Tubulins are encoded by small gene families in plants. Here we report the cloning and characterization of water foxtail α-tubulin genes (AaTUA), an economically important weed. The genome of water foxtail contains TUA family consisting of at least four genes. Using degenerate primers, four partial TUA genes were isolated from the complementary DNA (cDNA) of water foxtail. Using the partial gene sequences, specific primers for each TUA gene were designed and full-length TUA cDNAs were isolated. These genes were designated as AaTUA1 to AaTUA4. The deduced amino acid sequences of AaTUA genes showed significant homology to the TUA genes of barley, corn, and Arabidopsis. The coding sequences of the AaTUA1 and AaTUA3 genes were interrupted by three introns and there were four introns in the coding regions of AaTUA2 and AaTUA4. The organ-specific expression of AaTUA genes showed that AaTUA1 and AaTUA4 were predominantly expressed in all organs examined (root, stem, young leaf, mature leaf, and panicle), whereas AaTUA2 was expressed mainly in roots and AaTUA3 was expressed in stem, root, and panicle. Abscisic acid (ABA) and gibberellic acid (GA) differentially induced the expression of AaTUA1 and AaTUA3. Moreover, trifluralin, propham, and caffeic acid induced the expression of all AaTUA genes in a dose-dependent manner except AaTUA2. This is the first report of complete sequences of AaTUA genes and the first characterization of these genes for any Alopecurus species in the literature.

Herbicides were evaluated for weed control in seedling perennial grass stands at six locations in eastern Washington. Most annual weeds commonly found in grass seed fields were controlled by 2-methoxy-3,6-dichlorobenzoic acid (dicamba), 2,3,6-trichlorobenzoic acid (2,3,6-TBA), and 1-butyl-3-(3,4-dichlorophenyl)-1-methylurea (neburon). Dicamba was the most effective herbicide for annual weed control but caused some injury to Kentucky blue-grass seedlings. Seedling grasses injured by dicamba recovered and became established in each trial. Grasses were injured about the same extent when treated with 2,3,6-TBA as when treated with dicamba, but 2,3,6-TBA did not control as many weed species. Neburon did not control as many species as dicamba and 2,3,6-TBA but was effective in killing a large number of species without measurable injury to grass seedlings.

The main factor determining the effectiveness of dinitro pre-emergence weed killers in the control of annual grasses and weeds is its distribution and concentration in the soil.

Field studies were conducted in Saskatchewan to evaluate the effect of herbicides on annual canarygrass (Phalaris canariensis L.) and associated weeds. Bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) at 0.35 kg ai/ha, tank mixes of bromoxynil at 0.28 kg/ha plus the ester of MCPA [(4-chloro-2-methylphenoxy)acetic acid] at 0.28 kg ae/ha, linuron [N′-(3,4-dichlorophenyl)-N-methoxy-N-methylurea] at 0.28 kg ai/ha plus MCPA amine at 0.56 kg/ha, or propanil [N-(3,4-dichlorophenyI)propanamide] at 1.0 kg ai/ha plus MCPA ester at 0.28 kg/ha resulted in annual canarygrass seed and dry matter yields equal to the unsprayed check and excellent wild mustard (Sinapis arvensis L. # SINAR) and cow cockle (Vaccaria pyramidata Medik. # VAAPY) control. Metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] at 0.21 kg ai/ha plus MCPA amine at 0.56 kg/ha reduced the crop stand in 1 out of 5 yr and seed yield every year. Postemergence application of difenzoquat (1,2-dimethyl-3,5-dipheny1-1H-pyrazolium) at 0.84 kg ai/ha or flamprop [N-benzoyl-N-(3-chloro-4-fluorophenyl)-DL-alanine] at 0.53 kg ai/ha, or preplant-incorporated triallate [S-(2,3,3-trichloro-2-propenyl)bis(1-methylethyl)carbamothioate] at 1.40 kg ai/ha optimized wild oat (Avena fatua L. # AVEFA) control with seed yields. Diclofop {(±)-2-[4-(2,4-dichlorophenoxy)phenoxy)propanoic acid} at 0.70 kg ai/ha severely damaged annual canarygrass in all years. Triallate applied at 1.40 kg/ha preplant or preemergence incorporated marginally reduced the crop stand and seed yield compared to the untreated controls in tolerance tests.

Common seepweed [Suaeda glauca (Bunge) Bunge] is a common salt-tolerant weed species distributed across the agricultural regions of northern China. It produces dimorphic seeds with different phenotypic characteristics and seed sizes. However, there is no information regarding the germination biology of these dimorphic seeds. Studies were conducted to evaluate the effects of ecological factors such as temperature, light, pH, osmotic stress, salt concentration, and planting depth on seed germination and seedling emergence. The results showed that brown seeds were nondormant, whereas black seeds had an intermediate physiological dormancy. The germination percentage of brown seeds was more than 80% at all temperature regimes and light conditions, but the optimum germination occurred at the cold thermoperiod of 20/10 C. In contrast, less than 6% of black seeds germinated at all temperature regimes and light conditions. Eight weeks of cold stratification did not break the dormancy of black seeds, whereas low concentrations of gibberellic acid (0.1 and 1.0 mM) significantly increased seed germination. Removal of the testa of black seeds also promoted germination and produced normal seedlings. Brown seeds showed moderate tolerance to salt stress, with 16% germination percentage at a salt concentration of 600 mM NaCl. The germination of brown seeds was 38% at an osmotic potential stress of −0.8 MPa; above that, no germination was obtained. Brown seeds germinated well in a wide pH range (4 to 10), with a germination percentage higher than 95%. Seedling emergence percentage was higher than 90% at burial depths of 0 to 2 cm, while germination percentage severely decreased for brown seeds with burial depths >2 cm, indicating that shallow tillage could be an effective measure to minimize seed germination. Information gathered from this study will help to develop an effective protocols for controlling S. glauca.

African lovegrass [Eragrostis curvula (Schrad.) Nees] is a highly invasive C4 perennial grass that threatens global biodiversity. Appropriate management of this species has been hampered by a lack of knowledge concerning its seed ecology, resulting in significant economic and environmental impacts within various environments. Consequently, this study explored the effects of a selection of environmental factors (photoperiod, alternating temperature, pH, and salinity) by analyzing several measures of germination on four geographically distinct populations of E. curvula to assist in its extirpation from infested sites. Seeds were collected in Australia from Maffra and Shepparton, VIC; Tenterfield, NSW; and Midvale, WA. Key results showed that seeds from Maffra (54% vs. 79%), Tenterfield (38% vs. 61%), and Shepparton (34% vs. 71%) had significantly reduced germination in complete darkness compared with an alternating 12-h light and 12-h dark photoperiod, whereas Midvale had consistent germination (91% vs. 99%). Temperatures between 17/7 C reduced germination for Maffra (42% vs. 73%), Tenterfield (34% vs. 55%), and Shepparton (33% vs. 59%) compared with the mean of all other temperature combinations, whereas Midvale had consistent germination. Furthermore, germination for all populations was consistent between pH 4 and 9. For salinity, germination was significantly reduced at ≥100 mM for Maffra (29% vs. 67%), ≥150 mM for Tenterfield (29% vs. 94%) and Shepparton (39.5% vs. 81.5%), and 250 mM for Midvale (39% vs. 82%) compared with the mean of all other concentrations. Although each trial was conducted independently, the data can be used to generate species-targeted management. Such strategies include maintaining high levels of quarantine and hygiene programs to avoid future spread; where practical, applying light-limiting strategies (mulching, tilling, or scraping) for the Maffra, Tenterfield, and Shepparton populations; and maintaining management efforts year-round, as the species can germinate under a wide range of conditions.

Accurate weed emergence models are valuable tools for scheduling planting, cultivation, and herbicide applications. Multiple models predicting giant ragweed emergence have been developed, but none have been validated in diverse crop rotation and tillage systems, which have the potential to influence weed emergence patterns. This study evaluated the performance of published giant ragweed emergence models across various crop rotations and spring tillage dates in southern Minnesota. Across experiments, the most robust model was a mixed-effects Weibull (flexible sigmoidal function) model predicting emergence in relation to hydrothermal time accumulation with a base temperature of 4.4 C, a base soil matric potential of −2.5 MPa, and two random effects determined by overwinter growing degree days (GDD) (10 C) and precipitation accumulated during seedling recruitment. The deviations in emergence between individual plots and the fixed-effects model were distinguished by the positive association between the lower horizontal asymptote (Drop) and maximum daily soil temperature during seedling recruitment. This finding indicates that crops and management practices that increase soil temperature will have a shorter lag phase at the start of giant ragweed emergence compared with practices promoting cool soil temperatures. Thus, crops with early-season crop canopies such as perennial crops and crops planted in early spring and in narrow rows will likely have a slower progression of giant ragweed emergence. This research provides a valuable assessment of published giant ragweed emergence models and illustrates that accurate emergence models can be used to time field operations and improve giant ragweed control across diverse cropping systems.

Weeds represent a major cause of agricultural losses worldwide. Most weeds share a common set of life history characteristics that predispose them to weediness, two of which are self-compatibility, which allows for ease of colonization through reproductive assurance, and high trait plasticity, which allows for tolerance of a wide variety of environments and abiotic conditions. However, self-fertilization typically comes at the cost of inbreeding depression. This study investigates the role of inbreeding depression and trait plasticity under abiotic stress in the tall morningglory, a widespread self-compatible agricultural weed in the southeastern United States. Results show very little inbreeding depression in this species, likely due to purging of deleterious alleles through repeated founder events in agricultural landscapes. In contrast, abiotic stress induced substantial plasticity in ecophysiological traits, reproductive traits, and biomass allocation. In terms of performance, drought sharply impacted reproduction but not vegetative growth, and nitrogen limitation sharply impacted both. These findings are applicable to the control of weedy morningglory and underscore the usefulness of evolutionary ecology to weed management.

Although herbicide tolerance is not usually evaluated until the final stages of breeding programs, this trait is very important for grower adoption of new peanut cultivars. Understanding herbicide tolerance of breeding lines could help breeders develop selection strategies that maximize herbicide tolerance in new commercial cultivars. However, little is known about herbicide tolerance variability in peanut germplasm. Thirty-five randomly selected breeding lines from the peanut mini-core collection and cultivars ‘Florida-07’ and ‘Georgia-06G’ were evaluated for tolerance to 11 herbicides under greenhouse conditions. Variation among peanut lines in herbicide tolerance, measured as dry weight reductions (DWR), was similar across herbicides and was normally distributed. Florida-07 and Georgia-06G were in the lower two quartiles of injury and DWR among the evaluated peanut lines. Dose–response experiments showed that the most tolerant breeding lines had I50 (the rate required to cause 50% injury) and GR50 (the rate required to reduce dry weight 50%) values 0.4 to 2.5 times higher than the most susceptible lines, depending on the herbicide. A breeding line had a dicamba GR50 13 times higher than the most susceptible line and 2.8 and 4.7 times higher than Florida-07 and Georgia-06G, respectively. The most tolerant lines were consistently tolerant to herbicides with different mechanisms of action, suggesting that nontarget site mechanisms are more likely to be responsible for the tolerance than target-site mutations. These results confirmed peanut-breeding programs would greatly benefit from screening breeding lines for tolerance to key herbicides and developing an herbicide-tolerance catalog. This information can be used when designing new crosses to reduce the risk of developing cultivars with low herbicide tolerance especially considering that one-half of the breeding lines exhibited lower tolerance than the commercial cultivars.

While much research has focused on crop damage following foliar exposure to auxin herbicides, reports documenting the risk posed by exposure via root uptake of irrigation water are lacking. Herbicide residues circulated in tailwater recovery systems may pose threats of cross-crop impacts to nonresistant cultivars with known sensitivity to auxins. An auxin-susceptible soybean [Glycine max (L.) Merr.] cultivar was grown in a controlled growth chamber environment and exposed to dicamba dissolved in irrigation water applied to the soil surface, simulating furrow irrigation. Five herbicide treatment concentrations, ranging from 0.05 to 5.0 mg L−1 and encompassing estimated field doses of 3.1 to 310g ha−1, were applied to the soil of potted soybean plants at V3/V4 or R1 growth stages. Plant injury (0% to 100%), dry mass, height, number of pods, and number of pod-bearing nodes were measured. Kruskal-Wallis and logistic regression analyses were performed to determine treatment differences and examine dose effects. Yield losses were projected using (1) 14 d after treatment plant injury assessments based on injury–yield relationships described for foliar exposures and (2) pod counts. Dicamba concentration was the main significant factor affecting all growth response metrics, and growth stage was a significant explanatory variable only for the height response metric. A nonlinear response to dicamba dose was observed, with the threshold response dose required to affect 50% of plants being three times greater for 40% crop injury compared with 20% injury. Yield projections derived from plant response to root uptake compared with foliar exposure indicate that soybean may express both magnitude of injury and specific symptomology differently when exposure occurs via root uptake. Drift exposure–based models may be incompatible to predict soybean yield loss when injury results from irrigation. Data are needed to develop correlations for predicting yield losses based on field-scale exposure to dicamba in irrigation water, as well as assessment of real-world concentrations of herbicide residues in tailwater recovery systems.

A giant ragweed population with putative resistance to cloransulam was identified in a long-term corn–soybean rotation located in southern Wisconsin. The population represented the first potential instance of giant ragweed resistance to acetolactate synthase (ALS) inhibitors in the state. Seeds were collected from several plants and pooled for subsequent experiments. Whole-plant dose–response experiments showed a high level of resistance (>500-fold) of the resistant (R) accession to cloransulam compared with a sensitive (S) accession. In vivo ALS bioassays showed that the target enzyme was 10.6- to 13.6-fold less sensitive to cloransulam in R than in S plants. Partial sequence analysis of the ALS gene found a tryptophan-to-leucine substitution at the 574 amino acid position (W574L) in the R phenotype. To better understand the potential fitness costs associated with the target-site substitution, replacement series experiments performed under greenhouse conditions characterized the relative growth, development, and fecundity of the R accession compared with an S accession in the absence of cloransulam. Growth over time did not differ between the R and S accessions for plant height during the vegetative phase (21 to 98 d after planting [DAP]) or for plant leaf area (21 to 80 DAP). At the estimated maximum, proportional shoot dry mass of each accession did not differ from theoretical proportions representing competitive equivalence, indicating no difference in vegetative competitive ability. Fecundity of R plants (430±53 seeds plant−1) did not differ from that of S plants (451±47 seeds plant−1), nor did seed viability (74 to 75% across accessions). This is the first report of equal competitive ability, fecundity, and seed viability between giant ragweed accessions R or S to cloransulam. The results suggest that the cloransulam resistance trait may persist and spread in the giant ragweed field population over time, even in the absence of selection by cloransulam.

Predictions of weed emergence can be used by practitioners to schedule POST weed management operations. Common sunflower seed from Kansas was used at six Midwestern U.S. sites to examine the variability that 16 climates had on common sunflower emergence. Nonlinear mixed effects models, using a flexible sigmoidal Weibull function that included thermal time, hydrothermal time, and a modified hydrothermal time (with accumulation starting from January 1 of each year), were developed to describe the emergence data. An iterative method was used to select an optimal base temperature (Tb) and base and ceiling soil matric potentials (ψb and ψc) that resulted in a best-fit regional model. The most parsimonious model, based on Akaike's information criterion (AIC), resulted when Tb = 4.4 C, and ψb = −20000 kPa. Deviations among model fits for individual site years indicated a negative relationship (r = −0.75; P < 0.001) between the duration of seedling emergence and growing degree days (Tb = 10 C) from October (fall planting) to March. Thus, seeds exposed to warmer conditions from fall burial to spring emergence had longer emergence periods.

Preemergence herbicides for the control of crabgrass, (Digitaria ischaemum (Schreb.) Muhl. and D. sanguinalis (L.) Scop.) were applied on bluegrass sod at three different rates for three years to determine residual effects on the stand and vigor of perennial ryegrass, red fescue, tall fescue, and Merion and common Kentucky bluegrass seedlings. With few exceptions, the herbicides retarded stand and vigor of these turfgrasses seeded in turf killed with methyl bromide. Chlordane was least and a commercial arsenic complex plus 7% N most toxic to young seedlings. Seedlings of Merion Kentucky bluegrass were most resistant to herbicide injury. No appreciable decrease in original turf density was noted except for the arsenic complex material which severely injured bluegrass turf at the two heavier rates.

Germination of the same turfgrasses seeded in flats of sterilized soil in the greenhouse 1 day, 41 days, and 93 days after the application of preemergence crabgrass herbicides, showed the most reduction in emergence from treatments with DMPA [O-(2,4-dichlorophenyl) O-methyl isopropylphosphoramidoate], trifluralin (2,6-dinitro-N,N-di-n-propyl-alpha-alpha-alpha-trifluro-p-toluidine), DCPA (2,3,5,6-tetrachloroterephthalic acid), and dipropalin (N,N-di-n-propyl-2,6-dinitro-p-toluidine). Lead arsenate was least injurious to germinating seedlings. Tall and red fescue were more tolerant to herbicides than the other grasses studied.

Since the advent of the new and, generally, more efficient herbicides, a great deal of research has been done and a voluminous literature presented concerning their uses and possible mechanisms of action. The more obvious effects of the chemicals have been described at length but the basic physiological mechanisms remain relatively undefined.

A 7-year ecological study of natural infestations of globe-podded (Cardaria pubescens) and lens-podded (C. chalapensis) hoary cresses was conducted under conditions of irrigation and dry land farming in southern Saskatchewan. Density and area measurements were compared annually in competition with grasses, forbs and shrubs in several environments. The hoary cresses are well adapted to moist situations but are not particularly vigorous in dry, semi-arid environments. Globe-podded hoary cress was better able to survive a period of drought than the lens-podded species. Native roses (Rosa spp.), western snowberry (Symphoricarpos occidentalis) and Russian knapweed (Centaurea repens) were the most effective competitors of the hoary cresses. Alfalfa and to a lesser degree, bromegrass were also effective. As these infestations of hoary cress are situated upstream from the Saskatchewan River Irrigation Project, they constitute a serious threat to many acres of irrigable farmland. Control by cultural means is shown to be feasible.

Opuntia laevis or O. polyacantha (prickly pear) plants exhibited little water loss, exceptional viability, low nutrient requirements for growth, slight photosynthetic activity, slow translocation, and low transpiration rate as compared with corn or soybean plants. The limited number of stomata, thick wax cuticle, and high water binding ability of cell mucilage in prickly pear are largely responsible for the aforementioned physiological characteristics. These studies show that prickly pear pads, which are modified stems, are not efficient organs for metabolic activities. Water extracts of prickly pear tissue applied to corn seeds were found to induce pronounced growth stimulation of corn seedlings.

One of the major costs in the production of woody ornamentals is for weed control by cultivation and hoeing. In nurseries, plants are grown in the same location for two to five years, and several species often are grown in mixed blocks. Thus, there is a need for a herbicide which is non-toxic to as many species as possible.

ρ-Cymene was one of the major components of volatiles released by croftonweed. The allelopthy of ρ-cymene on the growth of upland rice seedlings was performed. Hydrogen peroxide generation, malondialdehyde (MDA) content, proline content, total ascorbate (ascorbate/dehydroascorbate), reduced/oxidized glutathione, and the levels of induction of antioxidant enzyme were studied in the seedlings of upland rice. ρ-Cymene inhibited the growth of upland rice seedlings. Exposure of upland rice seedlings to ρ-cymene increased levels of H2O2, MDA, and proline, indicating lipid peroxidation and induction of oxidative stress. Activities of the antioxidant enzymes superoxide dismutase, catalase, peroxidase, guaiacol peroxidase, ascorbate peroxidase, and glutathione reductase were significantly elevated during the treatment period (7–15 d) compared with enzymes in the upland rice seedlings unexposed to ρ-cymene, thereby indicating the enhanced generation of reactive oxygen species (ROS) upon ρ-cymene exposure. These results suggest that activation of the antioxidant system by ρ-cymene led to the formation of ROS that resulted in cellular damage and decreased growth of upland rice seedlings.

The release of soil-bound 14C-prometryne [N,N′-bis(l-methylethyl)-6-(methylthio)-1,3,5-triazine-2,4-diamine] residues was affected by soil pH, fertilizer treatments (with or without plants), and the crop species wheat [Triticum aestivum (L.) Merr. ‘Marquis’] and soybean [Glycine max (L.) Merr. ‘Maple Presto’]. More of the bound radioactivity was released following large pH changes in the soil than with small deviations. In addition, more 14C-prometryne was found in the extracts of the soil incubated with large pH alterations. Fertilizing with ionic nitrogen sources (NO3– and NH4+) in the absence of plants was also responsible for releasing higher levels of radioactivity than with the nonionic fertilizer urea. These fertilizer-induced differences in release were not apparent when wheat plants were added to the system. Release of the bound radioactivity, however, was plant specific, particularly in the rhizoplane, since soybean roots elicited a greater release in the rhizoplane than wheat roots. Transport and metabolism of these residues were also plant specific.