Gregory K. Breeden

PRE and POST Control of Annual Bluegrass (Poa annua) with Indaziflam

Abstract Indaziflam controls annual grassy weeds by inhibiting cellulose biosynthesis. Research was conducted from 2008 to 2011 in Tennessee, Texas, and Georgia evaluating the efficacy of indaziflam for PRE and POST control of annual bluegrass in bermudagrass turf. In Texas, indaziflam at 30, 40, 50, and 60 g ai ha−1 applied PRE provided 93 to 100% annual bluegrass control through 28 wk after treatment. When applied PRE at 80 g ai ha−1 and at 4, 8, and 12 wk after PRE (WAP), indaziflam controlled annual bluegrass 67 to 100% 32 wk after initial treatment (WAIT) in Tennessee; however, reduced efficacy was observed with 12 WAP treatments in a single year of a 2-yr study. Similarly, annual bluegrass control with PRE applications or with 4 and 8 WAP applications of indaziflam at 35 and 52.5 g ai ha−1 ranged from 88 to 100% at 30 WAIT in Tennessee. In Georgia, these rates of indaziflam applied PRE and 4 WAP controlled annual bluegrass 96 to 100% on all evaluation dates and resulted in 97 to 100% reduction in plant counts relative to the untreated control at 30 WAIT. When applied 8 WAP, the 35 and 52.5 g ai ha−1 rates of indaziflam controlled annual bluegrass only 51 to 71% at 30 WAIT in Georgia. Although increasing the application rate of indaziflam treatments 8 WAP provided greater annual bluegrass control, each rate provided significantly lower control when applied 8 WAP compared with PRE or at 4 WAP. No bermudagrass injury was observed in this research. Results suggest indaziflam provides effective PRE and early POST control of annual bluegrass in bermudagrass turf. However, additional research is needed to determine the effects of plant size and maturity on indaziflam efficacy for POST annual bluegrass control. Nomenclature: Annual bluegrass, Poa annua L.; bermudagrass, Cynodon dactylon (L.) Pers.

Smooth Crabgrass Control with Indaziflam at Various Spring Timings

Abstract Indaziflam is an alkylazine herbicide that controls annual grasses by inhibiting cellulose biosynthesis. Compared with other PRE herbicides like prodiamine, indaziflam has a longer half-life in soil (> 150 d), which may allow for greater flexibility with application timing. Research was conducted in 2010 in Tennessee and Georgia evaluating smooth crabgrass control efficacy with indaziflam applied at early PRE, PRE, and early POST timings on the basis of soil temperature. Regardless of application timing, all rates of indaziflam (35, 52.5, and 70 g ai ha−1) controlled smooth crabgrass 89 to 100%. Prodiamine at 840 g ai ha−1 applied PRE provided ≥ 99% smooth crabgrass control on all rating dates. Smooth crabgrass plant counts were significantly correlated (r  =  −0.961; p < 0.0001) with visual ratings of smooth crabgrass control at the end of the study. Application flexibility with indaziflam may benefit turf managers in scheduling herbicide applications for smooth crabgrass control in Tennessee and Georgia. Nomenclature: Indaziflam; prodiamine; smooth crabgrass [Digitaria ischaemum (Schreb.) Schreb. ex Muhl.].

Efficacy and Safening of Aryloxyphenoxypropionate Herbicides when Tank-Mixed with Triclopyr for Bermudagrass Control in Zoysiagrass Turf

Abstract Aryloxyphenoxypropionate (AOPP) herbicides are used to control bermudagrass contamination in various turfgrasses. Applying AOPP herbicides alone can cause unacceptable injury to zoysiagrass but injury can be reduced when tank-mixed with triclopyr. There are limited data illustrating the extent of bermudagrass control and zoysiagrass cultivar tolerance when these compounds are combined. Research was conducted to determine the efficacy of multiple AOPP herbicides applied alone and tank-mixed with triclopyr for bermudagrass control in zoysiagrass turf. Treatments include three sequential applications of cyhalofop (0.32 kg ai ha−1), fenoxaprop (0.14 kg ha−1), fluazifop (0.11 kg ha−1), or quizalofop (0.09 kg ha−1) applied alone and tank-mixed with triclopyr (1.12 kg ae ha−1) applied to ‘Tifway’ bermudagrass, and ‘Diamond’, ‘Palisades’, and ‘Zenith’ zoysiagrass. Tifway bermudagrass control ranged from 41 to 69% and digital image analysis turf coverage data ranged from 18 to 50% for AOPP herbicides applied alone. The addition of triclopyr to AOPP herbicides increased bermudagrass control (64–79%) and reduced turf coverage (8–29%). Palisades and Zenith zoysiagrass exhibited less injury (1–18%) and greater turf coverage (84–86%) when AOPP herbicides were tank-mixed with triclopyr compared to AOPP herbicides applied alone. Diamond zoysiagrass was not tolerant to any AOPP herbicides applied alone or tank-mixed with triclopyr, except for fluazifop alone (18% injury and 93% turf coverage). Visual ratings and digital image analysis turf coverage data had a strong negative correlation over all tested turfgrasses. In general, AOPP herbicides plus triclopyr will control bermudagrass greater and injure zoysiagrass less compared to AOPP herbicides applied alone; however, these mixtures can cause unacceptable injury to Diamond zoysiagrass. Nomenclature: Cyhalofop; fenoxaprop; fluazifop; triclopyr; quizalofop; bermudagrass, Cynodon spp. Rich.; hybrid bermudagrass, Cynodon dactylon (L.) Pers. × Cynodon transvaalensis Burtt-Davy ‘Tifway’ CYNDA; zoysiagrass species, Zoysia spp. Willd.; zoysiagrass, Zoysia japonica Steud. ‘Palisades’, ‘Zenith’ ZOYJA; zoysiagrass, Zoysia matrella (L.) Merr. ‘Diamond’ ZOYMA.

A Glyphosate-Resistant Biotype of Annual Bluegrass in Tennessee

Abstract Glyphosate is regularly used to control annual bluegrass populations in dormant bermudagrass turf. A population of annual bluegrass not controlled by glyphosate at 840 g ha−1 (glyphosate resistant, GR) was identified on a golf course in Humboldt, TN in 2010. Mature tillers of GR plants were established in a greenhouse and treated with glyphosate at 0, 210, 420, 840, 1,680, 3,360, and 6,720 g ha−1. Mature tillers of a biotype known to be susceptible to glyphosate (SS) were also established in the greenhouse and subjected to the same treatments. At 14 d after treatment (DAT), glyphosate controlled the SS biotype > 95% at rates > 420 g ha−1. Comparatively, the GR biotype was only controlled 76% with glyphosate at 6,720 g ha−1. The rates required to provide 50% control (I50 values) for SS and GR biotypes were 236 and 2,812 g ha−1 respectively, resulting in a resistance factor of 12. Photochemical efficiency (Fv/Fm) values on SS plants treated with glyphosate at > 210 g ha−1 measured 0.000 at 14 DAT, whereas Fv/Fm values on GR plants were not significantly different from the untreated control with glyphosate rates ≤ 840 g ha−1 on the same date. In laboratory experiments, the SS biotype accumulated greater shikimate concentrations than the GR biotype 3 to 6 DAT. Future research should evaluate strategies for managing GR and SS annual bluegrass with alternative modes of action. Nomenclature: Annual bluegrass, Poa annua L.; bermudagrass, Cynodon dactylon L. Pers.; glyphosate; photochemical efficiency.

A new amino acid substitution (Ala-205-Phe) in acetolactate synthase (ALS) confers broad spectrum resistance to ALS-inhibiting herbicides

AbstractMain ConclusionThis is a first report of an Ala-205-Phe substitution in acetolactate synthase conferring resistance to imidazolinone, sulfonylurea, triazolopyrimidines, sulfonylamino-carbonyl-triazolinones, and pyrimidinyl (thio) benzoate herbicides. Resistance to acetolactate synthase (ALS) and photosystem II inhibiting herbicides was confirmed in a population of allotetraploid annual bluegrass (Poa annua L.; POAAN-R3) selected from golf course turf in Tennessee. Genetic sequencing revealed that seven of eight POAAN-R3 plants had a point mutation in the psbA gene resulting in a known Ser-264-Gly substitution on the D1 protein. Whole plant testing confirmed that this substitution conferred resistance to simazine in POAAN-R3. Two homeologous forms of the ALS gene (ALSa and ALSb) were detected and expressed in all POAAN-R3 plants sequenced. The seven plants possessing the Ser-264-Gly mutation conferring resistance to simazine also had a homozygous Ala-205-Phe substitution on ALSb, caused by two nucleic acid substitutions in one codon. In vitro ALS activity assays with recombinant protein and whole plant testing confirmed that this Ala-205-Phe substitution conferred resistance to imidazolinone, sulfonylurea, triazolopyrimidines, sulfonylamino-carbonyl- triazolinones, and pyrimidinyl (thio) benzoate herbicides. This is the first report of Ala-205-Phe mutation conferring wide spectrum resistance to ALS inhibiting herbicides.

Methiozolin efficacy for annual bluegrass (Poa annua) control on sand- and soil-based creeping bentgrass putting greens.

Abstract Methiozolin is a new isoxazoline herbicide being investigated for selective POST annual bluegrass control in creeping bentgrass putting greens. Glasshouse and field research was conducted from 2010 to 2012 in Tennessee and Texas to evaluate annual bluegrass control efficacy with methiozolin. Application placement experiments in the glasshouse illustrated that root absorption was required for POST annual bluegrass control with methiozolin at 1,000 g ai ha−1. Soil-plus-foliar and soil-only applications of methiozolin reduced annual bluegrass biomass greater than treatments applied foliar-only. Field experiments evaluated annual bluegrass control efficacy with two application rates (500 and 1,000 g ha−1) and six application regimes (October, November, December, October followed by [fb] November, November fb December, and October fb November fb December) on sand- and soil-based putting greens. Annual bluegrass control with methiozolin at 1,000 g ha−1 on sand-based greens ranged from 70 to 72% compared to 87 to 89% on soil-based greens. Treatment at 500 g ha−1 controlled annual bluegrass 57 to 64% on sand-based greens compared to 72 to 80% on soil-based greens. Most sequential methiozolin application regimes controlled annual bluegrass more than single applications. On sand-based greens, sequential application programs controlled annual bluegrass 70 to 79% compared to 85 to 92% on soil-based greens. Responses indicate that methiozolin is a root-absorbed herbicide with efficacy for selective control of annual bluegrass in both sand- and soil-based creeping bentgrass putting greens. Nomenclature: Methiozolin [5-(2,6-difluorobenzyl) oxymethyl-5-methyl-3-(3methylthiophen-2-yl)-1,2-isoxazoline]; annual bluegrass, Poa annua L.; creeping bentgrass, Agrostis stolonifera L. Resumen Methiozolin es un herbicida isoxazoline nuevo que está siendo investigado para el control selectivo POST de Poa annua en “putting greens” del césped Agrostis stolonifera. Se realizaron investigaciones de invernadero y de campo desde 2010 a 2012, en Tennessee y Texas, para evaluar la eficacia de methiozolin en el control de P. annua. En el invernadero, experimentos de localización de la aplicación ilustraron que la absorción por la raíz fue requerida para el control POST de P. annua con methiozolin a 1,000 g ai ha−1. Aplicaciones de methiozolin al suelo y al follaje o solamente al suelo redujeron la biomasa de P. annua más que los tratamientos con aplicaciones solamente foliares. Los experimentos de campo evaluaron la eficacia en el control de P. annua con dos dosis de aplicación (500 y 1,000 g ha−1) y seis regímenes de aplicación (Octubre, Noviembre, Diciembre, Octubre seguido de (fb) Noviembre, Noviembre fb Diciembre, y Octubre fb Noviembre fb Diciembre) en putting greens en arena y en suelo. El control de P. annua con methiozolin a 1,000 g ha−1 en greens en arena varió entre 70 y 72% comparado con 87 a 89% en greens en suelo. Los tratamientos con 500 g ha−1 controlaron P. annua 57 a 64% en greens en arena, comparados con 72 a 80% en greens en suelo. La mayoría de los regímenes secuenciales de aplicación de methiozolin controlaron P. annua más que las aplicaciones individuales. En greens en arena, los programas de aplicaciones secuenciales controlaron P. annua 70 a 79% comparados con 85 a 92% en greens en suelo. Las respuestas indican que methiozolin es un herbicida absorbido por la raíz con eficacia para el control selectivo de P. annua en putting greens de A. stolonifera tanto en arena como en suelo.

Application Placement Affects Postemergence Smooth Crabgrass (Digitaria ischaemum) and Annual Bluegrass (Poa annua) Control with Indaziflam

Abstract Greenhouse experiments were conducted to determine the effects of herbicide placement on POST smooth crabgrass and annual bluegrass control. Soil-plus-foliar, soil-only, and foliar-only applications of indaziflam (52.5 g ai ha−1), dithiopyr (560 ai g ha−1), or quinclorac (840 g ai ha−1) were made to one-tiller smooth crabgrass plants. Similarly, indaziflam (52.5 g ha−1), foramsulfuron (29 g ai ha−1), or prodiamine (840 g ai ha−1) were applied to nontillering annual bluegrass plants in an identical manner. No differences in smooth crabgrass control were detected between soil-plus-foliar and soil-only applied indaziflam from 21 to 35 d after treatment (DAT). By 28 DAT, smooth crabgrass control and biomass reductions with these indaziflam treatments were ≥ 90% and not different than quinclorac. Comparatively, smooth crabgrass control with foliar-only applications of indaziflam never exceeded 28%. Responses on annual bluegrass were similar as soil-plus-foliar and soil-only applied indaziflam exhibited greater efficacy than indaziflam applied foliar-only. By 28 DAT, annual bluegrass control and aboveground biomass reductions with soil-plus-foliar and soil-only treatments were ≥ 86% and not different from foramsulfuron. Comparatively, foliar-only applications of indaziflam controlled annual bluegrass ≤ 2%. These results indicate that root absorption is required for POST control of smooth crabgrass and annual bluegrass with indaziflam. Further research is needed to determine if techniques to enhance indaziflam contact with soil will enhance POST smooth crabgrass and annual bluegrass control in the field. Nomencalture: Dithiopyr; indaziflam; foramsulfuron; prodiamine; quinclorac; annual bluegrass, Poa annua L.; smooth crabgrass, Digitaria ischaemum (Schreb.) Schreb. ex Muhl. Resumen Se realizaron experimentos de invernadero para determinar los efectos de la localización de herbicidas en el control POST de Digitaria ischaemum y Poa annua. Aplicaciones al suelo-más-foliar, solamente-suelo y solamente-foliar de indaziflam (52 g ai ha−1), dithiopyr (560 g ai ha−1) o quinclorac (840 g ai ha−1) fueron realizadas en plantas de D. ischaemum en estado de un hijuelo. Similarmente, indaziflam (52 g ai ha−1), foramsulfuron (29 g ai ha−1) o prodiamine (840 g ai ha−1) fueron aplicadas a plantas de P. annua sin hijuelos en forma idéntica. No se detectaron diferencias en el control de D. ischaemum entre suelo-más-foliar y solamente-suelo con indaziflam entre 21 y 35 d después del tratamiento (DAT). A 28 DAT, el control y la reducción de biomasa con estos tratamientos con indaziflam fueron ≥90% y no fueron diferentes del quinclorac. Comparativamente, el control de D. ischaemum con aplicaciones solamente-foliar de indaziflam nunca excedió 28%. Las respuestas de P. annua fueron similares, en tanto que las aplicaciones suelo-más-foliar y solamente-suelo de indaziflam exhibieron mayor eficacia que indaziflam aplicado solamente-foliar. A 28 DAT, el control y la reducción de biomasa aérea de P. annua con tratamientos suelo-más-foliar y solamente-suelo fueron ≥86% y no fueron diferentes al foramsulfuron. Comparativamente, aplicaciones solamente-foliar de indaziflam controlaron P. annua ≤2%. Estos resultados indican que se requiere absorción radicular para el control POST de D. ischaemum y P. annua con indaziflam. Se necesita investigación adicional para determinar si técnicas para mejorar el contacto de indaziflam con el suelo incrementarán el control en campo de D. ischaemum y P. annua.

Efficacy of Flazasulfuron for Control of Annual Bluegrass (Poa annua) and Perennial Ryegrass (Lolium perenne) as Influenced by Nitrogen

Abstract Certain sulfonylurea (SU) herbicides are used to remove overseeded cool-season species from bermudagrass. The effects of nitrogen (N) on the efficacy of a new SU herbicide, flazasulfuron, have not been determined. Field and laboratory studies were conducted in 2008 and 2009 evaluating the efficacy of flazasulfuron for control of overseeded perennial ryegrass contaminated with annual bluegrass. Flazasulfuron was applied at rates of 4.4, 8.8, and 17.5 g ha−1 alone, and in between sequential applications of N fertilizer at 73 kg N ha−1. N was granularly applied immediately prior to herbicide treatment and 4 wk later. In both years, the level of annual bluegrass control with flazasulfuron and two applications of N at 73 kg N ha−1 was significantly greater than following treatment with flazasulfuron alone. This response was observed for all application rates of flazasulfuron on every rating date. The level of annual bluegrass control with flazasulfuron at 4.4 g ha−1 and two applications of N at 73 kg ha−1 was greater than flazasulfuron at 17.5 g ha−1 alone each year. No significant differences in perennial ryegrass control were observed for flazasulfuron with and without N fertility. In laboratory studies with annual bluegrass, treatment with N fertilizer at 73 kg N ha−1 increased translocation of 14C flazasulfuron (and any potential metabolites) from treated annual bluegrass leaves to other shoot tissues by 18% at 1 h after treatment and 22% at 4 h after treatment compared to plants not treated with N fertilizer. This increase in translocation may explain the increased level of annual bluegrass control observed in the field. Nomenclature: Flazasulfuron; annual bluegrass, Poa annua L. POAN; bermudagrass, Cynodon dactylon (L.) Pers. CYNDA; perennial ryegrass, Lolium perenne L. LOLPE.

Nitrogen-Enhanced Efficacy of Mesotrione and Topramezone for Smooth Crabgrass (Digitaria ischaemum) Control

Abstract The herbicides mesotrione and topramezone inhibit 4-hydroxyphenylpyruvate dioxygenase (HPPD) and have efficacy against smooth crabgrass. Research was conducted to determine the impacts of soil-applied nitrogen (N) fertilizer on the effectiveness of single applications of mesotrione and topramezone for postemergence smooth crabgrass control. Field experiments in 2010 and 2011 evaluated the efficacy of mesotrione (280 g a.i. ha−1) and topramezone (9 g a.i. ha−1) for control of multitiller smooth crabgrass subjected to five N fertility treatments (0, 12, 25, 37, or 49 kg N ha−1). Greenhouse experiments evaluated the response of smooth crabgrass to mesotrione (0, 70, 140, 280, 560, and 1,120 g ha−1) and topramezone (0, 4.5, 9, 18, 36, and 72 g ha−1) with 0 or 49 kg N ha−1. Further research evaluated changes in smooth crabgrass leaf tissue pigment concentrations following treatment with mesotrione (280 g ha−1) and topramezone (18 g ha−1) with 0 or 49 kg N ha−1. In field experiments, N increased smooth crabgrass control with mesotrione and topramezone for 8 wk; however, increasing N rate above 25 kg ha−1 did not improve control on any rating date. In dose-response experiments, N application reduced I50 values for mesotrione and topramezone by 67 and 53%, respectively, 21 d after treatment (DAT). Reductions in aboveground biomass with both herbicides were greater when applied following N treatment as well. In leaf-response experiments, N decreased new leaf chlorophyll and carotenoid concentrations and new leaf production after treatment with topramezone. Future research should investigate whether increased translocation of these herbicides to meristimatic regions contribute to N-enhanced efficacy. Nomenclature: Mesotrione, smooth crabgrass (Digitaria ischaemum Schreb. ex Muhl.); topramezone.

Control of Silk Tree (Albizia julibrissin) with Aminocyclopyrachlor and Other Herbicides

Abstract Research was conducted to determine the efficacy of aminocyclopyrachlor in comparison to glyphosate, clopyralid, fluroxypyr, and triclopyr for silk tree (commonly known as mimosa) control. In the greenhouse, aminocyclopyrachlor was applied at 8.75, 17.5, 35, and 70 g ha−1 with and without methylated seed oil (MSO) at 0.5% v/v. Efficacy of these treatments was compared to glyphosate and triclopyr at 1,350 g ha−1, fluroxypyr at 103 g ha−1, and clopyralid at 100 g ha−1. Few differences in silk tree control were detected by 28 d after treatment (DAT), as aminocyclopyrachlor with MSO controlled silk tree 87 to 100% compared to 53 to 100% for aminocyclopyrachlor without MSO. Aminocyclopyrachlor at 35 g ha−1 provided silk tree control similar to glyphosate, triclopyr, clopyralid, and fluroxypyr regardless of adjuvant. Inclusion of MSO enhanced initial activity of aminocyclopyrachlor after application. At 7 DAT, 8.75 g ha−1 of aminocyclopyrachlor plus MSO controlled silk tree similar to aminocyclopyrachlor alone at 70 g ha−1. In laboratory studies, absorption of 14C-aminocyclopyrachlor 2 h after treatment (HAT) with MSO measured 93% compared to only 62% for 14C-aminocyclopyrachlor without MSO. By 24 HAT, absorption of 14C-aminocyclopyrachlor measured 99 and 71% for applications with and without MSO, respectively. Increased foliar absorption with MSO may explain enhanced activity observed 7 DAT in greenhouse studies, as no effects in 14C-aminocyclopyrachlor translocation due to adjuvant were observed. Responses suggest MSO increased the speed of silk tree control with aminocyclopyrachlor and may also improve rainfastness of aminocyclopyrachlor applications for control of silk tree and other woody species. Nomenclature: Aminocyclopyrachlor, fluroxypyr, glyphosate, triclopyr, clopyralid, silk tree, Albizia julibrissin Durazz