Information from taxonomic treatments and comparisons of accessions from numerous locations grown in the field and greenhouse were combined and summarized to produce a key and descriptions of common agricultural nightshades in North America (Solanum americanum Mill., S. nigrum L., S. ptycanthum Dun., and S. sarrachoides Sendt.). Quantitative and qualitative descriptions of key characters and photographs of important morphological structures are provided to facilitate field identification. Problems with nomenclature among these species are discussed, and a system of common names that would standardize usage is proposed.

Cogongrass is a difficult weed to control in small-scale farming systems and often causes significant crop yield reduction. Field experiments were conducted from 1996 to 1999 at three sites located in the forest/savanna transition zone of Nigeria to determine the influence of intercropping cover crops on cogongrass, corn, and cassava growth. Total cogongrass biomass (shoots and rhizomes) at the onset of the study was highest at Ijaiye (889 g m−2), followed by Umumba (445 g m−2), and least in Ezillo (138 g m−2). Velvetbean had the highest percent ground cover at Umumba and Ijaiye (67 to 89%) 10 wk after planting and shaded the ground longer at all locations. Twelve months after planting, plots with cover crops had 66, 71, and 52% lower cogongrass biomass than the weedy control without cover crops at Ijaiye, Umumba, and Ezillo, respectively. Velvetbean at all locations, L. purpureus at Ijaiye, and tropical kudzu at Umumba and Ezillo were the cover crops most effective in reducing rhizome biomass of cogongrass. Annual weeds dominated the plots sown to cover crops after 2 to 3 yr. At Ijaiye and Umumba, cogongrass competition affected the yield of cassava more than the yield of corn. At all locations, cover crops and weeded control treatments had 27 to 52% more corn grain yield than the weedy control. At Ijaiye, corn grain yields from velvetbean and L. purpureus plots were similar to that from the weeded control plot. At Umumba, all plots with cover crops had corn grain yields similar to that of the weeded control. At all locations, almost all cover crop treatments had cassava root yields higher than the weedy control. Except at Ijaiye, root yields from weeded control plots were 17 to 88% higher than in cover-cropped treatments, suggesting competition between cover crops and cassava.

Five fallow treatments in an alternate winter wheat (Triticum aestivum L.) fallow rotation experiment were compared over a 6-yr period at North Platte, Nebraska. During the 14-month fallow period from winter wheat harvest until winter wheat planting, plots receiving no tillage (weeds were controlled by herbicides) had the least weed growth, most soil water stored, and highest amount of surface mulch maintained. Also, the plots receiving only herbicides had the highest grain yields of all treatments. However, an average of 3.8 herbicide applications were needed to control grass weeds missed by 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) during the last 5.5 months of the fallow period. Greatest weed growth during the fallow period was on plots that received only tillage and occurred during the first 3 months after harvest.

Predictions of weed seedling populations from seedbank data should characterize the spatial distribution as well as the composition and abundance of weeds. The spatial distribution of seedbank and seedling populations of common lambsquarters and annual grasses (giant foxtail, large crabgrass, and fall panicum) were described in moldboard plow and no-tillage soybean fields from 1990 to 1993. Spearman rank correlations between seedbank and seedling densities were significant for common lambsquarters in both tillages and all years, but for annual grasses correlations were significant only in no-tillage. Semivariograms showed spatial autocorrelation in seedbank and seedling populations of common lambsquarters in all years in no-till, but less often in the moldboard plow field. Annual grass seed and seedling populations were autocorrelated in the no-till field every year except 1993, and in the moldboard plow field in 1992 and 1993 only. Cross-semivariograms showed spatial continuity between seedbank and seedling population densities in 3 of 4 yr in no-till for common lambsquarters, and in all years of no-till and 1 yr of moldboard plow for annual grasses. Grey-scale field maps of common lambsquarters seedbanks corresponded visually to maps of seedling populations and could have been used to target control efforts, but visual correspondence between annual grass seedbank and seedling maps was poor. Seedbank and seedling mapping may be useful for site-specific management, but additional information is needed to understand the variation in the relationships between these two populations over time and space.

Downy brome (Bromus tectorum L. # BROTE) may be a troublesome weed in winter small grains, perennial legumes, perennial grasses grown for seed, and orchards. In Nebraska, winter wheat (Triticum aestivum L.) yields have been depressed 30% by downy brome populations of 11 to 22 plants/m2 (8). In Oregon, downy brome densities of 108 to 160 and 538 plants/m2 reduced yields by 40 and 92%, respectively (22, 23). In Idaho, wheat yields were depressed 20 to 40% with 55 to 110 plants/m2 (18). Downy brome has also been shown to lower yields and quality of hay from infested fields of alfalfa (Medicago sativa L.) (29). In perennial grass seed fields, downy brome may cause a serious seed quality problem (16). Some grass seed lots have contained as much as 50 to 75% downy brome seed.

To manage or control nonindigenous species (NIS), we need to know where they are located in the landscape. However, many natural areas are large, making it unfeasible to inventory the entire area and necessitating surveys to be performed on smaller areas. Provided appropriate survey methods are used, probability of occurrence predictions and maps can be generated for the species and area of interest. The probability maps can then be used to direct further sampling for new populations or patches and to select populations to monitor for the degree of invasiveness and effect of management. NIS occurrence (presence or absence) data were collected during 2001 to 2003 using transects stratified by proximity to rights-of-way in the northern range of Yellowstone National Park. In this study, we evaluate the use of environmental and remotely sensed (LANDSAT Enhanced Thematic Mapper +) data, separately and combined, for developing probability maps of three target NIS occurrence. Canada thistle, dalmation toadflax, and timothy were chosen for this study because of their different dispersal mechanisms and frequencies, 5, 3, and 23%, respectively, in the surveyed area. Data were analyzed using generalized linear regression with logit link, and the best models were selected using Akaike's Information Criterion. Probability of occurrence maps were generated for each target species, and the accuracies of the predictions were assessed with validation data excluded from the model fitting. Frequencies of occurrence of the validation data were calculated and compared with predicted probabilities. Agreement between the observed and predicted probabilities was reasonably accurate and consistent for timothy and dalmation toadflax but less so for Canada thistle.

Leaves of a number of plant species were surveyed for their CO2 compensation concentration which is one of the distinguishing characteristics used to classify plants on the basis of their photosynthetic capacity. Monocot genera with low CO2 compensation values are mainly limited to tribes of Chlorideae, Paniceae, Andropogoneae, Tripsaceae, and a part of Festuceae in Gramineae. Major grain crops, except corn (Zea mays L.) and sorghum (Sorghum vulgare Pers.), are primarily in the tribes of Hordeae, Aveneae, and Oryzeae, and have high CO2 compensation concentrations. Seven genera of dicots with low CO2 compensation occur in the four families of Amaranthaceae, Chenopodiaceae, Portulacaceae, and Euphorbiaceae. Major dicot crops are in the families Leguminosae and Malvaceae and have high CO2 compensation points. Low CO2 compensation concentration also is correlated with low carbonic anhydrase activity. Conversely, high CO2 compensation concentration plants have a high carbonic anhydrase activity. Data on the influence of light intensity and temperature on the rate of photosynthetic CO2 fixation in leaves from plants with high and low CO2 compensation concentration indicate differential responses of photosynthesis to these environmental factors. The data are interpreted as supporting a hypothesis for competition by specific plants.

Field studies at three sites and growth chamber experiments were conducted to determine the reproductive potential, flower phenology, seed viability and germination, and overall seedbank longevity of yellow starthistle in the Central Valley of California. At the three study sites, seedheads contained an average of between 65 and 83 achenes. Overall, 85% of the achenes were the interior pappus-bearing type, and the remaining 15% were the outer nonpappus-bearing type. Germinable seed did not initially develop until the late corolla senescence stage 8 d after flower initiation. Seed germination and viability 1 wk after dispersal were similar (86 and 91%, respectively). Comparison in flower phenology in 1996 and 1997 indicated that development from initial anthesis to achene dispersal more closely corresponded to days, rather than thermal units. In the field, germinable seed was produced when more than 2% of the total seedheads had initiated anthesis. To minimize seed production with late-season control methods, such as prescribed burning, mowing, or herbicide treatment, management strategies should be timed before the plant population has advanced beyond the 2% flower initiation stage. Over 84% of the seed germinated under growth chamber conditions 1 wk after seedheads reached the dispersal stage. This indicates that most yellow starthistle seed had little or no after-ripening requirements. In a field experiment, yellow starthistle seed germination corresponded to seasonal rainfall. A total of 44 and 39% of the pappus-bearing and nonpappus-bearing seed, respectively, germinated after one growing season. Of seed recovered from the soil after the first growing season, 88 and 81% of the pappus-bearing and nonpappus-bearing seed, respectively, was either damaged or degraded. From projected values based on recovered and germinated seed, it was estimated that over 97% of the total seed was removed from the soil seedbank after two growing seasons. These findings should assist land managers in developing long-term yellow starthistle management strategies.

Dormant and nondormant kochia [Kochia scoparia (L.) Schrad. ♯3 KCHSC] seed populations were buried at six soil depths in Colorado. Portions of both populations remained viable for 36 months. Persistence increased with burial depth in both populations. Seed loss from the initially dormant population was limited to germination in situ, but seed loss from the initially nondormant population included significant viability loss at burial depths of 10 cm or less. Persistence of both populations was regulated by dormancy retention. Shallow tillage practices are predicted to decrease seed persistence in soil and increase successful seedling emergence. Deep tillage practices are predicted to reduce seedling emergence but increase soil seed populations.

Field experiments were established to investigate the effects of tank-mixing sethoxydim or quizalofop with imazaquin, chlorimuron, or lactofen for barnyardgrass control in soybeans. Sequential applications, where the grass herbicide was applied 24 h before or after the broadleaf weed herbicide, were also evaluated. There was an antagonistic decrease in barnyardgrass control when sethoxydim or quizalofop was tank mixed with any of the broadleaf weed herbicides. Antagonism was also observed when either grass herbicide was applied 24 h after imazaquin or lactofen, but not with chlorimuron. Control was not affected when the grass herbicide was applied 24 h before the broadleaf weed herbicide. In greenhouse experiments, the effects of tank-mixing sethoxydim, quizalofop, fluazifop-P, haloxyfop, fenoxaprop, or clethodim with imazaquin, lactofen, chlorimuron, acifluorfen, fomesafen, bentazon, or 2,4-DB were also evaluated for barnyardgrass control. Although acifluorfen provided 45% barnyardgrass control, tank-mixing it with fluazifop-P, haloxyfop, or fenoxaprop was antagonistic. Antagonism also occurred when chlorimuron was tank mixed with any of the grass herbicides except fenoxaprop. Barnyardgrass control by all of the grass herbicides applied in the field or greenhouse was most severely antagonized by tank mixes containing imazaquin.

The behavior of highly volatile pre-emergence herbicides in soil and their relative availability to plants under various conditions is poorly understood and pertinent information is much sought after by workers in chemical weed control. Ashton and Sheets reported an inverse relationship between injury to oats and soil adsorption of ethyl–N,N-di–n–propylthiolcarbamate (EPTC) in various soil types. Later, Sheets demonstrated a close relation between the initial toxicity of EPTC and soil types. EPTC was inactivated about one-third as rapidly in an autoclaved soil as in a corresponding unautoclaved one, from which he suggested that microbial breakdown may be a major pathway of EPTC inactivation when the chemical is incorporated in the soil.

The effects of weed density on the phytotoxicity of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] to white mustard (Brassica hirta Moench) and alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] to foxtail millet [Setaria italica (L.) Beauv.] were determined in the greenhouse. The fresh weight of both plants was reduced by the herbicide treatments, but as the weed density (plants per pot) increased, the herbicide rate required to cause equivalent fresh weight reductions per pot also increased. White mustard and foxtail millet grown in pots absorbed less 14C-atrazine or 14C-alachlor per plant from the soil at high weed density than low, regardless of herbicide rate. Foxtail millet seedlings grown in petri dishes absorbed less 14C-alachlor per plant from aqueous solution as the number of seedlings per petri dish increased. Data from field experiments in 1977 and 1979 indicated that more alachlor or metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide] was required for equal control of a high than low density of forage sorghum [Sorghum bicolor (L.) Moench ‘Rox Orange’] interseeded in maize (Zea mays L.). Rox Orange sorghum was used to simulate shattercane [Sorghum bicolor (L.) Moench], a problem weed in Nebraska. At the higher Rox Orange sorghum seeding rate used, both alachlor and metolachlor treatments decreased Rox Orange sorghum plant populations but not yield.

Aminocyclopyrachlor, a newly discovered synthetic auxin herbicide, and its methyl ester, appear to control a number of perennial broadleaf weeds. The potential volatility of this new herbicide and its methyl ester were determined under laboratory conditions and were also compared to dicamba and aminopyralid with the use of enclosed chamber and open-air plant bioassays. Bioassays consisting of visual estimates of epinastic responses and kidney bean and soybean leaf-width measurements were developed to measure vapor release from glass and plastic. Vapor release of aminocyclopyrachlor from glass surfaces was undetectable under laboratory conditions, and no phytotoxic responses were observed when plants were exposed to vapors emanating from various surfaces. Results were similar to those of aminopyralid, indicating the risk of plant injury from vapor movement of aminocyclopyrachlor and aminopyralid was very low. When combined with 1% methylated seed oil, vapor release of aminocyclopyrachlor-methyl ester reached 86% 192 h after application to glass surfaces. Phytotoxic responses of plants exposed to vapors emanating from various surfaces treated with aminocyclopyrachlor-methyl ester were similar to responses to dicamba under enclosed incubation conditions, but were less in outdoor, open-air environments. Studies are needed to understand better the risk of injury to nontarget plants due to vapor movement of aminocyclopyrachlor-methyl ester under field applications.

Remote sensing and associated spatial technologies provide tremendous opportunity to enhance weed management and improve–protect the environment through judicious use of the most efficacious control methods for a given site. They can also be invaluable assets for detection of invasions, assessment of infestation levels, monitoring rate of spread, and determining the efficacy of mitigation efforts for weed management. In combination with other technologies such as global positioning systems and geographic information systems, sampling strategies can be devised to efficiently determine the location of weed populations in agricultural and wildland situations. Maps created from remote sensing or sampling (or both) allow site-specific weed management of only the areas requiring corrective action. Potential benefits to the land managers and the ecosystem as a whole will come from reductions in inputs, reduced environmental liability from the detrimental effects of applying control measures to entire areas, crop yield increases through better management decisions, and early detection and effective management of invading species. Improvements in spatial and spectral resolution, temporal frequency, image turnaround time, and cost of image acquisition, combined with the realization of the value of the data, are enhancing the acceptance and usage of remote sensing technologies. However, remote sensing will be best used by providing accurate, site-specific data that can be converted into information used by decision support systems (DSSs). Advances in these DSSs, and their ability to incorporate remote sensing data, have been rapid and widespread in the past 10 yr. As a result, federal management and research agencies, academic institutions, and private entities have collectively developed efforts to use this information in monitoring and management efforts for invasive species in western rangelands, aquatic ecosystems and forestry, and site-specific weed management in agronomics.

Metribuzin-3-14C [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] was absorbed, translocated, and metabolized by both metribuzin-tolerant ‘Essex’ and metribuzin-sensitive ‘Coker 102’ soybean cultivars [Glycine max (L.) Merr.]. After 48 h Coker 102 accumulated 40% greater metribuzin equivalents in the shoots than Essex, but Essex shoots contained only 29% as much unaltered metribuzin as Coker 102, 1.08 and 3.68 μg per g dry weight, respectively. Essex is resistant to metribuzin primarily owing to a capacity to rapidly detoxify metribuzin to DA [6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one], to at least seven unidentified metabolites which remained in the aqueous fraction, and to an insoluble fraction. The unidentified metabolites in the aqueous fraction constituted the major detoxified breakdown products in both cultivars.

Studies were conducted on the growth and development of 55 morphologically distinct vegetative types of johnsongrass (Sorghum halepense (L.) Pers.) collected throughout the United States and from several foreign countries. Observations were made also on the growth of sorghum almum (Sorghum almum Parodi) from three foreign countries. Mature leaf-blades of the different johnsongrass ecotypes varied in length from 31 to 59 cm and in width from 1.7 to 3.4 cm. Plant height and culm density varied 2 to 4-fold for the different ecotypes. Floret production varied from 87 to 352 sessile spikelets for representative panicles of the different ecotypes. The number and arrangement of branchlets within panicles also varied as did the size of various spikelet components. Sorghum almum produced much taller plants than did johnsongrass although culm density and lateral growth were less than that of johnsongrass.

Cultivated rice yield losses due to red rice infestation vary by cultivar, red rice density, and duration of interference. The competition effects of red rice could be influenced further by emergence characteristics, red rice biotype, and planting time of cultivated rice. We aimed to characterize the emergence of red rice biotypes at different planting dates and evaluate the effect of red rice biotype, rice cultivar, and planting date on cultivated rice yield loss. Field experiments were conducted at the Southeast Research and Extension Center, Rohwer, AR, and at the Arkansas Rice Research and Extension Center, Stuttgart, AR, in the summer of 2005 and 2006. The experimental design was a split-split plot with three or four replications. Planting time, ClearfieldTM (CL) rice cultivar, and red rice biotype were the main plot, subplot, and sub-subplot factors, respectively. There were three planting times from mid-April to mid-May at 2-wk intervals. CL rice cultivars, CL161 and hybrid CLXL8, and 12 red rice biotypes were planted. The emergence rate and coefficient of uniformity of germination differed among some red rice biotypes within a planting time. Planting date affected the emergence characteristics of red rice biotypes. The mean emergence rate of red rice was 0.043 d−1 in the mid-April planting and 0.058 d−1 in the late April planting. For the mid-April planting, 50% of red rice biotypes emerged in 20 ± 2 d compared with 15 ± 2 d for CL rice cultivars. Yield losses due to red rice biotypes generally increased in later planting dates, up to 49%. Yield losses due to interference from red rice biotypes ranged from 14 to 45% and 6 to 35% in CL161 and CLXL8, respectively. Cultivated rice became less competitive with red rice in later plantings, resulting in higher yield losses.

In Australia, glyphosate resistance has been observed in rigid ryegrass in several states including New South Wales (NSW) and South Australia (SA). Several populations of glyphosate-resistant rigid ryegrass were analyzed for the inheritance of glyphosate resistance. Eight glyphosate-resistant populations were crossed to the same susceptible population to create first filial generation (F1) families. Individuals from the F1 families were subsequently treated with glyphosate. The response to glyphosate of F1 families from all eight crosses was more similar to the resistant parent than the susceptible parent. Within crosses, dose responses of reciprocal F1 families were not significantly different from each other, indicating glyphosate resistance is encoded on the nuclear genome in all eight populations. The level of dominance observed in dose–response experiments ranged from partial to total within the herbicide doses tested. F1 individuals from five of the populations were crossed with susceptible (S) individuals to create backcross (BC) populations. Most of the families from these BC populations segregated in a manner consistent with a single gene controlling glyphosate resistance. These results indicate that resistance is inherited as a single dominant allele in four out of the five glyphosate-resistant rigid ryegrass populations. Such information is vital in the development of management strategies for glyphosate resistance in Australia.

Field and laboratory studies were conducted to determine if differences existed in pinto bean varietal tolerance to postemergence application of imazethapyr under field conditions; if differences in tolerance were due to differential acetolactate synthase enzyme sensitivity or differences in 14C-imazethapyr absorption, translocation, and metabolism; and the heritability of imazethapyr tolerance in pinto bean. All rates of imazethapyr injured Olathe, Sierra, UI-114, P89405, Aztec, and P90570 pinto bean varieties 7 d after treatment in 1991 and 1992, except 53 g ai ha−1 of imazethapyr applied to Sierra pinto bean in 1991. Olathe was injured more than other varieties in 1991, and physiological maturity of Olathe was delayed more than Sierra in 1991 and 1992. Seed yields of all varieties were not reduced in 1991, and only P90570 had reduced seed yields from 53 g ha−1 of imazethapyr in 1992. Differential sensitivity of the acetolactate synthase enzyme to imazethapyr was not the mechanism of differential varietal response. Olathe pinto bean absorbed and translocated 1.4 and 1.3 times more 14C-imazethapyr, respectively, than Sierra pinto bean 24 h after application. No differences in 14C-imazethapyr metabolism were detected between Olathe and Sierra pinto bean. Broad heritability of imazethapyr tolerance in pinto bean was calculated to be 0.85. The number of genes controlling the inheritance of imazethapyr tolerance in pinto bean was greater than one.

2,4-D, discovered independently in the United States and Europe in the mid-1940s, was one of the first synthetic herbicides to be used selectively for weed control (Cobb and Reade 2010). Since then, several herbicides belonging to different chemical classes and possessing diverse mechanisms of action have been synthesized and marketed globally. Herbicides have vastly contributed to increasing world food, fiber, fuel, and feed production in an efficient, economic, and environmentally sustainable manner. Before receiving regulatory approval, all herbicides (pesticides) undergo rigorous testing for their toxicological, residual, physicochemical, and biological properties. Additionally, herbicides are suitably formulated to reach their target site and maximize their efficacy on target weeds while being safe on crops.