Purslane weed has long been used for animal feed in Thailand but has been underutilized, and no published data exist on the chemical and nutritional qualities of Thai wild purslane. In this study, we aimed to determine the microchemical components of purslane stem, leaf, and flower, including the phenolic acid, flavonoid, ascorbic acid, β-carotene, and fatty acid content. The water extract of the flower fraction contained the highest total phenolic acid content and had the highest O₂-scavenging activities, whereas leaf contained the highest amount of total flavonoids and ascorbic acid. The β-carotene content was not significantly different in leaf and flower fractions but was significantly greater than that in stem (P < 0.05). The predominant phenolic acid was chlorogenic acid for all fractions. Rutin was the major flavonoid found in leaf, and myricetin was highest in flower and stem. Alpha linolenic acid (18 : 3n-3) content ranged from 16% (149 mg per 100-g sample) of total fatty acid in stem to 50% (523 mg per 100-g sample) in leaf. We suggest that Thai wild purslane could be considered a nutritional source for animal feed or an excellent vegetable in the human diet.

Nomenclature: Thai wild purslane (common purslane), Portulaca oleracea L.

Experiments were conducted to determine the efficacy, absorption, and translocation of nicosulfuron, rimsulfuron, and nicosulfuron rimsulfuron on barnyardgrass, green foxtail, longspine sandbur, and large crabgrass. In the greenhouse, nicosulfuron, rimsulfuron, and nicosulfuron rimsulfuron were applied at 0.0625, 0.125, 0.25, 0.5, 0.75, 1, and 2 times their label rates of 35, 13, and 26 13 g ai ha⁻¹, respectively, on 5- to 10-cm plants. Three weeks after treatment (WAT), barnyardgrass was the most susceptible species to all three herbicides, and large crabgrass was the least susceptible. The nicosulfuron, rimsulfuron, or nicosulfuron rimsulfuron rates causing 50% visible injury (GR₅₀) for barnyardgrass were 10.9, 4.8, and 6 3 g ai ha⁻¹, respectively. Similarly, the GR₅₀ for large crabgrass were 25.6, 9.9, and 14.3 7.2 g ai ha⁻¹, respectively, 3 WAT. Absorption of nicosulfuron, rimsulfuron, and nicosulfuron rimsulfuron was greater in barnyardgrass than in large crabgrass. Absorption of nicosulfuron rimsulfuron in barnyardgrass and large crabgrass was 74% and 57%, respectively, 7 d after treatment (DAT). In addition, translocation of nicosulfuron, rimsulfuron, and nicosulfuron rimsulfuron out of the treated leaf was 14, 12, and 14% higher, respectively, in barnyardgrass than in large crabgrass. The differential response of these weed species to nicosulfuron, rimsulfuron, and nicosulfuron rimsulfuron might be due to differences in herbicide absorption and translocation.

Nomenclature: Nicosulfuron; rimsulfuron; barnyardgrass, Echinochloa crus-galli (L.) P. Beauv.; green foxtail, Setaria virdis (L.) Beauv.; large crabgrass, Digitaria sanguinalis (L.) Scop.; longspine sandbur, Cenchrus longispinus (Hack.) Fernald.

Bushkiller was evaluated under inter- and intraspecific competition. In experiment 1, bushkiller, trumpetcreeper, and wild grape were greenhouse-grown alone and in two or three species mixtures in pots. Of the three species, bushkiller grew the tallest and had the greatest final biomass when grown alone. When all three species were grown together, bushkiller grew over twice the height of trumpetcreeper, over three times the height of wild grape, and over four times the biomass of either competing species. Plots of height over time showed that competition did not affect bushkiller or wild grape growth rate, but trumpetcreeper growth was reduced when grown with bushkiller. In experiment 2, bushkiller was grown in cultures of one, two, and three plants per pot to determine intraspecific competition effects on growth. Final height of bushkiller was not affected by intraspecific competition; however, bushkiller biomass decreased with increasing competition.

Nomenclature: Bushkiller, Cayratia japonica (Thunb.) Gagnep.

Field studies were conducted in 2007 and 2008 at Clinton and Faison, NC, to evaluate the influence of Palmer amaranth density on ‘Beauregard’ and ‘Covington’ sweetpotato yield and quality and to quantify the influence of Palmer amaranth on light interception. Palmer amaranth was established at 0, 0.5, 1.1, 1.6, 3.3, and 6.5 plants m⁻¹ within the sweetpotato row and densities were maintained season-long. Jumbo, number (no.) 1, and marketable sweetpotato yield losses were fit to a rectangular hyperbola model, and predicted yield loss ranged from 56 to 94%, 30 to 85%, and 36 to 81%, respectively for Palmer amaranth densities of 0.5 to 6.5 plants m⁻¹. Percentage of jumbo, no. 1, and marketable sweetpotato yield loss displayed a positive linear relationship with Palmer amaranth light interception as early as 6 to 7 wk after planting (R²  =  0.99, 0.86, and 0.93, respectively). Predicted Palmer amaranth light interception 6 to 7, 10, and 13 to 14 wk after planting ranged from 47 to 68%, 46 to 82%, and 42 to 71%, respectively for Palmer amaranth densities of 0.5 to 6.5 plants m⁻¹. Palmer amaranth height increased from 177 to 197 cm at densities of 0.5 to 4.1 plants m⁻¹ and decreased from 197 to 188 cm at densities of 4.1 to 6.5 plants m⁻¹; plant width (69 to 145 cm) and shoot dry biomass plant⁻¹ (0.2 to 1.1 kg) decreased linearly as density increased.

Nomenclature: Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA; sweetpotato, Ipomoea batatas L. Lam. ‘Beauregard’ and ‘Covington’ IPOBA

Rice flatsedge and barnyardgrass are widespread and competitive weeds in direct-seeded rice. Developing integrated weed management strategies that elevate suppression of weeds by rice through crop density, nutrition, and cultivar choice requires better understanding of the extent to which rice interferes with the growth of these weeds and how these species respond to resource limitation with crop interference. Rice interference reduced the height of barnyardgrass but did not affect height of rice flatsedge. These weed species were able to grow taller than rice and thus avoided being shaded. Increased specific stem length under crop interference may demonstrate a strategy of stem elongation to allow the top portion of the weeds to be kept out of shade. Rice interference reduced inflorescence and shoot biomass of both weed species. Barnyardgrass showed the ability to reduce the effects of rice interference by increasing leaf weight ratio. The present study shows that crop interference alone may reduce weed growth but may not give complete control of these weed species. This highlights the need for the integration of management practices to achieve control of these weed species.

Nomenclature: Barnyardgrass, Echinochloa crus-galli (L.) Beauv., ECHCG; rice flatsedge, Cyperus iria L. CYPIR; rice, Oryza sativa L.

A 50-yr study at Fairbanks, AK, was started in 1984 to determine soil seed longevity of 17 weed species. Seeds were buried in mesh bags 2- and 15-cm deep and were recovered 0.7, 1.7, 2.7, 3.7, 4.7, 6.7, 9.7, 19.7, and 24.7 yr later. Viability was determined using germination and tetrazolium tests. By 24.7 yr after burial (YAB), no viable seeds were found for common hempnettle, flixweed, foxtail barley, quackgrass, and wild oat. Bluejoint reedgrass, which had no live seed 19.7 YAB, again had viability (1% at 15 cm) 24.7 YAB. Seeds of 11 other species were still viable: American dragonhead (52%), marsh yellowcress (11 and 3.0% at 2 and 15 cm respectively), common lambsquarters (2.8%), prostrate knotweed (2.8% at 15 cm), shepherd's-purse (2.8%), pineapple-weed (2.6%), rough cinquefoil (2.3%), Pennsylvania smartweed (1.1%), common chickweed (0.4%), wild buckwheat (0.3%), and corn spurry (0.1%). Seed dormancy 24.7 YAB was very low (< 10%) for all species except American dragonhead (99%), shepherd's-purse (40%), marsh yellowcress (23% at 2 cm), Pennsylvania smartweed (18%), and rough cinquefoil (14%). At the beginning of the study, declines in seed longevity were uniform between replicates, but variability between replicates increased over time for all species except American dragonhead, suggesting that some soil microsites are more favorable for seed survival and may be seedbank “safe sites.” Results of this study demonstrate that nonrandom seed mortality contributes to the spatial heterogeneity of seed populations in the soil seedbank.

Nomenclature: American dragonhead, Dracocephalum parviflorum Nutt. DRAPA; bluejoint reedgrass, Calamagrostis canadensis (Michx.) Beauv. CLMCD; common chickweed, Stellaria media (L.) Vill. STEME; common hempnettle, Galeopsis tetrahit L. GAETE; common lambsquarters, Chenopodium album L. CHEAL; corn spurry, Spergula arvensis L. SPRAR; flixweed, Descurainia sophia (L.) Webb. ex Prantl DESSO; foxtail barley, Hordeum jubatum L. HORJU; marsh yellowcress, Rorippa palustris (L.) Bess. RORIS (in previous manuscripts called Rorippa islandica (Oeder) Borbas); Pennsylvania smartweed, Polygonum pensylvanicum L. POLPY; pineapple-weed, Matricaria discoidea DC. MATMT (in previous manuscripts called Matricaria matricariodes (Less.) C.L. Porter); prostrate knotweed, Polygonum aviculare L. POLAV; quackgrass, Elymus repens (L.) Gould AGRRE (in previous manuscripts called Elytrigia repens (L.) Nevski); rough cinquefoil, Potentilla norvegica L. PTLNO; shepherd's-purse, Capsella bursa-pastoris (L.) Medik. CAPBP; wild buckwheat, Polygonum convolvulus L. POLCO; wild oat, Avena fatua L. AVEFA.

Predicting weed emergence dynamics can help farmers to plan more effective weed control. The hydrothermal time concept has been used to model emergence as a function of temperature and water potential. Application of this concept is possible if the specific biological thresholds are known. This article provides a data set of base temperature and water potential of eight maize weeds (velvetleaf, redroot pigweed, common lambsquarters, large crabgrass, barnyardgrass, yellow foxtail, green foxtail, and johnsongrass). For five of these species, two ecotypes from two extreme regions of the predominant maize-growing area in Italy (Veneto and Tuscany), were collected and compared to check possible differences that may arise from using the same thresholds for different populations. Seedling emergence of velvetleaf and johnsongrass were modeled using three different approaches: (1) thermal time calculated assuming 5 C as base temperature for both species; (2) thermal time using the specific estimated base temperatures; and (3) hydrothermal time using the specific, estimated base temperatures and water potentials. All the species had base temperatures greater than 10 C, with the exception of velvetleaf (3.9 to 4.4 C) and common lambsquarters (2.0 to 2.6 C). All species showed a calculated base-water potential equal or up to −1.00 MPa. The thresholds of the two ecotypes were similar for all the studied species, with the exception of redroot pigweed, for which the Veneto ecotype showed a water potential lower than −0.41 MPa, whereas it was −0.62 MPa for the Tuscany ecotype. Similar thresholds have been found to be useful in hydrothermal time models covering two climatic regions where maize is grown in Italy. Furthermore, a comparison between the use of specific, estimated, and common thresholds for modeling weed emergence showed that, for a better determination of weed control timing, it is often necessary to estimate the specific thresholds.

Nomenclature: Barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG; common lambsquarters, Chenopodium album L. CHEAL; green foxtail, Setaria viridis (L.) Beauv. SETVI; johnsongrass, Sorghum halepense (L.) Pers. SORHA; large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA; redroot pigweed, Amaranthus retroflexus L. AMARE; velvetleaf, Abutilon theophrasti Medik. ABUTH; yellow foxtail, Setaria pumila (Poir.) Roemer & J. A. Schultes SETLU.

Seed deterioration, and therefore seed germination potential, are highly influenced by relative humidity and temperature. However, limited species-specific information is available about the effect of long-term soaking in water on seed germination potential. Knowing the potential fate of a creeping bentgrass seed that falls in an irrigation canal is important for the study of transgene flow in this species at the landscape level. The objectives of this study were to evaluate the effect of soaking time and water temperature on germination of creeping bentgrass seed and to assess how fast a panicle could be moved in an irrigation canal. Germination was determined for seeds from panicles of three cultivars of creeping bentgrass that were soaked in water for up to 17 wk at two water temperatures, 4 and 20 C. Creeping bentgrass seeds did not lose their ability to germinate after 17 wk in water at 20 C and, although reduced, germination was still 46% after 17 wk in water at 4 C. The reduction in germination in seeds from panicles kept in water at 4 C was due to the induction of secondary dormancy, which was overcome by dry seed storage at room temperature. We quantified that a panicle that falls in an irrigation canal has the potential to travel downstream at an average rate of 19 m min⁻¹ and move seeds that could potentially establish seedlings elsewhere. Therefore, movement of creeping bentgrass seed by water has to be considered as a means of gene flow.

Nomenclature: Creeping bentgrass, Agrostis stolonifera L.

Seeding date and the duration of weed emergence influenced the duration of the critical weed-free period in carrot. The critical weed-free period extended up to 930 growing degree days (GDD), when carrot was seeded in late April. In contrast, the critical weed-free period was short and lasted 414 to 444 GDD, when seeded in mid to late May and weed biomass was less than 650 g m⁻². It is important for growers to scout fields for weeds until 930 GDD to protect the yield potential of the carrot crop in earlier planted crops; however, for carrot planted in mid to late May, weeds emerging after 444 GDD did not reduce yield. A useful strategy to reduce reliance on herbicide application would be to delay planting until late in May.

Nomenclature: Carrot, Daucus carota L.

Management practices and cropping systems that serve as integrated weed management practices, and at the same time can contribute to improved soil quality, will be important for the sustainability of agricultural production systems. The objective of this study was to assess weed species population density under contrasting tillage (conventional tillage [CT] and no tillage [NT]), residue burning (burn and no burn), and residue level (low and high) treatments after 5 and 6 yr of consistent management in a wheat–soybean double-crop production system. A field experiment was conducted from fall 2001 to fall 2007 in the Mississippi River Delta region of eastern Arkansas on a Calloway silt–loam. Weed assessments were conducted twice during the soybean growing season, before (early season) and after herbicide application (late season) in 2006 and 2007. Total weed density was greater under CT (513 plants m⁻²) than under NT (340 plants m⁻²) early in the growing season in 2006, but was greater under NT than CT late in the season in 2007, suggesting that the effectiveness of glyphosate on total weeds differs between CT and NT. Averaged across residue levels, grass species density was greatest in the NT–burn (68 to 167 plants m⁻²) combination and lowest in the NT–no-burn (41 to 63 plants m⁻²) early in the growing season in both years. Broadleaf density was greater early (200 to 349 plants m⁻²) than late (18 to 20 plants m⁻²) in the growing season under both CT and NT in 2006, but in 2007 broadleaf density did not differ by tillage treatment between seasons. Perennial weed density was greater in the burn (99 plants m⁻²) than in the no-burn (59 plants m⁻²) treatment in 2006. No tillage, no burning, and a high residue level appeared to contribute to the suppression of most weed species without reducing herbicide efficiency.

Nomenclature: Soybean, Glycine max Merr.; wheat, Triticum aestivum L.

ALS inhibitor-resistant biotypes are the fastest growing class of herbicide-resistant (HR) weeds. A Canadian ALS inhibitor-resistant biotype of Russian thistle was first reported in 1989. The molecular basis for ALS-inhibitor resistance is unknown for Canadian populations of this polyploid weed species, and was determined in this study for one Alberta and two Saskatchewan HR Russian thistle populations. HR plants survived spray application of the ALS-inhibitor mixture thifensulfuron  :  tribenuron in the greenhouse. All three HR Russian thistle populations were heterogeneous and contained both HR and herbicide-susceptible (HS) individuals. The molecular basis for resistance was determined by sequencing the ALS gene and/or conducting a TaqMan genotyping assay for single nucleotide polymorphism (SNP) for the Trp₅₇₄Leu mutation. Two target-site mutations were observed: Trp₅₇₄Leu in all three biotypes (554 individuals) and Pro₁₉₇Gln in one biotype (one individual), suggesting multiple-founding events for Russian thistle HR populations in western Canada. Segregation patterns among F1 and F2 progeny arrays of HR lines sprayed under greenhouse conditions varied; some segregated (i.e., had HR and HS progeny), whereas other lines were exclusively HR. In contrast, no segregation of molecular types, i.e., Trp₅₇₄, Trp/Leu₅₇₄ and Leu₅₇₄, as would be expected with heterozygosity at a single locus Trp/Leu₅₇₄, was observed. Such lack of segregation is consistent with the polyploid genome structure of Russian thistle and the presence of two copies of the ALS gene. The presence of more than one ALS gene confounded the ability of the molecular techniques to accurately identify “true” heterozygotes in this study.

Nomenclature: Thifensulfuron; tribenuron; Russian thistle, Salsola tragus L. SASKT.

The volatile compounds of crofton weed infested by cotton aphids and sprayed with MeJA were collected and analyzed by the TCT-GC/MS technique. The healthy weeds were controls. Seventeen volatiles identified from crofton weed included green leaf odors, monoterpenes and sequiterpenes, and oxo-compounds. Camphene, 2-carene, α-phellandrene, ρ-cymene, and caryophyllene were the major volatiles and constituted about 77% of the total volatile emissions from the control. In the aphid-infested weeds, no new induced component was found. Among the terpenes, ρ-cymene increased markedly in the infested weeds compared with the control, whereas all sesquiterpenes decreased markedly. Levels of endogenous JA in leaves and young stems of the aphid-infested weeds were markedly higher than in the control, whereas both endogenous SA level and ABA level were not significantly different. MeJA sprayed on crofton weed with the aphid infestation had a similar effect on volatile emissions. It is suggested that JA was one of the most important signals in crofton weed and could regulate the emission of volatile compounds.

Nomenclature: Crofton weed, Eupatorium adenophorum Spreng. (Compositae); cotton aphid, Aphis gossypii; JA, jasmonic acid; MeJA, methyl jasmonate; SA, salicylic acid; TCT-GC/MS, Thermal-desorption Cold Trapping-Gas Chromatograph/Mass Spectrum.

The allelopathic potential of a plant has been evaluated on the basis of two indicators: specific activity, which is the specific concentration of the allelochemical to exert a half-maximum effect on a receiver plant (EC₅₀), and total activity in a plant, which is the ratio of the concentration of an allelochemical in the producing plant to its EC₅₀. In the present study, a new indicator, total activity in a soil, which takes into account the effects of a soil on the allelopathy activity, is proposed because allelopathic activity is affected by the presence of soils. The total activity in a soil was calculated by multiplying the “total activity in a plant” with a “soil factor.” In this calculation, we assumed simplified cases for comparison, such that the allelopathic plant materials are evenly incorporated in the soils and the allelochemicals are released from the plant materials to the soils at a constant rate. We conducted bioassay experiments in the presence and absence of soils and cited some published data to calculate the specific activities and total activities in a plant and in a soil. The results indicated that the allelopathies of buckwheat caused by ( )-catechin, Leucaena leucocephala by l-mimosine, Xanthium occidentale by trans-cinnamic acid, and Brassica parachinensis by cis-cinnamic acid were not significant in a volcanic ash soil, an alluvial soil, and a calcareous soil, but the allelopathy of sweet vernalgrass caused by coumarin and Spiraea thunbergii by cis-cinnamoyl glucosides was highly effective in those soils. The allelopathies of Juglans species caused by juglone plus juglone precursors and Mucuna pruriens by l-DOPA would depend highly on the soil types. Although some limitations exist for this approach, the total activity approach would allow for a better quantitative estimation of the allelopathic potential of plant materials in soils.

Nomenclature: Brassica parachinensis Bailey; Juglans species; Leucaena leucocephala (Lam.) de Wit; Mucuna pruriens (L.) DC. var. utilis; Spiraea thunbergii Sieb. ex Blume; Xanthium occidentale Bertol; buckwheat, Fagopyrum esculentum Moench; sweet vernalgrass, Anthoxanthum odoratum L. AOXOD; l-DOPA, 3-(3′,4′-dihydroxyphenyl)-l-alanine.

Community assembly theory provides a useful framework to assess the response of weed communities to agricultural management systems and to improve the predictive power of weed science. Under this framework, weed community assembly is constrained by abiotic and biotic “filters” that act on species traits to determine community composition. We used an assembly approach to investigate the response of weed seed banks to 25 yr of management-related filtering in three different row-crop management systems in southeastern Pennsylvania: organic manure-based, organic legume-based, and conventional. Weed seed banks were sampled in April of 2005 and 2006 and quantified by direct germination in a greenhouse. We also assessed the filtering effects of weed management practices and relationships between assembled seed bank and emergent weed communities by allowing or excluding weed control practices within each management system and measuring emergent weed community response. Germinable weed seed bank densities and species richness in the final year of the study were over 40% and 15% higher, respectively, in the organic systems relative to the conventional system. Seed bank community structure in the organic systems was different from the conventional system, and the relationships between assembled seed banks and the emergent flora varied. Primary tillage, weed control, timing of planting, and fertility management appeared to be the main filters that differentiated weed seed banks in the three systems. Weed life history, emergence periodicity, seed size, and responsiveness to soil fertility and hydrology appeared to be the most important functional traits determining how weed species responded to management-related filters. Our results suggest that management systems can exert strong filtering effects that can persist over relatively long (greater than one growing season) time scales. Legacy effects of community-level filtering might be more important than previously assumed, and should be incorporated into predictive models of weed community assembly.

Glyphosate-resistant (GR) cropping systems are popular and used extensively by producers. However, the long-term impacts of heavy reliance of this technology on weed community structure are not known. Five fully phased field experiments (two no-tillage and three conventional tillage) were established at four locations in southwestern Ontario where the effects of herbicide system (glyphosate or conventional) in corn and soybean and crop rotation (corn–soybean or corn–soybean–winter wheat) on midseason weed communities were examined. Multivariate analysis on data over the last 3 yr of the 6-yr experiment showed that weed communities were distinctly different among the treatments within each experiment. At several locations, midseason weed communities were more similar in corn and soybean treated with glyphosate compared to the same crops treated with conventional herbicides, reflecting the continuous application of the same selection pressure in both crops. Analysis of trait-densities revealed an increase in species with late initiation of seedling recruitment at the expense of weed species with medium time of initiation of seedling recruitment rather than early recruiting species. Increases in perennial species, species with a short interval between recruitment and anthesis, and wind-dispersed species were also observed. Trait-density–based analysis of the weed community was an effective method for reducing the complexity of divergent weed communities that enabled direct quantitative comparison of the herbicide-induced effects on these weed communities.

Nomenclature: Glyphosate; corn, Zea mays L. ZEAMX; soybean, Glycine max (L.) Merr. GLXMA; winter wheat, Triticum aestivum L. TRZAW.

Mutation of a cytochrome P450 (CYP) allele on the short arm of chromosome 5 affects sensitivity in sweet corn to mesotrione and to tembotrione plus isoxadifen applied POST. Hybrids that are homozygous for the functional allele (i.e., CYPCYP) are rarely injured at registered use rates, hybrids that are homozygous for mutant alleles (i.e., cypcyp) are frequently injured, and hybrids that are heterozygous for a functional and mutant allele (i.e., CYPcyp) have more variable responses over trials. The objectives of this work were (1) to conduct side-by-side comparisons of sweet corn hybrid responses to mesotrione, tembotrione plus isoxadifen, and topramezone under field conditions; and (2) to compare dose–response relationships among CYPCYP, CYPcyp, and cypcyp hybrids. Among 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitors used POST in sweet corn, topramezone was safe on the 746 hybrids tested. When environmental conditions favored crop growth, mesotrione injured the largest number of hybrids, and these hybrids were almost exclusively cypcyp or CYPcyp. The safener isoxadifen added to the tembotrione product greatly reduced occurrence of injury to the CYPcyp genotypic class but not to the cypcyp hybrids. Despite a common genetic basis for herbicide metabolism, genotypic classes of sweet corn hybrids did not have identical field responses to mesotrione, tembotrione plus isoxadifen, and topramezone.

Nomenclature: Isoxadifen, ethyl-5, 5-diphenyl-2-isoxazoline-3-3-carboxylate; mesotrione; tembotrione; topramezone; sweet corn, Zea mays L.

Two separate studies were conducted to determine the relative importance of root and shoot competition in dry direct-seeded rice growing with junglerice and ludwigia. By growing rice in pots placed within larger pots such that the roots of the plants were either separated from or free to mingle with those of neighboring weeds, or by growing rice in the same pots but in the absence of weeds, the relative importance of shoot and root competition can be described. When rice was grown together with either weed species, shoot competition reduced the growth and yield of rice more than root competition. Results suggest that shoot competition for light may be the primary mechanism determining competitive outcomes between dry direct-seeded rice and junglerice or ludwigia. Junglerice was more competitive than ludwigia, which may reflect the C₄ metabolism efficiency of junglerice compared to the C₃ metabolism of ludwigia. Rice grain yield was highly correlated with above- and belowground biomass. The results also suggest the importance of measuring the whole plant when seeking to understand differences in the competitive ability of dry direct-seeded rice.

Nomenclature: Junglerice, Echinochloa colona (L.) Link; ludwigia, Ludwigia hyssopifolia (G. Don) Exell; rice, Oryza sativa L.

Termination of cover crops prior to no-till planting of soybean is typically accomplished with burndown herbicides. Recent advances in cover-crop roller–crimper design offer the possibility of reliable physical termination of cover crops without tillage. A field study within a no-till soybean production system was conducted in Urbana, IL, from 2004 through 2007 to quantify the effects of cover crop (cereal rye, hairy vetch, or bare soil control), termination method (chemical burndown or roller–crimper), and postemergence glyphosate application rate (0, 1.1, or 2.2 kg ae ha⁻¹) on soybean yield components, weed–crop interference, and soil environmental variables. Biomass of weeds surviving management within a soybean crop following either a vetch or rye cover crop was reduced by 26 and 56%, respectively, in the rolled system compared to the burndown system. Soybean yield loss due to weed interference was unaffected by cover-crop termination method in soybean following a rye cover crop, but was higher in the rolled than burndown treatment in both hairy vetch and bare soil treatments. In soybean following a rye cover crop, regardless of termination method, yield loss to weed interference was unaffected by glyphosate rate, whereas in soybean following a vetch cover crop or bare soil, yield loss decreased with glyphosate rate. Variation in soybean yield among cover crops and cover-crop termination treatments was due largely to differences in soybean establishment, rather than differences in the soil environment. Use of a roller–crimper to terminate a cover crop preceding no-till soybean has the potential to achieve similar yields to those obtained in a chemically terminated cover crop while reducing residual weed biomass.

Nomenclature: Common waterhemp, Amaranthus rudis Sauer, AMARU; giant foxtail, Setaria faberi Herrm., SETFA; hairy vetch, Vicia villosa Roth.; cereal rye, Secale cereale L. ‘FS Hi-Rye 500’; soybean, Glycine max (L). Merr.

This research compared effects of the weed control practice, soil cultivation, and the conventional practice, glyphosate application on weed seedbank, in a vineyard system. The experiment was conducted in a commercial wine-grape vineyard in the Napa Valley of northern California from 2003 to 2005. The annual treatments were “winter–spring glyphosate,” “spring cultivation,” “fall–spring cultivation,” and “fall cultivation–spring glyphosate,” and were applied “in-row,” under the vine. Composition of the weed seedbank collected in 2002 before treatment establishment did not differ among treatments. After 3 yr of weed treatments, detrended correspondence analysis indicated that the composition of spring cultivation and winter–spring glyphosate tended to differ from each other, but the remaining two treatments showed little differentiation. As determined by linear discriminant analysis, the specific weed species were associated with seedbanks of certain treatments. These were Carolina geranium, annual bluegrass, brome grasses, California burclover, and scarlet pimpernel, which do not pose problems with regard to physical aspects of grape production. Although ‘Zorro’ rattail fescue was ubiquitous among treatments, its distribution between depths in the cultivated treatments indicated that tillage provided some homogenization of seedbank along the vertical soil profile. The seedlings from the seedbank study were not congruent with those measured aboveground in the field, suggesting that both treatment and microclimatic effects in the field may have influenced germination, and thus, aboveground composition.

Nomenclature: Glyphosate; annual bluegrass, Poa annua L.; brome grasses, Bromus spp.; California burclover, Medicago polymorpha L.; Carolina geranium, Geranium carolinianum L.; scarlet pimpernel, Anagallis arvensis L.; ‘Zorro’ rattail fescue, Vulpia myuros var. hirsuta Hack.

Sheep sorrel is an invasive, creeping perennial weed of lowbush blueberry fields. It is one of the most prominent weeds in blueberry fields in Nova Scotia and is responsible for decreasing yields. Three levels of fertilizer (0, 20, 40 kg N ha⁻¹) and two levels of hexazinone (0 or 1.92 kg ai ha⁻¹) were applied to experimental plots to determine their effects on sheep sorrel density. Sprout-year hexazinone reduced sheep sorrel densities, which led to increased yields. Fertilizer increased weed density in the absence of herbicides, had no effect on density in the presence of herbicides, tended to have no impact on floral buds, and did not increase yields. Fruiting-year hexazinone decreased sheep sorrel densities in some situations, but did not result in yield increases.

Nomenclature: Hexazinone, Velpar; sheep sorrel, Rumex acetosella L.; lowbush blueberry, Vaccinium angustifolium Ait. and Vaccinium myrtilloides Michx.

Except for a small number of cases in which biocontrol agents were introduced from the site of origin of a weed (classical biocontrol), there have been few cases where a pathogen was virulent enough to perform cost effectively in the field as a mycoherbicide. Mycoherbicides are typically weed species specific, so compatibility with herbicides used to control other weeds is often studied. There can be a synergy between mycoherbicides and herbicides at the field level due to overlapping weed spectra (such synergies are not discussed in depth herein). Two approaches have been used to ascertain whether there is synergy in controlling the target weed: (1) random screening with herbicides; (2) using herbicides as antimetabolites to inhibit specific pathways, enhancing virulence. Glyphosate is the most common herbicide to synergize mycoherbicides, possibly due to its dual function as an inhibitor of biosynthesis of phenylpropanoid phytoalexins by suppressing enolphosphate-shikimate phosphate synthase, or by suppressing callose production (by inhibiting callose synthase) as well as inhibiting other calcium-dependent pathways due to the calcium-chelating properties of glyphosate.

Chemical ripening of sugarcane is an important component to profitable sugar production in the United States as well as other sugarcane industries throughout the world. Harvesting of sugarcane often begins before the sugarcane reaches the desirable maturity level. This is especially true in the Louisiana sugarcane industry where the window for harvesting is limited because of the risk of freezing temperatures encountered in a temperate climate. Research on the application of chemicals, mostly of herbicide origin, to enhance sucrose accumulation (ripening) or limit flowering to conserve stored sucrose has been conducted for more than 60 yr. The only sugarcane ripener currently registered for use in the United States is glyphosate applied before harvest. The herbicide fluazifop is used as the primary ripener of sugarcane in South Africa. The herbicides glyphosate, fluazifop, and sulfometuron-methyl and the growth regulators ethephon and trinexapac-ethyl are registered for use in Brazil. There is a continuing need to evaluate sugarcane ripeners to increase the utility of currently registered ripeners and to find additional ripeners for use by sugarcane industries. The need for alternatives to glyphosate is especially critical before a glyphosate-tolerant sugarcane can be utilized to improve control of problematic weeds.

Nomenclature: Ethephon; fluazifop; glyphosate; sulfometuron-methyl; trinexapac-ethyl; sugarcane, Saccharum interspecific hybrid.

For many years, virtually all pharmaceutical companies had an agrochemical division. This was partly to maximize the benefits of expensive chemical synthesis efforts by searching for many types of useful biological activities. Leads for pharmaceuticals and pesticides often overlap, in some cases leading to similar compounds used for human health and weed management purposes. This review will focus on herbicides and herbicide classes that have potential pharmaceutical properties, both as therapeutic agents that act through human molecular target sites and those that act on infectious agents. An example of the first case is compounds that target plant acetyl coenzyme A carboxylases, inhibiting fatty acid synthesis, and similar compounds used in humans as anti-inflammatory agents. Another such example is the triketone class of compounds that can act both as herbicides and as treatments for the genetic disease tyrosinemia, targeting the same enzyme in both cases. Examples of the second case are the relatively large number of herbicides that have activity against the malaria protozoan (Plasmodium spp.). It turns out that Plasmodium spp. and related disease organisms have an organelle that is apparently analogous to the plant plastid, the apicoplast. Herbicides such as dinitroanilines are active against several protozoan parasites by the same mechanism by which they kill plants, interaction with tubulin to halt cell division and other tubulin-dependent processes. These and other multiple activities of various herbicides and herbicide classes provide perspective on the broad biological activity of herbicides and related compounds.

Herbicides are small molecules that inhibit specific molecular target sites within plant biochemical pathways and/or physiological processes. Inhibition of these sites often has catastrophic consequences that are lethal to plants. The affinity of these compounds for their respective target sites makes them useful tools to study and dissect the intricacies of plant biochemical and physiological processes. For instance, elucidation of the photosynthetic electron transport chain was achieved in part by the use of herbicides, such as terbutryn and paraquat, which act on photosystem II and I, respectively, as physiological probes. Work stemming from the discovery of the binding site of PS II–inhibiting herbicides was ultimately awarded the Nobel Prize in 1988. Although not as prestigious as the seminal work on photosynthesis, our knowledge of many other plant processes expanded significantly through the ingenious use of inhibitors as molecular probes. Examples highlight the critical role played by herbicides in expanding our understanding of the fundamental aspects of the synthesis of porphyrins and the nonmevalonate pathway, the evolution of acetyl-coenzyme A carboxylase, cell wall physiology, the functions of microtubules and the cell cycle, the role of auxin and cyanide, the importance of subcellular protein targeting, and the development of selectable markers.

As all herbicides act on pathways or processes crucial to plants, in an inhibitory or stimulatory way, low doses of any herbicide might be used to beneficially modulate plant growth, development, or composition. Glyphosate, the most used herbicide in the world, is widely applied at low rates to ripen sugarcane. Low rates of glyphosate also can stimulate plant growth (this effect is called hormesis). When applied at recommended rates for weed control, glyphosate can inhibit rust diseases in glyphosate-resistant wheat and soybean. Fluridone blocks carotenoid biosynthesis by inhibition of phytoene desaturase and is effective in reducing the production of abscisic acid in drought-stressed plants. Among the acetolactate synthase inhibitors, sulfometuron-methyl is widely used to ripen sugarcane and imidazolinones can be used to suppress turf species growth. The application of protoporphyrinogen oxidase inhibitors can trigger plant defenses against pathogens. Glufosinate, a glutamine synthetase inhibitor, is also known to improve the control of plant diseases. Auxin agonists (i.e., dicamba and 2,4-D) are effective, low-cost plant growth regulators. Currently, auxin agonists are still used in tissue cultures to induce somatic embryogenesis and to control fruit ripening, to reduce drop of fruits, to enlarge fruit size, or to extend the harvest period in citrus orchards. At low doses, triazine herbicides stimulate growth through beneficial effects on nitrogen metabolism and through auxin-like effects. Thus, sublethal doses of several herbicides have applications other than weed control.

Nomenclature: 2,4-D; dicamba; fluridone; glyphosate; imazpic; lactofen; simazine; sulfometuron-methyl; soybean, Glycine max (L.) Merr.; sugarcane, Saccharum spontaneum L.; wheat, Triticum aestivum L.

Herbicides used as harvest aids are applied at crop maturity to desiccate weed and crop foliage. Weeds present in the harvested crop can increase moisture content and foreign material, reducing grade and market price. Weeds can also delay the harvest operation and reduce harvest efficiency. Glyphosate can be used to desiccate weeds in glyphosate-resistant crops without concern for crop injury. Carfentrazone and pyraflufen-ethyl used as harvest aids can be effective in desiccating broadleaf weeds in corn and soybean. Paraquat, although effective on grass and broadleaf weeds when applied late season, can cause significant crop injury if applied too early. With expanded production of early maturing soybean cultivars in the mid-South (Arkansas, Louisiana, Mississippi, Missouri bootheel, and west Tennessee), presence of green stems, green pods, or green leaf retention, or combinations of these at harvest has increased. Interest in harvest aids has shifted to use as a crop desiccant. Paraquat also is an effective soybean desiccant, but application timing differs for indeterminate and determinate cultivars. Paraquat applied after soybean seed reached physiological maturity reduced number of green stems, pods, and retained green leaves present, allowing harvest to proceed 1 to 2 wk earlier than nontreated soybean. Seed moisture, foreign material, and seed damage also were reduced when paraquat was applied.

Nomenclature: Corn, Zea mays L.; soybean, Glycine max (L.) Merr.

Assessing belowground plant competition is complex because it is very difficult to separate weed and crop roots from each other by physical methods. Alternative techniques for separating crop and weed roots from each other are needed. This article introduces a stable isotope method that can quantify the amounts of roots of rice and barnyardgrass intermixed in flooded field soils. It relies on the biological principle that rice, a C₃ (photosynthetic pathway) species, discriminates more effectively than barnyardgrass, a C₄ species, against a relatively rare isotopic form (¹³C) of CO₂. This results in different ¹³C : ¹²C isotope ratios (expressed as δ¹³C) in root tissues of the two species. δ¹³C values for monoculture barnyardgrass and rice grown in a standard flood-irrigated system were highly stable over 4 crop-years, averaging −13.12 ± 0.80 (SD) and −28.5 ± 0.11 (SD)‰, respectively, based on analysis by an isotope ratio mass spectrometer. Standard concentration curves relating measured δ¹³C values to set proportions of rice : barnyardgrass root biomass were described by linear regressions, typically with r² values of 0.96 or greater. Quantities of intermixed rice and barnyardgrass roots sampled 0 to 5 cm deep from soil between rice rows were estimated by extrapolation from standard curves based on δ¹³C values. About 50% more barnyardgrass root tissue was detected in plots of Lemont long-grain rice than in weed-suppressive PI 312777 indica rice, demonstrating the feasibility of using this stable carbon isotope method in flooded rice systems.

Nomenclature: Barnyardgrass, Echinochloa crus-galli (L.) Beauv.; rice, Oryza sativa L.