Yellow nutsedge is one of the most widely distributed and troublesome weeds in the world. Field and greenhouse studies were conducted to optimize strategies for increased yellow nutsedge control in turfgrass with halosulfuron and sulfentrazone. In the field study in yellow nutsedge and perennial ryegrass mixture, single or sequential applications (3 wk after initial) of halosulfuron or sulfentrazone were made on June 3, June 23, July 15, or August 5 in 2013, 2014, 2015, and 2016. Percent yellow nutsedge control was rated within the same growing season on September 17 and the following year on June 3 for carryover control. Field and greenhouse studies confirm that sequential applications of halosulfuron with a 3-wk interval resulted in >95% control in a yellow nutsedge–turfgrass mixture. In a greenhouse study, both herbicides reduced yellow nutsedge root and rhizome dry mass from 39% to 98%, reduced number of new tubers and tuber fresh weight from 38% to 100%, and prevented re-emergence. Sequential applications of either herbicide within a 3-wk interval early postemergence is recommended for optimal control. Herbicide application to yellow nutsedge using halosulfuron and sulfentrazone should be made as early as possible postemergence, preferably at the three- to five-leaf stage or 200 to 250 growing degree days (GDD, 10 C base). Mowing can be an effective method to reduce yellow nutsedge growth. Mowing at 7.6 cm weekly reduced yellow nutsedge rhizome dry mass by 55% and number of new tubers formed by 63% in the greenhouse study. Physical removal of yellow nutsedge plants such as hand-pulling can be an effective method to manage yellow nutsedge and is most effective at the three- to five-leaf stage (200 to 250 GDD). End-users can maximize yellow nutsedge control by integrating early herbicide treatments and cultural practices such as mowing and hand-pulling.

Artificial shading studies indicated that competition for photosynthetically active radiation (PAR) will limit tuber production in purple nutsedge. There were no data available to test whether there is a relationship between incident PAR underneath crop canopies and tuber production of this weed. In this study, the effect of crop competition on net reproductive rates of purple nutsedge tubers was measured under field conditions. Purple nutsedge plants were grown in association with bush beans, maize, maize and beans intercropped, sweet potato, pole beans, and bell pepper in a 2-yr field study in Costa Rica. Measurements were taken on the number of tubers produced during the growing season of each crop, and PAR transmittance was monitored weekly for the duration of the respective cropping cycles. Data on transmittance and incident solar radiation were used to calculate the daily average amount of PAR, available 15 cm above the soil surface. Regressions indicated that average incident PAR accounted for 95% of the variation in net reproductive rates. Average incident PAR also allowed a more precise competitive ranking of crops than either average or minimum transmittance. Bush beans had consistently the lowest average incident PAR values and therefore ranked as the most competitive crop in both years. Our data suggest that no net increase in tuber populations occurs if average incident PAR is below 2.7 MJ m−2 d−1. Differences in the duration of the cropping cycle accounted only for a small proportion of the overall variation in net reproductive rates of purple nutsedge tubers. Information on the competitive ranking of different crops can be used to design crop rotations that could reduce reliance on herbicides on small farms in Costa Rica.

Experiments were conducted to examine the effects of low soil moisture on yellow nutsedge emergence in relation to thermal and chronological time and test the ability of thermal models generated previously to predict emergence under water stress. Unsprouted tubers from California and Arizona were planted in pots, buried at field sites in California and Arizona, and subjected to wet or dry treatments. Pots were monitored weekly to determine date of emergence and number of emerged shoots. The California genotype emerged 47 to 61 days after planting (DAP) in the dry treatment and 33 to 49 DAP in the wet treatment, depending on planting site. The range for the Arizona genotype was 51 to 76 DAP in the dry treatment and 43 to 61 DAP in the wet treatment. Days and degree-day intervals to first emergence differed between irrigation treatments and planting sites but interactions were not significant. All models were accurate in predicting emergence dates for genotypes in the wet treatment at the California site, while emergence in Arizona was underestimated by 9 d. Tubers subjected to the dry treatment needed a higher number of accumulated degree-day units before emergence occurred and had fewer emerged shoots as compared to the wet treatment. Degree-day models generated for yellow nutsedge under optimal conditions lack sufficient robustness to be predictive under water stress conditions.

Competition of yellow nutsedge (Cyperus esculentus L.) with corn (Zea mays L.) was evaluated in the field at various yellow nutsedge densities over a 3-yr period. A relationship between yellow nutsedge density (shoots/m2) and percentage yield reduction revealed an 8% yield reduction for every 100 shoots/m2. Two 3-yr studies were conducted to determine the most effective combination of preplant-incorporated, postemergence, or postemergence-directed treatments for yellow nutsedge control in corn. The preplant incorporated treatments were alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide], EPTC (S-ethyl dipropylthiocarbamate), or nothing; postemergence treatments were bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-(4) 3H-one 2,2-dioxide], two cultivations, or nothing; and the postemergence-directed treatments were ametryn [2-(ethylamino)-4-(isopropylamino)-6-(methylthio)-s-triazine] or nothing. One preplant-incorporated treatment of EPTC or alachlor prevented yield reductions from yellow nutsedge competition. When no control was practiced, yields were reduced 17% in a moderate yellow nutsedge infestation (initially infested with 300 tubers/m2) and 41% in a heavy infestation (initially infested with 1200 tubers/m2). Yields were reduced 7 to 8% in the moderate infestation when no preplant-incorporated treatments were used regardless of whether postemergence or postemergence-directed treatments were also used. After 1 yr, all control measures resulted in less tuber density than no control measures, but all control treatments had essentially similar tuber densities. After the second year, several herbicide treatments were as effective as hand weeding in reducing tuber density. At least 2 yr of effective control treatments were required to reduce tubers to 20% of the original density, and 3 yr of treatment to reduce the density to 15% of the original density. No combination of treatments, including hand weeding, eliminated tubers after 3 yr.

Genetic variation of morphological and phenological characters of yellow nutsedge (Cyperus esculentus L.) from California was investigated and compared with isozyme data from the same populations. The importance of collection location, individual genotype, and isozyme genotype to phenotypic characteristics was evaluated. Analyses were conducted on 20 individuals collected from each of 10 widely separated populations in California. Replicate plants were started by tubers, grown in pots buried outdoors, and measured during the period from planting through flowering. Results showed that yellow nutsedge is variable across its range in California in all measured traits, including days to sprouting and flowering, height, rachis number and length, aboveground biomass, tuber weight, number of rays, ray length, number of spikelets per ray, as well as spikelet length and width. Population (collection location) was a larger variance component than genotype (individuals over all locations). As found in isozyme analysis, relatively more variation was found among than within populations, typical of clonally reproducing species. Overall, more variation was found in quantitative traits than in isozymes. The level of variation, based on coefficients of variation for each character and population, was similar within populations and not clearly related to cropping history or climate at each site. The two most common isozyme genotypes in the collection differed in four characters: date of emergence, weight of 10 tubers, rachis number, and mean ray length, which may represent different adaptive responses to cultural practices. These results indicate that isozymes do not reflect the high level of genetic and adaptive diversity of yellow nutsedge. Factors that are likely to determine the patterns of variation in this species include breeding system (vegetative reproduction), founder effects, polyploidy, and homogeneity of the agricultural environmental.

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.

We examined the relationship between temperature and emergence of yellow nutsedge tubers to generate predictive models for the arid southwestern United States. Field experiments were conducted in California and Arizona to obtain phenological and temperature data needed to generate degree-day models. The effect of air temperature on emergence was tested with available programs using four methods to calculate degree-days (single sine, double sine, single triangle, and double triangle). Separate models were tested for each genotype examined (Arizona source and California source) as no one model was a good predictor of emergence when data were pooled. Results indicate that there is year to year variation in model accuracy but predictions of date of emergence can be made to within 2 d of actual emergence. This information can be used to schedule cultivations to reduce early yellow nutsedge competition in the field.

Imazaquin {2-(4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl)-3-quinolinecarboxylic acid} site of uptake and toxicity from soil application were investigated in yellow nutsedge (Cyperus esculentus L. #3 CYPES) and purple nutsedge (C. rotundus L. # CYPRO). Imazaquin concentrations of 0.1 to 0.5 ppmw inhibited yellow nutsedge shoot emergence completely, while purple nutsedge shoots emerged at the lower concentrations. Herbicide placement above the tuber reduced shoot emergence and shoot and root dry weights of both species more than did placement below the tuber. Increasing herbicide rate increased the number of tuber buds that sprouted. Three-day-old nutsedge propagules absorbed 14C-imazaquin from both rhizome shoots and roots and the herbicide moved both acropetally and basipetally in nutsedge propagules.

Metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] toxicity, absorption, translocation, and metabolism were investigated in corn (Zea mays L.) and yellow nutsedge (Cyperus esculentus L.). Metolachlor did not inhibit seed germination in corn or tuber germination in yellow nutsedge. It did not kill yellow nutsedge tubers that were exposed to 4 ppmw for 9 weeks. Metolachlor (10 ppmw) applied in soil above the seed significantly reduced corn shoot growth, but the same concentration around or below the seed had no effect. A soil mixture with metolachlor (1 ppmw) placed above or around yellow nutsedge tubers significantly reduced shoot growth, but placement around the tuber was the most toxic; placement below the tuber had no effect on shoot growth. The concentration of metolachlor that resulted in 50% reduction of shoot growth of 4-day-old seedlings in solution culture was > 10−4 M for corn and <10−6M for yellow nutsedge. Root-applied 14C-metolachlor was acropetally translocated to shoots of both species following a 7- to 13-day absorption period, with yellow nutsedge translocating the highest portion of the absorbed material to shoots. In 2-day-old seedlings with roots exposed to 14C-metolachlor for up to 48 h, both species absorbed and translocated the radioactivity to shoots, but corn absorbed much more than yellow nutsedge. When the 14C-metolachlor was applied to shoots of both species, the radioactivity was translocated basipetally into roots. Yellow nutsedge exuded appreciable 14C-metolachlor out of the roots and absorbed more 14C-metolachlor through shoot tissues than corn. Both corn and yellow nutsedge seedlings readily converted the 14C-metolachlor to metabolites, but corn was able to metabolize the 14C-metolachlor at a faster rate than yellow nutsedge and also produced more metabolites.

Experiments were conducted to establish low temperature thresholds for initiation of bud sprouting in dormant vegetative propagules of johnsongrass, purple nutsedge, and yellow nutsedge, and seed germination in cotton. Weed propagule sprouting and cotton seed germination responses to temperature were determined in a series of experiments conducted on a temperature gradient bar. Four calculated indices were used to quantify germination: mean percent germination per day, reciprocal median response time, and two versions of germination rate index. Data were analyzed as a series of regressions of germination indices against temperature. Maximum and minimum temperatures for germination were derived directly from the regressions and compared among species. Yellow nutsedge had the lowest temperature threshold (6 C), while the other species had low temperature thresholds of 11 to 12 C. Upper temperature thresholds were similar among species and ranged from 42 to 44 C. The lower low temperature threshold of yellow nutsedge sprouting compared to those for cotton, johnsongrass, and purple nutsedge suggests that early establishment by yellow nutsedge is an important factor in competitiveness in mixtures of these species. The results presented here suggest that application of principles derived from studies in seed biology might advance our understanding and ability to manage perennial weeds.

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.

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−1 to 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, I50 for yellow nutsedge foliar growth was 0.73 kg ha−1, which was greater than the I50 for tuber biomass (0.41 kg ha−1). First-order tubers, those directly attached to the initial tuber, had an I50 of 0.70 and 0.44 kg ha−1 of glyphosate for purple nutsedge and yellow nutsedge tuber biomass, respectively. For all higher-order tubers, I50 values ranged from 0.29 to 0.60 and 0.14 to 0.30 kg ha−1 of glyphosate for purple nutsedge and yellow nutsedge tuber biomass, respectively. Glyphosate at 0.74 kg ha−1 prevented 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.

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

Dioscorea bulbifera is a serious invader of various ecosystems in Florida, where plants generated by its two morphotypes climb aggressively and smother supporting vegetation. There is a dearth of published research on its invasive biological attributes including vine growth and biomass production by plants generated from bulbils. Herein, we assessed these parameters in common garden studies by planting bulbils from four biomass categories (PBBCs I–IV) of both morphotypes. Vine lengths, longevity-based growth rates (VLGR), biomass, and quantities of leaves and daughter bulbils in both morphotypes showed positive correlation with the biomass of planted parental bulbils. This indicated similarity between corresponding attributes in two morphotypes. Total vine length showed strong positive correlation with VLGR, biomass, and quantities of leaves and bulbils. Overall vine longevity among plants from PBBCs I–IV did not significantly differ whereas the total vine lengths, VLGRs, number of branches, and quantities of leaves and bulbils increased with the biomass of the parental bulbils. Plants recruited by smaller bulbils allocated more biomass to leaves and tubers compared to stems and bulbils, whereas the plants recruited by larger bulbils allocated more biomass to leaves and bulbils compared to tubers and stems. Higher proportion of biomass allocation to leaves and bulbils presumably ensures immediate faster growth, longer vines, and a greater number of daughter bulbils for future recruitment of new plants. Vine length (associated with faster growth rate, capable of blanketing supporting structures and producing large quantities of bulbils) has been noted as the primary invasive biological attribute that facilitates D. bulbifera's status as a noxious exotic weed in Florida. Control measure that can reduce vine length should reduce or eliminate the invasive behavior of D. bulbifera in Florida.

The African root and tuber scale Stictococcus vayssierei Richard is the only known hypogeal species of the family Stictococcidae. Its wide range of host plants together with concurrently field observed differences in host preference provided evidence of polyphagy or the involvement of more than a single-scale species. To establish the baseline information for future taxonomic studies, newly emerged larvae were collected from infested cassava from three sites in the humid forest zone of southern Cameroon. A glass binocular magnifier was used to observe morphological changes of live individuals and slide-mounted individuals of all developmental stages were examined with a compound microscope. Stictococcus vayssierei females went through three developmental stages—two larval instars and an adult stage. The first and second instars were purple-red, while the adult was brown. Body size and the degree of sclerotization of the dorsal line increased in each developmental stage. White waxy secretions on the basal periphery of the second instar, and both dorsum and periphery of the adults, distinguished them from the first instar, which lacks the white waxy secretions. On slide-mounted specimens, certain aspects of the anal complex (i.e. number of opercular plates and -setae) were found to be the most discriminating features of S. vayssierei life stages. These results are useful for further studies on the diversity of subterranean stictoccocid scales.

CH3Cl emissions by freshly harvested tubers of 61 potato cultivars ranged from less than 4 to 650 ng g−1 f. wt d−1. In experiments with Anna, the cultivar displaying the highest release rate, maximum emission of CH3Cl occurred at 20°C but the rate diminished after 48 h, a decrease due in part to inhibition of CH3Cl release by the accumulation of CH3Cl in the headspace. In 1995 and 1996, CH3Cl emission by tubers was first detectable 6 wk before the normal harvest date. If tubers were stored at 20°C immediately following harvest, release attained a maximum of 350 ng g−1 f. wt d−1 about 4 d after harvest, falling to less than 4 ng g−1 f. wt d−1 within 3 wk of harvest. On storage at 6°C post-harvest, maximum release of CH3Cl (c. 600 ng g−1) was delayed until 5 wk after harvest and release fell below 4 ng g−1 f. wt d−1 after 200 d. Release of CH3Cl was not significantly affected by cutting or bruising tuber tissue, and CH3Cl biosynthesis occurred in both core and superficial tissues of the tuber. The S-methyl group of either L- or D-methionine acted as a precursor of CH3Cl in sliced tubers, but the methylating system was specific for Cl−. An isotope dilution technique using C2H3Cl demonstrated that the amount of CH3Cl metabolized by the intact tuber was approximately 36% of the net release. However, investigations with 14CH3Cl showed that only a small proportion (7%) of the CH3Cl metabolized was fixed in involatile form in the tuber. In both skin and core tissues, fixed 14C was located primarily (80%) in the fraction soluble in phosphate buffer, but the specific activity of skin tissue was about twice that of core tissue. Autoradiography demonstrated that 14C fixation in the tuber was greatest within the lenticels, possibly indicating a microflora adapted to use the locally high concentrations of CH3Cl. Significant 14C fixation was also associated with the periderm but was not attributable to labelling of the O-methyl groups of the phenolic components of suberin. Within the core of the tuber, 14C fixation was located primarily in the phloem, pith and medullary rays.