatures and diurnal variations, potentially shifting nutsedge emergence. Further studies are needed to determine if these data on tuber sprouting in response to alternating temperatures can facilitate more efficient weed management.

Soil solarization has been proposed as an alternative to methyl bromide for controlling nutsedges. Little is known, however, about the relationship between soil solarization and nutsedge tuber viability. Combinations of elevated temperatures and durations of exposure were evaluated for their effect on purple nutsedge and yellow nutsedge tuber viability and new tuber production in growth chamber studies. Estimates of the duration of exposure at each temperature that reduced nutsedge growth parameters 50% (TT50) were supplied by log-logistic regression analysis. Nutsedge tuber viability was reduced when temperatures were ≥ 45 C. Relative to purple nutsedge, yellow nutsedge tuber viability had smaller TT50 values for 45, 50, and 55 C. Tuber viability TT50 at 60 C was similar for both nutsedges. The TT50 for production of new purple nutsedge tubers at 50 C was larger than that for yellow nutsedge. However, there were no differences between species in TT50 values for new tuber production at higher temperatures. With sufficient durations of exposure, both purple and yellow nutsedge tubers were killed at temperatures ≥ 50 C. However, application of these data to field situations in Georgia may be limited using present technology because the soil temperature cannot be raised to high enough levels for acceptable solarization effects.

Weeds persist and cause economic losses in agricultural systems because they exploit underused portions of that system. Reducing the effect of weeds on agroecosystems begins with minimizing the number of propagules (e.g., seeds and tubers) that are produced and returned to the soil. Purple nutsedge is a problematic weed around the globe, persisting between growing seasons as tubers in the soil. Halosulfuron is an effective herbicide for controlling purple nutsedge foliage and is used in corn and several vegetable crops. Studies were conducted to evaluate the effect of various rates of halosulfuron on purple nutsedge tuber production. Single, presprouted purple nutsedge tubers were transplanted into outdoor microplots and treated after 6 wk of growth with six rates of halosulfuron (7 to 208 g ai ha−1) POST with a nontreated control (NTC). All shoots that had emerged at the time of application were marked with plastic rings; this allowed for classification of tubers at exhumation of (1) tubers attached to shoots that had emerged by the time of application, (2) tubers attached to shoots that emerged after application, and (3) tubers without an aerial shoot during the study. Seven weeks after application, the tubers in the microplots were exhumed and tubers were classified, quantified, and their ability to sprout was evaluated. In the NTC, there were 530 total tubers, with a log-logistic regression model describing the tuber population with increasing halosulfuron rate. The rate of halosulfuron that reduced total tuber population 50% (I50) was 8 g ha−1. In the NTC, 200 tubers were attached to shoots that emerged following halosulfuron application, and this class of tubers had an I50 of 19 g ha−1. Viability of tubers with shoots that emerged following halosulfuron application was 28% at the 52 g ha−1 halosulfuron, suggesting the action of the herbicide may have rendered the tuber nonviable after new shoots were produced. The final classification of tubers was those that did not have an aerial shoot during the study. These were tubers in which apical dominance suppressed shoot development or were likely the most-recent tubers to develop. Of the three classes, the tubers without shoots were the most numerous in the NTC, with 294 tubers and an I50 of 1 g ha−1. Halosulfuron is an effective herbicide that not only controls purple nutsedge foliage but also reduces the number of new tubers produced and overall tuber viability. This could be an important component to reduce the long-term population density of the weed.

Field and greenhouse studies were conducted to evaluate mesotrione alone and in combinations with low rates of atrazine and bentazon for control of yellow and purple nutsedge. Mesotrione alone at rates of 105 to 210 g ai/ha controlled yellow nutsedge 43 to 70%. Mixtures of mesotrione with atrazine at 280 g ai/ha did not always improve yellow nutsedge control over that by mesotrione alone, but increasing atrazine to 560 g ai/ha in these mixtures generally provided more consistent control of yellow nutsedge. Mesotrione at 105 g ai/ha mixed with bentazon at 280 or 560 g ai/ha controlled yellow nutsedge 88% or greater which was similar to control from the standard halosulfuron at 36 g ai/ha. Mesotrione, atrazine, and bentazon alone did not control purple nutsedge. Mixtures of mesotrione plus bentazon, however, did improve control of purple nutsedge over either herbicide applied alone, but this control was not considered commercially acceptable.

The biology of purple nutsedge was studied by growing it alone and in competition with 12 and 24 rice plants in a pot experiment. Compared with the weedy plants grown alone, competition from rice reduced purple nutsedge leaf number, shoot number, tuber production rate, and leaf biomass. At 10 wk after planting, interference from 12 and 24 rice plants reduced purple nutsedge leaf area by 79 and 86%, respectively, compared with weedy plants grown without rice interference. On the same date, purple nutsedge aboveground shoot biomass was 26.8 g plant−1 without interference, whereas in interference with 12 and 24 rice plants, purple nutsedge produced aboveground biomass of 4.8 and 2.2 g plant−1, respectively. A total of 95 tubers plant−1 were produced by purple nutsedge when grown alone. Growth with 12 and 24 rice plants reduced tuber production to 33 and 17 tubers plant−1, respectively. Without interference, purple nutsedge produced 40 g plant−1 of total biomass of tuber plus root plus rhizome, whereas in interference with 12 and 24 rice plants, purple nutsedge produced 14 and 5 g plant−1 of total belowground biomass, respectively.

Leaf-cover area is a widely required plant development parameter for predictive models of weed growth and competition. Its assessment is performed either manually, which is labor intensive, or via visual inspection, which provides biased results. In contrast, digital image processing enables a high level of automation, thereby offering an attractive means for estimating vegetative leaf-cover area. Nonetheless, image-driven analysis is greatly affected by illumination conditions and camera position at the time of imaging and therefore may introduce bias into the analysis. Addressing both of these factors, this paper proposes an image-based model for leaf-cover area and biomass measurements. The proposed model transforms color images into an illumination-invariant representation, thus facilitating accurate leaf-cover detection under varying light conditions. To eliminate the need for fixed camera position, images are transformed into an object–space reference frame, enabling measurement in absolute metric units. Application of the proposed model shows stability in leaf-cover detection and measurement irrespective of camera position and external illumination conditions. When tested on purple nutsedge, one of the world's most troublesome weeds, a linear relation between measured leaf-cover area and plant biomass was obtained regardless of plant developmental stage. Data on the expansion of purple nutsedge leaf-cover area is essential for modeling its spatial growth. The proposed model offers the possibility of acquiring reliable and accurate biological data from digital images without extensive photogrammetric or image-processing expertise.