Turfgrass Weed Research Articles

Extension event attendance increases adoption of weed management practices by sports field managers

AbstractData from a national survey of 348 U.S. sports field managers were used to examine the effects of participation in Cooperative Extension events on the adoption of turfgrass weed management practices. Of the respondents, 94% had attended at least one event in the previous 3 yr. Of this 94%, 97% reported adopting at least one practice as a result of knowledge gained at an Extension turfgrass event. Half of the respondents had adopted four or more practices; a third adopted five or more practices. Nonchemical, cultural practices were the most-adopted practices (65% of respondents). Multiple regression analysis was used to examine factors explaining practice adoption and Extension event attendance. Compared to attending one event, attending three events increased total adoption by an average of one practice. Attending four or more events increased total adoption by two practices. Attending four or more events (compared to one event) increased the odds of adopting six individual practices by 3- to 6-fold, depending on the practice. This suggests that practice adoption could be enhanced by encouraging repeat attendance among past Extension event attendees. Manager experience was a statistically significant predictor of the number of Extension events attended but a poor direct predictor of practice adoption. Experience does not appear to increase adoption directly, but indirectly, via its impact on Extension event attendance. In addition to questions about weed management generally, the survey asked questions specifically about annual bluegrass management. Respondents were asked to rank seven sources of information for their helpfulness in managing annual bluegrass. There was no single dominant information source, but Extension was ranked more than any other source as the most helpful (by 22% of the respondents) and was ranked among the top three by 53%, closely behind field representative/local distributor sources at 54%.

Survey of target site resistance alleles conferring resistance in Poa annua

AbstractPoa annua L. (annual bluegrass) is a common weed in turfgrass and has been reported resistant to 12 different herbicide sites of action, with various combinations of multiple‐herbicide resistance having been identified. To quantify the extent of herbicide‐resistant P. annua, the ResistPoa Project (resistpoa.org) surveyed 1349 P. annua populations for resistance to nine sites of action and one plant growth retardant. Herein, we report results from sequencing of known target site mutations found in 5‐enolpyruvylshikimate‐3 phosphate synthase (EPSPS), acetolactate synthase (ALS), photosystem II protein D (psbA), and 𝛼‐tubulin genes. Populations were sequenced using either capillary or amplicon sequencing (AmpSeq), depending on the complexity of the gene, and were analyzed for target‐site resistance. After additional resistance screening, a total of 389 suspected resistant populations were sequenced—131 for ALS, 83 for EPSPS, 93 for psbA, and 82 for 𝛼‐tubulin. From the resistant populations, 64 displayed resistance to multiple sites of action. After sequencing, it was determined that target‐site resistance was the common form of resistance for all sites of action outside of psbA with 65.6% of ALS populations, 73.5% of EPSPS, 39.8% of psbA, and 91.5% of 𝛼‐tubulin having presented a target‐site mutation.

Effect of spray droplet spectra on control of Poa annua with pronamide

AbstractAnnual bluegrass is a troublesome weed in turfgrass, with reported resistance to at least 12 herbicide sites of action. The mitotic-inhibiting herbicide pronamide has both preemergence and postemergence activity on susceptible annual bluegrass populations. Previous studies suggest that postemergence activity may be compromised due to lack of root uptake, as well as target-site- and translocation-based mechanisms. Research was conducted to determine the effects of spray droplet spectra on spray coverage and control of annual bluegrass with pronamide, flazasulfuron, and a mixture of pronamide plus flazasulfuron. Herbicides were delivered to annual bluegrass plants having two to three leaves via five different spray spectra based on volume median diameters (VMD) of 200, 400, 600, 800, and 1,000 µm. Fluorescent tracer dye was added to each treatment solution to quantify the effects of herbicide and spray droplet spectra on herbicide deposition. In another experiment, the efficacy of 0.58, 1.16, and 2.32 kg pronamide ha−1; 0.022, 0.044, and 0.088 kg flazasulfuron ha−1, or a combination of the two, were assessed in iteration with droplet spectrum sprays of 400 and 1,000 µm on two pronamide-resistant and two pronamide-susceptible annual bluegrass populations. Spray droplet spectrum affected the deposition of pronamide and flazasulfuron, applied alone and in combination. Pronamide foliar deposition decreased with increasing droplet spectra. Pronamide efficacy was affected by droplet spectrum, with the largest (1,000 µm) exhibiting improved control. Flazasulfuron efficacy and pronamide plus flazasulfuron efficacy were not affected by droplet spectra. Pronamide plus flazasulfuron mixture controlled all four populations more effectively than pronamide alone, regardless of droplet spectra. A mixture of pronamide plus flazasulfuron applied with relatively large droplets may be optimal for annual bluegrass control, which offers valuable insights for optimizing herbicide application and combatting herbicide resistance. However, applications in this controlled-growth pot study may not mimic conditions in which thatch and turfgrass canopy limit the soil deposition of pronamide.

Festuca sp. interfere with germination and early growth of three weeds

AbstractHerbicide restrictions require alternative strategies for turfgrass weed control. This growth chamber study investigated the interference of 27 Festuca cultivars selected from five Festuca species using white clover (Trifolium repens L.), lawn daisy (Bellis perennis L.), and yarrow (Achillea millefolium L.) as indicator species. At 13 days after sowing (DAS), 20 weed seeds were placed in between 60 grass seeds. Lawn daisy was highly sensitive to the presence of all grasses, and results are not presented. Festuca species or individual cultivars did not affect the germination percentage and mean germination period of white clover and yarrow. The presence of tall fescue [Schedonorus arundinaceus (Schreb.) Dumort., nom. cons.]) species reduced white clover root length by 71.6% and slender creeping red fescue [Festuca rubra L. ssp. littoralis (G.Mey.) Auquier] by 44.5% at 30 DAS. Within cultivars, reductions of white clover roots ranged from 81.7% (Regenerate) to 24.8% (Cathrine). Root length for yarrow was reduced by an average of 75% with no difference among Festuca species. Cultivar effects ranged from 91.8% for Barcesar to 62.9% for Samanta. For both white clover and yarrow, negative correlations were determined between Festuca biomass and the root length of both weeds: −0.241*** (white clover) and yarrow −0.168* (yarrow). Such a relationship suggests that part of the inhibiting effect can be directly attributed to Festuca biomass. We conclude that differences in interference potential between cultivars within species are as important as differences between species. White clover appeared to be the most discriminative species for growth interference studies with Festuca.

Effect of herbicides on pollinator foraging behavior and flower morphology in white clover (Trifolium repens L.)–infested turfgrass

AbstractThe recent decline in pollinator abundance is a cause of concern for sustaining global food production. Several common weeds of managed turfgrass systems attract honeybees and other wild pollinators. As turfgrass often requires treatment with insecticides that harm bees, best practices are needed to prevent bees from visiting weed-infested turf areas that will be treated for insect pests. Weed control tactics can protect pollinator exposure to insecticides by reducing the floral resources afforded to bees from turfgrass weeds. Three field studies were conducted in 2021 and 2022 to evaluate the effect of various herbicides and herbicide formulation constituents on pollinator foraging and white clover floral morphology in managed tall fescue turfgrass. Treatments included a nontreated control; MCPP; 2,4-D; dicamba; Trimec Classic™ (2,4-D, MCPP, dicamba); Speedzone™ (carfentrazone, 2,4-D, MCPP, dicamba); and an herbicide-formulation constituent (inert ingredients of Speedzone™). All response variables were evaluated for 8 d, starting from one day before treatment and ending 6 d after treatment (DAT). The herbicide formulation constituent did not alter white clover flower density, floral discoloration, floral quality, or insect visitation compared to nontreated plots. Herbicides reduced flower density and floral quality to the same extent, but MCPP discolored white clover floral tissue 16% per day and less than all other herbicides except dicamba. Floral quality completely declined in approximately 5 d following any herbicide treatment. Bee visitation to white clover–infested turf increased by 3 bees min–1 for every 100 white clover blooms m–2. Honeybees and other insects vacated herbicide-treated areas in less than 2 d, despite minimal effects on floral quality and density at that time. The data suggest that practitioners could apply insecticides 2 d after auxin herbicide treatment and avoid harm to pollinators, but additional work is needed to directly measure pollinator exposure following such treatments.

Biological Control of Weeds in turfgrass: opportunities and misconceptions.

Turfgrass systems may offer opportunities for overcoming some constraints on the successful implementation of weed biocontrol. Of the roughly 16.4million ha of turfgrass in the USA, ≈60-75% are in residential lawns and 3% are golf turf. Annual expenditures for a standard herbicide treatment regimen for residential turf are estimated to be ≈US$326 ha-1 , about 2-3-fold greater than that for USA corn and soybean growers. Expenditures can be >US$3000 ha-1 for control of certain weeds such as Poa annua in high-value areas including golf fairways or greens, but those applications are made to far smaller areas. Regulatory actions and consumer preferences are creating market opportunities for alternatives to synthetic herbicides in both commercial and consumer markets, but the size of these markets and willingness-to-pay are poorly documented. Turfgrass sites are intensively managed, yet despite the ability to modify site conditions through irrigation, mowing and fertility management, microbial biocontrol agents tested thus far have not provided the consistently high levels of weed control expected in the market. Recent advances in microbial bioherbicide products may offer a path to overcome many of the obstacles to success. No single herbicide will control the diversity of turfgrass weeds, nor will any single biocontrol agent or biopesticide. Successful development of weed biocontrol for turfgrass systems will require numerous, effective biocontrol agents for the many weed species found in turfgrass environments, as well as a deeper understanding of different turfgrass market segments, and weed management expectations for each segment. © 2023 The Author. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

A deep learning-based method for classification, detection, and localization of weeds in turfgrass.

Precision spraying of synthetic herbicides can reduce herbicide input. Previous research demonstrated the effectiveness of using image classification neural networks for detecting weeds growing in turfgrass, but did not attempt to discriminate weed species and locate the weeds on the input images. The objectives of this research were to: (i) investigate the feasibility of training deep learning models using grid cells (subimages) to detect the location of weeds on the image by identifying whether or not the grid cells contain weeds; and (ii) evaluate DenseNet, EfficientNetV2, ResNet, RegNet and VGGNet to detect and discriminate multiple weed species growing in turfgrass (multi-classifier) and detect and discriminate weeds (regardless of weed species) and turfgrass (two-classifier). The VGGNet multi-classifier exhibited an F1 score of 0.950 when used to detect common dandelion and achieved high F1 scores of ≥0.983 to detect and discriminate the subimages containing dallisgrass, purple nutsedge and white clover growing in bermudagrass turf. DenseNet, EfficientNetV2 and RegNet multi-classifiers exhibited high F1 scores of ≥0.984 for detecting dallisgrass and purple nutsedge. Among the evaluated neural networks, EfficientNetV2 two-classifier exhibited the highest F1 scores (≥0.981) for exclusively detecting and discriminating subimages containing weeds and turfgrass. The proposed method can accurately identify the grid cells containing weeds and thus precisely locate the weeds on the input images. Overall, we conclude that the proposed method can be used in the machine vision subsystem of smart sprayers to locate weeds and make the decision for precision spraying herbicides onto the individual map cells. © 2022 Society of Chemical Industry.

Effects of spray droplet size on pronamide control of Poa annua

AbstractAnnual bluegrass (Poa annua L.) is a problematic weed in turfgrass that has evolved resistance to 12 different herbicide sites of action. The mitotic inhibiting herbicide pronamide has both pre‐ and postemergence activity on susceptible annual bluegrass populations, but on certain resistant populations, postemergence activity is hypothetically compromised due to lack of root uptake or due to an unknown foliar resistance mechanism. Spray droplet size may affect foliar and soil deposition of pronamide, thus potentially explaining variation in population control or differential shoot and root uptake. Greenhouse experiments were conducted to quantify pronamide, flazasulfuron, and pronamide + flazasulfuron (a common tank mixture) deposition on annual bluegrass as affected by spray‐droplet size. Five droplet sizes (200, 400, 600, 800, and 1,000 μm) were sprayed in an enclosed spray chamber on two‐ to three‐leaf stage annual bluegrass plants. Fluorescent dye was added to each treatment solution to quantify the effects of herbicide and spray droplet size on herbicide deposition. Results indicate that spray droplet size affects deposition of pronamide and flazasulfuron, applied alone and in combination, on annual bluegrass. The highest foliar deposition was produced with 400‐μm spray droplets in pronamide treatments and with 200 μm spray droplets in flazasulfuron and pronamide + flazasulfuron treatments. The addition of flazasulfuron to pronamide did not affect herbicide deposition when compared with pronamide‐alone treatments. Results suggest that 200‐ to 400‐μm spray droplets are optimal for foliar deposition of pronamide. Alternatively, larger droplet sizes may facilitate better soil deposition of pronamide where root uptake is optimal.

Resolving issues related to target‐site resistance detection in Poa annua alpha‐tubulin

AbstractAdvanced sequencing techniques have improved the ability to identify and understand target‐site resistance in herbicide‐resistant species. Despite innovations in sequencing, polyploid species can still face issues that are typically not seen in diploid species, often because of the presence of conflicting subgenomes. Further confounding the difficulties of polyploidy is the α‐tubulin gene, which has subgenomic duplication of gene family copies. Poa annua L., an allotetraploid, is a persistent weed in turfgrass that has developed resistance to multiple herbicide modes of action, including mitotic‐inhibiting herbicides. Sequencing α‐tubulin cannot be performed by simple Sanger sequencing to identify target‐site mutations because of frequent nucleotide conflictions between the numerous α‐tubulin copies present on both subgenomes, which was illustrated by vector cloning in combination with Sanger. Improved sequencing is needed to understand resistance to mitotic‐inhibiting herbicides. Amplicon sequencing via Illumina technology was used to identify target‐site mutations. Eighty‐two populations resistant to mitotic‐inhibiting herbicides were sequenced via next‐generation sequencing. Seventy‐five populations presented with the known single nucleotide polymorphism, Thr239Ile. The ability to successfully sequence and analyze α‐tubulin data provides a vehicle for further insight into herbicide resistance.

Response of creeping bentgrass (Agrostis stolonifera) and weed species to plant growth regulators

AbstractFrequent use of plant growth regulators (PGRs) may decrease the recovery of turfgrass from wear and competition with weeds. The response of new creeping bentgrass (Agrostis stolonifera L.) cultivars to PGRs is unknown. Therefore, we aimed to evaluate the response of several creeping bentgrass cultivars and common turfgrass weeds to PGRs. Creeping bentgrass cultivars (‘Penncross’, ‘L‐93’, ‘007’, ‘V‐8’, and ‘Tour Pro’) and weed species – goosegrass [Eleusine indica (L.) Gaertn.] and large crabgrass (Digitaria sanguinalis L.) – were examined. The PGR treatments were trinexapac‐ethyl (TE) (48 and 96 g a.i. ha–1) and prohexadione calcium (PC) (116 and 231 g a.i. ha–1). Plants were cut to 2.5 cm after 2 wk, and aboveground plant tissue was weighed to obtain biomass. Only 116 g a.i. ha–1 of PC was required to regulate creeping bentgrass, although the higher rate (96 g a.i. ha–1) of TE was needed for moderate regulation [40–50% growth inhibition (GI)], regardless of the cultivar. Some creeping bentgrass cultivars exhibited a differential response to PGRs. The lowest response to TE (22–33% GI) was observed in ‘V‐8’; however, ‘V‐8’ was strongly regulated by PC (79–80% GI). Neither PGR successfully regulated goosegrass (14–30% GI), regardless of the rate, but moderate regulation of large crabgrass (40–49% GI) was achieved by TE at 96 g a.i. ha–1, and PC at 116 and 231 g a.i. ha–1. Recurrent PGR applications may shift turfgrass–weed competition dynamics towards weeds such as goosegrass; however, this effect may be PGR‐specific.

Effects of soil compaction and moisture on the growth of Juncus tenuis

AbstractJuncus tenuis Willd. is a warm‐season, perennial weed of turfgrass. In wet and compacted soils, it is well documented, yet little is known regarding the interaction effects of compaction and soil moisture on its rooting and foliar growth. A greenhouse experiment examined the effects of soil compaction and moisture on the above‐ and belowground growth of J. tenuis. The experimental design was completely randomized with a 3 × 3 arrangement with four replications and two runs. Factors included soil compaction (bulk densities of 1.56, 1.77, and 2.00 g cm–3) and soil moisture (10.9, 27.9, and 59.6% volumetric water content). Juncus tenuis was transplanted into pots, acclimated for 7 d, and subjected to the treatments for a 10‐wk period. Foliar growth was harvested every 2 wk and root growth was destructively assessed. Cumulative foliar and root biomass varied in response to compaction and soil moisture; however, no significant soil moisture × compaction interactions were detected. The effect of compaction on foliar and root biomass accounted for 15 and 12% of the explained variation, respectively. Increasing the bulk density from 1.56 to 2.00 g cm–3 reduced foliar and root biomass by 29 and 40%, respectively. Soil moisture accounted for ≥84% of the variation in foliar and root biomass. Increasing the soil moisture from 10.9 to 59.6% increased foliar and root biomass by 150 and 230%, respectively. The results suggested that cultural practices that prioritize soil moisture modification while alleviating compaction may reduce the presence of J. tenuis within maintained turfgrass.

Wood vinegar for control of broadleaf weeds in dormant turfgrass

AbstractWood vinegar, a product of pyrolysis, can induce phytotoxicity on plants when applied at an adequate rate and concentration. The objective of this research was to investigate wood vinegar obtained from the pyrolysis of apple tree branches for weed control in dormant zoysiagrass. In environment-controlled growth chambers, white clover visual injury and shoot mass reduction were evaluated and compared to the nontreated control after wood vinegar application at 1,000, 2,000, or 4,000 L ha−1 under 10 C or 30 C temperature conditions. Averaged across rates, wood vinegar rapidly desiccated white clover and caused 83% and 71% visual injury at 10 C and 30 C, respectively, at 1 d after treatment (DAT). Averaged across temperatures, wood vinegar at 1,000, 2,000, and 4,000 L ha−1 reduced white clover shoot mass by 56%, 81%, and 98% from the nontreated control at 10 DAT, respectively. In field experiments, weed control increased as wood vinegar rates increased from 1,000 to 5,000 L ha−1 in dormant zoysiagrass. The effective application dose of wood vinegar required to provide 90% control (ED90) of annual fleabane, Persian speedwell, and white clover was determined to be 2,450, 2,300, and 4,020 L ha−1, respectively, at 2 wk after treatment. Turf quality did not differ among the wood vinegar treatments and the nontreated control when zoysiagrass completely recovered from dormancy. Overall, results illustrate that wood vinegar resulting from the pyrolysis of apple tree branches can be used as a nonselective herbicide in dormant turfgrass, offering a new nonsynthetic herbicide option for weed control in managed turf.

Assessing Competitiveness of Fine Fescues (Festuca L. spp.) and Tall Fescue (Schedonorus arundinaceous (Schreb.) Dumort) Established with White Clover (Trifolium repens L., WC), Daisy (Bellis perennis L.) and Yarrow (Achillea millefolium L.)

Regulatory restrictions on herbicide use for managing turfgrass weeds has prompted the search for alternative control strategies. Fescue (Festuca) species were identified for their potential to interfere with growth of annual and perennial weeds. In a study conducted in 2018 and 2019, six fescue cultivars were tested from five different species for interference with the growth of three common turfgrass weeds: white clover (Trifolium repens L., WC), daisy (Bellis perennis L.) and yarrow (Achillea millefolium L.). Fine (Festuca L. spp.) and tall fescues (Schedonorus arundinaceus (Schreb.) Dumort.) were sown and grown in a field trial for 14 days before overseeding with different weeds. vigor and visual quality of grasses, weed cover, and vegetation cover was recorded regularly for 84 days. Differences in mean temperatures and precipitation between the two years of the study resulted in differences in growth of grasses and weeds, as well as in the extent of weed interference of fescue cultivars. Cultivars Musica (F. rubra L. ssp. commutata Gaudin) and Barpearl (F. rubra L. ssp. littoralis) were least affected by weed growth during both years, but there was overlap with other cultivars for the measured parameters. Melyane (tall fescue) was deemed unsuitable for natural weed suppression because growth and vigor declined after first mowing, ultimately leading to unacceptable visual quality. Turfgrass visual scores were moderately negatively correlated to weed cover in both years. Future research should focus on F. rubra L. ssp. rubra Gaudin and F. rubra L. ssp. littoralis subspecies and identify the mechanisms used to interfere with weed growth.

Detection and quantification of broadleaf weeds in turfgrass using close-range multispectral imagery with pixel- and object-based classification

ABSTRACT The current practice used to evaluate broadleaf weed cover in turfgrass is visual assessment, which is time consuming and often leads to inconsistencies among evaluators. In this study, we investigated the effectiveness of constructing Random Forest models (RF), either pixel-, object-based (OBIA) or a combination of both to detect and quantify broadleaf weed cover. High resolution multispectral images were captured of 136 turfgrass plots, seeded with five species of Festuca L. and overseeded with either clover (Trifolium repens L.), daisy (Bellis perennis L.), yarrow (Achillea millefolium L.), or a mixture of all three weeds. Ground measurements of vegetation cover and bare soil were taken with a point quadrat and digital image analysis. Weeds were detected with 99% accuracy by OBIA, followed by the combined approach (98%) and Pixel-based approach (93%). Accuracy at distinguishing among weed species was somewhat lower (89%, 81% and 90%, respectively), with yarrow contributing most to the decrease in accuracy. The predictions based on ground measurements were further compared to field measurements. For both soil and weed classification, models that used shape features (OBIA and combined) resulted in better agreement with field measurements compared to Pixel- based classifications. Our study suggests that broadleaf weed cover comprised of species such as clover and daisy can be accurately quantified with high resolution multispectral images; however, quantifying yarrow cover remains challenging.

Modeling seasonal emergence of Poa annua in urban greenspace

Turfgrasses are perennial components of urban greenspaces found in parks, recreational areas, golf courses, sports fields, and lawns that confer many ecosystem services. A copious seed producer, Poa annua is the most troublesome weed of turfgrass and continually threatens the ecosystem services provided by urban greenspaces. Field research was conducted in Knoxville, TN to better understand environmental conditions triggering P. annua seedling emergence patterns to assist managers with optimally timing interventions—both chemical and non-chemical—for control. Fluctuations in cooling degree day (CDD21C) accumulation accounted for 82% of the variance in yearly cumulative P. annua emergence data collected in a single irrigated sward of hybrid bermudagrass [C. dactylon (L.) Pers. x. C. transvaalensis Burtt-Davy]. However, non-linear models using CDD21C data developed ex post were not able to accurately predict P. annua emergence patterns ex ante. In both years, P. annua emergence changed most rapidly between the 40th and 43rd week of the year when seven-day mean soil temperature and rainfall were 18.9 °C and 12.7 mm, respectively. Future research should explore the efficacy of herbicide mixtures applied when P. annua emergence is most rapidly changing in lieu of developing models to predict when specific emergence thresholds occur.

Spray nozzle selection contributes to improved postemergence herbicide crabgrass control in turfgrass

For optimum postemergence crabgrass (Digitaria spp.) control, a single quinclorac herbicide application could be properly timed and delivered with spray nozzles that produce spray droplets ranging from very coarse (401-500 μm) to medium (226-325 μm) in size to maximize target coverage and minimize the potential for drift. Crabgrass is an invasive annual grass weed of cool-season turfgrass maintain as lawns, golf courses, and sports pitches. Postemergence herbicide applications for crabgrass control in turfgrass swards often rely on repeated applications for effective control. Optimizing postemergence crabgrass applications can reduce pesticide inputs and contribute to sustainable turfgrass management practices. Two field studies evaluating crabgrass control were conducted in 2020 in a mixed stand of Kentucky bluegrass (Poa pratensis L.) with perennial ryegrass (Lolium perenne L.) in Ohio (USA) and in perennial ryegrass in Pennsylvania (USA). Both sites have histories of natural crabgrass [Digitaria sanguinalis (L.) Scop.] infestation. A postemergence herbicide, quinclorac, was applied at the product label rate and tank-mixed with methylated seed oil at the crabgrass plant stage of three-leaf to one tiller. Different spray nozzles were selected to deliver the following spray droplet classifications and sizes at 275 kPa: Delavan Raindrop 1/4, ultra coarse (>650 μm); TurfJet 1/4TTJO4, extremely coarse (501-650 μm); Air Induction AA8004 or XRTeeJet 8015, very coarse (401-500 μm); XR TeeJet 8008 or GreenLeaf TDAD04, coarse (326-400 μm); XR TeeJet 8004, medium (226-325 μm); and XRTeeJet 8003 fine (145-225 μm). Crabgrass pressure was low in Ohio, and herbicide efficacy at 60 days after treatment was considered acceptable when applied from all spray nozzles that produced spray droplet sizes ranging from ultra coarse to fine. Crabgrass pressure was severe in Pennsylvania, and herbicide efficacy at 60 DAT was considered marginally acceptable when applied from spray nozzles that produced spray droplet sizes ranging from very coarse to medium. Future research should consider cultural practices that would be complementary to postemergence herbicide applications with the goal to reduce pesticide use further and minimize any potential environmental impacts related to spray drift. Highlights - In turfgrass sites with low crabgrass pressure, one postemergence application of quinclorac herbicide could potentially achieve acceptable control with spray nozzles that produce spray droplets ranging from ultra coarse (>650 μm) to fine (145-225 μm). - In turfgrass sites with heavy crabgrass population and pressure, one postemergence application of quinclorac herbicide is best optimized with spray nozzles that produce spray droplets ranging from very coarse (401-500 μm) to medium (226-325 μm). - Overall, turfgrass management practitioners should avoid using spray nozzles that produce a hollow cone spray pattern with ultra coarse (>650 μm) spray droplets which can result in poor or irregular herbicide coverage, or fine (145-225 μm) spray droplets which are subject to potential drift and possible negative off-target effects. - Overall, in an effort to reduce herbicide use for postemergence crabgrass control, a single quinclorac herbicide application could be properly timed and optimized with nozzles that produce spray droplets ranging from very coarse (401-500 μm) to medium (226-325 μm) in size, however, future research should consider cultural practices that would further optimize and also reduce herbicide applications.

Curvularia eragrostidis isolates (Dematiaceae) for biocontrol of crabgrass (Digitaria spp.) in Canada

ABSTRACT Large crabgrass (Digitaria sanguinalis (L.) Scop.) and smooth crabgrass (Digitaria ischaemum (Schreb.) Schreb. ex Muhl.) arrived into North America from Eurasia with immigrants as promising grain and forage crops, but they have become troublesome invasive weeds in cropland and turfgrass. Twenty-three foliar pathogens were isolated from crabgrass near Ste-Anne-de-Bellevue, QC, Canada and evaluated as potential microbial herbicides. Four Curvularia eragrostidis (Henn.) J. A. Mey., [Anamorph, (Meyer, 1959). Moisissures du sol et des litières de la région de yangambi (Congo belge). Publications de L'Institut Agronomique du Congo Belge, 75, 211 pp., Synonym of Cochliobolus eragrostidis (Tsuda & Ueyama) Sivan, Teleomorph, (Sivanesan, 1987). Graminicolous species of Bipolaris, Curvularia, Drechslera. Exserohilum and Their Teleomorphs. Mycological Papers, 158, 1–261] isolates were pathogenic on both large and smooth crabgrass. Two isolates with superior virulence proceeded to a host range assessment on 21 non-target grass species. Many plant species tested were not damaged, but timothy, creeping bentgrass, colonial bentgrass, and smooth bromegrass, were highly susceptible to these isolates. In addition, oats, millet, and sorghum were also susceptible. Susceptibility of these crops raises conflicts of interest and highlights the non-target risks of proceeding with the development of this microbial herbicide. Contra-wise these forage grass species are also recognised as undesirable invasive weeds in native North American grasslands. When the efficacy of Canadian isolate Dip0307 was compared to C. eragrostidis QZ-2000 bioherbicide from China, there was no difference in the control of large crabgrass. Further studies with the isolates are needed to verify their microbial herbicide potential for crabgrass suppression. Resolution of any conflict of interest will require consultation amongst various stakeholders, and if there is an apparent conflict, this needs to be resolved, if not beforehand then at least in parallel with any further studies.

Simulated controlled-release mesotrione for turfgrass tolerance and weed control

AbstractMesotrione typically requires multiple applications to control emerged weeds in turfgrass. As it is absorbed by both foliage and roots, a controlled-release (CR) formulation could eliminate the need for multiple applications. Research was conducted to evaluate simulated-release scenarios that mimic a potential CR mesotrione formulation. A soluble-concentrate formulation of mesotrione was titrated to produce a stepwise change in mesotrione rates, which were applied daily to mimic predetermined release scenarios over a 3-wk period. CR scenarios were compared to a broadcast treatment of mesotrione at 280 g ai ha–1 applied twice at 3-wk intervals, and a nontreated. Mesotrione applied in three temporal-release scenarios controlled creeping bentgrass, goosegrass, nimblewill, smooth crabgrass, and white clover equivalent to the standard sprayed mesotrione treatment in every comparison. However, each CR scenario injured tall fescue two to seven times more than the standard treatment. Soil- and foliar-initiated repeat treatments were equivalent in most comparisons. Our data indicate that mesotrione applied in a temporal range to simulate controlled-release scenarios can deliver desired weed control efficacy comparable to sequential broadcast applications. More research is needed to elucidate proper timings and release scenarios to minimize turfgrass injury.

Biology and Management of Florida Betony (Stachys floridana) in Ornamental Plants in Landscape Planting Beds

Florida betony (Stachys floridana) is a perennial weed in Florida landscape planting beds, gardens, turfgrass, and agricultural production systems. This new 4-page article is written for green industry professionals and others to aid in the identification and management of Florida betony in and around ornamental plants in landscape planting beds. Written by Thomas Smith and Chris Marble, and published by the UF/IFAS Environmental Horticulture Department.https://edis.ifas.ufl.edu/ep597

Managing cool‐season turfgrass without herbicides: Optimizing maintenance practices to control weeds

AbstractBans on the use of synthetic herbicides require innovative management approaches to maintain the attractiveness and usability of turfgrass swards. Such measures should include the use of locally adapted cultivars that germinate and establish quickly, resulting in the densest possible stands. Additionally, a number of turfgrasses have been reported to produce allelopathic substances that inhibit common turfgrass weeds. Mowing heights should be set to achieve maximum weed suppression while still providing acceptable quality for desired use. Sustainable turfgrass management programs have led to a reduction in fertilizer inputs; however, without the availability of herbicides, fertilization regimes need to be re‐examined. The literature suggests that broadleaf weeds are reduced but never fully controlled when more N is applied; therefore, finding a balance between what is needed and what is environmentally safe and sustainable is critical. Organic herbicides include plant pathogens from the fungus Phoma and strains of the bacterium Pseudomonas fluorescens. Both can be used to control several weeds common to turfgrasses. Acetic acid has also been shown to have herbicidal activity; however, it has limited residual activity, and its efficacy remains questionable on mature weeds. Thermal weed control can be used to sterilize a seedbank or spot treat existing weeds. Future turfgrass breeding programs could focus on understanding and enhancing the allelopathic potential of turfgrasses to outcompete weeds more effectively. Furthermore, more research should be directed at assessing the competitiveness of certain turfgrasses against weeds within the limitations of producing turfgrass areas of acceptable aesthetics and playing quality.