Black nightshade was subjected to two degrees of water stress by adding polyethylene glycol 20,000 (PEG) to the nutrient solution 5 d before treatment with glyphosate. The ED50 values for glyphosate, determined from dose-response curves, demonstrated that both degrees of water stress strongly increased the ED50, with and without the surfactant Ethomeen T/25 in the spray solution. The surfactant reduced the ED50 5-, 4.6-, and 6.9-fold at 0, 15, and 20% PEG, respectively. A 14C study demonstrated that unstressed plants absorbed 22% of applied glyphosate. Without surfactant, water stress reduced foliar absorption 2.2-fold at 15% PEG and 4.5-fold at 20% PEG. With surfactant, the foliar absorption was 35% of the applied amount in unstressed and water-stressed plants. The surfactant and PEG reduced the translocation efficiency of glyphosate. The surfactant had the most pronounced influence and reduced the translocation efficiency 1.5-fold at 0% PEG, 2.2-fold at 15% PEG, and 1.8-fold at 20% PEG. Induction or removal of water stress 24 h after glyphosate treatment indicated that plant growth rate is positively correlated with glyphosate efficacy. It was concluded that the surfactant can overcome the adverse influence of water stress on foliar absorption of glyphosate but not the adverse, postapplication influence of water stress on glyphosate efficacy.

Activity, adsorption, mobility, and field persistence of one emulsifiable concentrate (EC) and three microencapsulated (ME) formulations of alachlor were studied with petri dish bioassay, based on root response of oats grown in sand or soil. Both bioassays indicated that activity of all formulations was increased with increasing herbicide concentration. EC-alachlor in sand showed the highest activity, while ME-alachlorL and ME-alachlorA, the lowest; the activity of ME-alachlorC was intermediate. In silty clay loam soil, EC-alachlor had the highest activity, while ME-alachlorL had the lowest; and ME-alachlorA showed intermediate activity and was similar to that of ME-alachlorC More alachlor was adsorbed on the soil or remained encapsulated (not biologically available) after ME-alachlorL and ME-alachorA application compared to EC-alachlor. An intermediate amount of alachlor was adsorbed or remained inside the capsules when the ME-alachlorC formulation was applied. Greater amounts of alachlor were leached through a silty clay loam after EC-alachlor application compared to the three ME-alachlor formulations. Biologically available alachlor was not detected below 15 or 10 cm after application of EC- and ME-alachlor formulations, respectively. All alachlor formulations applied alone or in mixture with atrazine showed similar field persistence. Biologically available alachlor was not detected in the 0- to 10-cm soil depth 30 d after their application. All alachlor formulations applied alone gave excellent control of redroot pigweed and black nightshade, but only partial control of jimsonweed. None of the herbicide treatments showed any detrimental effect on corn, and all of them increased corn yield to the level of weed-free control.

Saflufenacil (Kixor™) is a new herbicide of the pyrimidinedione chemical class for preplant burndown and selective preemergence dicot weed control in multiple crops, including corn. In this study, the mode of action of saflufenacil was investigated. For initial characterization, a series of biotests was used in a physionomics approach for comprehensive physiological profiling of saflufenacil effects. With the use of treated duckweed plants, metabolite profiling was performed based on quantification of metabolite changes, relative to untreated controls. Physiological and metabolite profiling suggested a mode of action similar to inhibitors of protoporphyrinogen IX oxidase (PPO) in tetrapyrrole biosynthetic pathway. Saflufenacil inhibited PPO enzyme activity in vitro with 50% inhibition of 0.4 nM for the enzymes isolated from black nightshade, velvetleaf, and corn. PPO inhibition by saflufenacil caused accumulations of protoporphyrin IX (Proto) and hydrogen peroxide (H2O2) in leaf tissue of black nightshade and velvetleaf. In corn, only slight increases in Proto and H2O2 were found, which reflects in planta tolerance of this crop. The results show that saflufenacil is a new PPO-inhibiting, peroxidizing herbicide.

Greenhouse and growth-chamber experiments were conducted to determine the influence of the ratio of red to far-red (R:FR) radiation and of neutral filtration of plant-available radiation on the vegetative and reproductive growth of selected nightshade species. Exposure of eastern black nightshade and black nightshade to far-red radiation resulted in greater partitioning of resources to stem tissue, resulting in taller plants. Number of flowers, timing of flowering, branching, and biomass production of black nightshade and eastern black nightshade were not influenced by the ratio of red to far-red radiation. Eastern black nightshade shoot and berry dry weight decreased as neutral density shading increased from 0 to 71%. Shoot dry weight decrease was associated with lower stem weight and production of fewer berries per plant. Neutral shading did not reduce leaf weight or leaf area per plant but increased the specific leaf area of eastern black nightshade. Internode elongation of nightshade species into a soybean canopy should primarily be associated with exposure to low R:FR irradiance ratios, whereas the thinner leaves of eastern black nightshade growing under shade should be associated with lower irradiance levels. Both responses are common adaptations of shade-avoiding plants.

Organic vegetable producers have limited options for managing weeds. They cite weed management as their number one research priority. Studies were conducted in 2004 and 2005 at the Black Sea Agricultural Research Institute, Samsun, Turkey, to determine the weed suppressive effects of summer cover crops in organic kale production. Treatments consisted of grain sorghum, sudangrass, hairy vetch, grain amaranth, pea, and fallow. Weed density and total weed dry biomass were assessed before and at 14, 28, and 56 d after incorporation (DAI) of the cover crops. Kale was transplanted 14 DAI and hand weeded once after last weed evaluation (56 DAI). All cover crops produced at least 1 ton/ha (t/ha) biomass; grain sorghum produced more dry matter than all other cover crops in both years. After incorporation of the cover crops, hairy vetch and sorghum treatments showed fewer species, lower weed density, and total weed dry biomass compared with other treatments. Cover crops suppressed emergence of common purslane, common lambsquarters, redroot pigweed, European heliotrope, field pennycress, annual sowthistle, black nightshade, shepherd's-purse, wild mustard, sun spurge, Persian speedwell, annual mercury, and jimsonweed up to 56 DAI. Total kale yield in hairy vetch treatments was more than double that of the no cover crop, and was significantly higher than yield from the other cover crop treatments. These results indicate that hairy vetch, grain sorghum, and sudangrass have ability to suppress early-season weeds in organic kale production.

Weed suppression by cover crops grown during the winter fallow period in continuous corn may lead to a reduction in herbicide use. Rye, crimson clover, and subterranean clover cover crops were compared with corn stubble under a conventional management system (CS) that included plowing and use of preemergence residual herbicides and a low-input management system (LIS) that included no-tillage and use of a presowing nonresidual herbicide for three consecutive years (1994–1996). Cover crop and above-ground weed biomass prior to desiccation were not influenced by management system. Cover crop biomass ranged from 1,420 to 5,657 kg ha−1 for rye, from 563 to 4,217 kg ha−1 for crimson clover, and from 563 to 4,248 kg ha−1 for subterranean clover. At crop planting, rye reduced weed biomass from 54 to 99%, crimson clover from 22 to 46% (with a negative value in 1995), and subterranean clover from 21 to 67%. Weed growth suppression was usually higher in years when cover crop biomass was higher. There were no differences in weed suppression by cover crops later in the season (corn in the fourth leaf stage), while total weed density was higher in LIS than CS in 2 of 3 yr. Total weed cover at corn's ‘full dent’ stage ranged from 1 to 7% in CS and from 24 to 47% in LIS. Cover crops influenced weed composition only in years when cover crop growth was high; otherwise their effect was masked by that of the management system. Weed communities showed higher diversity under LIS than under CS. Consistency of associations between weed species and treatments over sampling dates and years was found especially for some of the species associated with LIS. After 3 yr, redroot pigweed, common lambsquarters, and black nightshade were regularly associated with rye-LIS at an early corn growth stage; this may indicate a species shift toward a more troublesome composition.

Crops that effectively compete with weeds may be more suitable in low-input agricultural systems. A 2-yr field experiment was conducted in northern Greece to assess the competitiveness of seven annual aromatic plants (anise, sweet fennel, sweet basil, dill, coriander, parsley, and lacy phacelia) on common purslane, common lambsquarters, black nightshade, and barnyardgrass. The phytotoxicity of the essential oils produced by these aromatic plants was also determined using a perlite-based bioassay with barnyardgrass. Separation, identification, and quantification of the volatile compounds of these essential oils were also performed. After the harvest of the aromatic plants (8 wk after planting), the greatest weed fresh weight reduction (94 to 100%) was recorded in lacy phacelia, whereas the least (0 to 30%) was recorded in parsley. Lacy phacelia and sweet fennel produced the greatest fresh biomass yield in weedy and weed-free treatments, whereas parsley, dill, and coriander produced the lowest. Biomass of sweet fennel and anise was reduced by only 9 to 11% by weed competition, whereas biomass of lacy phacelia was not significantly affected. The essential oils isolated from sweet fennel and sweet basil were the most phytotoxic on barnyardgrass, whereas those isolated from lacy phacelia and anise were the least phytotoxic. Conclusively, aromatic plants with great competitiveness such as lacy phacelia, anise, and sweet fennel provided great weed suppression and they could be cultivated with low inputs in herbicides. However, high competitiveness of aromatic plants may not always be correlated with high essential oil phytotoxicity.

Experiments were conducted to determine the efficacy, absorption, and translocation of glyphosate, glufosinate, and imazethapyr with selected weed species. In the greenhouse glyphosate, glufosinate, and imazethapyr were applied at 0.25, 0.5, and 1 times their label rates of 1,121, 410, and 70 g ha−1, respectively, on 10- to 15-cm black nightshade, common waterhemp, eastern black nightshade, field bindweed, giant ragweed, ivyleaf morningglory, prairie cupgrass, velvetleaf, and yellow nutsedge. Glyphosate applied at the 1-time rate caused injury greater than or similar to injury from the 1-time rate of glufosinate or imazethapyr on black nightshade, common waterhemp, eastern black nightshade, field bindweed, giant ragweed, prairie cupgrass, and velvetleaf. The 1-time rate of glufosinate injured ivyleaf morningglory and yellow nutsedge more than did the 1-time rate of glyphosate or imazethapyr. Under field conditions glyphosate caused the greatest injury to common waterhemp, prairie cupgrass, and velvetleaf across plant growth stages. Giant ragweed and ivyleaf morningglory injury was more dependent on growth stage, with the 15- and 30-cm growth stages more susceptible to glyphosate than to glufosinate or imazethapyr. Differential response of these weed species may be caused by differences in herbicide translocation. Glyphosate was translocated more in both giant ragweed and ivyleaf morningglory, and these species were injured more by glyphosate than by glufosinate or imazethapyr at the larger growth stages.

The use of eucalyptus leaves for weed control in maize-based cropping systems is proposed. Aqueous extracts of eucalyptus are known to exert phytotoxicity on many weeds and crops, but there is also experimental evidence of the relative tolerance of maize. Based on in vitro dose-response bioassays of leaf aqueous extracts, we conducted greenhouse pot experiments testing incorporated eucalyptus leaves as green manure. The phytotoxic effects were tested on the germination, establishment and growth of maize and some representative accompanying weeds, in comparison to the PRE herbicide metolachlor. Eucalyptus fresh leaves incorporated into the soil as green manure at 1 and 2% w/w reduced the emergence of the dicot weed species redroot pigweed and black nightshade. After one month of incorporation, both doses reduced aerial biomass >94% two monocot weed species (barnyardgrass + large crabgrass) with respect to the eucalyptus-free pots, and around 80% for the small seeded dicots. Although the aerial biomass of maize was reduced by 33%, the final relative yield of maize biomass with respect to the untreated control increased by 37%. On the assessment of the temporal phytotoxic effects, the reduction of aerial biomass in maize could be overcome by adopting a relay-planting of maize after 12 to 15 days from eucalyptus incorporation. Our results constitute evidence that the incorporation of E. globulus residues to soil could be a feasible practice to reduce the reliance on synthetic herbicides in maize-based cropping systems.

Garden huckleberry, a member of the Solanaceae family and a close relative of black nightshade, is an exotic plant introduced from Africa. Information on garden huckleberry response to a new environment and to herbicides is useful for determining the potential of this species to become an invasive weed, predicting the potential range of this species in the United States, and developing an optimum garden huckleberry management program. Germination and survival of garden huckleberry seed, as affected by environmental factors, were studied under greenhouse and controlled-environment growth chamber conditions. Garden huckleberry seed became viable between 2 and 3 wk after anthesis and was nondormant when separated from fresh berries. Garden huckleberry seed was not photoblastic and germinated equally well under both a 14-h photoperiod and continuous darkness. Seed germinated at constant temperatures from 17 to 35 C, with optimum germination between 22 and 30 C. Germination of garden huckleberry seed markedly declined as the osmotic potential of the germination medium decreased. The optimum pH for germination of garden huckleberry was between 5 and 9. Paraquat, dicamba, and bromoxynil provided excellent garden huckleberry control (95 to 100%); atrazine and glyphosate were more phytotoxic (90%) than imazamox (80%); and acifluorfen and foramsulfuron gave inadequate control.

The application of the acetolactate synthase (ALS)–inhibiting herbicide metsulfuron on greenhouse- and field-grown black nightshade and greenhouse-grown ladysthumb resulted in progressive inhibition of the level of carbon dioxide (CO2) fixation, the relative quantum efficiency of electron transport through photosystem I (ΦPSI) and II (ΦPSII), and the leaf chlorophyll content. Photosynthetic-related measurements, measured 2 to 4 d after treatment (DAT) at photon flux densities of 400 to 500 μmol m−2 s−1, provided valuable information before the visual symptoms that first appeared at 7 to 10 DAT with the herbicide. Measurements of the quantum efficiency for electron transport by photosystem II and the loss in leaf chlorophyll content appeared to be two of the most practical parameters to use when designing an early detection method to assess the toxicity of metsulfuron. The use of chlorophyll fluorescence would require a comparison of steady-state ΦPSII measurements for control and treated plants, which could be realized by either measuring in time (before/after application) or space (treated/untreated patch).

Mortality of weed seeds at temperatures of 39, 42, 46, 50, 60, and 70 C was recorded through time under controlled laboratory conditions similar to those of soil solarization for six weed species: annual sowthistle, barnyardgrass, black nightshade, common purslane, London rocket, and tumble pigweed. Time and temperature requirements for thermal death varied considerably among the species studied. Barnyardgrass, London rocket, and annual sowthistle were more susceptible to heat treatment than black nightshade, common purslane, and tumble pigweed. Temperatures of 50 C and above were lethal for seeds of all species. Common purslane seeds were unaffected at 46 C and below, tumble pigweed and barnyardgrass seeds were unaffected at 42 C and below, and black nightshade seeds were unaffected at 39 C. Nonlinear models for mortality as a function of duration of heat treatment were developed for each species at each temperature at which mortality occurred. These models provide an empirical relationship for the construction of field-applicable decision models that could predict the accumulation of time and temperature combinations for effective solarization of weed seeds.

Productivity of dry bean is constrained by the competition with weeds for scarce nutrients and water in eastern Africa. Trials were conducted at Cornell University in 1996 and in central Uganda during the two seasons of 1997 to test the hypothesis that bean crop nutrition can be improved while increasing the relative competitiveness of bean with annual weed species. Soil levels of available N, P, and K were varied in the main plots. Subplots consisted of bean and two weed species in pure stands and bean mixed with each of the weed species. The weed species were black nightshade and smallflower galinsoga at Cornell and smallflower galinsoga and hairy beggarticks in Uganda. Bean yield was the most suppressed by hairy beggarticks with a mean reduction of 48%. Bean nutrient uptake and growth decreased relative to the weed nutrient uptake and growth when N and P were applied, but the relative competitiveness of bean increased with K application. The K effect on bean yield was greater than the P effect in two out of three trials. Alternative practices for the supply of N and P need to be evaluated for increasing bean yields while reducing the relative benefit to weeds.

Jerusalem artichoke has been reported to colonize several ecological niches and agronomic crops in southern Europe. This plant is also of interest because of its high biomass production and its potential to produce ethanol for biofuel. Allelopathy may be an advantageous trait in Jerusalem artichoke under cultivation, as it potentially reduces weed interference with the crop, theoretically allowing a reduction of mechanical or chemical input required for weed management. However, this trait may also be unfavorable if other crops are cultivated in rotation with Jerusalem artichoke or in areas infested by this species. The aim of this study was to investigate the sensitivity of selected diverse crops (wheat, lettuce, corn, tomato, rice, and zucchini) and weeds (barnyardgrass, black nightshade, common lambsquarters, common purslane, large crabgrass, and pigweed) to the presence of Jerusalem artichoke dried leaf tissues in laboratory experiments performed under controlled conditions. The simulated soil incorporation of different Jerusalem artichoke residues (four cultivars and a weedy population) was carried out in a series of laboratory and greenhouse experiments. Jerusalem artichoke reduced the radicle growth of seedling lettuce (60%), tomato (30%), large crabgrass (70%), and barnyardgrass (30%), whereas total germination of these species was less affected. Sensitivity to Jerusalem artichoke residues was species dependent; germination and initial growth of corn were not affected, whereas winter wheat, lettuce, tomato, rice, and zucchini seedlings were more sensitive to residue presence. Our experiments show that both wild and cultivated decomposing Jerusalem artichoke residues, particularly leaves and stems, possess phytotoxic potential. Additional field experimentation remains to be conducted to determine if allelopathy in the field contributes to its invasibility.

The overall objective of this study was to identify common patterns in the spatial distribution of the major weed species present in the corn-growing region of central Spain, exploring the scale dependence of these patterns and the possible associations or dissociations between individual species. Weed density was assessed in 16 commercial fields using digital images acquired in a 9-m by 9-m sampling grid. A set of six species was found in all the fields: black nightshade, common cocklebur, fierce thornapple, johnsongrass, purple nutsedge, and velvetleaf. Spatial analysis by distance indices and inverse distance weighting interpolation methods were performed to create weed distribution maps. The results showed aggregated spatial distribution patterns for all individual species regardless their life cycle, annual or perennial. Some associations and dissociations among species were found in the analysis of interactions. Nevertheless, the spatial patterns of co-occurrence of weed species were field-specific and therefore cannot be considered general patterns of weed co-occurrence. In order to explore the scale dependence of these results, an additional study was conducted in an experimental field located in the same area using a 1.0-m by 0.75-m sampling grid. Although this resolution allowed for a better definition of the positions of the weed patches and weed-free gaps, the results obtained revealed similar patterns to those observed with a coarser sampling resolution.