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Fomesafen is a protoporphyrinogen oxidase (PROTOX) inhibitor that has the potential to be used as an alternative mechanism of action for PRE nutsedge and broadleaf weed control in Florida production of small fruit and vegetables. Fumigation in the raised-bed plasticulture system may increase herbicide persistence. Fomesafen persistence could dissuade Florida growers from using the herbicide for fear of injury to subsequent susceptible crops. Field experiments were conducted in Balm, FL, in 2015 and 2016 to investigate the effect of fumigation on fomesafen dissipation, eggplant tolerance, and purple nutsedge control. Treatments included fomesafen at 0.42 kg ai ha−1,S-metolachlor at 1.06 kg ai ha−1, and a nontreated control in either a fumigated bed injected with a combination of 39% 1,3-dichloropropene and 59.6% chloropicrin at 336 kg ha−1or no fumigant. Fomesafen concentration in the soil decreased by 83% and 96% from application to harvest in 2015 and 2016, respectively. Fumigation did not affect fomesafen dissipation in either year. At 2 wk after transplant (WATr), fomesafen caused 14% eggplant injury. Injury decreased to less than 5% at 6 WATr. Fomesafen andS-metolachlor treatments did not reduce eggplant height or yields compared with the nontreated control. Fumigation and fomesafen did not decrease purple nutsedge density; however,S-metolachlor applications resulted in a 48% reduction. Further research is needed to assess efficacy on broadleaf and grass weeds.

Mulches used in plasticulture systems could decrease dissipation of fomesafen, a protoporphyrinogen oxidase inhibitor, and dissuade producers from using the herbicide for fear of crop injury in subsequent growing seasons. Field experiments were conducted in Balm, FL, in 2015 and 2016 to investigate the effect of different plastic mulches on fomesafen dissipation, squash tolerance, and efficacy on purple nutsedge. Squash was injured less than 5% from fomesafen applications. The use of plastic mulches reduced purple nutsedge density at transplant by 60% compared with the no-mulch treatment. At transplant, treatments with low-density polyethylene mulch (LDPE), virtually impermeable film (VIF), and totally impermeable film (TIF) mulch had greater than 2-fold the fomesafen concentrations than treatments with clear or no mulch. At harvest in 2015, LDPE, VIF, and TIF treatments had greater fomesafen concentrations than clear and no-mulch treatments; however, concentrations in 2016 were similar for all treatments. Fomesafen can persist at high concentrations throughout the growing season in Florida plasticulture possibly limiting producer options for crop rotation and the use of cover crops.Nomenclature: Fomesafen; purple nutsedge; Cyperus rotundus L.; squash, Cucurbita pepo L.

Weeds exploit underutilized space, causing economic losses in cropping systems. Weed management tactics alter that underutilized space until the crop can mature and efficiently use that space. One tactic is to reduce the weed propagules (e.g., seeds and tubers) that persist quiescently in the soil, which includes minimizing production and addition of new propagules to the soil. Purple nutsedge is a problematic weed around the globe, persisting between growing seasons as tubers in the soil. Imazapic is a peanut herbicide often used in Georgia for control of purple nutsedge. The objective of the experiment was to evaluate the effect of various rates of imazapic 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 imazapic (5 to 140 g ai ha−1) POST. A nontreated control was included. All emerged shoots at the time of application were marked with plastic rings; this allowed for classification of tubers at exhumation as (1) tubers attached to shoots that were emerged at time of application, (2) tubers attached to shoots that emerged after application, and (3) tubers without an aerial shoot during the study. At 7 wk after application, the tubers in the microplots were exhumed, classified, and quantified, and their ability to sprout was evaluated. In the nontreated control, there were 544 total tubers, with a log-logistic regression model describing the declining tuber population with increasing imazapic rate. The rate of imazapic that reduced total tuber population 50% (I50) was 36 g ha−1. In the nontreated control, there were 161 tubers attached to shoots that emerged, as when compared with plots that received an imazapic application that had an I50=60 g ha−1. Viability of purple nutsedge tubers was 44% at 70 g ha−1imazapic, suggesting the action of the herbicide may have rendered the tubers nonviable after new shoots were produced. The final classification of tubers included 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 prevalent in the nontreated control, with 358 tubers and an I50=18 g ha−1. Imazapic controls purple nutsedge foliage but also reduces the number of new tubers produced, and overall tuber viability and is a valuable tool in management of the long-term population density of this weed.

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. Nomenclature: Purple Nutsedge, Cyperus rotundus L.

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−1trifloxysulfuron 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.

Purple nutsedge is a troublesome C4weed, characterized by high photosynthetic efficiency, compared to C3weeds. As its dispersal is based on vegetative growth, accurate prediction of its growth could help in arriving at favorable management decisions. This article details the development and validation of predictive models of purple nutsedge spatial growth, based on temperature (thermal model), and temperature and radiation (photothermal model) measurements. Plants were grown in six experiments in the summers of 2008, 2009, and 2010, under different temperature and radiation conditions. Results indicate that under optimal temperatures, radiation becomes the main growth-limiting factor, and is highly related to the final leaf-cover area (R2= 0.89). Comparison of the thermal and photothermal models showed that under all conditions, including varied temperature and radiation, the photothermal model performs significantly better, with differences in root-mean-square error values reaching up to 0.073, compared to 0.195 with the thermal model. Validation experiments confirmed the ability of the photothermal model to predict purple nutsedge spatial growth accurately.

The phase-out of methyl bromide requires alternative nutsedge management options in vegetable systems. Options that target tuber production, the primary means of reproduction, will be most beneficial. A study was conducted to evaluate the response of purple nutsedge and yellow nutsedge foliar growth and tuber production to a range of glyphosate rates. Glyphosate was applied at six rates between 0.41 and 2.57 kg ae ha−1to 5-wk-old nutsedge plants with multiple shoots. The rate of glyphosate needed to reduce growth 50% (I50) was similar for purple nutsedge foliar growth (0.58 kg ha−1) and tuber biomass (0.55 kg ha−1). In contrast,I50for yellow nutsedge foliar growth was 0.73 kg ha−1, which was greater than theI50for tuber biomass (0.41 kg ha−1). First-order tubers, those directly attached to the initial tuber, had anI50of 0.70 and 0.44 kg ha−1of glyphosate for purple nutsedge and yellow nutsedge tuber biomass, respectively. For all higher-order tubers,I50values ranged from 0.29 to 0.60 and 0.14 to 0.30 kg ha−1of glyphosate for purple nutsedge and yellow nutsedge tuber biomass, respectively. Glyphosate at 0.74 kg ha−1prevented fourth-order purple nutsedge and third-order yellow nutsedge tuber production (terminal tubers for yellow nutsedge). Fifth- and sixth-order purple nutsedge tuber production was eliminated by the lowest tested rate of glyphosate (0.41 kg ha−1). Effective nutsedge management options will require consistent control between spring and autumn crops. Glyphosate is economical, poses no herbicide carryover issues to vegetables, and minimizes nutsedge tuber production; therefore, it is a suitable candidate to manage nutsedges.

Research was initiated in March 2005 to test various integrated purple nutsedge management strategies over two growing seasons in an organic production system in which bell pepper was grown as a fall crop. Main plots consisted of integrated purple nutsedge management strategies from mid-March through July 2005 and 2006. The main-plot factors were (1) green polyethylene film, (2) clear polyethylene film, (3) turnip followed by (fb) green polyethylene film, (4) turnip fb clear polyethylene film, (5) tillage every 3 wk, and (6) fallow. Subplots consisted of hand-weeding, mulching with wheat straw, and no weeding following bell pepper transplanting in early August. Purple nutsedge tuber density was determined in March, August, and November each year. Viable tubers were categorized into three sizes: small (0.1 to 0.25 g), medium (0.26 to 0.50 g), and large (> 0.50 g). The initial tuber density averaged 500 small, 300 medium, and 110 large tubers m−2in mid-March 2005 (910 total tubers m−2). Total tuber density increased to > 5,400 tubers m−2in fallow, nonweeded plots by November 2006. Yearly tuber density remained relatively constant over the 2 yr when the fallow period was fb hand-weeding in the bell pepper crop. Density of large and medium tubers in the season-long management systems remained stable, whereas small tubers were prone to depletion over time. Frequent tillage or use of a polyethylene film with or without turnip resulted in a lower density of large tubers in November 2006 relative to fallow treatments, regardless of management intensity in bell pepper. The density of large tubers after 2 yr was similar among treatments involving frequent tillage or use of a polyethylene film with or without turnip, regardless of subplot treatment; this was also observed for medium tubers, but not for small tubers. All hand-weeded plots had comparable densities of small tubers, ranging from 25 to 194 viable tubers m−2. Intensive management involving frequent tillage or use of a translucent polyethylene film with or without turnip fb hand-weeding was not effective in eradicating purple nutsedge over two growing seasons. Purple nutsedge management costs calculated for each main-plot treatment revealed that use of a translucent polyethylene film alone was at least 4.5-fold more costly than frequent tillage. This research demonstrates that season-long management is essential to prevent purple nutsedge proliferation over time.

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 nutsed...

The identities of two novel perennial nutsedge biotypes collected near Bakersfield, CA, were assessed using isozyme and random-amplified polymorphic deoxyribonucleic acid markers in conjunction with morphological analysis. The two biotypes, designated as CK (Cyperus rotundus cv. ‘Kempeni’) and CR (Cyperus esculentus cv. ‘Robusta’), morphologically resemble purple nutsedge and yellow nutsedge, respectively. Plants from both biotypes exhibited more prolific growth than the typical forms and possessed some traits that are not characteristic of the species they resemble. The morphological study was conducted on a total of 15 purple nutsedge, yellow nutsedge, CK, and CR populations collected in the first year and on 20 additional nutsedge populations were collected in the second year. The genetic analysis was performed on populations from the first year only. In general, there was agreement among the results obtained from the morphometric, isozymatic, and deoxyribonucleic acid studies. Populations of ...

Because of interest in monitoring crop response to weed interference, greenhouse experiments were conducted to evaluate interference of purple and yellow nutsedge on the growth, development, and spectral response of cotton and soybean. Cotton fresh weight was reduced 9 to 42% compared with the control when grown with yellow and purple nutsedge. Fresh weight of soybean was reduced 27 to 60% when it emerged simultaneously with yellow nutsedge and 45 to 63% when it emerged 7 d after yellow nutsedge. Soybean fresh weight was reduced 30 to 35% when it emerged simultaneously with purple nutsedge and 44 to 72% when it emerged 7 d after purple nutsedge. Reflectance data were analyzed using wavelet transformation techniques with the HAAR mother wavelet. Nine extracted features from the cotton and soybean leaf reflectance measurements were used to classify single-leaf cotton and soybean reflectance measurements to predict whether cotton or soybean was growing in the presence or absence of purple and yellow...

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...

Studies were conducted to evaluate the absorption, translocation, and metabolism of 14C–CGA-362622 when foliar-applied to purple and yellow nutsedge. Less than 53% of the herbicide was absorbed after 96 h. Both nutsedge species translocated appreciable amounts of herbicide (30%) out of treated leaves. Translocation was both acropetal and basipetal, with at least 25% transported basipetally. Neither nutsedge species translocated more than 4% of applied radioactivity to the tubers and roots. Most of the metabolites formed by the nutsedge species were more polar than 14C–CGA-362622 and averaged 69 and 61% of the radioactivity in purple and yellow nutsedge, respectively. The half-life of CGA-362622 was estimated at 4 h in both purple and yellow nutsedge. Nomenclature: CGA-362622, N-([4,6-dimethoxy-2-pyrimidinyl]carbamoyl)-3-(2,2,2,-trifluoroethoxy)-pyridin-2-sulfonamide sodium salt; purple nutsedge, Cyperus rotundus L. CYPRO; yellow nutsedge, Cyperus esculentus L. CYPES.

Field studies were conducted in 1996 and 1997 to determine the response of Cyperus rotundus and Cyperus esculentus, Kyllinga brevifolia, and Kyllinga gracillima to mowing regimens common to recreational turfgrass. Treatments were selected to simulate Cynodon dactylon golf course management and included mowing at 1.3 and 3.8 cm with mowing frequencies of three times per week and once a week, respectively. A nonmowed check was included for comparison. Reductions in C. rotundus shoot number were observed beginning 6 wk after initial treatment (WAIT) in 1996 and 9 WAIT in 1997 for the 1.3-cm mowing regime. The 3.8-cm mowing regime did not reduce C. rotundus shoot number until the final evaluation of each year. Reductions in C. rotundus rhizome length, tuber number, and tuber size were observed for both mowing regimes in both years. Cyperus esculentus shoot number was reduced by the 1.3-cm treatment at each evaluation date in 1996 and 1997. Cyperus esculentus shoot number reductions in the 3.8-cm regi...

The objective of this study was to identify some epidemiological conditions that affect the pathogenicity and weed control efficacy of the fungal pathogen Dactylaria higginsii on Cyperus rotundus. In controlled environments, the fungus required a minimum dew period of 12 h and a temperature of 25 C during the dew period to produce severe disease on four- and six-leaf-stage plants inoculated with 106 conidia ml−1. Under these conditions, 75% disease (percent leaf area damaged) and excellent weed control (nearly 100% plant mortality) were achieved. In experiments to test the interaction among dew period temperature, dew period duration, and plant growth stages, younger plants (four- to six-leaf) were more susceptible to D. higginsii than older (eight-leaf-stage) plants. At the dew period duration of 24 h and dew period temperature of 30 C, the number of days to obtain 50% disease severity on four- to six-leaf-stage plants was significantly less (10 d) compared with older plants (16 d). To achieve e...

Studies were conducted to determine lethal temperatures forCyperus esculentusandCyperus rotundustubers using diurnal oscillations in soil temperature with maxima of 40, 45, 50, and 55 C and a minimum of 26 C. Growth ofCyperusspp. plants was faster at 40 C than at a constant temperature of 26 C. The 45 C treatment delayedCyperusspp. emergence but was not lethal to tubers. Tuber mortality was 100% for bothCyperusspp. 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-μm low-density polyethylene (LDPE) clear film. With TIR films, greater proportions of emergedC. rotundusplants were killed by foliar scorching, and 6 wk of soil solarization was more effective at reducingC. rotundusdensity than with the LDPE film. Four weeks after film removal, the lowest level of control was obtained with the LDPE film. ForC. rotundustubers planted 5 and 10 cm deep, 62% control was obtained with the LDPE film, and it decreased to 32% with a 15-cm planting depth. The best residual control was 95 and 92% with the 75-and 100-μm TIR films, respectively. With the TIR films, there was no significant change inC. rotunduscontrol with planting depth.

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.

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−2were established. Nitrogen rates of 0, 110, 220, or 330 kg ha−1were 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−2were 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−2at 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.

Clarence J. Swanton Corresponding author. Department of Plant Agriculture, University of Guelph, Guelph, Ontario, Canada Ni G 2W1; cswanton@plant.uoguelph.ca 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.

Salvadore J. Locascio Horticultural Sciences Department, University of Florida, Gainesville, FL 32611 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 19and 30-jxm 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 5to 10-mm space between the soil and the film, the lowest irradiance level (30 ,umol m-2 s-1) was as effective as 320 ,umol m-2 s-1 in reducing penetration by purple nutsedge. The film penetration by nutsedge rhizomes appears to be linked to a lightdependent 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 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−1applied 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.

Survival and dormancy of purple nutsedge tubers has not been studied quantitatively. Yet this is fundamental to our understanding of the population dynamics of this highly noxious weed. Field studies were conducted to determine the effect of age on tuber survival and dormancy. A modified exponential decay function accurately described the age-dependent decline in tuber survival. This model is biologically meaningful, has good statistical properties, and can describe a wide range of responses. Tuber population half-life was 16 mo, and the predicted longevity (99% mortality) was 42 mo. Burial depth at 8 and 23 cm had no significant effect on survival or dormancy. Tuber dormancy increased with age. After 18 mo, the proportion of dormant tubers in the surviving population was two-and-one-half times higher than in the 3-mo-old population. We report for the first time that tubers were able to enter a state of secondary dormancy after sprouting. The finding that tubers persist after sprouting has important implications for population dynamics of this species. This is also the first report of tuber predation by the larvae of a billbug.

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.

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.

Greenhouse studies were conducted to determine the response of purple and yellow nutsedge to selective placement of 5 cm of soil treated with AC 263,222 above and/or below nutsedge tubers. AC 263,222 applied early POST (EPOST) or POST at 71 g ai ha-1as a foliar, soil, or foliar + soil application also was evaluated. AC 263,222 applied below nutsedge tubers did not reduce purple or yellow nutsedge shoot number, shoot dry weight, shoot regrowth dry weight, or root-tuber dry weight. However, when it was applied above purple nutsedge tubers, shoot dry weight was reduced; and when it was applied above yellow nutsedge tubers, shoot dry weight and root dry weight were reduced. AC 263,222 applied 5 cm above + 5 cm below purple nutsedge tubers reduced shoot number, shoot dry weight, shoot regrowth dry weight, and root dry weight to 9, 4, 10, and 16% of the control, respectively, in purple nutsedge and to 23, 16, 9, and 15% of the control, respectively, in yellow nutsedge. AC 263,222 applied EPOST or POST reduced shoot dry weight, shoot regrowth dry weight, and root dry weight of purple nutsedge to less than or equal to 11, 7, and 27% of the control, respectively, and to less than or equal to 10, 16, and 29% of the control, respectively, for yellow nutsedge with no differences between application methods. The foliar and soil activity of AC 263,222 for purple and yellow nutsedge control provides an advantage over currently registered peanut herbicides.

Yellow and purple nutsedge and southern root-knot nematode are common pests in intensively managed chile pepper production. Greenhouse studies were conducted to identify relationships among nutsedge species, chile peppers, and root-knot nematode. All practical combinations of the plant species and nematodes were grown together in pots for 14 wk. Both nutsedges and root-knot nematode reduced chile pepper height over time with no interaction. Competition from purple nutsedge or either nutsedge species plus nematodes reduced chile pepper top weight more than yellow nutsedge or nematodes alone. All pest combinations reduced chile pepper root weight. Chile pepper and nematodes individually reduced rates of shoot production, as well as top and belowground weights of yellow and purple nutsedge. Chile pepper and purple and yellow nutsedge hosted root-knot nematode host race 3. Nematode egg production was greater on chile pepper roots than on either nutsedge species. Purple nutsedge growing with chile pepper increased nematode production g−1 of chile pepper root. Purple nutsedge grown with chile pepper was the most detrimental for chile pepper growth, but most efficient for maintaining the root-knot nematode population on the least amount of root biomass. Since root-knot nematode infests yellow and purple nutsedge, and few nematicides are available for nematode control, root-knot nematode cannot be managed with crop rotation if nutsedge is not controlled.

Growth characteristics and competitive relation- ships of cotton and three perennial weeds (johnsongrass, purple nutsedge, and yellow nutsedge) were investigated at the USDA Cotton Research Station in Shafter, CA.. In growth analysis experiments, yellow nutsedge and john- songrass had highest values for height, biomass, leaf area production, growth rate, and photosynthetic efficiency. The weeds exhibited greater overall resource use and production efficiency than cotton, while cotton attained greater leafiness and canopy closure than weeds over the 10-wk experiment. Linear correlation indicated that most growth variables were significantly correlated with ag- gressivity (competitiveness); however, all correlation coef- ficients were less than 0.80. Stepwise multiple regression, using aggressivity as the dependent variable, defined 4 growth variables out of 12 that best described competi- tiveness. These were unit leaf rate (ULR), height, relative growth rate (RGR), and initial propagule weight (PWT). Thus, parameters of light utilization (ULR, height) and early establishment (RGR, PWT) were best predictors of competitive success in this system. Nomenclature: John- songrass, Sorghum halepense (L.) Pers. #3 SORHA; purple nutsedge, Cyperus rotundus L. #CYPRO; yellow nutsedge, C. esculentus L. #CYPES; cotton, Gossypium hirsutum L. Acala 'IS2'. Additional index words. Aggressivity, growth analysis, interference, replacement series, CYPES, CYPRO, SORHA.

The effects of 8-, 12-, and 16-h photoperiods on the growth and reproductive biology of purple nutsedge(Cyperus rotundusL.) were investigated over a 3-month period. Plants under the 8-h photoperiod produced the least total, shoot, root, rhizome, and tuber dry weight. Flowering occurred only at the 12-h photoperiod; thus, purple nutsedge is intermediate in flowering response to daylength. Although the total dry weight varied with photoperiod, the relative amount of dry weight (as percent of total weight) partitioned to shoots, roots, rhizomes, and tubers was constant.

Field and greenhouse experiments were conducted on bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)one 2,2-dioxide] at 2.2 and 4.4 kg/ha and perfluidone {1,1,1-trifluoro-N-[2-methyl-4-(phenylsulfonyl) phenyl] methanesulfonamide} at 4.5 and 9.0 kg/ha for purple nutsedge (Cyperus rotundusL.) control and tolerance of five turfgrasses. A single application of each herbicide was applied to purple nutsedge, but single and repeated applications were applied to turfgrasses. Purple nutsedge control during the initial year of treatment was 98 to 100% when bentazon was applied in late spring, but the control was only 28 to 68% when applied in mid or late summer. Perfluidone controlled 76 to 87% of purple nutsedge when applied in late spring and 95 to 100% when applied in late summer. Bentazon treatments generally did not cause turf injury. In the field, perfluidone treatments injured St. Augustinegrass [Stenotaphrum secundatum(Walt.) Kuntze], zoysia grass (Zoysia japonica×Z. teniuflolia‘Emerald’), centipedegrass [Erenoehloa ophiuroides(Munro) Hack.], and common bermudagrass [Cynodon dactylon(L.) Pers.]. ‘Tifway’ bermudagrass was generally tolerant to perfluidone treatments. In the greenhouse, perfluidone reduced the root growth of all turfgrasses except centipedegrass when compared with untreated checks.

Solar heating (SH) of wet soil by mulching it with transparent polyethylene (PE) during the hot season increased soil temperature in a typical daily course which varied with soil depth. Annual weed species responded to soil heating in the laboratory with the same pattern as under SH conditions in the field. Rhizomes of bermudagrass (Cynodon dactylonL. Pers. ♯3CYNDA) and johnsongrass (Sorghum halepenseL. Pers. ♯ SORHA) were very sensitive to heat treatment, but purple nutsedge (Cyperus rotundusL. ♯ CYPRO) tubers were able to survive temperatures as high as 80 C for 30 min. Species having big and heavy seeds or vegetative propagules were able to emerge from deep layers of soil, thus practically escaping the lethal temperature prevailing in the upper layer. Transparent and black PE mulching effectively prevented water loss from soil, as compared with perforated PE and nonmulched control. CO2concentration in the soil atmosphere under transparent PE mulching increased rapidly during the first week and reached a maximal level which was 20-fold higher than that formed in nonmulched soil. Ethylene at 0.2 ppm was detected only in a mulched soil environment. No differences in levels of CH4or CO were detected.

In six years of field studies, early-season releases of the native mothBactra verutanaZeller were evaluated as a biological control for purple nutsedge(Cyperus rotundusL.). Establishment from adult releases required at least 10 pairs of moths per release; establishment from larval release could be achieved with a single release of two or five newly-emerged larvae per shoot. When shoots averaged 4 or 7.5 cm high at the time of such releases, aboveground growth was reduced 32 to 62% after 30 days. Three to eight weekly releases of larvae reduced the topgrowth of nutsedge planted in rows of cotton(Gossypium hirsutumL. ‘Stoneville 213’) 30 to 68% 6 to 8 weeks after the last release. Weekly releases of about five larvae per shoot repeated three, four, or five times in 1976 and 1977 reduced nutsedge growth so that seed cotton yield equalled that of cotton in plots without nutsedge. MSMA (monosodium methanearsonate) applied at the rate of 2.2 kg/ha 5 and 7 weeks after cotton emergence gave greater control of purple nutsedge topgrowth and a yield of seed cotton equal to that resulting from three to five larval releases of about five larvae per shoot beginning when purple nutsedge averaged 7.5 cm high. When MSMA was applied at 7.5 and 8.5 weeks after cotton emergence, the addition of two early-season releases of larvae were also necessary to achieve nutsedge control and seed cotton yield equal to that produced by three to five releases of larvae.

Tubers from purple nutsedge (Cyperus rotundusL.) plants grown in the greenhouse for 2 to 10 weeks did not germinate after foliar applications of 4 kg/ha glyphosate (N-(phosphonomethyl)glycine). Some tubers from 12- and 24-week-old purple nutsedge plants survived glyphosate application. Translocation of14C-glyphosate from treated purple nutsedge leaves to other plant parts increased from 5% of the amount applied at 1 day to 19% at 4 days after application. Specific activity of14C in tubers was greater than in leaves of plants 2- to 6-week-old. With increasing plant age, specific activity decreased in both tubers and leaves. As purple nutsedge grew older, total14C translocated increased in tubers, and decreased slightly in leaves. Thin layer chromatography showed no evidence of glyphosate metabolism in purple nutsedge.

Purple nutsedge (Cyperus rotundusL.) and yellow nutsedge (C. esculentusL.) appeared to be equally acceptable for oviposition by cagedBactra verutanaZeller, but purple nutsedge was significantly more suitable as a host: 90% of the larvae survived to maturity on purple nutsedge compared with 65% on yellow nutsedge. Responses of the plant species to both larval feeding injury and plant density were similar but purple nutsedge tended to be injured more than yellow nutsedge. At a high shoot density (nine shoots per pot), production of tubers by purple nutsedge was more adversely affected by feeding of five larvae per shoot than was production by yellow nutsedge: tuber dry weights were reduced 93 and 80% and numbers of tubers per pot were reduced 77 and 62%, respectively. Production of inflorescences was greatly reduced in both species. The effect ofB. verutanaon inflorescences may be more important for yellow nutsedge, which is generally considered to reproduce freely by seeds. Both species of nutsedge probably would be about equally affected by augmentation ofB. verutanapopulations as a method of biological control.

The effects of intraspecific competition on the growth and development of purple nutsedge (Cyperus rotundusL.) were studied under greenhouse conditions. Increases in plant density increased the dry weight accumulation on a per pot basis but decreased the dry weight accumulation on a per plant basis. The partitioning of dry weight, whether on a per pot or per plant basis, indicated a shift in the method of reproduction as to density. Under low density conditions more dry weight was partitioned into inflorescences than into tubers. However, under high density conditions more dry weight was partitioned into tubers rather than inflorescences. Dry weight partitioned into rhizomes did not vary as to density. Dry weight partitioned into shoots and roots decreased with the concomitant increase in dry weight partitioned into reproductive structures. This shift to vegetative reproduction under stress conditions caused by competition provides further insight into the difficulties of controlling purple nutsedge.

Tubers of purple nutsedge (Cyperus rotundusL.) were soaked in distilled water, 9.3 × 10−6M 6-benzylamino-9 (tetrahydropyran-2yl)-9 H-purine (SD8339), or 1.39 × 10−7M kinetin and sprouted in darkness. Excised plants from tubers sprouted in sand culture were grown in half-strength Hoagland solution in 50-ml erlenmeyer flasks enclosed with aluminum foil. The leaves and upper part of the stem of each plant were exposed to an illumination of 32 klux. Rhizomes as well as untreated and treated tubers were exposed to red (R), red followed by far-red (R-FR), or red followed by far-red and red (R-FR-R) monochromatic light. R, R-FR, and R-FR-R illuminations of rhizomes from untreated tubers and plants produced basal bulbs while dark controls did not. Pfr did not revert to Pr. Dark controls produced significantly fewer basal bulbs than did rhizomes of untreated tubers and plants exposed to R, R-FR, or R-FR-R illuminations. There was no significant difference between R, R-FR, and R-FR-R illuminations. Tubers treated with SD8339 or kinetin produced basal bulbs in darkness but untreated tubers did not. Rhizomes of tubers treated with SD8339 or kinetin and exposed to R illumination produced basal bulbs. There was a significant difference in the number of bulbs produced by SD8339 or kinetin treatments and R illumination in contrast with the water controls in darkness. The effect of R illumination was similar to that of SD8339 or kinetin.

The effects of several inorganic salts on the toxicity and translocation of nonradiolabeled and14C-radiolabeled MSMA (monosodium salt of MAA) and the isopropylamine salt of glyphosate [N-(phosphonomethyl)glycine] following foliar applications to purple nutsedge (Cyperus rotundusL. ♯ CYPRO) were evaluated. Salts of the monovalent cations NH4+, K+, and Na+and to a lesser degree the anion PO4generally resulted in increased toxicity of these herbicides. Salts of the divalent and trivalent cations Zn++and Fe+++frequently reduced the activity of glyphosate and MSMA, whereas salts of the divalent Ca++ion caused little or no effect on activity. Salts of the anions Cl–, NO3–, CO3—-, and SO4–resulted in increased, decreased, or unchanged glyphosate toxicity as influenced by the associated cation. Translocation of the radiolabel of14C-glyphosate and14C-MSMA was increased by the addition of NH4Cl, while retention of the radiolabel within the tissue of the treated area was increased by the addition of FeCl3to the treated leaf surface.

The effects of shade on dry-matter production, leaf area, and biomass partitioning in purple nutsedge (Cyperus rotundusL.) and yellow nutsedge (C. esculentusL.) were determined in a controlled-environment greenhouse with a day/night temperature regime of 32/26 C. For comparison with a full-light treatment, screening provided 40, 70, and 85% shade. Shading significantly reduced height of yellow nutsedge and dry-matter production, leaf-area production, and rhizome and tuber formation of both species. Shading decreased the partitioning of plant biomass into tubers and rhizomes and increased partitioning into leaves. Yellow nutsedge had a higher net-assimilation rate than purple nutsedge at all levels of shading, but the greater leaf-area duration or total amount of leaf area present in purple nutsedge resulted in greater dry-matter production by that species. The responses of the two species showed no differences in shade tolerance.

Imazaquin {2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid} absorption, translocation, and toxicity were investigated in yellow nutsedge (Cyperus esculentusL. # CYPES) and purple nutsedge (C. rotundusL. # CYPRO) after foliar treatment. Imazaquin rates from 0.125 to 0.375 kg ai/ha were sprayed on nutsedge plants at the four-leaf stage. Compared to untreated plants, these rates reduced the main shoot growth of yellow nutsedge by 70 to 86% and that of purple nutsedge by 80 to 92% at 28 days after application (DAA). However, the regrowth as measured by tiller production was significantly greater at 0.125 and 0.188 kg/ha rates than at higher rates. The plants treated with 0.313 and 0.375 rates had no rhizomes or tubers at the 28 DAA sampling. In yellow nutsedge, absorption of14C-imazaquin increased from 36% at 1 DAA to 57% at 8 DAA. of the total absorbed14C, 12% translocated from the treated area by 8 DAA. Roots and rhizomes accumulated equal amounts of radioactivity. In purple nutsedge, the absorption of imazaquin increased from 17% at 1 DAA to 53% at 8 DAA. Translocation of absorbed14C in purple nutsedge at 8 DAA was 21%. Rhizomes accumulated significantly greater amounts of14C than the roots.

Field experiments were conducted on clay and clay loam soils at the International Rice Research Institute to investigate the effects of competition between upland rice (Oryza sativa L.) and varying populations of purple nutsedge (Cyperus rotundus L.) for nitrogen, moisture, and light on the grain yield of upland rice. ‘IR5’ was used in 1972, while the experimental line ‘IR442-2-58’ was used in 1973. Grain yields of ‘IR5’ and ‘IR442-2-58’ increased with 60 kg/ha of nitrogen, and decreased with increased purple nutsedge population. The application of nitrogen to weedy upland rice fields benefited the purple nutsedge more than the rice. Purple nutsedge and upland rice competed extensively for moisture and the competition was much more serious with increased nitrogen fertilization. Purple nutsedge competition reduced the light transmission ratio (LTR). The reduction was proportional to the increase in purple nutsedge population density. Reductions in the LTR were greater at higher nitrogen levels during the three seasons.

Genetic diversity within and among populations of yellow nutsedge (Cyperus esculentusL. # CYPES) was analyzed to evaluate and quantify the genetic consequences of the reported predominance of asexually-produced tubers as colonizing agents. Ten populations were examined using starch gel electrophoresis for allozyme analysis. Four populations of purple nutsedge (Cyperus rotundusL. # CYPRO) were surveyed for comparison. Twelve loci were identified in yellow nutsedge among the eight enzyme systems examined; ten of these loci were found in purple nutsedge. Yellow nutsedge showed relatively low genetic diversity. Most of the genetic diversity occurred as differences among individuals within populations (Hs), compared to differences among populations (Dst) for the four variable loci identified in this species. Thus, most genetic distancesbetween its populations were small. Generally, only a few genotypes occurred within each population. Purple nutsedge was found to possess even lower within- and among-population gene and genotypic diversity. This study supports the view that tubers account for most of the establishment of new populations of both species.

For effective biological control through augmentation,Bactra verutanaZeller, would have to be released against purple nutsedge(Cyperus rotundusL.) in May and June when temperatures are cooler than they are from late July through September when maximal natural populations of this biological control agent occur.Bactralarvae exposed to simulated mid-May (24/13 C) and mid-June (29/18 C) temperature regimes developed more slowly than larvae exposed to the mid-July (32/26 C) temperature regime, but nutsedge plant growth was also slower. Thus, the relative amounts of feeding injury were similar at all three regimes. Larval feeding generally increased the number of shoots slightly, but not significantly, reduced significantly the production of inflorescences, and reduced the weight of total dry matter produced between 28 and 49%.

Research was conducted to determine effects of glyphosate [N-(phosphonomethyl)glycine] on the chlorophyll and carotenoid and on the catalase specific activity in purple nutsedge(Cyperus rotundusL.). The isopropylamine salt of glyphosate caused chlorosis to appear on the center leaves of plants maintained under lighted conditions after treatment. Glyphosate-induced chlorosis was delayed by darkness but occurred when treated plants were placed in the light. Glyphosate caused significant reducations in the chlorophyll and carotenoids content of purple nutsedge leaves. Based on levels in untreated plants, carotenoid content was reduced more rapidly than chlorophyll in glyphosate-treated plants. The catalase specific activity was reduced by glyphosate to about 70% of the level in untreated plants. Interrelationships among the effects of glyphosate on the carotenoid and chlorophyll content and catalase activity were not determined but possible interactions are discussed.

Postemergence applications of imazaquin {2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid} controlled higher levels of purple nutsedge (Cyperus rotundusL. # CYPRO) in common bermudagrass [Cynodon dactylon(L.) Pers.] and hybrid bermudagrass (′Tifgreen’ and ‘Tifdwarf′,C. dactylon×C. transvaalensisBurtt-Davy) than monosodium salt of methylarsonic acid (MSMA). Control was better at 560 or 840 g ai/ha of imazaquin than at lower rates. Postemergence applications of imazaquin plus 2240 g ai/ha of MSMA controlled more purple nutsedge than equivalent rates of imazaquin alone. Preemergence applications of imazaquin were not effective. Bermudagrass discoloration was observed in some experiments on turfs mowed at a height of 1.3 cm or less but usually disappeared within 2 to 3 weeks, especially when MSMA was used in combination with imazaquin. No injury was observed on bermudagrasses, zoysiagrass (Zoysia japonicaSteud. ‘Meyer′), St. Augustinegrass [Stenotaphrum secundatum(Walt.) Ktze. ‘Raleigh′], and centipedegrass [Erernochloa ophiuroides(Munro) Hack.] maintained at mowing heights above 1.3 cm.

Two 1-yr field studies were conducted to evaluate preemergence and preplant incorporated treatments of alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide], EPTC (S-ethyl dipropylthiocarbamate), fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone}, and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] for the control of yellow nutsedge (Cyperus esculentusL.). Preemergence applications of metolachlor at 2.24, 3.36, and 4.48 kg/ha gave the best control with no significant differences observed among rates of metolachlor. Depth of herbicide incorporation did not result in any significant increase in control. Preplant incorporation of metolachlor at all rates, or fluridone at 0.56 and 0.84 kg/ha provided seasonal control of yellow nutsedge. Translocation of14C-metolachlor applied to the root or shoot of yellow nutsedge was primarily acropetal with some limited basipetal movement. Application of14C-metolachlor to the root or shoot of purple nutsedge (Cyperus rotundusL.) resulted in mostly acropetal translocation with little movement of14C from the treatment site.

Varying concentrations of benzyladenine (BA), indoleacetic acid (IAA), gibberellic acid (GA), abscisic acid (ABA), and 2-chloroethylphosphonic acid (ethephon) were used to induce sprouting of dormant purple nutsedge (Cyperus rotundusL.) tubers. BA at 50 to 300 ppm stimulated sprouting. The continuous presence of BA during the sprouting period was necessary to give significant sprout stimulation. Neither IAA at 1, 10, or 100 ppm; GA at 10, 100, or 1000 ppm; nor ethephon at 10, 100, or 1000 ppm had stimulatory effects on sprouting. ABA counteracted the stimulatory effects of BA when tubers were treated with ABA following BA treatment. Sprouting was markedly greater at 33 C day, 25 C night than at 24 C day, 17 C night. Growth of plants originating from tubers pretreated with 100 ppm BA did not differ significantly from the controls. Sustained BA applications at 100 and 200 ppm produced numerous plants with tuft-type growth habit, delayed flowering, and reduced the number of inflorescences. Numerous short, diageotropic rhizomes were produced.

The evapotranspiration of six dominant emersed and floating weeds was studied. Evapotranspiration of water-chestnut (Trapa natans L. var. bispinosa Roxb.), waterlettuce (Pistia stratiotes L.), and swamp morningglory (Ipomea aquatica Forsk.) did not increase water losses significantly. Evapotranspiration of waterhyacinth (Eichornia crassipes (Mart) Solms.) was 30 to 40% higher, that of narrowleaf cattail (Typha augustifolia L.) was 60 to 70% higher, and that of purple nutsedge (Cyperus rotundus L.) was 130 to 150% higher than evaporation from a free water surface under equivalent conditions. Positive correlations (significant at the 1% level) were found between some meterological factors (daily maximum air temperature and daily average wind velocity), evaporation from free water surface, and evapotranspiration from aquatic plants studied.

The translocation of disodium methanearsonate (DSMA) and amine methanearsonate (hereinafter referred to as AMA) in purple nutsedge (Cyperus rotundus L.) was studied following foliar applications. Tracer techniques with DSMA-14C and chemical analyses for elemental arsenic (hereinafter referred to as As) suggested apoplastic and symplastic movement of both arsenicals. Chromatographic studies of extracts from DSMA-14C-treated plants indicated that the compound was not readily broken down. The carbon-arsenic bond appeared to remain largely intact, although some 14C activity was found in respiratory CO2 several days after treatment. A comparison between the Rf value of the radioactive plant extract to that of standard DSMA-14C suggested that a plant extract-DSMA complex may have been formed. Over 85% of the material applied to the plant remained in the treated shoots. DSMA moved in both acropetal and basipetal directions, and such movement within a single leaf was not influenced by relative leaf age. The arsenicals were not redistributed in the shoot or in the tuber system, but As was accumulated in terminal tubers following repeated applications.

Purple nutsedge(Cyperus rotundus L.)develops as a series of shoots connected by bulbs, rhizomes, and tubers. The leaves contain parallel, collateral vascular bundles with the majority of the photosynthetic cells concentrated in the sheathing girdle around each bundle. The upper leaf surface consists of a single layer of large epidermal cells covered by a thick cuticle. Stomates occur only in the lower surface. The vascular bundles vary from collateral to amphivasal as they pass from the leaves through the bulb into the rhizomes and tubers. Newly developing rhizomes and tubers appear white and fleshy with a parenchymatous epidermis and cortex. Mature rhizomes appear brown and wiry with a deteriorated outer cortex and a lignified inner cortext and endodermis. Tubers and bulbs form similarly at the rhizome apices with each accumulating starch. The interconnecting vascular system appears to remain intact throughout the growing season.

We sprayed yellow nutsedge (Cyperus esculentus L.) with 0.56, 1.12, and 2.24 kg/ha of (2,4-dichlorophenoxy)acetic acid (2,4-D) at the two and four-leaf stages in both field and growth chamber studies. Compared to non-treated plants, these rates significantly reduced shoot weight, rhizome weight, and rhizome number 12 days after application. There were no significant differences in these growth responses among the rates tested, when applied one, two, and three times at consecutive 12-day intervals. We pretreated two and four-leaf plants with 0.56, 1.12, and 2.24 kg/ha of 2,4-D immediately before foliar application of 14C-2,4-D. The increase in pretreatment 'rates decreased the percentage of the applied radioactivity which was absorbed and translocated. Of the radioactivity absorbed, a rather constant percentage translocated from the treated area in the different treatments. The radioactivity translocated from the application site for at least 288 hr after treatment. Less than 19% of the 14C-2,4-D applied was absorbed into the leaves 24 hr after application. Niniety-eight to 100% of the methianol-soluble radioactivity that translocated to developing leaves, rhizomes, and roots clhromatographed identically to 14C-2,4-D. ELLOw nutsedge (Cyperus esculentus L.) infestation Iis increasing in many crop and noncrop areas (12). This perennial weed propagates principally by tubers. When a tuber germinates, the sprout develops into a plant with a crown region (3). The crown is below the soil surface and contains meristems which develop leaves, rhizomes, and roots. To be effective, foliarly-applied lherbicides should translocate to the crown. The herbicide (2,4-dichlorophenoxy)acetic acid (2,4-D), when applied to leaves, translocates in the phloem. Its translocation follows the pattern of food distribution in the plant as conditioned by the relative activity of "source" and "sink" (5). In young yellow nutsedge, the meristematic activity in the crown region could provide an active "sink" for the foliarly-applied 2,4-D. Toxicity of 2,4-D has been studied more in purple nutsedge (Cyperus rotundus L.) than in yellow nutsedge. Repeated applications were much more effective than single applications in controlling purple nutsedge (4, 7), particularly when treatments were initiated within 2 weeks of emergence (7). Susceptibility of purple nutsedge to 2,4-D appears to decrease with increased plant age (7, 8). Rates of 1.68 to 16.8 kg/ha of 2,4-D have resulted in suppression and control of yellow nutsedge (2, 10). The effect of low rates of 2,4-D on young yellow nutsedge plants has not been thoroughly investigated. 'Received for publication April 24, 1970. Cooperative investigations of the Crops Research Division, Agr. Res. Serv., U. S. Dep. of Agr., and the Illinois Agr. Exp. Sta., Urbana, Illinois. 2Visiting lecturer in Agronomy, U. P. Agricultural University, Pantnager, India; Plant Physiologist, Crops Research Division, Agricultural Research Service; Professor, Department of Agronomy, University of Illinois, Urbana, Illinois. This research was a study of the effects of 2,4-D on young yellow nutsedge plants. We hypothesized that 2,4-D applied early postemergence, would be toxic to the plants, partly because of the potential movement of the herbicide into the meristematic tissues originating from the crown region. MATERIALS AND METHODS

Soil incorporated into the tuber zone of purple nutsedge (Cyperus rotundusL.) at 1 to 9 kg/ha,O,O-diisopropyl phosphorodithioateS-esterwithN-(2-mercaptoethyl)benzenesulfonamide (bensulide) inhibited the growth of roots on plants developing from these tubers. The inhibitory effect was temporary and occurred only when bensulide was in intimate contact with the tubers and developing plants. When tubers were removed from bensulide-treated soil, washed, and replanted in untreated soil, root growth was normal. The production of shoots from tubers planted in bensulide-treated soil apparently was not affected, but shoot-growth was retarded when root growth was suppressed. When bensulide was incorporated into the upper 5-cm layer of soil, the shoots of nutsedge plants developing from tubers located below this layer grew through the treated soil with no adverse effect; the roots of these plants developed from basal bulbs below the layer of treated soil and were normal. Leaching bensulide-treated soil with 37.6 hectare-cm of water did not move enough bensulide into the soil to cause inhibitory growth effects on purple nutsedge.