The compositions of the germinable weed seedbank and aboveground weed communities in a long-term tillage and rotation study were characterized 4, 5, and 6 yr (2002 to 2004) after the adoption of glyphosate-tolerant corn and soybean. Averaged across rotation, mean germinable weed seed density and diversity were greatest in the no-tillage treatment as compared to the minimum- and conventional-tillage treatments. Averaged over tillage, density and diversity were greater in the corn–oat–hay (ryegrass + alfalfa) system as compared to the continuous corn and corn–soybean rotations. Similar trends in density and diversity were observed for the aboveground weed communities. Differences in community composition among treatments were quantified with the use of a multiresponse permutation procedure. Results indicated that the weed seedbank community in a corn–oat–hay rotational system differed from the communities associated with the continuous corn and corn–soybean rotational systems. Weed seedbank communities developing under a no-tillage operation differed from those in minimum- and conventional-tillage scenarios. Compositional differences among the aboveground weed communities were less pronounced in response to tillage and rotation. Indicator species analyses indicated that the number of significant indicator weed species was generally higher for no tillage than minimum or conventional tillage for both the seedbank and the aboveground weed communities. The number of significant indicator species for the seedbank and weed communities was generally greater in the three-crop rotation as compared to the continuous corn and corn–soybean rotations. The trends observed in density, diversity, and community composition after the adoption of glyphosate-tolerant corn and soybeans, and a glyphosate-dominated weed management program, were also observed when soil-applied herbicides were included in the study. We suggest that the switch to a POST-glyphosate protocol did not significantly alter weed communities in the short term in this study.

In greenhouse and field studies, sethoxydim {2-[1-(ethoxyimino)-butyl]-5-(2-ethylthio)-propyl]-3-hydroxy-2-cyclohexen-1-one} provided good control of quackgrass [(Agropyron repens L. (Beauv.) ♯ AGRRE] in potato (Solanum tuberosum L. ‘Russet Burbank’). Level of control with sethoxydim at 0.6 kg ai/ha in the greenhouse was improved by the addition of a surfactant at 1.0% (v/v) of spray volume. Removal of quackgrass shoots at 6 or 24 h after treatment resulted in decreased control at application rates of 0.6, 1.0, and 1.6 kg ai/ha. Application of sethoxydim at 1.2 or 1.6 kg ai/ha in the field gave excellent control of quackgrass when applied at either the three- or six-leaf stage. Cultivation at 2 days after treatment did not adversely affect level of control obtained. Sethoxydim did not cause any adverse effect on potato yield, but delaying application until the six-leaf stage of quackgrass resulted in yield loss due to quackgrass competition.

Saflufenacil, a pyrimidinedione herbicide, is used for contact and residual broadleaf weed control in various crops. Bioactivity of saflufenacil in soil was tested in greenhouse and laboratory studies on 29 soils representing a wide range of soil properties and geographic areas across the United States. A greenhouse bioassay method was developed using various concentrations of saflufenacil applied PPI to each soil. Whole canola plants were harvested 14 d after treatment, and fresh and dry weights were recorded. Nonlinear regression analysis was used to determine the effective saflufenacil doses for 50% (ED50,), 80% (ED80), and 90% (ED90) inhibition of total plant fresh weight. Bioactivity of saflufenacil in soil was strongly correlated to soil organic (R = 0.85) and humic matter (R = 0.81), and less correlated to cation exchange capacity (R = 0.49) and sand content (R = −0.32). Stepwise regression analysis indicated that organic matter was the major soil constituent controlling bioactivity in soil and could be used to predict the bioactivity of saflufenacil. Saflufenacil phytotoxicity was found to be dependent on soil property; therefore, efficacy and crop tolerance from PRE and PPI applications may vary based on soil organic matter content and texture classification.

Field and pot studies were conducted in Central New York to determine the potential weed-management benefits of a buckwheat cover crop grown before winter wheat. Specific objectives were to determine buckwheat residue effects on (1) emergence and growth of winter annual weeds; (2) wheat establishment and yield; and (3) emergence of summer annual weeds in the spring following overwinter seed burial. In a field study, buckwheat was sown at two timings (July or August), mowed, and either incorporated or left on the soil surface. Winter wheat was drilled into buckwheat residue in September and weed and crop growth were monitored. In a complementary pot study, four winter annual weeds were sown in soil removed from buckwheat and bare-soil plots at 0 or 15 d after incorporation and monitored for emergence and early growth. To assess buckwheat residue effects on spring emergence from overwintering seeds, seeds of three weed species were buried in buckwheat residue and bare-soil plots in the fall, exhumed in April, and evaluated for emergence. To investigate the mechanism for possible effects of buckwheat residue on overwintering seeds, two levels each of seed treatment (none or fungicide) and fertilization (none or 170 kg ha−1) were applied before burial. Buckwheat residue had no negative effect on wheat yields but suppressed emergence (22 to 72%) and growth (0 to 95%) of winter annual weeds, although effects were often small and inconsistent. Buckwheat residue had no effect on the emergence of buried weed seeds in spring. However, fungicide treatment enhanced the emergence of Powell amaranth seeds by 12.5 to 25.5% and of barnyardgrass seeds by 0 to 12%. Our results suggest that buckwheat residue can contribute to weed management in wheat cropping systems, but that further studies investigating the mechanistic basis for the inconsistent selective effects of buckwheat residue on weeds are needed before buckwheat use can be optimized.

The effect of photoperiod and growth stage on translocation of 14C-glyphosate was compared in Canada thistle plants at the bud and rosette stage of growth. Canada thistle plants grown under controlled environment conditions with a 10 h photoperiod remained as low growing rosettes and developed a mature root system. When the photoperiod for half of these plants was increased to 16 h, stem elongation occurred and flowering was initiated. Growth stage at the time of application affected the distribution of 14C-glyphosate within the elongated shoot and between the shoot and root. The shoot tissue of the bud stage plants contained 25.9% of the 14C-glyphosate recovered, while the rosette plants contained only 3.6%; a seven-fold difference. 14C-glyphosate was applied to leaves 19 and 20, which corresponded to the mid-point of the elongated stem of the bud-stage plants. In the bud-stage plants, 14C-glyphosate moved preferentially into the apical portion of the stem, with three to four times as much in the apical portion of the elongated stem as in the basal portion. In the roots, the effect of growth stage on distribution of 14C-glyphosate was reversed, application at the rosette stage resulted in a four-fold increase in the amount of 14C-glyphosate in the root. When applied in the rosette stage, 19.1% of the 14C-glyphosate detected was in the root compared to only 4.9% when applied at the bud stage. Although the root of the rosette plants was larger than in bud-stage plants, the concentration of 14C-glyphosate in the root tissue of the rosette plants was three times greater. Photoperiod indirectly affected the distribution of 14C-glyphosate in Canada thistle by its effect on growth.

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.

Changes in dormancy and viability of freshly harvested seed of yellow nutsedge buried in the field, at depths of 5, 25, and 50 mm, were studied over a 2-yr period. The number of dormant, viable seed decreased most rapidly at 5 mm because more seed lost their dormancy and germinated (up to 30%) than at lower depths. Loss of viability through decay of seed appeared similar at all depths. No seedlings emerged from any depth. In a laboratory experiment, conducted in optimal soil moisture conditions, seedlings emerged from all seed that germinated, demonstrating that adequate soil moisture was critical for seedling establishment. This was substantiated in a second field experiment in which irrigation and mulching greatly increased seedling survival. The number of seedlings surviving in irrigated plots was 0.78% of seed sown and 0.03% in the rain-fed plots. The role of seed in the establishment of yellow nutsedge infestations is probably of little importance in dryland cropping areas despite the longevity and viability of the seed.

Seven dinitroaniline herbicides were tested in the field for 3 yr at rates up to twice that normally used for annual grass control. Trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) and profluralin [N-(cyclopropylmethyl)-α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine] gave 95 and 94% control of johnsongrass [Sorghum halepense (L.) Pers.] from rhizomes, respectively, after the third year at the double rate. These two herbicides controlled johnsongrass from rhizomes better than nitralin [4-methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline], butralin [4-(1,1-dimethylethyl)-N-(1-methylpropyl)-2,6-dinitrobenzenamine] and pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] at comparable rates. After 3 yr, seed cotton (Gossypium hirsutum L. ‘Stoneville 213’) yields were higher with double rates of trifluralin, profluralin, fluchloralin [N-(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl)aniline], and pendimethalin, than with nitralin, dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine), and butralin. In greenhouse studies, reduction of cotton raproot length by the dinitroaniline herbicides incorporated at the normal rate of use followed the order: butralin ≤ pendimethalin ≤ fluchloralin ≤ trifluralin < profluralin < dinitramine. All herbicides except pendimethalin at 0.28 and 0.56 kg/ha reduced lateral root production of cotton. The dinitroaniline herbicides at normal rates of use reduced fresh weight of cotton seedlings from 12 to 34%. The mean vapor toxicity of the dinitroaniline herbicides to Japanese millet [Echinochloa crus-galli (Roxb.) Wight ‘frumentacea’] shoots averaged from no injury with oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide) and nitralin to 66% injury with dinitramine and trifluralin.

Johnsongrass leaves were covered with epicuticular wax that varied from 16 to 25 μg/cm2 on leaf blades and 56 to 206 μg/cm2 on leaf sheaths. At emergence, leaves were covered with a layer of smooth amorphous wax, but crystalline wax (wax plates) began to form on the amorphous wax within 1 or 2 days. This continued until all leaf surfaces were covered with wax plates. At 3 to 4 weeks of age, a smooth layer of coalescence wax was deposited over the wax plates. Formation of coalescence wax continued until nearly all leaf surfaces were covered with a smooth wax layer. Production of wax filaments began when plants were 3 to 4 weeks old and these tubular structures extended 100 to 200 μm above all other wax formations. Deposition of amorphous wax continued after stomata closed in the darkness, sealing over stomata, but the wax layer was broken when stomata opened again in the light. A capillary method was devised that was used to evaporate chloroform containing leaf waxes through 0.1- to 1.2-μm pores in inert filters to recrystallize amorphous wax and wax plates similar to that produced on johnsongrass leaves. Recrystallization of wax from wax filaments dissolved in chloroform produced the same structures of amorphous wax and wax plates as when only wax from leaves with amorphous wax and wax plates was used. Wax washed from leaves also produced wax plates and a variety of crystalline structures on the walls of glass vials after chloroform solutions were evaporated. This result indicated that the morphology of epicuticular waxes is influenced more by their inherent chemical and physical properties than by underlying cells or the cuticular membrane.

Weedy red rice is a major weed pest of rice in the southern United States. Outcrossing between red rice and commercial tropical japonica rice cultivars has resulted in new weed biotypes that further hinder the effectiveness of weed management. In recent years, indica rice has been used increasingly as a germplasm source for breeding and for reduced-input systems in the United States, but little is known about its outcrossing potential with U.S. weedy red rice biotypes. In a 2-yr study, simple sequence repeat marker analysis was used to show that blackhull (BH) red rice (PI 653424) outcrossing to four, late-maturing indica cultivars averaged 0.0086% and ranged from 0.002% for ‘TeQing’ to 0.0173% for ‘4484’ (PI 615022). Rates of outcrossing to a tropical japonica cultivar standard, ‘Kaybonnet’ (0.032%), were substantially greater than for the indica cultivars. These differences in outcrossing were due largely to synchronization of flowering times between rice and red rice, with Kaybonnet and TeQing exhibiting the greatest and least synchronization, respectively. Outcrossing rates also may have been affected by rice–red rice flower density differences within the rice plots. Outcrossing from cultivated rice to the red rice (as pollen recipient), which was taller than all rice cultivars, was undetectable in these studies, and environmental conditions (e.g., temperature, humidity, solar radiation, and rainfall) were not strongly correlated with the outcrossing rates observed. Grain yields of the original BH red rice line were greatest in the Kaybonnet plots, demonstrating that the indica cultivars were superior competitors against this weed. Collectively, these results suggest that red rice biotypes that flower synchronously with rice cultivars are a potential source of pollen for outcrossing and gene flow in rice fields in the southern United States.

Seedbank sampling and quantification methods vary in their ability to describe weed diversity and density, so proper method selection is critical for studying weed communities. The germinable seedbank (GSB) method is commonly preferred over extractable seedbank method (ESB), because the latter is more time-consuming. However, these two methods have only been compared using a few weed species and a relatively small number of samples. A total of 204 weed seedbank samples were used to compare both methods for weed density, richness, evenness, and Shannon-Weiner diversity using a split-sample approach. The two methods yielded dramatically different results. The ESB had 418% higher density and 35% more species per sample but 11% less evenness than the GSB. Diversity was estimated to be only 9% higher using the extractable compared with the germinable method. While the extractable method had higher density and richness overall, this was not true for every species, with only 7 of 14 common species detected in higher amounts by the extractable method. The results indicate the two methods are not strongly correlated, limiting the possibility of generating a conversion factor between methods. Nevertheless, evenness and Shannon-Weiner diversity might allow comparisons between both methods when the emphasis is on characterizing predominant weed species. The GSB is a practical approach to compare treatments or conditions; however, the ESB is more useful to accurately quantify weed species richness, diversity, and density.

The rise of on-line open access (OA) has profound implications for academic publishing, not least the shift from subscribers to authors as the primary transactional partners for peer-reviewed journals. Although OA offers many benefits, it also paves the way for predatory publishers, who exploit the author-as-customer model to obtain revenue from author fees while providing few of the editorial services associated with academic publishing. Predatory journals publish papers with little or no peer review, and often disguise their real geographical location while exaggerating their scope and editorial expertise. Such journals also attempt to attract authors by promising unrealistically rapid editorial decisions while falsely claiming peer review, and fabricating impact factors and inclusion in academic indexes. The explosive increase in predatory OA journals is not only a risk to inexperienced authors, but also threatens to undermine the OA model and the legitimate communication of research.

Field experiments were conducted to evaluate common cocklebur and entireleaf morningglory interference on soybean under irrigated and nonirrigated conditions. Total leaf area index (LAI), LAI within the soybean canopy, crop growth rate, and seed yield of soybean were decreased more by common cocklebur than by entireleaf morningglory. Interference from entireleaf morningglory, common cocklebur, or both species reduced soybean yields 21, 57, and 64%, respectively, with irrigation and 12, 60, and 76%, respectively, without irrigation. Soybean yield reduction from interference with entireleaf morningglory, common cocklebur, or both species was not influenced by soybean date of planting. Soil water was extracted from greater soil depths by soybean growing with the weeds than by soybean alone. High WUE without irrigation suggests that soybean uses water more efficiently when soil moisture is limiting than when soil moisture is available under irrigated conditions.

A simulation model was developed to predict the population dynamics and economics of velvetleaf control in a corn-soybean rotation. Data compiled from the literature were used to parameterize the model for two situations, one in which velvetleaf was infected by a Verticillium spp. wilt and one without infection. Verticillium was assumed to have no effect on corn or soybean yield. In the absence of control, simulated seedbank densities of a Verticillium-infected velvetleaf population were 5 to 50 times lower than for an uninfected velvetleaf population. The model was used to evaluate a threshold weed management strategy under the assumption that velvetleaf was the only weed and bentazon the only herbicide available for its control. In the absence of Verticillium, an economic optimum threshold of 2.5 seedlings 100 m−2 afforded the highest economic returns after 20 yr of simulation. Simulations in which velvetleaf was infected in 8 out of 20 randomly assigned years indicated a 6% increase in annualized net return and an 11 % reduction in the number of years that control was necessary. Sensitivity analysis indicated the parameter estimates having the greatest impact on economic optimum threshold were seedling emergence and survival, maximum seed production, and herbicide efficacy. Under an economic optimum threshold of 2.5 seedlings 100 m−2, management practices that manipulate the most sensitive demographic processes increased annualized net return by up to 13% and reduced long-term herbicide use by up to 26%. Results demonstrate that combining an economic optimum threshold with alternative weed management strategies may increase economic return and reduce herbicide use.

A replacement series experiment was conducted in the field to quantify the interaction between Canada thistle and buckwheat, and to determine if allelopathy was the mechanism of interference. Plant biomass data indicated that buckwheat only responded to intraspecific competition and not interspecific competition from Canada thistle. Canada thistle responded to interspecific competition from buckwheat plants but not to intraspecific competition. The absence of one of the interspecific competition components (no measurable effect of Canada thistle density on buckwheat) indicates that the value for niche differentiation is probably greater than unity, signifying that there is no mutual antagonism between buckwheat and Canada thistle. Because allelopathy is one mechanism that causes mutual inhibition, data do not support the hypothesis that buckwheat interferes with Canada thistle by allelopathy.

The freezing resistance of overwintering buds of four perennial weed species was evaluated in artificial freezing experiments conducted in the winters of 1986 and 1987. Survival, dry weight of surviving shoots, and number of shoots produced/surviving section were determined at −4, −8, −12, −16, and −20 C for Canada thistle roots, leafy spurge roots, leafy spurge crowns, perennial sowthistle roots, and quackgrass rhizomes. The temperature required to reduce survival (LT50) and total dry weight (GR50) by 50% was determined. The response to freezing temperatures varied among species and in some cases between years. The LT50 was −7, −13, colder than −20, −17, and colder than −20, and the GR50 was −5, −11, −14, −15, and −13 for Canada thistle roots, leafy spurge roots, leafy spurge crowns, perennial sowthistle roots, and quackgrass rhizomes, respectively. The relative susceptibility to freezing among species appears to be directly related to the depth at which the overwintering buds generally are located.

Bensulide [0,0-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide] and trifluralin (α,α,α-trifluroro-2,6-dinitro-N,N-dipropyl-p-toluidine) were incorporated to a depth of 2.5 and 7.5 cm in sandy loam soil on the same plots in three annual applications to study the effect of incorporation depth on movement and persistence of the herbicides in furrow-irrigated soil. Bioassays and gas-liquid chromatographic assays indicated that, regardless of rainfall, both herbicides remained within the original soil zones of incorporation. Trifluralin persisted longer in soil as depth of incorporation was increased. Neither bensulide at 4.5 or 9.0 kg/ha nor trifluralin at 1.1 kg/ha persisted in appreciable amounts 12 months after treatment. At these rates, significant residues of bensulide and trifluralin were detected after 6 months only when tillage was restricted. Herbicide concentrations that persisted 6 months as determined in laboratory assays caused severe reduction in growth of field-grown sorghum [Sorghum bicolor (L.) Moench].

The basis for selectivity of phenmedipham (methyl-m-hydroxycarbanilate m-methylcarbanilate) and desmedipham (ethyl m-hydroxycarbanilate carbanilate) on wild mustard [Brassica kaber (DC.) L.C. Wheeler ‘pinnatifida’ (Stokes) L.C. Wheeler], redroot pigweed (Amaranthus retroflexus L.), and sugar beet (Beta vulgaris L.) was studied by evaluating spray retention, absorption, translocation, and metabolism. Total photosynthesis in wild mustard was severely inhibited in less than 5 hr after foliar application of either herbicide and did not recover. Total photosynthesis in sugar beet was slightly inhibited but recovered after 24 hr. Photosynthesis in redroot pigweed recovered from a treatment of phenmedipham but did not recover when treated with desmedipham. Differences in spray retention or foliar absorption did not explain selectivity. Within 5 hr after herbicide application, redroot pigweed had translocated more desmedipham than phenmedipham from the site of absorption and had metabolized a large amount of the phenmedipham but little desmedipham. The key factor explaining selectivity appeared to be at the initial detoxication reaction of the parent compound.

Florida beggarweed seeds were collected in Georgia, Florida, and South Carolina from plants differing in morphological characteristics. Seedlings were transplanted into peanut rows in field studies at Tifton, GA, and Jay, FL, in 1986 and 1987, and frequent observations of vegetative and reproductive characteristics were made. The competitiveness of the Florida beggarweed selections was evaluated by comparing pod weights from peanut plants grown in rows adjacent to the individual weed selections with pod weights of weed-free peanuts. There were significant differences among selections of Florida beggarweed in days to maximum height, maximum node formation, maximum branching, and initial flowering and fruiting at both locations. Selection GA-1 generally reached these growth stages earliest, was shorter, narrower, had fewer nodes, and produced less dry matter and fewer seeds than GA-2, which was generally the latest maturing selection. GA-4 produced fewer branches and smaller seeds than the other selections. Peanut pod weights adjacent to Florida beggarweed plants were reduced 12 to 18% in 1986 and 10 to 24% in 1987 compared to weed-free checks. Florida beggarweed selection GA-2 was the most competitive and GA-4 was among the least competitive both years. The variation of measured parameters among Florida beggarweed selections in this study may contribute to the survival and adaptability of this weed with changing environmental conditions, cultural practices, and control measures.

Residues in soil, following application of 0.25 lb/A of 4-amino-3,5,6-trichloropicolinic acid (picloram) to semi-arid rangelands, usually were restricted to the top 12 inches for 60 days. Five ppb or less picloram were detected below 12 inches at 120 to 180 days after application; but picloram usually dissipated from the soil profile within a year. More picloram was detected 5 months after application at 6 to 18 inches deep at the lower ends of plots with 3% slopes than in plots with 0, 1, or 2% slopes. Runoff water from plots irrigated 10 days after treatment contained 17 ppb picloram. Irrigation or rainfall at 20, 30, or 45 days after picloram application resulted in less than 1 ppb picloram in runoff water. No more than 1 or 2 ppb picloram were detected after dilution of runoff water in large ponds.