J. Scott McElroy

A Trp574 to Leu Amino Acid Substitution in the ALS Gene of Annual Bluegrass (Poa annua) Is Associated with Resistance to ALS-Inhibiting Herbicides

Abstract Annual bluegrass is commonly controlled by acetolactate synthase (ALS)-inhibiting herbicides in managed turfgrass. An annual bluegrass population with suspected resistance to ALS-inhibiting herbicides was collected from Grand National Golf Course in Opelika, AL (GN population). Subsequent testing confirmed resistance of the GN population to foramsulfuron, trifloxysulfuron, bispyribac-sodium (bispyribac), and imazaquin when compared to a susceptible population collected locally at Auburn University (AU population). Sequencing of the ALS gene revealed a point mutation resulting in an amino acid substitution at Trp574. Cloning of the ALS gene surrounding the Trp574 region yielded two distinct ALS gene sequences: one producing Trp574 and one producing Leu574. Trp574 to Leu has been previously correlated with resistance to ALS-inhibiting herbicides. Both AU and GN gene sequences contained other similar silent and missense mutations. This research confirms resistance of annual bluegrass to ALS-inhibiting herbicides with Trp574 to Leu amino acid substitution being the most likely mode of resistance based on past literature. Nomenclature: Bispyribac; foramsulfuron; imazaquin; trifloxysulfuron; annual bluegrass, Poa annua L.

Annual bluegrass (Poa annua) populations exhibit variation in germination response to temperature, photoperiod, and fenarimol

Abstract Laboratory studies were conducted to evaluate variation in germination response of eight annual bluegrass ecotypes (‘Augusta 4’, ‘Augusta 8’, ‘Augusta 14’, ‘Augusta 17’, ‘Auburn’, ‘Birmingham’, ‘Columbia’, and ‘Purchased’) to photoperiod, temperature, and fenarimol, a fungicide–herbicide used for preemergence annual bluegrass. Seed collected from greenhouse-grown plants and stored for > 2 mo were evaluated under 18 environments (three day and night temperatures by six day and night durations). There was a significant ecotype by environment interaction affecting annual bluegrass germination. High temperature markedly restricted germination, with only the Birmingham ecotype exceeding 20% germination at day and night temperatures of 39 and 29 C, respectively. Maximum germination of all ecotypes was observed at a day and night temperature of 19 and 10 C, respectively. Maximum germination for a specific photoperiod was not consistent across ecotypes; however, all ecotypes germinated to some degree in complete darkness, which indicates that maintaining a dense turf canopy to eliminate annual bluegrass germination may not be completely effective. Ecotypes did not differ with respect to root length response to fenarimol but did vary with respect to shoot length response. Purchased and Columbia shoot growth were the most tolerant to increasing fenarimol concentrations. This information will be used to develop improved management strategies for annual bluegrass. Nomenclature: Fenarimol, α-(2-chlorophenyl)-α-(4-chlorophenyl)-5-pyrimidine-methanol; annual bluegrass, Poa annua var. annua (L.) Timm. and Poa annua var. reptans (Hauskn.) Timm. POANN.

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.

A Guide to Establishing Seeded Bermudagrass in the Transition Zone

Aaron J. Patton, Assistant Professor, Mike D. Richardson, Professor, and Doug E. Karcher, Associate Professor, Department of Horticulture, University of Arkansas, Fayetteville 72701; John W. Boyd, Professor, Crop, Soil & Environmental Science, University of Arkansas Cooperative Extension Service, Little Rock 72203; Zachary J. Reicher, Professor, Department of Agronomy, Purdue University, West Lafayette, IN 47907; Jack D. Fry, Professor, Department of Horticulture, Forestry, and Recreation Resources, Kansas State University, Manhattan, KS 66506; J. Scott McElroy, Assistant Professor, Department of Agronomy and Soils, Auburn University, Auburn, AL 36849; and Gregg C. Munshaw, Assistant Professor, Mississippi State University, Department of Plant and Soil Sciences, Mississippi State 39762

Control of Silvery-Thread Moss (Bryum argenteum Hedw.) in Creeping Bentgrass (Agrostis palustris Huds.) Putting Greens1

Field experiments were conducted to evaluate chemicals for silvery-thread moss control and bentgrass turfgrass quality. Treatments included iron (Fe)-containing products, nitrogen fertilizers, Ultra Dawn dishwashing detergent (UD) at 3% (v/v), and oxadiazon. In general, greater silvery-thread moss control was achieved with Fe-containing products. Ferrous sulfate at 40 kg Fe/ha plus ammonium sulfate at 30 kg N/ha, a combined product of ferrous oxide, ferrous sulfate, and iron humates (FEOSH) at 125 kg Fe/ha, and a combined product of iron disulfide and ferrous sulfate (FEDS) at 112 kg Fe/ha reduced silvery-thread moss populations 87, 81, and 69%, respectively, 6 wk after initial treatment (WAIT). UD reduced silvery-thread moss populations 57% 6 WAIT. The addition of oxadiazon to Fe-containing treatments did not improve silvery-thread moss population reduction. Other experiments evaluated two formulations of chlorothalonil, each applied at two rates, chlorothalonil with zinc at 9.5 and 17.4 kg ai/ha and chlorothalonil without zinc at 9.1 and 18.2 kg/ ha, and two spray volumes (2,038 and 4,076 L/ha). Greater silvery-thread moss population reduction was observed at Jefferson Landing in 1999 compared with Elk River in 1999 and 2000. Rainfall events at Elk River in 1999 and 2000 within 24 h after application and no rain at Jefferson Landing may account for variation in performance of products between sites. However, no difference in chlorothalonil formulation, rate, or spray volume was observed in any location or year. These data indicate that Fe-containing fertilizers or chlorothalonil can be used to reduce silvery-thread moss populations in creeping bentgrass putting greens. Nomenclature: Chlorothalonil, tetrachloroisophthalonitrile; oxadiazon; silvery-thread moss, Bryum argenteum Hedw.; creeping bentgrass, Agrostis palustris Huds. ‘Penncross’. Additional index words: Bryology, moss control, turfgrass injury. Abbreviations: BM, Black Mountain Golf Club; ER, Elk River Country Club; JL, Jefferson Landing Golf Club; MNP, micronutrient package; NPK, 20:20:20 nitrogen–phosphorus–potassium; UD, Ultra Dawn dishwashing detergent; WAIT, weeks after initial treatment.

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

Increase in Nutritionally Important Sweet Corn Kernel Carotenoids following Mesotrione and Atrazine Applications

The herbicide mesotrione inhibits a critical enzyme, phytoene desaturase, in plant carotenoid biosynthesis. Mesotrione is currently labeled for selective weed control in sweet corn ( Zea mays var. rugosa). Mesotrione applied alone, or in mixtures with the photosystem II inhibitor atrazine, acted to increase concentrations of kernel antheraxanthin, lutein, and zeaxanthin carotenoids in several sweet corn genotypes. Kernel lutein and zeaxanthin levels significantly increased 15.6% after mesotrione + atrazine early postemergence applications, as compared to the control treatment. It appears that mesotrione applications resulted in greater pools of kernel carotenoids once the sweet corn genotypes expressing moderate injury overcame the initial herbicidal photo-oxidative stress. This is the first report of herbicides directly up-regulating the carotenoid biosynthetic pathway in corn kernels, which is associated with the nutritional quality of sweet corn. Enhanced accumulation of lutein and zeaxanthin is important because dietary carotenoids function in suppressing aging eye diseases such as macular degeneration, now affecting 1.75 million older Americans.

Annual Bluegrass (Poa Annua) Control in Creeping Bentgrass (Agrostis Stolonifera) Putting Greens with Bispyribac-sodium

Annual bluegrass is one of the most difficult-to-control weeds in creeping bentgrass putting greens. Field trials were conducted in 2003 and 2005 to evaluate bispyribac-sodium for annual bluegrass management in creeping bentgrass greens maintained at a 3 mm mowing height. Bispyribac-sodium applied weekly at 12 or 24 g ai/ha controlled annual bluegrass 86% 12 wk after initial treatment (WAIT). In 2003, bispyribac-sodium applied at 12 and 24 g/ha/wk injured creeping bentgrass approximately 15 and 50% by 4 WAIT, respectively. However, injury was transient and was not evident by 12 WAIT. In 2005, the 12 and 24 g/ha/wk injured creeping bentgrass 15 and 85% by 8 WAIT, respectively, and was still evident throughout the trial. Putting green quality was reduced when compared to nontreated creeping bentgrass by the same treatments. The removal of annual bluegrass caused soil exposure until creeping bentgrass grew over the bare areas, contributing to decreased quality evaluations. Management of annual bluegrass in creeping bentgrass putting greens is possible with bispyribac-sodium. However, these results indicate bispyribac-sodium can cause excessive injury when applied to creeping bentgrass mowed at 3 mm. Nomenclature: Bispyribac-sodium; annual bluegrass, Poa annua L. POANN; creeping bentgrass, Agrostis stolonifera L. AGSST, ‘Penncross’.

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.