The prolific seed production and polyploidy of annual bluegrass allow for the rapid development of herbicide resistance. Ethofumesate-resistant annual bluegrass plants were identified in the 1990s in grass seed production in Oregon, but their prevalence and distribution are not well documented. Therefore a dose–response experiment was initiated to determine the potential level of ethofumesate resistance in seed production systems. Seeds from 55 annual bluegrass populations were obtained from three sources: seed production fields (31 populations), the seed cleaning process (6 populations), and seed testing lots prior to retail distribution (18 populations). Additionally, two populations, one with known ethofumesate resistance and one with known susceptibility, were identified in preliminary testing and used as controls in this experiment. Seed from each collected population was increased. Individual seedlings were then transplanted into separate cone-tainers, grown to a size of 2 to 3 tillers in the greenhouse, and then sprayed using a compressed air track spray chamber with 10 doses of ethofumesate at 0, 0.56, 1.1, 2.8, 5.6, 8.4, 11.2, 16.8, 22.4, and 44.8 kg ai ha−1, with 0.84 to 2.2 kg ha−1 as the label application rate for perennial ryegrass. The resistant to susceptible ratio of populations across all sources ranged from 0.5 to 5.5. The most resistant populations found in production fields, seed cleaning, and seed testing lots had the effective dose necessary to kill 50% of the population (ED50) of 12.1, 9.4, and 13.1 kg ha−1, respectively. Furthermore, 68% of the populations found in production fields had ED50 higher than 6 kg ha−1, indicating common annual bluegrass resistance in grass seed production. As such, growers should implement integrated weed management strategies, as herbicides alone will likely be ineffective at controlling annual bluegrass.

Yellow nutsedge is one of the most widely distributed and troublesome weeds in the world. Field and greenhouse studies were conducted to optimize strategies for increased yellow nutsedge control in turfgrass with halosulfuron and sulfentrazone. In the field study in yellow nutsedge and perennial ryegrass mixture, single or sequential applications (3 wk after initial) of halosulfuron or sulfentrazone were made on June 3, June 23, July 15, or August 5 in 2013, 2014, 2015, and 2016. Percent yellow nutsedge control was rated within the same growing season on September 17 and the following year on June 3 for carryover control. Field and greenhouse studies confirm that sequential applications of halosulfuron with a 3-wk interval resulted in >95% control in a yellow nutsedge–turfgrass mixture. In a greenhouse study, both herbicides reduced yellow nutsedge root and rhizome dry mass from 39% to 98%, reduced number of new tubers and tuber fresh weight from 38% to 100%, and prevented re-emergence. Sequential applications of either herbicide within a 3-wk interval early postemergence is recommended for optimal control. Herbicide application to yellow nutsedge using halosulfuron and sulfentrazone should be made as early as possible postemergence, preferably at the three- to five-leaf stage or 200 to 250 growing degree days (GDD, 10 C base). Mowing can be an effective method to reduce yellow nutsedge growth. Mowing at 7.6 cm weekly reduced yellow nutsedge rhizome dry mass by 55% and number of new tubers formed by 63% in the greenhouse study. Physical removal of yellow nutsedge plants such as hand-pulling can be an effective method to manage yellow nutsedge and is most effective at the three- to five-leaf stage (200 to 250 GDD). End-users can maximize yellow nutsedge control by integrating early herbicide treatments and cultural practices such as mowing and hand-pulling.

Pinoxaden is a POST acetyl coenzyme A carboxylase (ACCase) inhibitor in the phenylpyrazolin chemical family and is labelled for turfgrass use at broadcast rates of 35.5 to 71 g ai ha−1 and spot spray rates of 156 to 310 g ai ha−1. A greenhouse rate-response study was conducted to characterize the efficacy of pinoxaden against common grassy weeds. Weed species examined in this study were yellow foxtail, southern sandbur, annual bluegrass, roughstalk bluegrass, large crabgrass, dallisgrass, bahiagrass, goosegrass, and perennial ryegrass. Nonlinear regressions were modelled to determine visible injury rates (the application rate at which 50% of the weed species were injured and the 90% [I90] rate) and weight reduction rates (the application rate at which there was a 50% reduction in fresh weight and 90% reduction [WR90]) for each weed species. Only annual bluegrass, bahiagrass, and goosegrass had visible injury I90 values greater than the maximum labelled spot spray rate of 310 g ai ha−1. Annual bluegrass, bahiagrass, southern sandbur, and goosegrass all had WR90 values greater than the maximum labelled spot spray rate of 310 g ai ha−1. Results from this study indicate that the evaluated weed species can be ranked, according to visible injury I90 values, from most to least susceptible: perennial ryegrass > yellow foxtail > dallisgrass > large crabgrass > southern sandbur > roughstalk bluegrass > bahiagrass > goosegrass > annual bluegrass.

Field surveys were conducted across the Blacklands region of Texas during 2016 and 2017 to document the distribution of herbicide-resistant Lolium spp. infesting winter wheat production fields in the region. A total of 68 populations (64 Italian ryegrass, four perennial ryegrass) were evaluated in a greenhouse for sensitivity to herbicides of three different modes of action: an acetolactate synthase (ALS) inhibitor (mesosulfuron-methyl), two acetyl-coenzyme-A carboxylase (ACCase) inhibitors (diclofop-methyl and pinoxaden), and a 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) inhibitor (glyphosate). Herbicides were applied at twice the label-recommended rates for mesosulfuron-methyl (29 g ai ha−1), diclofop-methyl (750 g ai ha−1), and pinoxaden (118 g ai ha−1); and at the recommended rate for glyphosate (868 g ae ha−1). The herbicide screenings were followed by dose-response assays of the most-resistant ryegrass population for each herbicide at eight rates (0.5, 1, 2, 4, 8, 16, 32, and 64×), compared with a susceptible population at six rates (0.0625, 0.125, 0.25, 0.5, 1, and 2×). The initial screening and dose-response experiments were conducted in a completely randomized design with three replications and two experimental runs. Survivors (<80% injury) were characterized as highly resistant (0% to 20% injury) or moderately resistant (21% to 79%). Results showed that 97%, 92%, 39%, and 3% of the Italian ryegrass populations had survivors to diclofop-methyl, mesosulfuron-methyl, pinoxaden, and glyphosate treatments, respectively. Of the four perennial ryegrass populations, three were resistant to diclofop-methyl and mesosulfuron-methyl, and one was resistant to pinoxaden as well. Perennial ryegrass populations did not exhibit any resistance to glyphosate. Dose-response assays revealed 37-, 196-, and 23-fold resistance in Italian ryegrass to mesosulfuron-methyl, diclofop-methyl, and pinoxaden, respectively, compared with a susceptible standard. One Italian ryegrass population exhibited three-way multiple resistance to ACCase-, ALS-, and EPSPS-inhibitors. The proliferation of multiple herbicide–resistant ryegrass is a challenge to sustainable wheat production in Texas Blacklands and warrants diversified management strategies.

2,4-dimethylamine salt (2,4-D) is a synthetic auxin herbicide used extensively in turfgrass for selective broadleaf weed control. Previous research has shown that 2,4-D can dislodge from treated turf, notably in the presence of canopy moisture. Practitioners commonly apply 2,4-D in combination with various commercially available surfactants to increase efficacy. Field research was completed to evaluate the effect of surfactant inclusion and sample collection time within a day on dislodgeable 2,4-D residue from perennial ryegrass. Research was initiated May 24, 2016 in Raleigh, NC and repeated in time to quantify dislodgeable 2,4-D following application (2.1 kg ae ha–1) either alone or with a nonionic surfactant (0.5% vol/vol). Sample collection occurred 1, 2, 3, 6, 12 or 24 d after treatment (DAT) at AM [7:00 AM Eastern Standard Time (EST)] and PM (2:00 PM EST) sample timings within a day. 2,4-D applied with surfactant (0.4% to 25.4% of applied) reduced dislodgeable foliar residue compared to 2,4-D applied alone (0.5% to 31.2%) from 1 through 6 DAT, whereas dislodgeable 2,4-D was not detected at 12 and 24 DAT. Regardless of surfactant inclusion or absence, samples collected in the AM resulted in a 5- to 10-fold increase in dislodgeable 2,4-D compared to samples collected in the PM from 1 through 6 DAT, suggesting that 2,4-D dislodgeability may be influenced by conditions favoring canopy moisture development. This research will improve turfgrass management practices and research designed to minimize human 2,4-D exposure.

Treerow vegetation abundance and biodiversity were measured in response to six orchard floor management strategies in organic peach in northern Utah for three growing seasons. A total of 32 weed species were observed in the treerow; the most common were field bindweed, dandelion, perennial grasses (e.g., red fescue and ryegrass), clovers, and prickly lettuce. Weed biomass was two to five times greater in unmanaged (living mulch) than in manipulated treatments. Tillage greatly reduced weeds for approximately one month; however, vegetation rebounded midseason. Tillage selected for species adapted to disturbance, such as common purslane and field bindweed. Straw mulch provided equivalent weed suppression to tillage in the early season. Straw required annual reapplication with material costs, labor, and weed-seed contamination (e.g., volunteer grains and quackgrass) as disadvantages. Plastic fabric mulch reduced weeds the most, but had high initial costs and required seasonal maintenance. Weed biomass declined within seasons and across the three years of the study, likely due to tree canopy shading. Neither birdsfoot trefoil nor a perennial grass mixture planted in the alleyways influenced treerow weeds. Our results demonstrate several viable alternatives to tillage for weed management in treerows of organic peach orchards in the Intermountain West.

Field experiments were conducted in 1986 to 1990 to determine the effect of different rates and application times of BAS 514 and dithiopyr alone and in combination on control of large crabgrass and dandelion in Kentucky bluegrass, tall fescue, and perennial ryegrass. Herbicides evaluated were applied PRE, early POST, and late POST. Results indicated that both herbicides provided excellent PRE control in all years. BAS 514 rates ranged from 0.84 to 0.56 kg ai ha-1. Rates of dithiopyr ranged from 0.43 to 0.56 kg ai ha-1. In addition to crabgrass control, both herbicides controlled dandelion, BAS 514 exhibiting slightly better activity than dithiopyr. BAS 514 at 0.84 to 1.12 kg ai ha-1 and dithiopyr at 0.26 to 0.56 kg ai ha-1 resulted in excellent early POST crabgrass control when applied at the one- to three-leaf stage of crabgrass. BAS 514 and dithiopyr applied late POST (2 to 3 tillers of crabgrass) resulted in 63 to 85% control of crabgrass and 29 to 85% control of dandelion at 10 wk after application. No weed control enhancement was evident from tank mixing the two herbicides. Excellent turf safety was demonstrated by both herbicides on all three turf species.

Overseeding established kikuyugrass swards with tall fescue or perennial ryegrass reduced kikuyugrass cover. Renovation prior to seeding did not aid in the establishment of these two species. Increasing the seeding rate from 79 to 157 kg/ha improved the establishment of perennial ryegrass but not tall fescue. When kikuyugrass plugs were introduced into established turf, tall fescue reduced the invasion of kikuyugrass stolons more than perennial ryegrass. Tall fescue reduced percent kikuyugrass cover, number and spread of stolons, and biomass (compared to perennial ryegrass). The newer turf-type tall fescue cultivars ‘Bonsai,’ ‘Falcon,’ and ‘Olympic’ were more effective than the older tall fescue cultivar ‘Fawn’ in reducing kikuyugrass invasion by reducing stolon number, stolon length, and biomass.

Italian ryegrass is a major weed problem in wheat production worldwide. Field studies were conducted at Fayetteville, AR, to assess morphological characteristics of ryegrass accessions from Arkansas and differences among other Lolium spp.: Italian, rigid, poison, and perennial ryegrass. Plant height, plant growth habit, plant stem color, and node color were recorded every 2 wk until maturity. The number of tillers per plant, spikes per plant, and seeds per plant were recorded at maturity. All ryegrass accessions from Arkansas were identified as Italian ryegrass, which had erect to prostrate growth habit, green to red stem color, green to red nodes, glume (10 mm) shorter than spikelet (19 mm), and medium seed size (5 to 7 mm) with 1 to 3 mm awns. However, significant variability in morphological characteristics was found among Arkansas ryegrass accessions. When Lolium species at the seedling stage (1- to 2-wk-old plants) were compared, poison ryegrass was characterized as having a large main-stem diameter and wide droopy leaves, whereas perennial ryegrass exhibited a short and a very narrow leaf blade. These two can be distinguished from Italian and rigid ryegrass, which have leaf blades wider than perennial ryegrass but narrower than poison ryegrass. Italian and rigid ryegrass are difficult to distinguish at the seedling stage but are distinct at the reproductive stage. At maturity, Italian ryegrass and poison ryegrass seeds are awned, but perennial and rigid ryegrass seeds are awnless. Poison ryegrass awns were at least 4-fold longer than Italian ryegrass awns. Perennial ryegrass flowered 3 wk later than the other species. Poison ryegrass glumes were longer than the spikelets, whereas Italian ryegrass glumes were shorter than the spikelets. Morphological traits indicate that some Italian ryegrass populations are potentially more competitive and more fecund than others.

An experiment was conducted on a specially designed hard surface to study the impact of time interval between flaming treatments on the regrowth and flower production of two grass weeds. The goal of this experiment was to optimize the control of annual bluegrass and perennial ryegrass, both species that are very difficult to control without herbicides. Aboveground biomass from 72 plants per treatment was harvested and dry weights were recorded at regular intervals to investigate how the plants responded to flaming. Regrowth of the grasses was measured by harvesting aboveground biomass 2 wk after the second flaming treatments that were implemented at different time intervals. Flaming treatments decreased plant biomass of both species and also the ratio of flowering annual bluegrass plants. However, few plants were killed. The first flaming treatment affected aboveground biomass more than the second flaming treatment. A treatment interval of 7 d provided the greatest reduction in regrowth of perennial ryegrass, whereas the effect of treatment interval varied between the first and second repetitions of this experiment for annual bluegrass. In general, short treatment intervals (3 d) should be avoided, as they did not increase the reduction of aboveground biomass compared with the 7-d treatment interval. Knowledge on the regrowth of grass weeds after flaming treatments provided by this study can help improve recommendations given to road keepers and park managers for management on these weeds.

Indaziflam is a cellulose biosynthesis-inhibiting herbicide for annual weed control in various agricultural systems. Sporadic cases of unacceptable injury to desirable plants have been reported after indaziflam application, which may have been due to conditions favoring increased indaziflam–soil bioavailability. Research was conducted from 2013 to 2015 on a sandy soil to elucidate the effects of soil organic matter content (SOMC) and soil volumetric water content (SVWC) on indaziflam–soil bioavailability. Indaziflam was applied (50 or 100 g ha–1) at fall only, fall plus spring, and spring only timings to plots in a factorial arrangement of SOMC, pre–indaziflam application (PrIA) SVWC, and post–indaziflam application (PoIA) SVWC. After application, field soil cores were collected for a subsequent greenhouse bioassay experiment, where foliage mass reduction of perennial ryegrass seeded from 0 to 15 cm soil depth was used as an indicator of indaziflam–soil bioavailability throughout the profile. Significant edaphic effects were observed at 0 to 2.5, 2.5 to 5, and 5 to 7.5 cm depths, with increased bioavailability at low compared with high SOMC. Pre–indaziflam application SVWC did not affect bioavailability, whereas PoIA high SVWC increased indaziflam–soil bioavailability at 2.5 to 7.5 cm depth compared with PoIA low SVWC. Low SOMC–PoIA high SVWC decreased perennial ryegrass foliage mass 40 and 37% at 5 to 7.5 cm depth from cores collected 10 and 14 wk after treatment, respectively, whereas reductions from all other SOMC–PoIA SVWC combinations were < 12% and did not vary from each other. Pearson's correlation coefficients showed a moderate, positive relationship between perennial ryegrass mass reductions at 0 to 2.5, 2.5 to 5, 0 to 5, and 0 to 10 cm depths and hybrid bermudagrass cover reduction, which suggests conditions favoring increased indaziflam–soil bioavailability can adversely affect plant growth. Data from this research will aid land managers to use indaziflam effectively without adversely affecting growth of desirable species.

Methiozolin selectively controls annual bluegrass in cool-season turfgrasses, and practitioners may wish to reseed desirable species in treated areas. Field experiments were conducted to evaluate reseeding intervals for creeping bentgrass, perennial ryegrass, and tall fescue following methiozolin applications. Turfgrass establishment varied for species, application timing (0, 2, 4, or 6 wk before seeding, WBS), and rates tested (0.56, 1.12, or 2.24 kg ai ha−1). Reductions in turf cover suggest that seeding of creeping bentgrass, perennial ryegrass, and tall fescue should be delayed 2 wk after methiozolin treatments at 0.56 kg ha−1. However, reseeding should be delayed after methiozolin treatments at 1.12 kg ha−1 for approximately 4, 4, and 2 wk for creeping bentgrass, perennial ryegrass, and tall fescue, respectively. Similarly, establishment was reduced on all dates from the nontreated after 2.24 kg ha−1 was applied at 4 WBS, suggesting that reseeding should be delayed for at least 6 wk on all three species at the high rate.

Flucarbazone controls certain grassy weeds in wheat and may have potential for controlling perennial ryegrass in tall fescue turf. The objective of these experiments was to investigate perennial ryegrass and tall fescue tolerance to flucarbazone at two application timings. In field experiments, flucarbazone applications in May were more injurious to both species than in February and March. Single applications of flucarbazone from 30 to 60 g ai ha−1 in May injured both species 35 to 50% and sequential treatments increased injury approximately twofold. Two applications of flucarbazone at 60 g ha−1 in May injured both grasses > 90%, similar to sequential applications of trifloxysulfuron at 29 g ai ha−1. In growth chamber experiments, injury from flucarbazone on both grasses increased as temperature increased from 10 to 30 C. Flucarbazone reduced total shoot biomass of both grasses at all temperatures after 4 wk. Overall, perennial ryegrass and tall fescue are tolerant to flucarbazone at moderate temperatures (10 to 20 C). However, injury increased substantially under warmer conditions (30 C), suggesting flucarbazone could control perennial ryegrass and tall fescue during late spring and early summer.

Indaziflam is a PRE herbicide for annual broadleaf and grass control in turfgrass systems and requires a 40-wk minimum interval between application and overseeding perennial ryegrass. Currently, activated-charcoal application is recommended to reduce that interval; however, preliminary evaluations determined activated charcoal alone was not a robust mitigation practice for successful establishment during perennial ryegrass overseeding. Field research was conducted in North Carolina and Tennessee to evaluate various mitigation practices to effectively overseed perennial ryegrass into indaziflam-treated turfgrass areas. Immediately following indaziflam application (53 g ai ha−1), two scenarios were created by delivering 0 or 0.3 cm H2O before mitigation practice. Irrigated plots were air-dried before conducting mitigation practices. Evaluated mitigation practices included scalping (0.6 cm cut height; debris removed), verticutting (1.25 cm depth; debris removed), and activated-charcoal application (167 kg ha−1 applied as an aqueous slurry in 3,180 L ha−1), evaluated individually and in each two-way combination in the order scalp followed by (fb) activated charcoal, scalp fb verticut, or verticut fb activated charcoal. Twenty-four hours after mitigation practice completion, perennial ryegrass was seeded (976 kg ha−1) and maintained as a golf course fairway. Overall, perennial ryegrass cover was reduced ≥ 93% at 8 and 20 wk after treatment (WAT) when no mitigation practices were performed. Stand-alone mitigation practices variably improved perennial ryegrass establishment; however, no practice provided acceptable results for end users. Combining mitigation practices improved overseeding establishment, most notably by adding activated charcoal application or verticutting to scalping before irrigation. Across experimental runs and locations, scalp fb activated-charcoal application before irrigation reduced perennial ryegrass cover 22 to 27% at 20 WAT. Results from this research suggest mitigation practices in addition to the currently recommended activated-charcoal application should be performed by turfgrass managers to improve perennial ryegrass overseeding establishment in indaziflam-treated turfgrass areas.

Broadleaf weeds are common and troublesome pests in cool-season turfgrass species such as tall fescue, Kentucky bluegrass, perennial ryegrass, and creeping bentgrass. Broadleaf weeds are primarily managed in these grasses through POST applications of growth regulator herbicides in the phenoxy, benzoic acid, and pyridine chemical classes. There are disadvantages to use of these chemicals, including nontarget plant damage and limited residual control. Certain annual broadleaf weeds can be controlled through application of isoxaben or a PRE crabgrass herbicide, but these herbicides do not control emerged broadleaf weeds. There are advantages to use of sulfonylurea herbicides, including PRE and POST control of annual and perennial weeds, a different mode of action, and these herbicides have low vapor pressure, reducing the potential for offsite movement. There are disadvantages to the use of sulfonylurea herbicides, including limited spectrum of broadleaf weed species controlled and limited tolerance in cool-season turfgrass species. The primary sulfonylurea herbicides used in cool-season turfgrass are chlorsulfuron, halosulfuron, metsulfuron, and sulfosulfuron. There have been specialized uses for primisulfuron and tribenuron-methyl.

Laboratory and greenhouse experiments were conducted to determine the allelopathic potential of centipedegrass. Germination and growth of indicator species were evaluated in soil leachates, leaf debris, and aqueous leaf extracts of centipedegrass. Centipedegrass soil leachates did not inhibit annual bluegrass, goosegrass, henbit, large crabgrass, or perennial ryegrass germination compared with the nonfertilized control. Incorporated centipedegrass leaf debris did not reduce lettuce germination, shoot weight, or root weight compared with the control. However, shoot and root dry weights of radish were reduced with increasing rates of centipedegrass leaf debris. Six and 9 mg debris g−1 soil reduced radish shoot weight by 49 and 64%, respectively, compared with the control. Aqueous leaf extracts of centipedegrass reduced lettuce germination; however, radicle and hypocotyl length were similar to the control. These data do not conclusively suggest centipedegrass has widespread allelopathic activity; however, significant reductions in shoot and root weight of radish with increasing centipedegrass leaf debris demonstrate a pattern of inhibition of one species against another, which fulfills a requirement of allelopathic interactions.

Several commercial and experimental adjuvants were evaluated for efficacy in enhancing activity and selectivity of quinclorac in two cultivars of canola and four turfgrass species. Weed species investigated included cleavers, annual sowthistle, large crabgrass, and goosegrass. Turfgrass species evaluated included Kentucky bluegrass, perennial ryegrass, tall fescue, and creeping bentgrass. A variety of adjuvant types were selected, such as a methylated seed oil (Sunit II), a petroleum-based crop oil concentrate, the silicone-based Sylgard 309, a cationic fatty amine ethoxylate surfactant (Frigate), and modified crop oils (Dash and Merge). Adjuvant efficacy was evaluated by calculating the quinclorac rate required to reduce plant growth 50% (GR50) based on rates applied at 0, 15.6, 31.2, 62.5, and 125 g ai/ha. For goosegrass, quinclorac rates evaluated were increased to 250, 500, 1,000, and 2,000 g ai/ha. All evaluated adjuvants provided similar enhancement of control for cleavers and annual sowthistle. Sylgard 309 was the least effective adjuvant for control of large crabgrass. Goosegrass was tolerant to quinclorac across the evaluated rate range regardless of adjuvant; therefore, GR50 values could not be determined. None of the adjuvants alone caused phytotoxicity to canola or any turfgrass species.

Recent advances in genetic engineering have led to the development of glyphosate-resistant (GR) crops for genetic markers and selective weed control. The effects of glyphosate residue on turfgrass clippings could be toxic to non-GR species. The objective of this experiment was to determine whether glyphosate would retain activity within clippings of creeping bentgrass when applied to Kentucky bluegrass and perennial ryegrass. Greenhouse-grown ‘Penncross’ and GR ‘ASR-368’ were treated with glyphosate at 2.24 kg/ha. Clippings were collected 1, 3, 7, and 12 d after application and applied to greenhouse-grown Kentucky bluegrass and perennial ryegrass. Kentucky bluegrass and perennial ryegrass dry weight and percent cover were reduced by clippings receiving glyphosate that were harvested 1 and 3 d after glyphosate application from both susceptible and resistant creeping bentgrass. Results indicate that glyphosate remains active in clippings for up to 3 d after treatment within creeping bentgrass clippings. Glyphosate-applied creeping bentgrass clippings will need to be managed to prevent injury to susceptible species.

Annual bluegrass is a cosmopolitan, cool-season grass that adapts to different environmental conditions. It is one of the main weeds of turfgrass, and its control is mainly achieved through chemical and cultural practices, although little importance is given to the competitive ability of turfgrass species or cultivars. A field study was performed in northeastern Italy from October 2012 to June 2014 to evaluate the competitive ability of selected perennial ryegrass cultivars to suppress emergence and establishment of annual bluegrass seedlings. Two creeping perennial ryegrasses (‘CSI' and ‘PPG-PR171’) and two traditional cultivars (‘Azimuth' and ‘Presidio') were compared. In late autumn in both years, annual bluegrass was sown in a marked area (30 cm by 30 cm) in the turfgrass. Emerged seedlings were counted weekly, and emergence dynamics were modeled. In the second year, final density of annual bluegrass allowed to grow in turfgrass was also evaluated in summer. Results showed that both seedling emergence and density of annual bluegrass were significantly reduced by creeping perennial cultivars, supporting the hypothesis that these cultivars may reduce annual bluegrass establishment in turfgrass. Seedling emergence pattern of annual bluegrass did not differ in creeping and traditional cultivars of perennial ryegrass, suggesting the possibility of creating a general emergence model suitable in any turfgrass to help turfgrass managers in the control of this weed species.

Thermal weed control methods have been incorporated into weed control programs in organic and conventional production systems. Flaming is commonly used, but steaming has been proposed to increase efficiency of heat transfer to weeds and reduce the risk of fire. The objective of this research was to measure injury to leaves of plant species that differ in leaf morphology and to measure injury to plants at different stages of plant development. The study was conducted in a glasshouse and plants were exposed to steaming at 400 C for 0.36 s—equivalent to a steaming speed of 2 km/h. Overall, leaf thickness was the best morphological characteristic to predict injury ( = 0.51), with greater thickness resulting in less injury. For broadleaf species only, species with wider leaves were injured more than species with narrower leaves ( = 0.64). Injury was greatest when plants had fewer than six true leaves and when their shoots were less than 10 cm long. There was a wide range of injury across species, and the grass species bermudagrass and perennial ryegrass were injured (68 to 81%) more than other species such as common purslane and English daisy (23 to 34%). Biomass of all species tested was reduced by approximately 40%, indicating that leaf injury was not the sole effect of steaming on plant growth. These results indicated that considering both visual estimates of injury and morphological characteristics is important to properly assess thermal weed control effectiveness.