Daniel V. Weisenberger

Amicarbazone Efficacy on Annual Bluegrass and Safety on Cool-Season Turfgrasses

Abstract Amicarbazone has potential for selective annual bluegrass control in cool-season turfgrasses, but seasonal application timings may influence efficacy. To test this hypothesis, field experiments in New Jersey and Indiana investigated amicarbazone efficacy from fall or spring applications and growth chamber experiments investigated the influence of temperature on efficacy. Fall treatments were more injurious to creeping bentgrass and Kentucky bluegrass than spring applications, but fall applications were also more efficacious for annual bluegrass control. In growth chamber experiments, injury and clipping weight reductions were exacerbated by increased temperatures from 10 to 30 C on annual bluegrass, creeping bentgrass, Kentucky bluegrass, and perennial ryegrass. Results suggest that amicarbazone use for annual bluegrass control in cool-season turf may be limited to spring applications, but increased temperature enhances activity on all grasses. Nomenclature: Amicarbazone; annual bluegrass, Poa annua L.; creeping bentgrass, Agrostis stolonifera L. ‘L-93’; Kentucky bluegrass, Poa pratensis L. ‘Baron’, ‘Fairfax’, ‘Freedom’, ‘Merit’, ‘Midnight’, ‘SR2100’; perennial ryegrass, Lolium perenne L. ‘Manhattan IV’.

Safety of Herbicides on 'Zenith' Zoysiagrass Seedlings

Improved cultivars of zoysiagrass established by seed are now available, but little is known about the safety of herbicides on zoysiagrass seedlings. Our objective was to determine the turf safety of various herbicides when applied from emergence to 4 wk after emergence (WAE) of ‘Zenith’ zoysiagrass. Oxadiazon (3.4 kg ai/ha), MSMA (2.3 kg ai/ha), and pronamide (1.1 kg ai/ha) did not reduce coverage 7 WAE when applied at emergence or later and caused only temporary discoloration of seedlings. Foramsulfuron (0.03 kg ai/ha) injured seedling zoysiagrass both years of testing and reduced cover in the final year. Fluazifop (0.07 kg ai/ha) caused significant injury in all 3 yr of the study and reduced coverage in the final year. Fenoxaprop (0.14 kg ai/ha) caused visible injury and reduction in zoysiagrass coverage in all 3 yr of the study. Our studies indicate pronamide, MSMA, or oxadiazon are the safest herbicides to use over Zenith zoysiagrass seedlings, and selection among these three depends on the primary weed species present. Nomenclature: Fenoxaprop, fluazifop-P, foramsulfuron, MSMA, oxadiazon, pronamide, zoysiagrass, Zoysia japonica Steud. ‘Zenith’ ZOYJA

Potential Damage to Sensitive Landscape Plants from Wood Chips of Aminocyclopyrachlor Damaged Trees

Abstract Applications of aminocyclopyrachlor in 2011 to turf resulted in brown and twisted shoots, leaves, and needles; shoot dieback; and in some cases, death of trees and ornamental plants adjacent to treated turf areas. Our research objective was to determine if a sensitive plant could be injured from wood chips (mulch) obtained from aminocyclopyrachlor-damaged trees, and to quantify movement of aminocyclopyrachlor from contaminated wood chips into soil and its subsequent uptake by roots into landscape plant tissues. Tomatoes were grown under greenhouse conditions and mulched with chipped tree branches collected from honey locust and Norway spruce damaged 12 mo previously by aminocyclopyrachlor. Analysis of tomato tissue for aminocyclopyrachlor residues 32 d after mulching found aminocyclopyrachlor in all mulched tomato plants, which was consistent with observations of epinasty on tomato leaflets. Aminocyclopyrachlor residues ranged from 0.5 to 8.0 ppb in tomato plants while chipped tree branches contained 1.7 to 14.7 ppb. Aminocyclopyrachlor residues in the potting soil below the mulch ranged from below the quantifiable limit to 0.63 ppb, indicating that aminocyclopyrachlor can leach from wood chips into soil, causing plant injury. These results indicate that trees damaged by aminocyclopyrachlor should not be chipped and used for mulch or as an ingredient in compost. Nomenclature: Aminocyclopyrachlor; honey locust; Gleditsia triacanthos L.; Norway spruce; Picea abies (L.) Karst.; tomato; Solanum lycopersicum L. Resumen En 2011, aplicaciones de aminocyclopyrachlor en céspedes resultó en tejido aéreo y hojas café y enrolladas, muerte del tejido aéreo, y en algunos casos, la muerte de árboles y plantas ornamentales adyacentes a las áreas tratadas en el césped. El objetivo de nuestra investigación fue determinar si una planta sensible podría ser dañada por una cobertura de chips de madera (mulch) que se obtuvo a partir de árboles dañados con aminocyclopyrachlor, y cuantificar el movimiento de aminocyclopyrachlor desde chips de madera hacia el suelo y su subsiguiente absorción por las raíces de plantas presentes en el paisaje. Plantas de tomate fueron crecidas en invernadero y con cobertura de chips hecha a partir de ramas colectadas de árboles de Gleditsia triacanthos y Picea abies dañados 12 meses antes con aminocyclopyrachlor. El análisis de aminocyclopyrachlor en el tejido de tomate 32 d después de poner la cobertura encontró aminocyclopyrachlor en todas las plantas de tomate con cobertura, lo cual fue consistente con observaciones de epinastia en las hojas de tomate. Los residuos de aminocyclopyrachlor variaron entre 0.5 y 8.0 ppb en plantas de tomate mientras que en las ramas de los árboles fue de 1.7 a 14.7 ppb. Los residuos de aminocyclopyrachlor en la mezcla de suelo de las macetas debajo de la cobertura varió desde niveles por debajo del límite de cuantificación a 0.63 ppb, indicando que aminocyclopyrachlor puede lixiviarse desde los chips de madera al suelo, causando daño en las plantas. Estos resultados indican que árboles dañados con aminocyclopyrachlor no deberían ser usados para producir coberturas o como ingrediente en compost.

Turf Safety to Dithiopyr of Newly Seeded Kentucky Bluegrass (Poa pratensis)1

Abstract: Competition from large crabgrass is often responsible for the establishment failure of spring-seeded cool-season turfgrasses. The objective of this study was to determine how soon after seedling emergence dithiopyr could be applied without causing unacceptable damage to Kentucky bluegrass. Dithiopyr at 0.28 and 0.56 kg/ha was applied at various times prior to seeding and after emergence of Kentucky bluegrass in the field and greenhouse. Dithiopyr damaged Kentucky bluegrass seedlings in the greenhouse when applied earlier than 10 d after emergence (DAE) at 0.28 kg/ha and 14 DAE at 0.56 kg/ha. In the field study with heavy large crabgrass infestation, no significant phytotoxicity or long-term thinning occurred with any application of dithiopyr after emergence of Kentucky bluegrass. Dithiopyr applied as early as 3 DAE improved cover of Kentucky bluegrass by reducing competition from large crabgrass. When seeding is done early in spring before large crabgrass germination, dithiopyr could be applied at 0.28 kg/ha 10 DAE or at 0.56 kg/ha 14 DAE without risk of injury. Dithiopyr could be applied as early as 3 DAE on sites with heavy large crabgrass pressure or to late spring seedings when large crabgrass is germinating because the risk of turf thinning is warranted given the benefit of reduced large crabgrass competition for the desired turf. Nomenclature: Dithiopyr; large crabgrass, Digitaria sanguinalis (L.) Scop. #3 DIGSA; Kentucky bluegrass, Poa pratensis L. ‘America’, # POAPR. Additional index words: Preemergence herbicides. Abbreviations: DAE, days after emergence; POST, postemergence; PRE, preemergence; WAE, weeks after emergence.

Herbicide Selection and Application Timing in the Fall Affects Control of Ground Ivy

Specific timing of fall applications of broadleaf weed herbicides is not refined to maximize control of ground ivy. The objective of our three-year study was to determine how application timing in fall affects control of ground ivy with five different herbicide treatments. Herbicides were applied on 1 and 15 September, 1 and 15 October, and 1 and 15 November of 2003, 2004, and 2005. When rated in December following application, applications of all herbicides were most effective if applied prior to 1 November. However, November applications of all herbicides resulted in control similar to earlier applications when rated the following June. Triclopyr was the most effective and consistent in controlling ground ivy, with 27 of 36 applications reducing cover to ≤ 1% compared to > 50% in untreated plots. Long-term control from triclopyr was not affected significantly by application date. Adding isoxaben to triclopyr improved long-term control over triclopyr alone in five of six November applications. Fluroxypyr provided ≤ 10% cover by June in 15 of the 18 applications and applications on 1 September through 1 November were most effective. Poorest control resulted from 2,4-D+MCPP+dicamba. Adding carfentrazone to 2,4-D+MCPP+dicamba dramatically improved short-term control of ground ivy from November applications, but had little long-term benefit on any application date.

Divalent Cations in Spray Water Influence 2,4-D Efficacy on Dandelion (Taraxacum officinale) and Broadleaf Plantain (Plantago major)

2,4-dichlorophenoxyacetic acid (2,4-D) is a common ingredient in POST broadleaf herbicides labeled for use in turf, pastures, rangeland, and grain crops. The herbicide 2,4-D is a weak acid, and when dissociated can bind to cations present in hard-water spray solutions and/or fertilizer solutions. Experiments were conducted with 2,4-D dimethylamine to evaluate the effect of cation solutions on herbicide efficacy on the perennial broadleaf weeds dandelion and broadleaf plantain. The objectives of this research were to (1) determine if 2,4-D efficacy is influenced by the divalent cations, calcium (Ca), magnesium (Mg), manganese (Mn), and zinc (Zn) in spray solution; and (2) determine if adding the adjuvant ammonium sulfate (AMS) to the spray solution can overcome antagonism. Broadleaf plantain and dandelion control was reduced and plant size and mass increased when 2,4-D was applied in a Ca solution in comparison to deionized water. However, 2,4-D antagonism was overcome when AMS was added as an adjuvant to the spray solution. Magnesium caused 2,4-D antagonism on both weed species in one run of the experiment similar to Ca solution and AMS was successful at overcoming antagonism when added to the tank mixture. Some 2,4-D antagonism from Mn was noticed even when AMS was in the tank mix, but Zn fertilizer solutions did not antagonize 2,4-D activity on either weed species. Although divalent cations can antagonize 2,4-D dimethylamine and reduce perennial broadleaf weed control, adding AMS can overcome this antagonism when Ca and Mg are the primary cations in spray solution. Applicators should avoid using Mn fertilizers when applying 2,4-D dimethylamine because AMS did not successfully overcome antagonism. Nomenclature: 2,4-D; broadleaf plantain, Plantago major L., PLAMA; dandelion, Taraxacum officinale G. H. Weber ex Wiggers, TAROF. 2,4-dichlorophenoxyacetic acid (2,4-D) es un ingrediente común en herbicidas POST para el control de malezas de hoja ancha registrados para su uso en céspedes, pasturas, y cultivos de granos. El herbicida 2,4-D es un ácido débil, y cuando este se disocia puede adherirse a cationes presentes en soluciones de aspersión con aguas pesadas y/o soluciones con fertilizantes. Se realizaron experimentos de campo con 2,4-D dimethylamine para evaluar el efecto de soluciones con cationes en la eficacia del herbicida para el control de las malezas perennes de hoja ancha Taraxacum officinale y Plantago major. Los objetivos de esta investigación fueron (1) determinar si la eficacia de 2,4-D es influenciada por los cationes divalentes calcium (Ca), magnesium (Mg), manganese (Mn), y zinc (Zn) en la solución de aspersión; y (2) determinar si el agregar el adyuvante ammonium sulfate (AMS) a la solución de aspersión puede reducir el antagonismo. El control de P. major y T. officinale se redujo y el tamaño y masa de planta aumentó cuando 2,4-D fue aplicado en una solución de Ca en comparación con agua desionizada. Sin embargo, el antagonismo con el 2,4-D fue reducido cuando se agregó AMS como adyuvante para la solución de aspersión. Magnesium causó antagonismo con 2,4-D en ambas especies de malezas en una de las corridas experimentales, la cual fue similar a la solución de Ca y AMS fue exitoso en reducir el antagonismo cuando se agregó a la mezcla en tanque. Se notó un poco de antagonismo entre 2,4-D y Mn inclusive cuando AMS estuvo en la mezcla en tanque, pero las soluciones de Zn no antagonizaron la actividad del 2,4-D en ninguna de las especies. Aunque los cationes divalentes pueden antagonizar al 2,4-D dimethylamine y reducir el control de malezas perennes de hoja ancha, el agregar AMS puede reducir este antagonismo cuando Ca y Mg son los cationes primarios en la solución de aspersión. Los aplicadores deberían evitar usar fertilizantes con Mn cuando apliquen 2,4-D dimethylamine porque AMS no reducirá exitosamente el antagonismo.

2,4-D–Resistant Buckhorn Plantain (Plantago lanceolata) in Managed Turf

Abstract A population of buckhorn plantain with suspected resistance to 2,4-D was identified in central Indiana following 30 yr of 2,4-D-containing herbicide applications. Our objectives were to (1) confirm and quantify the level of herbicide resistance in the buckhorn plantain population using dose-response experiments and (2) find alternative herbicides that could be used to control this population. Greenhouse experiments were conducted to quantify the dose-response of resistant (R) and susceptible (S) biotypes of buckhorn plantain to both 2,4-D and triclopyr, two synthetic auxin herbicides from different chemical families. The R biotype was ≥6.2 times less sensitive to 2,4-D than the S biotype. The efficacy of triclopyr was similar on both the R and S biotypes of buckhorn plantain, suggesting the absence of cross-resistance to this herbicide. This is the first report of 2,4-D resistance in buckhorn plantain and the first report of 2,4-D resistance in turf. The resistance mechanism was limited to within a chemical family (phenoxycarboxylic acid) and did not occur across all WSSA Group 4 synthetic auxin herbicides, as the pyridinecarboxylic acid herbicides clopyralid and triclopyr and the arylpicolinate herbicide halauxifen-methyl provided control in our experiments. Nomenclature: 2,4-D, clopyralid, halauxifen-methyl, triclopyr, buckhorn plantain, Plantago lanceolata L. PLALA

Mesotrione Activity on Crabgrass (Digitaria spp.) as Influenced by Nitrogen Fertilization Rate, Source, and Timing

Abstract Mesotrione, a 4-hydroxyphenylpyruvate dioxygenase-inhibiting herbicide, is labeled for PRE and POST crabgrass control. It has enhanced efficacy on smooth and large crabgrass when applied in conjunction with soil-applied nitrogen (N). The objectives of this study, using crabgrass as the weed species, were to (1) determine the influence of N rate and tissue N concentration on mesotrione activity, (2) determine the influence of N source on mesotrione activity, and (3) determine the influence of N application timing on mesotrione activity. Large crabgrass plants that received 12 kg N ha−1 or more before mesotrione application had more bleached and necrotic leaves compared with plants that received 0 kg N ha−1 7 d after treatment (DAT) in the greenhouse. Although N application rates as high as 98 kg N ha−1 were tested, 90% leaf bleaching and necrosis were observed with rates of 8.9 or 10.1 kg N ha−1 in Tennessee and Indiana, respectively. Nitrogen concentration in large crabgrass leaf and stem tissue on the day of the mesotrione application was closely related to the bleaching and necrosis symptoms observed 7 DAT. Although N rate influenced mesotrione activity, N source did not. Nitrogen application timing was also important, with N applications 3, 1, and 0 d before a mesotrione application having the highest percentage of bleached and necrotic leaves in greenhouse experiments. Both greenhouse and field trials support the finding that N applications in proximity to the mesotrione application enhance herbicide activity. Thus, practitioners can pair N and POST mesotrione applications together or in proximity to enhance crabgrass control. Nomenclature: Mesotrione; large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA; smooth crabgrass, Digitaria ischaemum (Schreb.) Schreb. ex Muhl. DIGIS. Resumen Mesotrione es un herbicida inhibidor de 4-hydroxyphenylpyruvate dioxygenase que está registrado para el control PRE y POST de especies del género Digitaria. Tiene una actividad mayor en Digitaria ischaemum y Digitiaria sanguinalis cuando se aplica en forma conjunta con nitrógeno aplicado al suelo (N). Los objetivos de este estudio, enfocándose en Digitaria, fueron: (1) determinar la influencia de la dosis de N y la concentración de N en el tejido sobre la actividad de mesotrione, (2) determinar la influencia de la fuente de N sobre la actividad de mesotrione, y (3) determinar la influencia del momento de aplicación de N sobre la actividad de mesotrione. Plantas de D. sanguinalis que recibieron 12 kg N ha−1 o más antes de la aplicación de mesotrione, tuvieron más hojas blanqueadas y necróticas que las plantas que recibieron 0 kg N ha−1 a 7 d después del tratamiento (DAT), en el invernadero. Aunque se evaluaron dosis de aplicación de N de hasta 89 kg N ha−1, con dosis de sólo 8.9 ó 10.1 kg N ha−1 se observó 90% blanqueamiento y necrosis foliar, en Tennessee e Indiana, respectivamente. La concentración de N en el tejido foliar y del tallo de D. sanguinalis, el día de la aplicación de mesotrione, estuvo altamente relacionada a los síntomas de blanqueamiento y necrosis observados a 7 DAT. Aunque la dosis de N influenció la actividad de mesotrione, la fuente de N no lo hizo. El momento de aplicación de N también fue importante. Así, las aplicaciones de N a 3, 1, y 0 d antes de la aplicación de mesotrione tuvieron el mayor porcentaje de hojas blanqueadas y necróticas en experimentos de invernadero. Tanto los estudios de invernadero como los de campo apoyan los resultados de que aplicaciones de N cercanas a la aplicación de mesotrione mejoran la actividad del herbicida. De esta forma, los usuarios pueden combinar aplicaciones de N y mesotrione POST o realizarlas en momentos cercanos para mejorar el control de malezas del género Digitaria.

Weed Control and Turf Safety of Single and Sequential Applications of Herbicides Over Spring Seedings

Weed control is important during establishment of cool-season grasses, especially when seeded in spring near summer annual weed germination. Our objectives were to determine (i) turf safety and weed control from sequential applications of newly-released herbicides on tall fescue at three seeding dates (May, June, July) and (ii) turf safety and weed control from newly-released herbicides applied at seeding or shortly after emergence of spring-seeded Kentucky bluegrass or tall fescue. No herbicides tested negatively affected turfgrass establishment and usually improved turf establishment by reducing weed competition. Mesotrione consistently provided effective weed control and turf cover from either single or sequential applications over different locations, years, seeding dates, and turf species. Quinclorac or siduron applied as single or sequential applications or quinclorac+carfentrazone as a single application provided effective weed control and turf cover depending on seeding date and application regime. Although spring seeding can be achieved with high maintenance, it is strongly recommended to seed cool season grasses at the optimal time from late summer to early fall.