James D. McCurdy

Effects of Mesotrione on Perennial Ryegrass (Lolium perenne L.) Carotenoid Concentrations under Varying Environmental Conditions

Mesotrione is a carotenoid biosynthesis inhibiting herbicide, which is being evaluated for use in turfgrass. Carotenoids are important light harvesting and photoprotecting pigments that dissipate and quench excess light energy. The effects of mesotrione on carotenoid concentrations in turf and weed species, such as perennial ryegrass (Lolium perenne L.), are poorly understood. Mesotrione injury to perennial ryegrass has been reported, and symptomology may differ due to postapplication environmental factors such as irradiance and temperature. Research was conducted to investigate the effects of mesotrione on perennial ryegrass under varying irradiance (600, 1100, or 1600 micromol/m (2)/s) at three different temperatures (18, 26, and 34 degrees C). Postapplication irradiance and temperature levels did not affect visual injury symptoms in perennial ryegrass. Bleaching of treated plants was highest 7 days after treatment (DAT; 8%) and recovered to nontreated levels by 21 DAT. Mesotrione applications did not decrease perennial ryegrass foliar biomass accumulations. Carotenoid concentrations of nontreated plants were similar to those reported in creeping bentgrass and many green leafy vegetable crops. However, chlorophyll a and b, beta-carotene, lutein, and violaxanthin concentrations decreased due to mesotrione applications, while phytoene and zeaxanthin, a photoprotecting carotenoid, increased. The photochemical efficiency (F v/ F m) of treated plants was lower than nontreated plants at 3 and 7 DAT; however, treated plants recovered to nontreated levels 21 DAT. Results indicate that postapplication irradiance and temperature levels may not affect mesotrione efficacy in perennial ryegrass. Preferential accumulation of zeaxanthin following mesotrione applications may be a stress-related response, which may reduce light harvesting complex size and directly quench excess light energy.

Mesotrione plus Prodiamine for Smooth Crabgrass (Digitaria ischaemum) Control in Established Bermudagrass Turf

Crabgrass species are problematic weeds in bermudagrass turf that can be controlled by PRE herbicide applications. Because of the difficulty in predicting crabgrass emergence and other prevailing management constraints, PRE herbicide applications are not always properly timed. Mesotrione controls crabgrass both PRE and POST; however, relatively short soil-residual activity limits its use as a PRE herbicide. Two experiments were conducted to evaluate smooth crabgrass control with PRE applications of mesotrione plus prodiamine. The first experiment evaluated the influence of application timing on the efficacy of mesotrione-plus-prodiamine combinations. Applications were made every 2 wk from March 15 to May 24. Mesotrione plus prodiamine controlled smooth crabgrass more consistently across all application dates than either mesotrione or prodiamine applied alone. The second experiment evaluated mesotrione along with current PRE and early POST herbicide treatments used for control of crabgrass. When applied at one to two tillers growth stage, mesotrione plus prodiamine controlled smooth crabgrass 99% when rated on August 31. Bermudagrass injury from mesotrione ranged from 9 to 44%, but did not result in any reduction in turf plant density. Mesotrione plus prodiamine is an effective tank mixture when prodiamine alone is not applied in a timely fashion; however, variable and excessive turf injury is a potential impediment to mesotrione use on bermudagrass turf. Nomenclature: Mesotrione, prodiamine, smooth crabgrass, Digitaria ischaemum (Schreb) Schreb. ex Muhl Schreb. DIGIS, bermudagrass, Cynodon dactylon L. CYNDA

Differential Response of Four Trifolium Species to Common Broadleaf Herbicides: Implications for Mixed Grass-Legume Swards

Abstract Clovers are commonly included as utility plants within mixed grass swards, such as pastures and roadside right-of-ways. As such, they provide supplemental nitrogen, quality forage, and insect habitat. Yet weed control within mixed swards is often hampered by the lack of selective herbicides that are tolerated by clovers. Differential tolerance of legumes to common row-crop and pasture herbicides has previously been reported, yet little information is available that is specific to clover species. Herbicide injury of clover is often inconsistent, hypothetically due to differential species tolerance. Field and greenhouse experiments were conducted with the objective of testing differential tolerance amongst four clover species. Our experiments suggest varying tolerances amongst clover species and common broadleaf herbicides. Only imazaquin control differed due to species; however, treatment by clover interactions were further demonstrated due to variable reductions in clover height. Imazaquin, 2,4-D, 2,4-DB, and triclopyr height reductions differed due to clover species. Differential clover response to herbicide treatment should be an important consideration when managing mixed grass–clover swards and should be accounted for in future research. On a more practical level, our experiments demonstrate a range of herbicides that effectively control clover species, including atrazine, dicamba, clopyralid, 2,4-D, triclopyr, metsulfuron, and trifloxysulfuron. However, results suggest that 2,4-DB, imazethapyr, and bentazon are candidate herbicides for weed control in scenarios in which clover is a desirable crop. Nomenclature: 2,4-D; 2,4-DB; atrazine; bentazon; clopyralid; dicamba; imazaquin; imazethapyr; MCPA; metsulfuron; triclopyr; trifloxysulfuron; ball clover, Trifolium nigrescens Viv.; crimson clover, Trifolium incarnatum L. TRFIN; small hop clover, Trifolium dubium Sibth. TRFDU; white clover, Trifolium repens L. TRFRE. Resumen Los tréboles son comúnmente incluidos como plantas útiles dentro de zonas con coberturas mixtas de zacates, tales como pastizales y bordes de caminos. De tal forma, que brinden nitrógeno suplementario, calidad de forraje y hábitat para insectos. Sin embargo, dentro de esas zonas de cobertura mixta, el control de malezas se ve frecuentemente obstaculizado por la ausencia de herbicidas selectivos que sean tolerados por los tréboles. La tolerancia diferencial de leguminosas a herbicidas para cultivos extensivos y pasturas ha sido reportada anteriormente, aunque hay poca información disponible que sea específica para especies de trébol. El daño causado por los herbicidas es usualmente inconsistente, hipotéticamente debido a las diferencias en tolerancia entre especies. Se realizaron experimentos de campo y de invernadero con el objetivo de evaluar la tolerancia diferencial entre cuatro especies de trébol. Nuestros experimentos sugieren que existe variación entre especies de trébol en la tolerancia a herbicidas de hoja ancha comunes. Solamente el control con imazaquin difirió debido a las especies, aunque interacciones entre tratamiento y especie de trébol fueron demostradas debido a reducciones variables en la altura del trébol. Las reducciones en altura, producto del efecto de imazaquin, 2,4-D, 2,4-DB y triclopyr, variaron según la especie de trébol. La respuesta diferencial de los tréboles a los tratamientos con herbicidas debería ser una consideración importante cuando se manejan áreas con coberturas mixtas de zacates y tréboles y debería ser incluida en investigaciones futuras. A un nivel más práctico, nuestros experimentos muestran un rango de herbicidas que efectivamente controlan especies de trébol, incluyendo atrazine, dicamba, clopyralid, 2,4-D, triclopyr, metsulfuron, and trifloxysulfuron. Sin embargo, los resultados sugieren que 2,4-DB, imazethapyr y bentazon son herbicidas candidatos para el control de malezas en escenarios en los cuales el trébol es un cultivo deseable.

Mesotrione control and pigment concentration of large crabgrass (Digitaria sanguinalis) under varying environmental conditions

BACKGROUND Mesotrione is a carotenoid biosynthesis-inhibiting herbicide currently labeled for crabgrass (Digitaria spp.) control. Mesotrione control of large crabgrass has been reported to vary with temperature and relative humidity; however, the effect of irradiance on mesotrione efficacy has not previously been reported. Likewise, little is known about pigment concentrations of Digitaria spp. The present research investigated the effects of mesotrione on large crabgrass, Digitaria sanguinalis (L.) Scop., control and pigment concentrations under varying irradiance at three temperatures. RESULTS Mesotrione (0.28 kg ha(-1)) control of large crabgrass did not differ between temperature levels (18, 26 and 32 degrees C). Control was similar at tested irradiance levels (600, 1100 and 1600 micromol m(-2) s(-1)). Mesotrione reduced large crabgrass chlorophyll a, chlorophyll b and total carotenoid concentrations, as well as chlorophyll a to b ratios. Treated plant bleaching was highest 7 days after treatment (DAT) but decreased by 21 DAT. Treated plants were less than 10% necrotic 3 and 7 DAT but nearly 35% necrotic 21 DAT. Treated large crabgrass bleaching was highest and photochemical efficiency was lowest 7 DAT. These results indicate that some plant recovery occurs prior to 21 DAT. CONCLUSION Although mesotrione efficacy has previously been reported to vary according to environmental factors, mesotrione control of large crabgrass did not vary with measured temperature and irradiance levels in this study. On account of crabgrass convalescence, secondary applications of mesotrione may control large crabgrass more effectively when applied prior to 21 DAT.

Tolerance of Six Zoysiagrass Cultivars to Aminocyclopyrachlor

Abstract Aminocyclopyrachlor (AMCP) is labeled for use on zoysiagrass, but some injury has been observed. Differential zoysiagrass cultivar response to herbicide treatment has been previously reported. This greenhouse study evaluated the response of ‘BK-7’, ‘Cavalier’, ‘Emerald’, ‘Empire’, ‘Meyer’, and ‘Zorro’ zoysiagrass to 0, 0.005, 0.02, 0.11, 0.52, and 2.4, 11 kg ai ha−1, AMCP. Visual estimation of percent necrosis and normalized difference vegetative index (NDVI) analysis were conducted. Based on rating dates and data types three tolerance groups were established: Cavalier, Meyer, and Zorro are the most tolerant; Emerald and Empire are intermediate; and BK-7 is the least tolerant to AMCP. All zoysiagrass cultivars had sufficient tolerance at the labeled rate. Visual and NDVI analyses were highly correlated; however, NDVI data were subject to greater standard error and pseudo R2 values. Nomenclature: Aminocyclopyrachlor, DPX-MAT28; zoysiagrass, Zoysia japonica Steud. ‘Empire’, ‘Meyer’; Z. matrella (L.) Merr. ‘Cavalier’, ‘Zorro’; Z. japonica Steud. × Z. pacifica Goudsw. ‘Emerald’, ‘BK-7’.

Yellow nutsedge (Cyperus esculentus) and large crabgrass (Digitaria sanguinalis) response to soil- and foliar-applied mesotrione.

Abstract Mesotrione, a carotenoid biosynthesis inhibitor, is being evaluated for use in turfgrass systems. It was hypothesized that root absorption of soil-applied mesotrione is necessary for effective weed control. Greenhouse studies were conducted to compare the effects of foliar-, soil-, and soil-plus-foliar–applied mesotrione at 0.14 and 0.28 kg ai/ha on yellow nutsedge and large crabgrass. In general, greatest control of yellow nutsedge and large crabgrass was by treatments that included soil application. In addition, mesotrione applied at 0.28 kg/ha generally controlled both yellow nutsedge and large crabgrass more effectively than mesotrione applied at 0.14 kg/ha. Soil- and soil-plus-foliar–applied mesotrione at 0.28 kg/ha controlled yellow nutsedge more than foliar-applied mesotrione 56 d after treatment. Soil-plus-foliar–applied mesotrione at 0.28 kg/ha controlled large crabgrass more than any other treatment 28 d after treatment. Soil- and soil-plus-foliar–applied mesotrione at both rates reduced large crabgrass foliar dry weight more effectively than did foliar-applied mesotrione. Results indicate that root absorption of mesotrione from soil is beneficial for the effective control of both yellow nutsedge and large crabgrass. For this reason, methods such as granular or high-volume applications, which enhance delivery of mesotrione to soil, would be potentially beneficial for turfgrass weed control. Nomenclature: Mesotrione; large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA; yellow nutsedge, Cyperus esculentus L. CYPES

Preemergence Herbicide Effects on Hybrid Bermudagrass Root Architecture and Establishment

Determine the effects of commonly used PRE herbicides on hybrid bermudagrass root architecture and establishment. Introduction Hybrid bermudagrass (Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy) is commonly produced as sod in the southern US and other warm-season climates around the world. Preemergence herbicides are sometimes used to control annual weeds. However, these herbicides may negatively affect hybrid bermudagrass establishment from sprigs and/or sod. Preemergence Herbicide Effects on Hybrid Bermudagrass Root Architecture and Establishment Erick G. Begitschke, James D. McCurdy, Te-Ming (Paul) Tseng, T. Casey Barickman, Barry R. Stewart, Christian M. Baldwin, Michael P. Richard, and Maria Tomaso-Peterson Mississippi State University

Annual Bluegrass (Poa annua) Control with Methiozolin and Nutrient Tank-Mixtures

Methiozolin is a selective herbicide that has been reported to control annual bluegrass in creeping bentgrass putting greens. Golf course managers frequently tank-mix fertilizers with herbicides to reduce time and labor, but no information is available regarding such mixtures with methiozolin. Research was conducted to evaluate methiozolin for annual bluegrass control and creeping bentgrass safety when tank-mixed with ammonium sulfate or iron sulfate. Mixtures with ammonium sulfate did not influence annual bluegrass control while they did reduce creeping bentgrass injury in some instances. Mixtures with iron sulfate varied by experimental run but annual bluegrass control was either similar or increased while creeping bentgrass injury did not vary. Paclobutrazol was included as an alternative agrochemical comparison for annual bluegrass management; its application resulted in similar control and injury with and without iron sulfate addition, and injury and control were similar to methiozolin at appropriate rates. While some differences were observed, overall annual bluegrass and creeping bentgrass response to methiozolin was not affected by tank-mix nutrient partner relative to methiozolin applied alone. Nomenclature: Methiozolin, MRC-01, 5-(2, 6-difluoro-benzyloxymethyl)-5-methyl-3-(3-methylthiophen-2-yl)-4, 5-dihydro-isoxazole; paclobutrazol, (2RS, 3RS)-1-(4-chlorophenyl)-4, 4-dimethyl-2-(1, 2, 4-triazol-1-yl)pentan-3-ol; annual bluegrass, Poa annua L.; creeping bentgrass, Agrostis stolonifera L.

Tolerance of Three Clovers (Trifolium spp.) to Common Herbicides

Clover inclusion may increase the sustainability of certain low-maintenance turfgrasses. However, selective weed control within mixed turfgrass–clover swards proves problematic because of clover susceptibility to herbicides. Research was conducted to identify common turf herbicides that are tolerated by three Trifolium species, including white clover, ball clover, and small hop clover, within low-maintenance turfgrass. Leaf and flower density, as well as plant height, were measured 4 wk after treatment as indicators of clover response to 14 herbicides. The three Trifolium spp. were moderately tolerant of bentazon (< 35% decrease in leaf density, height, or flowering). Simazine was well tolerated by white clover (< 5% decrease in all response variables), yet moderate injury to ball clover and small hop clover was observed (> 32% decrease in leaf density and > 27% decrease in flower density). Pronamide was well tolerated by white and ball clovers, with no effect on measured response variables; however, pronamide decreased small hop clover height and flower density (38 and 42%, respectively). Imazethapyr and imazamox were moderately well tolerated by white clover and small hop clover (< 39% decrease by all response variables), yet ball clover may be more susceptible to these herbicides than was anticipated based on previously reported tolerance. The herbicides 2,4-DB, halosulfuron, and metribuzin were well tolerated by white clover, with no effect on measured response variables; however, results suggest ball and small hop clovers were less tolerant. Clopyralid, 2,4-D, glyphosate, imazaquin, metsulfuron-methyl, and nicosulfuron resulted in varying degrees of injury across clover species and response variables, but, in general, these herbicides may not be viable options when attempting to maintain any of the three clover species tested. Further research is needed to quantify long-term effects of herbicide application on sward composition and clover succession. Nomenclature: 2,4-D; 2,4-DB; bentazon; clopyralid; glyphosate; halosulfuron; imazaquin; imazethapyr; imazamox; metribuzin; nicosulfuron; pronamide; simazine; metsulfuron-methyl; ball clover, Trifolium nigrescens Viv., small hop clover, Trifolium dubium Sibth. TRFDU, white clover, Trifolium repens L. TRFRE. La inclusión de Trifolium podría incrementar la sostenibilidad de varios céspedes de bajo mantenimiento. Sin embargo, el control selectivo de malezas en mezclas de céspedes con Trifolium es problemático debido a la susceptibilidad de Trifolium a muchos herbicidas. Se realizó una investigación para identificar herbicidas comunes para céspedes que son tolerados por tres especies de Trifolium, incluyendo Trifolium repens, Trifolium nigrescens, y Trifolium dubium, en céspedes de bajo mantenimiento. La densidad de hojas y flores, al igual que la altura de planta, fueron medidas 4 semanas después del tratamiento, como indicadores de la respuesta de Trifolium a 14 herbicidas. Los tres Trifolium spp. fueron moderadamente tolerantes a bentazon (< 35% de disminución en densidad de hojas, altura, o floración). T. repens también toleró simazine (< 5% disminución en todas las variables de respuesta), aunque se observó un daño moderado en T. nigrescens y T. dubium (> 32% disminución en densidad de hojas y > 27% disminución en densidad de flores). Pronamide fue tolerado por T. repens y T. nigrescens, sin ningún efecto en las variables de respuesta medidas. Sin embargo, pronamide disminuyó la altura y densidad de flores de T. dubium (38 y 42%, respectivamente). Imazethapyr e imazamox fueron moderadamente tolerados por T. repens y T. dubium (< 39% disminución de todas las variables de respuesta), aunque T. nigrescens podría ser más susceptible a estos herbicidas que lo que se anticipó con base en reportes previos de tolerancia. Los herbicidas 2,4-DB, halosulfuron, y metribuzin fueron bien tolerados por T. repens, sin efectos en las variables de respuesta medidas. Sin embargo, los resultados sugieren que T. nigrescens y T. dubium fueron menos tolerantes. Clopyralid, 2,4-D, glyphosate, imazaquin, metsulfuron-methyl, y nicosulfuron resultaron en varios grados de daño entre las especies de Trifolium y las variables de respuesta, pero en general, estos herbicidas no serían opciones viables al tratar de mantener alguna de las especies de Trifolium evaluadas. Investigaciones adicionales son necesarias para cuantificar los efectos a largo plazo de la aplicación de herbicidas en la composición del césped y la sucesión de especies de Trifolium.