Knotroot foxtail [Setaria parviflora (Poir.) Kergu & eacute;len], a perennial Setaria species, is becoming more problematic in forage and grazing systems across the southeastern United States. Setaria parviflora reproduces through the production of rhizomes and seeds, further complicating management strategies. Significant knowledge gaps exist regarding the biology and control of this species. This research aimed to understand the influence of burial depth on S. parviflora propagules and the physiological differences between it and other Setaria spp. Experiments were conducted between October 2019 and February 2021 in Clarke County, GA, to investigate the influence of burial depth (1, 2, 4, 8, and 16 cm) on the emergence and growth of S. parviflora rhizomes and seeds. Zero emergence was estimated at 8.7, 10.8, and 11.2 cm for small rhizomes, large rhizomes, and seeds, respectively. Therefore, producers could implement tillage events to a depth of 11.2 cm or greater to control S. parviflora. A separate study compared S. parviflora, yellow foxtail [Setaria pumila (Poir.) Roem. & Schult.], green foxtail [Setaria viridis (L.) P. Beauv.], and giant foxtail (Setaria faberi Herrm.) plant morphology. Despite similar aboveground appearances, S. pumila and S. parviflora had different total and belowground biomass 2 to 5 mo after emergence, which suggests differences in root formation and perennialization of S. parviflora. The present research determined that burying propagules using tillage could be included in management recommendations concerning S. parviflora; however, it should be complemented with herbicide applications during the growing season to assist in controlling S. parviflora plants produced by seeds.

Plain Language SummaryPoa annua is a troublesome weed in turfgrass areas such as golf courses, athletic fields, lawns, and sod farms. Controlling P. annua is made more difficult by the growing problem of herbicide resistance, the inherited ability of plants to survive herbicide applications that would normally be lethal. Researchers from 13 academic institutions collected 866 P. annua populations from different states and turfgrass systems to better understand the extent of this problem. Collections were divided and treated with four herbicides and one plant growth regulator. Plants were categorized as “susceptible” or “suspected resistant” based on their response to treatments. Suspected resistance (to at least one or more treatments) was observed in 16.8% of P. annua collections. Herbicide resistance in P. annua is a problem spanning different geographies and management practices. Therefore, coordinated research is needed to explore the scope and nature of the problem in a systematic way.

Knotroot foxtail has become more prevalent and problematic in pastures and hayfields in the southeastern United States. Gaps exist in our knowledge of which herbicide practices are best for managing this species in bermudagrass forage production. This study was conducted to determine the efficacy of various ways to control knotroot foxtail in bermudagrass with herbicide applications in autumn, postemergence (POST), with and without also applying a herbicide in preemergence (PRE), in spring. The study was a randomized complete block with a factorial arrangement of treatments and included a nontreated control for both fall and spring timings. Glyphosate at two rates (0.35 or 0.7 kg ae ha(-1)), nicosulfuron (0.07 kg ai ha(-1)) + metsulfuron (0.012 kg ai ha(-1)), and hexazinone (1.3 kg ai ha(-1)) were applied alone in the fall or followed by indaziflam (0.067 kg ai ha(-1)) or pendimethalin (4.46 kg ai ha(-1)) in the spring. Three harvests were conducted throughout the growing season to evaluate weed species (knotroot foxtail, large crabgrass, and horsenettle) and bermudagrass biomass as well as overall species composition. The combination of fall and spring treatments did not affect weed species or bermudagrass biomass. Therefore, treatment main effects were analyzed by fall or spring application timing. A spring application of either pendimethalin or indaziflam increased bermudagrass biomass compared with that of the nontreated control. However, neither PRE herbicide effectively reduced knotroot foxtail biomass compared with the nontreated control, although pendimethalin did reduce season-long knotroot foxtail composition. Spring PRE herbicides are an effective tool for forage producers, but further research is needed to identify effective herbicides and additional approaches for the control of knotroot foxtail.

Deep learning methods for weed detection typically focus on distinguishing weed species, but a variety of weed species with comparable plant morphological characteristics may be found in turfgrass. Thus, it is difficult for deep learning models to detect and distinguish every weed species with high accuracy. Training convolutional neural networks for detecting weeds susceptible to herbicides can offer a new strategy for implementing site-specific weed detection in turf. DenseNet, EfficientNet-v2, and ResNet showed high F1 scores (≥0.986) and MCC values (≥0.984) to detect and distinguish the sub-images containing dollarweed, goosegrass, old world diamond-flower, purple nutsedge, or Virginia buttonweed growing in bermudagrass turf. However, they failed to reliably detect crabgrass and tropical signalgrass due to the similarity in plant morphology. When training the convolutional neural networks for detecting and distinguishing the sub-images containing weeds susceptible to ACCase-inhibitors, weeds susceptible to ALS-inhibitors, or weeds susceptible to synthetic auxin herbicides, all neural networks evaluated in this study achieved excellent F1 scores (≥0.995) and MCC values (≥0.994) in the validation and testing datasets. ResNet demonstrated the fastest inference rate and outperformed the other convolutional neural networks on detection efficiency, while the slow inference of EfficientNet-v2 may limit its potential applications. Grouping different weed species growing in turf according to their susceptibility to herbicides and detecting and distinguishing weeds by herbicide categories enables the implementation of herbicide susceptibility-based precision herbicide application. We conclude that the proposed method is an effective strategy for site-specific weed detection in turf, which can be employed in a smart sprayer to achieve precision herbicide spraying.

Precision application of specific herbicides to susceptible weeds can significantly save herbicide. This is the first study evaluating the performances of precision sprayer for weed control in turf based on the herbicide weed control spectrum in field conditions. The results showed that EfficientNet-v2 and ResNet never fall below 0.992 for discriminating and detecting the grid cells encompassing weeds susceptible to ACCase-inhibiting and synthetic auxin herbicides. MCPA, a synthetic auxin herbicide, is used to evaluate the performance of the developed smart sprayer for precision control of broadleaf weeds in dormant bermudagrass turf. The developed smart sprayer prototype detected and sprayed every grid cell containing broadleaf weeds in field experiments. Compared to the broadcast application, precision spraying of MCPA provided the same level of control of broadleaf weeds. By 18 days after treatment (DAT), the nontreated control had 13 weeds no. m−2, while the plots that received broadcast and precision spraying had 0 and 1 broadleaf weed plant no. m−2, respectively. Precision herbicide application according to the herbicide weed control spectrum (HWCS) with the developed smart sprayer provided the same level of broadleaf weed control and could save more herbicides compared to an approach without discriminating weed species. Overall, these findings clearly indicated that the developed smart sprayer prototype could effectively detect, discriminate, and spray herbicides onto the grid cells containing target weeds based on the HWCS.

Background: Diagnostic bioassays are used to screen the suspected R population. They are conducted at a single herbicide dose and evaluated at a specific time after treatment that can differentiate resistant from susceptible population.Objective: Three different bioassays were evaluated to assess the detection of acetyl CoA carboxylase-inhibiting herbicides resistance in D. ciliaris.Method: Increasing herbicide rates were used to evaluate the three bioassays for differentiating R from S populations.Results: R1 and R2 differed from S in all employed bioassays. In the Agar-based gel box box assay, the S biotype had greater plant damage at the lower herbicide concentration relative to the R biotypes 3 DAT but differences between R and S decreased over time. In the leaf flotation assay, R biotypes floated at the lower concentration on the surface, whereas the leaves of S biotypes failed to float. For the electrical conductivity assay, the S biotype contained high electrical conductivity due to the high leaching of electrolyte into the water across all four herbicides tested than the R biotypes.Conclusion: While these assays were able to separate R and S biotypes, the level of resistance difference for any assay was no greater than 40% depending on rating data and exposure dose. While a statistical separation could be achieved using a rate response regression analysis for these bioassays, our data highlights the challenges associated whether these methods could provide an obvious difference at any single rate or rating data to be used as a consistent, effective first-phase resistance screen.

Poa 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.

AbstractResearch was conducted using a functional malachite green colorimetric assay to evaluate acetyl-coenzyme A carboxylase (ACCase) activity previously identified as resistant to sethoxydim and select aryloxyphenoxypropionate (FOPs) herbicides, fenoxaprop, and fluazifop. Two resistant southern crabgrass [Digitaria ciliaris (Retz.) Koeler] biotypes, R1 and R2, containing an Ile-1781-Leu amino acid substitution and previously identified as resistant to sethoxydim, pinoxaden, and fluazifop but not clethodim was utilized as the resistant chloroplastic ACCase source compared with known susceptible (S) ACCase. Dose-response studies with sethoxydim, clethodim, fluazifop-p-butyl, and pinoxaden (0.6 to 40 µM) were conducted to compare the ACCase–herbicide interactions of R1, R2, and S using the malachite green functional assay. Assay results indicated that R biotypes required more ACCase-targeting herbicides to inhibit ACCase activity compared with S. IC50 values of all four herbicides for R biotypes were consistently an order of magnitude greater than those of S. No sequencing differences in the carboxyltransferase domain was observed for R1 and R2; however, R2 IC50 values were greater across all herbicides. These results indicate the malachite green functional assay is effective in evaluating ACCase activity of R and S biotypes in the presence of ACCase-targeting herbicides, which can be used as a replacement for the 14C-based radiometric functional assays.

Acetolactate synthase (ALS) inhibitors provide postemergence control of green kyllinga (Kyllinga brevifolia Rottb.) in turfgrass and other cropping systems. A suspected resistant (R) biotype of K. brevifolia was collected from a golf course and evaluated for resistance to ALS inhibitors. In greenhouse experiments, the sulfosulfuron rates required to cause 50% shoot biomass reduction from the nontreated at 4 wk after treatment (WAT) were 10 and 792 g ai ha(-1) for the susceptible (S) and R biotypes, respectively. The rates required to cause 50% injury at 4 WAT were 189 and >3,360 g ai ha(-1), respectively. In other experiments, shoot mass of the R biotype was not reduced by imazaquin, trifloxysulfuron-sodium, pyrimisulfan, thiencarbazone + foramsulfuron + halosulfuron, florasulam + halauxifen-methyl, and bentazon compared with the nontreated, while sulfentrazone reduced biomass similarly for both R and S biotypes. Gene sequencing of the R biotype revealed a mutation at Asp-376-Glu that has previously conferred resistance to five families of ALS inhibitors. This is the first report of ALS-inhibitor resistance in K. brevifolia.

Due to complex interactions between social and ecological systems, herbicide resistance has classic features of a “wicked problem”. Herbicide-resistant (HR) Poa annua poses a risk to sustainably managing U.S. turfgrass systems, but there is scant knowledge to guide its management. Six focus groups were conducted throughout the United States to gain understanding of socio-economic barriers to adopting herbicide-resistance management practices. Professionals from major turfgrass sectors (golf courses, sports fields, lawn care, and seed/sod production) were recruited as focus-group participants. Discussions emphasized challenges of the weed management of turfgrass systems as compared to agronomic crops. This included greater time constraints for managing weeds and more limited chemical control options. Lack of understanding about the proper use of compounds with different modes of action was identified as a threat to sustainable weed management. There were significant regional differences in perceptions of the existence, geographic scope, and social and ecological causes of HR in managing Poa annua. Effective resistance management will require tailoring chemical and non-chemical practices to the specific conditions of different turfgrass sectors and regions. Some participants thought it would be helpful to have multi-year resistance management programs that are both sector- and species-specific.

BACKGROUND 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 (1) investigate the feasibility of training deep learning models using grid cells (sub-images) to detect the location of weeds on the image by identifying if the grid cells contain weeds, and (2) 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). RESULTS 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 sub-images 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 sub-images containing weeds and turfgrass. CONCLUSION 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. This article is protected by copyright. All rights reserved.

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White clover (Trifolium repens L.) is cultivated as a forage crop and planted in various landscapes for soil conservation. There are numerous reports of failed white clover stands each year. A good understanding of the seed germination biology of white clover in relation to environmental factors is essential to achieve successful stand establishment. A series of experiments were conducted to investigate the impacts of light, temperature, planting depth, drought, and salt stress on seed germination and the emergence of white clover. White clover is negatively photoblastic, and seed germination averaged 63 and 66% under light and complete dark conditions 4 weeks after planting (WAP), respectively. Temperature affected the seed germination speed and rate. At 1 WAP, seeds incubated at 15 to 25 °C demonstrated a significantly higher germination rate than the low temperatures at 5 and 10 °C; however, the germination rate did not differ among the temperature treatments at 4 WAP. The results suggest that white clover germination decreases with increasing sowing depths, and the seeds should be sown on the soil surface or shallowly buried at a depth ≤1 cm to achieve an optimal emergence. White clover seeds exhibited high sensitivity to drought and salinity stress. The osmotic potential and NaCl concentration required to inhibit 50% seed germination were −0.19 MPa and 62.4 mM, respectively. Overall, these findings provide quantifiable explanations for inconsistent establishment observed in field conditions. The results obtained in this research can be used to develop effective planting strategies and support the successful establishment of white clover stands.

Soil seedbank management via collecting clippings may be a means of combatting herbicide resistance in annual bluegrass (Poa annua L.) by minimizing recruitment from the deposition of viable seed into the soil. Our objective was to assess the germinability of annual bluegrass seed in spring to determine when collecting clippings would be most impactful. Research was conducted across 2019 and 2020 in five locations: Knoxville, TN; Starkville, MS; Griffin, GA; West Lafayette, IN; and University Park, PA. Annual bluegrass seed was harvested every 100 growing degree-days (GDD(0C); base 0 degrees C with accumulation beginning on 1 January each year from 400 to 1,100 GDD(0C). Seeds from each harvest timing were placed on moistened blotter paper in petri dishes and randomized in a growth chamber set to a 77:68 degrees F and 8:16 h light-dark cycle. Germination was assessed every 3 d until 21 d of incubation. Cumulative germination percentage after 21 d of incubation increased at research locations in northern latitudes. In Tennessee, germination was greatest from 600 to 900 GDD(0C). In Indiana, germination did not exceed 50% until 600 GDD(0C) and increased with GDD(0C) accumulation. Clippings should not be collected until at least 600 GDD(0C) in these locations. In Pennsylvania, little variation existed among GDD(0C) harvest times, indicating that clipping collection may be a valuable practice any time mature seedheads are present. Turfgrass managers should consider geographic location when selecting a time to implement clipping collections and will probably need to conduct multiple clipping collection events.

An herbicide-resistant weed control system that utilizes naturally occurring mutations to acetyl-coenzyme A carboxylase (ACCase)-inhibiting herbicides could provide herbicide selectivity and improve control of grassy weeds in turf. Knowledge regarding the presence of these mutations in grasses is needed to guide development of this type of system. This research subjected 24 species of warm-season, cool-season, and grassy weed species to rates of 0, 400, and 1200 g a.i. ha(-1) of fenoxaprop herbicide and surveyed these species for the presence of site-of-action mutations in ACCase at amino acid (aa) positions 1781, 1999, 2027, 2041, 2076, 2088, and 2096. Nine species including Agrostis capillaris L., Festuca ovina L., Festuca rubra L., Lolium multiflorum Lam., Lolium perenne L., Paspalum dilatatum Poir., Poa annua L., Zoysia japonica Steud., and Z. matrella [L.] Merr. were tolerant to fenoxaprop. Site of action point mutations conferring resistance to ACCase herbicides were found at aa position 1781 in only three of 24 species surveyed (Festuca ovina, Festuca rubra, and Poa annua). The information obtained from this study provide guidance for the development of ACCase resistant weed control systems for turfgrass.

To understand the observed injury, the objectives of this research were (a) to correlate combination of nitrogen fertilization and metsulfuron [methyl 2-(4-methoxy-6-methyl-1,3,5-triazine-2-ylcarbamoylsulfamoyl) benzoate] with excessive injury to centipedegrass [Eremochloa ophiuroides (Munro) Hack.] and (b) to determine how simultaneous high nitrogen fertilizer and the resulting increased metsulfuron rates exacerbated the observed injury. Field research was conducted at Auburn University, Clemson University, University of Florida, the University of Georgia, and H&H Sod Company in St. Cloud, FL, in 2015. Treatments included: a nontreated control, fertilizer alone (32-0-10 N-P-K and 32-0-9 N-P-K), metsulfuron (60% water-dispersible granules), metsulfuron on an inert carrier, metsulfuron on fertilizer (32-0-9 N-P-K), and atrazine (2-chloro-4-ethylamino-6-isopropylamino1,3,5-triazine) on fertilizer (29-0-10 N-P-K) applied at rates ranging from one to eight times the labeled rate. Metsulfuron on fertilizer induced more injury as the rate increased than any other treatment across all locations. The highest rates of metsulfuron on fertilizer (348.5 lb N acre(-1) plus 0.24 lb metsulfuron acre(-1)) reduced centipedegrass ground cover by 79 and 81% at 28 and 42 d after treatment, respectively. From these data, we conclude that metsulfuron applied on a granular fertilizer carrier can induce greater injury than metsulfuron on an inert granular carrier.

Bermudagrass is a major forage species throughout Georgia and the Southeast. An essential part of achieving high-yielding, top-quality forages is proper weed control. Indaziflam is a residual herbicide that controls many broadleaf and grass species by inhibiting cellulose biosynthesis. Research conducted in Tift and Colquitt counties in Georgia determined optimal PRE rates for indaziflam for bermudagrass forage production. Treatments applied at spring greenup of established 'Alicia' bermudagrass included indaziflam at 47, 77, 155, or 234 g ai ha(-1) PRE, pendimethalin at 4,480 g ha(-1) PRE, a split application of indaziflam at 47 g ha(-1) PRE followed by the same rate applied POST after the first cutting, and a nontreated control (seven treatments in all). Forages were machine harvested three times each year for each location beginning at least 47 d after treatment (DAT), with final cuttings up to 168 DAT. For all treatments, fresh- and dry-weight yields at each harvest and totals for the season did not differ from the nontreated control. Indaziflam at 155 and 234 g ha(-1) did cause minor stunting at 44 DAT, but this was transient and not observed at the second harvest. Indaziflam applied PRE has the potential to provide residual control of troublesome weeds in bermudagrass forage and hay production, with ephemeral stunting at the recommended application rates.

Southern crabgrass [Digitaria ciliaris (Retz.) Koeler] is an annual grass weed that commonly infests turfgrass, roadsides, wastelands, and cropping systems throughout the southeastern United States. Two biotypes of D. ciliaris (R1 and R2) with known resistance to cyclohexanediones (DIMs) and aryloxyphenoxypropionates (FOPs) previously collected from sod production fields in Georgia were compared with a separate susceptible biotype (S) collected from Alabama for the responses to pinoxaden and to explore the possible mechanisms of resistance. Increasing rates of pinoxaden (0.1 to 23.5 kg ha(-1)) were evaluated for control of R1, R2, and S. The resistant biotypes, R1 and R2, were resistant to pinoxaden relative to S. The S biotype was completely controlled at rates of 11.8 and 23.5 kg ha(-1), resulting in no aboveground biomass at 14 d after treatment. Pinoxaden rates at which tiller length and aboveground biomass would be reduced 50% (I-50) and 90% (I-90) for R1, R2, and S ranged from 7.2 to 13.2 kg ha(-1), 6.9 to 8.6 kg ha(-1), and 0.7 to 2.1 kg ha(-1), respectively, for tiller length, and 7.7 to 10.2 kg ha(-1), 7.2 to 7.9 kg ha(-1), and 1.6 to 2.3 kg ha(-1), respectively, for aboveground biomass. Prior selection pressure from DIM and FOP herbicides could result in the evolution of D. ciliaris cross-resistance to pinoxaden herbicides. Amplification of the carboxyl-transferase domain of the plastidic ACCase by standard PCR identified a point mutation resulting in an Ile-1781-Leu amino acid substitution only for the resistant biotype, R1. Further cloning of PCR product surrounding the 1781 region yielded two distinct ACCase gene sequences, Ile-1781 and Leu-1781. The amino acid substitution, Ile-1781-Leu in both resistant biotypes (R1 and R2), however, was revealed by next-generation sequencing of RNA using Illumina platform. A point mutation in the Ile-1781 codon leading to herbicide insensitivity in the ACCase enzyme has been previously reported in other grass species. Our research confirms that the Ile-1781-Leu substitution is present in pinoxaden-resistant D. ciliaris.

Annual sedge (Cyperus compressusL.) populations with resistance to halosulfuron were identified in turfgrass at two new locations in Georgia. Research was conducted to evaluate (1) resistance levels to two acetolactate synthase (ALS) inhibitors, (2) ALS enzyme susceptibility, (3) genetic differences associated with resistance, and (4) differential levels ofALSgene expression in these biotypes. In dose-response experiments, the biotypes were >160 times resistant to halosulfuron but only 12 times more resistant to imazaquin compared with a susceptible biotype. In vitro enzyme assays indicated that resistant (R) biotypes required 6.1-fold greater concentrations of imazaquin to reduce ALS activity 50% compared with the susceptible (S) biotype. Both R biotypes had a similar Pro-197-Ser amino acid substitution in theALSgene that confers resistance to sulfonylureas. Compared with the S biotype, R biotypes had 4.4 times higherALSgene expression than the S biotype. No differences in gene copy number were found between any biotypes for theALSgene. Overall, ALS-resistantC. compressusselected by halosulfuron use in turfgrass may be exhibiting partial susceptibility to imazaquin but complete resistance to sulfonylureas. Differential levels of susceptibility to ALS inhibitors for these biotypes are associated with the Pro-197-Ser substitution and enhanced expression of theALSgene.

POST goosegrass and other grassy weed control in bermudagrass is problematic. Fewer herbicides that can control goosegrass are available due to regulatory pressure and herbicide resistance. Alternative herbicide options that offer effective control are needed. Previous research demonstrates that topramezone controls goosegrass, crabgrass, and other weed species; however, injury to bermudagrass may be unacceptable. The objective of this research was to evaluate the safening potential of topramezone combinations with different additives on bermudagrass. Field trials were conducted at Auburn University during summer and fall from 2015 to 2018 and 2017 to 2018, respectively. Treatments included topramezone mixtures and methylated seed oil applied in combination with five different additives: triclopyr, green turf pigment, green turf paint, ammonium sulfate, and chelated iron. Bermudagrass bleaching and necrosis symptoms were visually rated. Normalized-difference vegetative index measurements and clipping yield data were also collected. Topramezone plus chelated iron, as well as topramezone plus triclopyr, reduced bleaching potential the best; however, the combination of topramezone plus triclopyr resulted in necrosis that outweighed reductions in bleaching. Masking agents such as green turf paint and green turf pigment were ineffective in reducing injury when applied with topramezone. The combination of topramezone plus ammonium sulfate should be avoided because of the high level of necrosis. Topramezone-associated bleaching symptoms were transient and lasted 7 to 14 d on average. Findings from this research suggest that chelated iron added to topramezone and methylated seed oil mixtures acted as a safener on bermudagrass.