Goosegrass is a problematic weed of golf courses, sports fields, and residential lawns that decreases playability and aesthetic quality of turf. With the recent banning of MSMA in sports fields and intensive restrictions in golf and sod production, turfgrass managers are seeking alternatives for postemergence goosegrass control and how to utilize currently labeled goosegrass control products more effectively. Studies were conducted to investigate a suspected-resistant (SR) goosegrass accession in Richmond, VA and characterize the resistance mechanism if present. The SR accession showed a hypersensitive response to oxadiazon treatment and reached maximum electrolyte leakage quicker than the susceptible (S) accession, but had significantly lower electrolyte leakage indicating less tissue damage and suggesting there is a physiological resistance mechanism within the SR accession. In absorption and translocation studies, percent oxadiazon absorption and translocation was not significantly affected by goosegrass biotype. Roots of both the S and resistant (R) biotypes contained over 95% of total detected oxadiazon, while the plant tissue above the treated foliage only contained small quantities. These results suggest that absorption or translocation is not the mechanism conferring oxadiazon resistance in the goosegrass biotype from Richmond, VA. Greenhouse and field trials were conducted to determine the lowest rate at which topramezone, with or without the addition of triclopyr, controls goosegrass while maintaining commercially-acceptable bermudagrass quality. In field trials, topramezone rate did not significantly affect goosegrass cover at 56 and 70 days after initial treatment (DAIT). All treatments reduced goosegrass cover below 3 and 7% with and without the addition of triclopyr, respectively at 70 DAIT. A significant herbicide effect on bermudagrass cultivar showed higher injury from topramezone within three weeks of application, but injury persisted longer from treatments containing triclopyr. Bermudagrass cultivars completely recovered by 4 weeks after treatment (WAT) from all treatments. Greenhouse trials were conducted to determine if goosegrass growth stage affects efficacy of nine postemergent herbicides or programs documented to have goosegrass activity. As goosegrass growth stage increased from four- to five-leaf to greater than eight-tiller stage, goosegrass control and biomass reduction decreased among all of the herbicides except topramezone and MSMA plus metribuzin at 4 and 8 WAT. These data suggest that one application of sulfentrazone is only effective for seedling stage (pre-tiller) goosegrass control; foramsulfuron, topramezone, and metribuzin suppress all growth stages of goosegrass; and diclofop, sulfentrazone plus metribuzin, fenoxaprop, and metamifop control up to three-tiller stage goosegrass. / Ph. D.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / In general, in Rio Grande do Sul, the control of weeds in crops genetically modified soybean and resistant to the herbicide Roundup Ready® (RR® soybeans) in no-tillage is performed with glyphosate. However, weeds escapes to the treatment can occur as is the case of goosegrass which is considered by soybean growers plant is difficult to control by glyphosate. In this context, this study aims to evaluate the best combination of herbicide to control goosegrass, combining herbicides applied pre-seeding and post-emergence RR® soybean in two stages of development of this weed (Chapter I). Further evaluate the response of a biotype of goosegrass coming from the municipality of Tupanciretã (RS) to the glyphosate herbicide (Chapter II). The experiment I (Chapter I) was conducted in 2012/2013 harvest in Argisoil Yellow-Red hapludox typical belonging to unit Tupanciretã mapping. The results of the experiment I showed that the paraquat + diuron (200 g i.a. ha-1) and ammonium glufosinate (400 g i.a. ha-1) herbicides are efficient alternatives to glyphosate aiming to desiccation of goosegrass in operation management in RR® soybean pre-seeding. Regardless of desiccant herbicide, the control of goosegrass is higher when the plants receive the application of glyphosate (712 g e.a. ha-1) in vegetative stage three to four tillers, and clethodim (96 g i.a. ha-1) and imazethapyr (106 g i.a. ha-1) herbicides did not satisfactorily control goosegrass in vegetative stage from three tillers in RR® soybeans. Grain yield is higher with the application of glyphosate compared to the clethodim and imazethapyr, when the target is goosegrass with plants in stage three to six tillers. The experiment II (Chapter II) was conducted in the greenhouse of the Department (UFSM), in plastic pots (5 L) containing three seedlings of goosegrass (two to three tillers) with suspected resistance to glyphosate. The treatments consisted of five concentrations of the product (0, 25, 50, 100, 200 and 400% of the dose registry of glyphosate, which is 712 g e.a. ha-1). The results for the control evaluations and production of dry biomass showed that biotype of goosegrass is susceptible to glyphosate, once at the lowest dose registration (712 g e.a. ha-1) tested, the control was greater than 98%. / Em geral, no Rio Grande do Sul, o controle de plantas daninhas em lavouras de soja geneticamente modificada e resistente ao herbicida Roundup Ready® (soja RR®) no sistema plantio direto, é realizado com o glifosato. Entretanto, plantas daninhas escapes ao tratamento podem ocorrer, como é o caso de Eleusine indica (capim pé-de-galinha) que é considerada pelos sojicultores planta de difícil controle pelo glifosato. Neste contexto, este trabalho tem por objetivos avaliar a melhor associação de herbicidas no controle de capim pé-de-galinha, combinando herbicidas aplicados em pré-semeadura e pós-emergência de soja RR® em dois estádios de desenvolvimento desta planta daninha (Capítulo I). Avaliar ainda a resposta de um biótipo de capim pé-de-galinha oriundo do município de Tupanciretã (RS) ao herbicida glifosato (Capítulo II). O experimento I (Capítulo I) foi conduzido na safra 2012/2013 em Argissolo Vermelho-Amarelo distrófico típico pertencente à unidade de mapeamento Tupanciretã. Os resultados do experimento I mostraram que os herbicidas paraquate + diurom (200 g i.a. ha-1) e glufosinato de amônio (400 g i.a. ha-1) são alternativas eficientes ao glifosato visando à dessecação do capim pé-de-galinha na operação de manejo em pré-semeadura da soja RR®. Independente do herbicida dessecante aplicado, o controle de capim pé-de-galinha é superior quando as plantas recebem a aplicação de glifosato (712 g e.a. ha-1) em estádio vegetativo de três a quatro afilhos; e os herbicidas cletodim (96 g i.a. ha-1) e imazetapir (106 g i.a. ha-1) não controlam satisfatoriamente o capim pé-de-galinha em estádio vegetativo a partir de três afilhos em soja RR®. A produtividade de grãos é superior com a aplicação do glifosato em comparação às de cletodim e imazetapir, quando o alvo for capim pé-de-galinha com as plantas no estádio de três a seis afilhos. O experimento II (Capítulo II) foi conduzido em casa de vegetação do Departamento de Fitotecnia (UFSM), em vasos plásticos (5 L) contendo três mudas de plantas de capim pé-de-galinha (dois a três afilhos) com suspeita de resistência a glifosato. Os tratamentos consistiram da aplicação de cinco concentrações do produto (0, 25, 50, 100, 200 e 400% da dose de registro de glifosato, que é de 712 g e.a. ha-1). Os resultados para as avaliações de controle e produção de biomassa seca mostraram que este biótipo de capim pé-de-galinha é suscetível ao glifosato, uma vez que na menor dose de registro (712 g e.a. ha-1) testada, o controle foi superior a 98%.

Annual grassy weeds are problematic in intensively managed turfgrass systems due to a lack of selective and affordable control options. Four projects were conducted from 2020-2023 to evaluate novel techniques for Annual bluegrass (Poa annua L.), goosegrass (Eleusine indica L. Gaertn.), and smooth crabgrass (Digitaria ischaemum Schreb.) control on golf course putting greens or putting green surrounds. Hybrid bermudagrass Cynodon transvaalensis Burtt. Davy. x dactylon L. Pers.) tolerated cumyluron regardless of application timing, endothall when applied during full dormancy, and methiozolin when applied during mid-transition. Methiozolin half-life in the upper 2-cm of 12 hybrid bermudagrass putting greens was approximately 14 days and was prolonged in similar studies by seven orders of magnitude when herbicide was applied to bare ground compared to adjacent Kentucky bluegrass (Poa pratensis L.) turf. In a study conducted in Alabama, California, Florida, and Virginia, methiozolin at labeled use rates applied biweekly controlled smooth crabgrass >80% in creeping bentgrass (Agrostis stolonifera L.) and hybrid bermudagrass turf. Although similar programs also controlled goosegrass, acceptable control required more applications than are allowed on the product label. Targeted application devices (TAD), such as spot sprayers and dabbers that are used for individual plant treatment of escaped weeds, were tested for uniformity of fluid delivery. Fluid output of dabbing devices was highly variable and dependent on reservoir fill level, reservoir air seal, human user, and contact time, but largely independent of peak force exerted during the dabbing event. These studies suggest that new products are available to improve annual grassy weed control in turfgrass systems, but proper application timing and device calibration is important to achieve best results. / Doctor of Philosophy / Annual grasses are difficult to control in "high-end" golf turf because few herbicides can be safely used near greens and key weeds have become resistant to the most common products. Several new products were tested for safety on hybrid bermudagrass greens. Methiozolin (PoaCure) was safe for use after post-dormancy greenup, endothall was safe when used while turf was still dormant, and cumyluron was safe regardless of application timing. The duration of preemergence weed control with methiozolin is reduced as temperatures increase and in turfgrass compared to bare ground systems. Half of the methiozolin product will dissipate in 14 days or less when applied to hybrid bermudagrass putting greens or Kentucky bluegrass lawns in spring. Methiozolin controlled smooth crabgrass for the entire season in several Southeastern states, but goosegrass control was slightly below acceptable levels when the product was used within annual dose restrictions. Applicators, such as dabbers and spot sprayers, that are used to treat individual plants improve turf safety and reduce chemical cost, but these devices had not been previously tested for uniformity of fluid output. Studies found that these devices can vary in output by several orders of magnitude depending on the type of devices used, the person using the device, and duration of contact with the turf as the user presses a dabbing device over a weed. Within-device errors were equally problematic and governed by the amount of downward pressure exerted by the fluid contained in the device reservoir. For every 10% of fluid capacity added, fluid dispense rate increases approximately 33%. When the air seal of the fluid fill cap is broken, fluid output approximately doubles compared to when this seal is maintained because loss of vacuum increases downward force of the fluid column. These studies suggest that new products are available to improve annual grassy weed control in ornamental turf, but proper application timing and device calibration is important to achieve best results.

Goosegrass [Eleusine indica (L.) Gaertn.] and smooth crabgrass [Digitaria ischaemum (Schreb.) Schreb. ex Muhl.] are problematic weeds in bermudagrass and creeping bentgrass turf. Increased incidences of herbicide resistant weed populations and severe use restrictions on formerly available herbicides have increased need for selective, postemergence control options for these weeds in creeping bentgrass and bermudagrass turf. This weed management exigency has led turf managers to utilize less effective, more expensive, and more injurious options to manage goosegrass and smooth crabgrass. Although potentially injurious, topramezone can control these weeds, especially goosegrass, at low doses. Low-dose topramezone may also improve bermudagrass and creeping bentgrass response. An initial investigation of three 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibiting herbicides in different turf types showed that Kentucky bluegrass, perennial ryegrass, and tall fescue were highly tolerant to topramezone, while creeping bentgrass and bermudagrass could tolerate topramezone doses that may control grassy weeds. Further investigation suggested that frequent, low-dose topramezone applications or metribuzin admixtures could enhance weed control and may conserve turfgrass quality. A novel mixture of topramezone at 3.7 g ae ha-1 and metribuzin at 210 g ai ha-1 controlled goosegrass effectively and reduced bermudagrass foliar bleaching associated with topramezone 10-fold compared to higher doses of topramezone alone in 19 field and 2 greenhouse trials. In an attempt to further enhance bermudagrass tolerance to topramezone, post-treatment irrigation was applied at various timings. When bermudagrass turf was irrigated with 0.25-cm water at 15 or 30 minutes after herbicide treatment, bermudagrass injury was reduced to acceptable levels when following low-dose topramezone plus metribuzin but not when following high-dose topramezone alone. Goosegrass control was reduced significantly by post-treatment irrigation in all cases, while irrigation reduced goosegrass control by low-dose topramezone plus metribuzin to below-commercially-acceptable levels. Novel, low-dose, frequent application programs containing topramezone or siduron were developed for season-long crabgrass or goosegrass control on creeping bentgrass greens. Greens-height creeping bentgrass quality was preserved following five biweekly treatments of siduron at rates between 3,400 to 13,500 g ai ha-1 and topramezone at 3.1 g ha-1. Siduron programs controlled smooth crabgrass and suppressed goosegrass while topramezone programs controlled goosegrass and suppressed smooth crabgrass. In laboratory and controlled-environment experiments, goosegrass absorbed three times more 14C than bermudagrass within 48 hours of 14C-topramezone treatment. Bermudagrass also metabolized topramezone twice as fast as goosegrass. Metribuzin admixture reduced absorption by 25% in both species. When herbicides were placed exclusively on soil, foliage, or soil plus foliage, topramezone controlled goosegrass only when applied to foliage and phytotoxicity of both bermudagrass and goosegrass was greater from topramezone than from metribuzin. Metribuzin was shown to reduce 21-d cumulative clipping weight and tiller production of both species while topramezone caused foliar discoloration to newly emerging leaves and shoots with only marginal clipping weight reduction. These data suggest that selectivity between bermudagrass and goosegrass is largely due to differential absorption and metabolism that reduces bermudagrass exposure to topramezone. Post-treatment irrigation likely reduces topramezone rate load with a concomitant effect on plant phytotoxicity of both species. Metribuzin admixture decreases white discoloration of bermudagrass by decreased topramezone absorption rate and eliminating new foliar growth that is more susceptible to discoloration by topramezone. / Doctor of Philosophy / Goosegrass and smooth crabgrass are problematic weeds in bermudagrass and creeping bentgrass turf. Increased incidences of herbicide resistant weed populations and severe use restrictions on formerly available herbicides have increased need for selective, postemergence control options for these weeds in creeping bentgrass and bermudagrass turf. Although potentially injurious, topramezone (Pylex™) can control these weeds, especially goosegrass, at low doses. Low-dose Pylex™ may also improve bermudagrass and creeping bentgrass response. An initial investigation evaluating tembotrione (Laudis®), Pylex™, and mesotrione (Tenacity®) in different turfgrass species showed that Kentucky bluegrass, perennial ryegrass, and tall fescue were highly tolerant to Pylex™ at rates ranging from 0.75 to 2.25 fl. oz./A, while creeping bentgrass and bermudagrass were low to moderately tolerant to Pylex™. Further investigation suggested that frequent, low-dose (less than 0.25 fl. oz./A) Pylex™ applications or metribuzin (Sencor®) admixtures could enhance weed control and may conserve turfgrass quality. A novel mixture of Pylex™ at 0.15 fl. oz./A and Sencor® at 4 oz. wt./A controlled goosegrass effectively and reduced bermudagrass injury to near acceptable levels and significantly less than Pylex™ applied alone at 0.25 fl. oz/A. In an attempt to further enhance bermudagrass tolerance to Pylex™, post-treatment irrigation was applied at different timings. When bermudagrass turf was irrigated at 15 or 30 minutes after herbicide treatment, bermudagrass injury was reduced to acceptable levels when following Pylex™ at 0.25 fl. oz./A plus Sencor® at 4 oz but not when following Pylex™ applied alone at 0.5 fl. oz./A. Goosegrass control was reduced significantly by post-treatment irrigation in all cases, while irrigation reduced goosegrass control by low-dose Pylex™ plus Sencor® to below-commercially-acceptable levels. Novel, low-dose, frequent application programs containing Pylex™ or siduron (Tupersan®) were developed for season-long crabgrass or goosegrass control in creeping bentgrass greens. Greens-height creeping bentgrass quality was preserved following five biweekly treatments of Tupersan® at rates between 6 and 24 lb./A and Pylex™ at 0.125 fl. oz./A. Tupersan® programs controlled smooth crabgrass and suppressed goosegrass while Pylex™ programs controlled goosegrass and suppressed smooth crabgrass. The data from these studies indicate that utilizing low-dose Pylex™ in combination with Sencor® can impart acceptable bermudagrass safety while also controlling goosegrass effectively. For creeping bentgrass greens, the low-dose, frequent application of Tupersan® is the safest legal option for golf course superintendents to control smooth crabgrass effectively, while having some ability to suppress goosegrass.