In the Pacific Northwest, downy brome continues to infest winter wheat, especially in low-rainfall areas where the winter wheat–summer fallow rotation is the dominant production system. In Washington, a study was conducted for 2 yr at two locations in the winter wheat–summer fallow region to determine the influence of four postharvest tillage treatments on vertical seed movement, seedbank depletion, and plant densities of downy brome. The four tillage implements included a disk, sweep plow, harrow, and skew treader. The study also included a no-till treatment for comparison. The sweep plow and disk led to the most vertical movement of downy brome seed compared with the no-till treatment. Approximately 75% of the fall postharvest seed in the no-till treatment was located either on the soil surface or in the 0- to 3-cm depth at both locations. In contrast, 75% of the seed in the disked treatment was located from 0 to 6 cm deep at both locations. The disk and sweep plow both decreased downy brome seed in the soil at the 0- to 3-cm depth compared with the harrow and no-till treatments. There was no difference in downy brome plant densities following postharvest tillage in the summer fallow due to any of the treatments. However, plant densities in the subsequent winter wheat crop were reduced by the disk and sweep plow compared with the no-till and skew-treader treatments. In general, seed densities as affected by the skew treader fell between the disk and the no-till treatments. The use of the sweep plow and the disk should be integrated into a weed management strategy for downy brome in the wheat–fallow region of the Pacific Northwest.

Vinasse and biochar are by-products of biofuel production that can be used as sources of nutrients to crops or soil amendments to improve soil quality. Despite the recent interest in biochar and vinasse effects on soil properties, little is known about their effect on weed communities. We hypothesized that the addition of biochar and vinasse to the soil could affect weed seed germination and growth, and that different weed species would show different responses to these soil amendments. Therefore, the objectives of this study were to determine the effects of vinasse and biochar on the germination and growth of Palmer amaranth, sicklepod, and southern crabgrass. The study was conducted under laboratory and growth chamber conditions. Treatments consisted of four levels of vinasse (0, 10, 20, and 40 L m−2) and biochar (0, 0.5, 2.5, and 12.5 kg m−2) applied to a sandy loam soil. Biochar at 0.5 and 2.5 kg m−2 increased germination of Palmer amaranth but had no effect on sicklepod and southern crabgrass. Vinasse reduced germination of all species. However, sicklepod germination was less affected by vinasse at 10 and 20 L m−2 than the other two species. Vinasse at 40 L m−2 decreased Palmer amaranth, southern crabgrass and sicklepod germination 57, 26 and 87%, respectively. Biochar had no consistent effect on the vegetative growth of the species studied. Vinasse at 10 L m−2 stimulated growth of sicklepod and southern crabgrass compared to the nontreated control. Our results suggested that vinasse used as a soil amendment could affect weed community structure by decreasing germination of susceptible species, but plants and weed species that can get established in vinasse amended soils might show higher growth rates.

Kochia is a troublesome weed in the western Great Plains and many accessions have evolved resistance to one or more herbicides. Dicamba-resistant soybean is being developed to provide an additional herbicide mechanism of action for POST weed control in soybean. The objective of this study was to evaluate variation in response to dicamba among kochia accessions collected from across Nebraska. Kochia plants were grown in a greenhouse and treated when they were 8 to 12 cm tall. A discriminating experiment with a single dose of 420 g ae ha−1 of dicamba was conducted on 67 accessions collected in Nebraska in 2010. Visual injury estimates were recorded at 21 d after treatment (DAT) and accessions were ranked from least to most susceptible. Four accessions representing two of the most and least susceptible accessions from this screening were subjected to dose-response experiments using dicamba. At 28 DAT, visible injury estimates were made and plants were harvested to determine dry weight. An 18-fold difference in dicamba dose was necessary to achieve 90% injury (I90) between the least (accession 11) and most susceptible accessions. Approximately 3,500 g ha−1 of dicamba was required in accession 11 to reach a 50% dry weight reduction (GR50). There was less than twofold variation among the three more susceptible accessions for both the I90 and GR90 parameters, suggesting that most kochia accessions will be similarly susceptible to dicamba. At 110 DAT, accession 11 had plants that survived doses of 35,840 g ha−1, and produced seed at doses of 17,420 g ha−1. The identification of one resistant accession among the 67 accessions screened, and the fact that dicamba doses greater than 560 g ha−1 were required to achieve GR80 for all accessions suggest that repeated use of dicamba for weed control in fields where kochia is present may quickly result in the evolution of dicamba-resistant kochia populations.

Field studies were conducted at Clinton, NC (2009, 2010), and Kinston, NC (2010), to determine ‘Covington' sweetpotato tolerance to flumioxazin applied after transplanting. Flumioxazin was directed to 25% of the sweetpotato vine beginning at the distal end (shoot tip), 25% of the vine beginning at the proximal end (crown), or to the entire vine (over-the-top) and was applied at 2 or 5 wk after transplanting (WAP). Applications made at 2 WAP resulted in 10 to 16% foliar necrosis at 3 WAP. Necrosis was transient and ≤ 2% by 6 WAP. Stunting injury at 6 WAP for flumioxazin applied at 2 WAP was greatest (12%) with the over-the-top application, followed by crown (5%), and shoot tip (1%) applications. Applications made at 5 WAP resulted in 35, 23, and 15% foliar necrosis at 6 WAP for over-the-top, crown, and shoot tip applications, respectively. By 12 WAP, stunting injury for all treatments was ≤ 3%. No. 1, jumbo, canner, and total marketable sweetpotato yield of the nontreated check was 36,670; 7,610; 7,170; and 51,450 kg ha−1, respectively. No. 1 and total marketable sweetpotato yields were reduced when flumioxazin was applied at 2 or 5 WAP. No. 1 sweetpotato yield was reduced when flumioxazin was applied to the crown or over-the-top (27,240 and 28,330 kg ha−1, respectively). Sweetpotato receiving flumioxazin applied to the shoot tip had similar no. 1 (31,770 kg ha−1) yields as the nontreated check, crown, and over-the-top applications. Total marketable sweetpotato yield was reduced by flumioxazin application to shoot tip, crown, and over-the-top (45,350; 40,100; 40,370 kg ha−1, respectively). Neither flumioxazin application timing nor placement influenced either jumbo- or canner-grade sweetpotato yields. Currently, after-transplant applications of flumioxazin do not appear to be a suitable fit for POST weed control in North Carolina sweetpotato production systems.

RIM, or “Ryegrass Integrated Management,” is a user-friendly weed management software that integrates long-term economics. As a model-based decision support system, RIM enables users to easily build 10-year cropping scenarios and evaluate the impacts of management choices on annual rigid ryegrass populations and long-term profitability. Best used in a workshop format to enable learning through interactions, RIM can provide insights for the sustainable management of ryegrass through “what-if” scenarios in regions facing herbicide resistance issues. The upgrade of RIM is presented, with changes justified from an end-user perspective. The implementation of the model in a new, intuitive software format is presented, as well as the revision, update, and documentation of over 40 management options. Enterprises, establishment systems, and control options were redefined to represent current practices, with the notable inclusion of customizable herbicide options and techniques for weed seed control at harvest. Several examples of how RIM can be used with farmers to demonstrate the benefits of adopting recommended practices for managing or delaying the onset of herbicide resistance are presented. Originally designed for the dryland broadacre systems of the Australian southern grainbelt, RIM's underlying modeling was restructured to facilitate future updates and adaptation to other weed species and cropping regions.

Field studies were conducted in 2011 and 2012 at the Sandhills Research Station near Jackson Springs, NC to determine the influence of weed-free strip width (WFSW) on newly planted ‘Navaho' blackberry plant growth, fruit yield, and fruit quality. Treatments consisted of 0-, 0.3-, 0.6-, 1.2-, 1.8-, and 2.4-m WFSW. Predicted blackberry yield increased from 718 to 1,015 kg ha−1 at WFSW of 0 to 2.4 m. The currently recommended WFSW of 1.2 m resulted in a blackberry yield of 1,013 kg ha−1. Predicted individual blackberry fruit weight displayed a positive linear response to WFSW and increased from 3.1 to 3.6 g fruit−1 at WFSW of 0 to 2.4 m. Soluble solids content (SSC) of dull black blackberry fruit was greatest (15.1 Brix) when WFSW was 0 m. Relative to a WFSW of 0 m, SSC was reduced 2.3 to 3.4% as WFSW increased from 0.3 to 2.4 m, respectively. WFSW did not influence shiny black blackberry fruit SSC, nor titratable acidity, sugar-to-acid ratio, or pH of shiny or dull black blackberry fruit or primocane number, length, and stem caliper.

Dinitroaniline and amide herbicides have been continually applied in garlic in China, leading to the change of weed community and dominant weed species. Catchweed bedstraw, shepherd's-purse, and flixweed have become major troublesome weeds. Crop safety of fluorochloridone to 18 crops (at rates of 500 and 1,000 g ai ha−1) and weed efficacy against 35 weeds (at rates of 125 and 250 g ha−1) were determined in greenhouse studies. Visual estimate indicated that fluorochloridone was not safe to many crops, especially cruciferous crops. Among all of the trial crops, garlic was the only crop which was not injured in both PRE and POST application at rate of 500 g ha−1, even when treated with 1,000 g ha−1. Fluorochloridone showed high efficacy against most weeds tested in this experiment when applied PRE, but could not offer a satisfactory control when applied POST. Further rate-response study of fluorochloridone to garlic and six weeds was also investigated. PRE application of fluorochloridone to garlic was safer than POST, and the rates for 10% growth reductions (GR10s) were 1,959 g ha−1 for PRE and 537 g ha−1 for POST. When applied PRE, GR90s of shepherd's-purse and flixweed were 19.2 and 70.3 g ha−1, respectively. Though GR90 of catchweed bedstraw was 541 g ha−1, it could be totally controlled without injuring garlic. On the basis of these results, fluorochloridone has an excellent prospect for weed control in garlic fields.

Small burnet is a hardy, relatively long-lived evergreen forb with the potential to improve grazing lands, particularly to extend grazing into late fall and winter. Small burnet was evaluated for tolerance to spring and fall POST applications of aminopyralid, bromoxynil, clethodim, clopyralid, dicamba, dimethenamid-P, imazamox, metribuzin, pendimethalin, quinclorac, and 2,4-DB. Injury, seed yield, seed viability, and dry matter yield (DMY) were measured in the spring following application. Injury was observed in response to all spring and fall herbicide applications. Injury from aminopyralid was the highest for both spring and fall applications at 24 and 79%, respectively. Fall application of imazamox and dicamba resulted in 57 and 31% injury, respectively. Spring-applied aminopyralid and 2,4-DB both reduced DMY by 16%, whereas fall applications of imazamox, dicamba, and aminopyralid reduced DMY by 36, 12, and 67%, respectively. Fall applications of imazamox and aminopyralid reduced seed yield by 33 and 65%, respectively. Fall-applied aminopyralid reduced seed germination by 43%. None of the spring-applied herbicides affected seed yield or seed germination. Small burnet is severely injured by aminopyralid and to a lesser degree by imazamox and dicamba. Bromoxynil, clethodim, clopyralid, dimethenamid-P, metribuzin, pendimethalin, and quinclorac did not affect small burnet DMY, seed yield, or germination the year after application.

Enhanced dissipation of atrazine has been documented in many parts of the world where the herbicide has been extensively used. Atrazine is widely used in corn in Illinois, but enhanced dissipation in the field has not been documented. In this study, the dissipation of atrazine was measured in three fields. Two of the fields (URB-1 and URB-2) had not been treated with atrazine for 3 and 4 yr, respectively, whereas the third field (ORR-1) had received annual applications of atrazine for 9 yr. A laboratory assay conducted on soil collected from these fields prior to atrazine application indicated that soil from ORR-1 had enhanced atrazine dissipation (half life [DT50] 1.7 d). Soil from fields URB-1 and URB-2 dissipated atrazine much slower (DT50 was 13 and 11d, respectively). In the field, the rates of atrazine dissipation were similar to those measured in the laboratory. The DT50s were 2.4, 8.4, and 12.6 d for ORR-1, URB-2, and URB-1, respectively. Testing the soils collected from the fields at the last sampling time for atrazine dissipation showed that all of them had enhanced atrazine dissipation, suggesting that the soil microbial populations had adapted to the presence of atrazine in the field.

Scotch broom is a large, nonnative shrub that has invaded forests and grasslands in 27 U.S. states. Without treatment, Scotch broom's persistent seedbank ensures a continuing source of regeneration after soil disturbance. In growth chamber studies, five rates of three synthetic auxin herbicides, aminocyclopyrachlor (AC), aminopyralid (AP), and clopyralid (CP), were compared for PRE control of Scotch broom. Cumulative 90-d emergence, mortality, and biomass of seedlings did not vary among herbicides, averaging 42% of seeds sown, 75% of emerged seedlings, and 9 mg seedling−1 for treated containers, respectively, versus 46%, 17%, and 26 mg seedling−1 for nontreated containers. Low rates of each herbicide (< 50% of the maximum labeled rate [MLR]) provided 60 to 80% control, whereas 100% MLR provided 69 to 89% control. Although the herbicides differed in cost per unit seedling mortality (AP < CP < AC), each demonstrated strong potential as a viable treatment for PRE control of Scotch broom.

Understanding seed biology and onset of germination requirements is a key point for designing effective weed management programs. Gibberellins (GAs) are known to play a role in onset of germination of several species. Onset of germination often requires an increase in de novo GA content or an increase in sensitivity to GAs. Reduced germination of seeds incubated in solutions containing compounds that inhibit GA synthesis provide evidence that GAs are required to trigger germination. Trinexapac-ethyl (TE), a GA synthesis inhibitor, is frequently used as a plant growth regulator in crop production. However, to the best of our knowledge, TE has not been used to study the requirement of GAs in onset of germination. Germination studies were conducted using seeds of artichoke thistle and common teasel under a range of TE concentrations (0 to 500 μM TE), a combined solution of 125 μM TE + 100 μM GA3 for artichoke, and 250 μM TE + 100 μM GA3 for common teasel. Germination tests were conducted at 20/10 C (12-h thermoperiod) in darkness for artichoke and at constant 15 C with 12 h of light for common teasel. Germination of artichoke in 125 μM TE was reduced to 47% when compared with the check (95%), but the combined TE + GA3 solution maintained germination at 84%. Germination of common teasel in 250 μM TE was reduced to 10% when compared with the check (91%), and the combined TE + GA3 solution increased germination to 63%. These results demonstrate the utility of TE to study the role of GAs in onset of germination. This novel use of TE is a valuable option to study germination requirements of weed species, and therefore contributes to the design of weed management programs.

A commercial intrarow rotating cultivator was tested for weed removal and impact on hand-weeding times in bok choy, celery, lettuce, and radicchio. The rotating cultivator was tested as an automated crop thinner and weeder in direct-seeded bok choy and lettuce as an alternative to hand-thinning and -weeding. The rotating cultivator utilized machine-vision guidance to align a rotating disk with the crop plant to be saved and to remove weeds and undesired crop plants. The rotating cultivator was compared to a standard interrow cultivator, which could not remove weeds from the plant line. Main plots were cultivator type, rotating, or standard, and subplots were herbicides: pronamide for lettuce or prometryn for celery. Weed densities, hand-weeding times, crop stand, and yields were monitored. Economic analysis was performed on a subset of the data. The intrarow rotating cultivator was generally more effective than the standard interrow cultivator for reducing weed densities and hand-weeding times. However, the rotating cultivator reduced seeded lettuce stands by 22 to 28% when compared to hand-thinning and standard cultivation, resulting in lower yields and net returns. In transplanted celery, lettuce, and radicchio, the rotating cultivator removed more weeds than the standard cultivator, and reduced stands by just 6 to 9% when compared to the standard cultivator. In transplanted lettuce, the rotating cultivator was more precise and did less damage to the crop. Because transplanted crops were larger than the weeds, they were more easily differentiated using this technology. Net returns were therefore similar between the two cultivators. What is needed for celery and leafy vegetables is an effective intrarow weed removal system that reduces or eliminates the need for hand-weeding yet does not reduce yields. The rotating cultivator was developed for transplanted crops, where it performs adequately, but it cannot be recommended in the seeded crops evaluated.

Experiments were conducted throughout central Florida from 2010 to 2014 to determine the effectiveness of fluroxypyr or aminopyralid for control of spreading pricklypear. Aminopyralid + 2,4-D (0.09 + 0.75 kg ae ha−1) was not effective and provided only 15% control by 18 mo after application (MAT). However, fluroxypyr at 0.55 kg ae ha−1 or sequential applications of 0.27 kg ha−1 provided greater than 82% control at 18 MAT. Reducing fluroxypyr rates to 0.32 kg ha−1 reduced control to 40 and 71% for spring versus fall applications, respectively. However, the addition of aminopyralid + 2,4-D to fluroxypyr at 0.32 kg ha−1 improved pricklypear control to 92%, regardless of application timing.

Field experiments were conducted in 2010 and 2011 at two locations in Michigan to determine the effects of nitrogen and weed removal on glyphosate-resistant sugarbeet yield and quality. Nitrogen rates were 0, 67, 100, 134, and 67 : 67 kg N ha−1, and weeds were removed when they were < 2, 8, 15, and 30 cm tall. At the beginning of the growing season, weeds responded to N sooner than sugarbeet. Nitrogen assimilation by weeds was three times greater than sugarbeet at 0, 67, 100, and 134 kg N ha−1 and four times greater than sugarbeet with the split application of N (67 : 67 kg N ha−1) averaged over the weed removal timings. Higher N rates increased N sufficiency index values and sugarbeet canopy closure; weeds 30 cm tall had lower N sufficiency index values and a smaller sugarbeet canopy. The effect of N on root yields varied, but the highest N rates (134 kg N ha−1 or 67 : 67 kg N ha−1) were among the highest sugarbeet yields at all locations. Highest yields were achieved when weeds were controlled before reaching 2 cm tall at three of the four site-years. Delaying weed control until weeds were 8 or 15 cm tall reduced yield by 15%, whereas 30-cm-tall weeds reduced yield up to 21%. Recoverable white sucrose ha−1 (RWSH) also was reduced by 8 to 16% if weeds were 8 cm tall. These results indicate that weeds are highly competitive with sugarbeet and can assimilate large quantities of N early in the growing season, especially at larger growth stages. However, it appears that sugarbeets were able to scavenge sufficient N at the N rates used in this study to overcome N removal effects from larger weeds, resulting in no interaction between N rate and weed removal timing for sugarbeet root yield, quality, or RWSH.

Nutsedge control is challenging in commercial vegetable production in the absence of methyl bromide, and therefore, an effective alternative is needed. This study investigated allyl isothiocyanate (ITC) as a methyl bromide alternative for purple nutsedge control under polyethylene-mulch. Greenhouse experiments were conducted to compare the retention of allyl ITC in treated soil (3,000 nmol g−1) under low-density polyethylene (LDPE) and virtually impermeable film (VIF) mulches. Field experiments were conducted to evaluate the effectiveness of allyl ITC (6 rates: 0, 15, 75, 150, 750, 1500 kg ai ha−1) under VIF mulch against purple nutsedge. Additionally, a standard treatment of methyl bromide+chloropicrin (67 : 33%) at 390 kg ai ha−1 under LDPE mulch was included for comparison. In the greenhouse experiment, the predicted half-life of allyl ITC under LDPE and VIF mulch was 0.15 and 0.59 d, respectively. In the field experiment, it was predicted that allyl ITC at 1,240 and 1,097 kg ha−1 under VIF mulch is required to control purple nutsedge shoot and tubers equivalent to methyl bromide + chloropicrin at 4 wk after treatment (WAT). It is concluded that allyl ITC under VIF mulch would need to be applied at 2.8 to 3.2 times the standard treatment of methyl bromide + chloropicrin under LDPE mulch for commercially acceptable purple nutsedge control.

Use of PRE herbicides for control of annual grassy weeds during commercial sod production has been limited. Research was conducted from 2010 to 2013 evaluating the effects of pendimethalin (3.36 kg ai ha−1), dithiopyr (0.56 kg ai ha−1), prodiamine (0.6 kg ai ha−1), oxadiazon (3.36 kg ai ha−1), prodiamine + sulfentrazone (0.84 + 0.41 kg ai ha−1), dimethenamid-P (1.68 kg ai ha−1), and indaziflam (0.03 and 0.05 kg ai ha−1) applications at sprigging on the establishment rate and tensile strength of ‘Tifway' hybrid bermudagrass sod at harvest (377 d after sprigging). All herbicides increased the days required to reach 50% hybrid bermudagrass cover compared with the nontreated control. Days required to reach 50% hybrid bermudagrass cover were lowest for oxadiazon and prodiamine (39 to 44 d), greatest for both rates of indaziflam (65 to 141 d), with dimethenamid-P, prodiamine plus sulfentrazone, pendimethalin, and dithiopyr ranking intermediate (45 to 63 d). Both rates of indaziflam reduced sod tensile strength at harvest compared with the nontreated control during a single year of the study; no other differences in sod strength due to herbicide treatment were detected at any time.

‘Replay' and ‘JS501’ perennial ryegrass cultivars have been conventionally bred for reduced sensitivity to glyphosate, potentially allowing the herbicide to be used for selective weed control in overseeded bermudagrass. Field experiments were conducted to evaluate optimal glyphosate application rate, regime (single and sequential applications), and timing for annual bluegrass control in bermudagrass overseeded with these cultivars. Additionally, greenhouse experiments were conducted to compare the sensitivity to glyphosate of Replay and JS501 to susceptible cultivars ‘Caddy Shack' and ‘Top Gun II' through log-logistic rate-response analysis. In field experiments, only two treatments resulted in > 90% annual bluegrass control and < 25% perennial ryegrass injury. These two treatments were a single application of 280 g ae ha−1 glyphosate in January and 140 g ha−1 followed by an additional 140 g ha−1 applied in January. Perennial ryegrass cultivars were compared using 50% inhibition (I50) values, i.e. 50% visible estimates of injury or 50% reduction in clipping weight. I50 values obtained 6 wk after treatment from injury data were 2.56, 2.64, 0.81, and 0.84 g ha−1 glyphosate for Replay, JS501, Caddy Shack, and Top Gun II, respectively. Replay and JS501 were similar in sensitivity to glyphosate and were up to four times more tolerant than Caddy Shack and Top Gun II across rating dates and data types.

Tall fescue is a commonly used turfgrass in the temperate and transition zone areas of the United States. During hot, humid summers, tall fescue is under stress and is susceptible to Rhizoctonia solani (brown patch) infection, causing turf thinning, leading to encroachment from weeds, such as bermudagrass. Field trials were established to evaluate the effect of mowing height and fertility programs on disease severity and bermudagrass encroachment in tall fescue. Mowing at 10 cm resulted in less bermudagrass encroachment than did a 6-cm mowing height. Increasing the nitrogen fertilization level from 49 to 171 and 220 kg N ha−1 generally led to more bermudagrass encroachment at the 6-cm, but not the 10-cm, mowing height. Plots receiving 220 kg N ha−1 annually at the 6-cm mowing height had the most brown patch. Turfgrass cover was greatest in plots mowed at 10 cm and receiving 220 kg N ha−1 annually.

Propane flaming could be an alternative tool for PRE control or suppression of early-emerging weeds in organic and conventional crops. The objective of this study was to test the tolerance of selected early-season weeds to broadcast flaming in no-till systems. Four winter annuals (tansy mustard, henbit, cutleaf evening primrose, and field pennycress), one summer annual (common lambsquarters), and one perennial (dandelion) species were included in the study. Except for dandelion, the response to propane flaming was evaluated at two growth stages. Flaming treatments were applied using an all-terrain-vehicle-mounted flamer moving 4.8 km h−1, and propane pressure was adjusted to deliver doses of 0 (nonflamed control), 22, 34, 48, 67, and 90 kg ha−1. The response of each species to propane doses was described by log-logistic models based on visual ratings of weed control and dry matter reduction. Response to broadcast flaming varied among species and growth stages. Common lambsquarters, tansy mustard, and henbit were more susceptible to flaming than cutleaf evening primrose, field pennycress, and dandelion. On the basis of visual ratings, propane doses between 54 and 62 kg ha−1 effectively controlled (90% control) common lambsquarters at the early growth stage (five-leaf), tansy mustard at both growth stages (nine-leaf and flowering), and henbit (flowering). However, a higher propane dose (> 80 kg ha−1) was necessary to obtain 90% control of common lambsquarters in later growth stage (11-leaf) and early growth stage of henbit (nine-leaf). Cutleaf evening primrose, field pennycress, and dandelion exhibited higher levels of tolerance to broadcast flaming. A 90% control of these species was not achieved even with the highest propane dose (90 kg ha−1) utilized in the study. Results of this study indicate that a single application of broadcast flaming can be an effective tool for controlling tansy mustard, henbit, and common lambsquarters and temporary suppression of cutleaf evening primrose, field pennycress, and dandelion.