Brent A. Sellers

Factors Affecting Seed Germination of Cadillo (Urena lobata)

Abstract Cadillo is an invasive species commonly found in pastures, rangelands, and disturbed areas. It is becoming a significant problem weed in Florida pastures and natural areas. The objectives of this research were to determine effective techniques to break seed dormancy and the effect of light, temperature, pH, water stress, and depth of seed burial on Cadillo germination. Cadillo seeds had significant levels of innate dormancy imposed by a hard seed coat; chemical scarification was the most effective technique for removing dormancy. Seeds germinated from 15 to 40 C, with an optimal temperature of 28 C. Germination was unaffected by pH levels. Water stress below −0.2 MPa reduced seed germination. Cadillo germination was not light-dependent and seeds emerged from depths up to 9 cm, with the greatest occurring emergence near the soil surface. Considering that Cadillo seed can germinate under a wide range of environmental conditions, it is not surprising that it has become a serious invasive weed in Florida. Nomenclature: Cadillo, Urena lobata L. URLO

Diurnal fluctuations and leaf angle reduce glufosinate efficacy

Velvetleaf plants have diurnal leaf movements, which may result in decreased interception of herbicides when applications are made near sunset. However, it is not known if leaf angle alone accounts for diurnal fluctuations in efficacy. Greenhouse experiments were conducted to determine the effect of time of day (TOD) of application and velvetleaf leaf angle on glufosinate efficacy and spray interception. Glufosinate at 90, 180, and 360 g ai/ha was applied to 10-cm-tall plants at 4:00, 6:00, 7:00, 7:30, and 8:00 p.m., respectively. Leaf angles were either manipulated physically to −90° or the plants natural 2:00 p.m. leaf angle (approximately −10°) or were allowed to exhibit their natural leaf movements. Plant dry weight 3 wk after treatment revealed that TOD effects were observed for all leaf angle treatments after glufosinate application at 90 g/ha. At 180 g/ha glufosinate, there was no TOD effect for plants with 2 p.m. leaf angles, whereas there was a TOD effect for plants with −90° and natural leaf angles. At 360 g/ha glufosinate, biomass for the −90° leaf angle plants was similar to that for the natural and the 2:00 p.m. leaf angle plants when glufosinate was applied at 4:00 p.m. but was significantly different at or after 6:00 p.m.. This suggests that at least 4 h of light is needed to provide optimum herbicide activity when spray interception is reduced as a result of leaf movements. Leaf angle decreased by as much as 70% from 4:00 to 8:00 p.m., which resulted in approximately 50% less spray interception at 8:00 p.m. than at 4:00 p.m. These data provide evidence that leaf angle plays a pivotal role in reducing glufosinate efficacy when applications are made near sundown. However, leaf angle is not the sole reason for reduced efficacy because TOD effects were observed at different leaf angles with 4 h of light, after an application of 360 g/ha glufosinate. Nomenclature: Glufosinate; velvetleaf, Abutilon theophrasti Medicus #3 ABUTH. Additional index words: Application timing, glufosinate, herbicide interception, time of day. Abbreviations: GS, glutamine synthetase; POST, postemergence; TOD, time of day; WAT, weeks after treatment.

Influence of formulation and glyphosate salt on absorption and translocation in three annual weeds

Abstract Absorption and translocation of three commercial formulations of glyphosate, the isopropylamine salt formulated as Roundup Ultra™ (IPA1) and Roundup UltraMax™ (IPA2) and the diammonium salt formulated as Touchdown™ IQ (DA), were compared in three- to five-leaf velvetleaf, common waterhemp, and pitted morningglory. Absorption of 14C-glyphosate in velvetleaf was not significantly different among the three formulations up to 50 h after treatment (HAT). More absorption of 14C-glyphosate occurred in the IPA1 (26.0%) vs. the IPA2 (17.7%) formulation over 74 h. Of the total 14C-glyphosate absorbed, 20 to 35% was translocated from the treated leaf to the rest of the plant. Initial absorption of 14C-glyphosate was rapid in common waterhemp with the IPA1 (42.7%) and IPA2 (30.7%) formulations; both were higher compared with absorption of the DA formulation (11.5%) by 2 HAT. These differences continued up to 26 HAT, but no differences were evident by 74 HAT. Up to 65% of the 14C-glyphosate absorbed was translocated out of the treated leaf by 74 HAT, with roots the primary sink. Initial absorption of 14C-glyphosate was slow in pitted morningglory compared with the other species. More foliar absorption occurred in plants treated with the DA (13.6%) vs. the IPA2 formulation (4.9%) by 6 HAT. Absorption beyond 26 HAT was not different among the three glyphosate formulations. Translocation of 14C-glyphosate to roots was 27% greater as the DA salt than IPA1 and IPA2 by 74 HAT. The distribution pattern of glyphosate was similar in all species; phosphorimages demonstrated movement both acropetal and basipetal, with accumulation in roots greater than in any other plant parts. An efficacy study parallel to the 14C study showed no difference among the three glyphosate formulations on the species investigated at both 74 HAT and 2 wk after treatment. Nomenclature: Glyphosate; common waterhemp, Amaranthus rudis Sauer AMATA; pitted morningglory, Ipomoea lacunosa L. IPOLA; velvetleaf, Abutilon theophrasti Medicus ABUTH.

Application Time of Day Influences Glyphosate Efficacy

Variability in glyphosate efficacy has been observed following late day field applications, but the influence of this “time-of-day effect” on weed control and soybean yield is unknown. Additionally, the basis for differences in weed control due to application time of day has not been fully elucidated. In field trials, broadleaf weed biomass was ≥5-fold greater when glyphosate was applied at 6:00 a.m. compared to 6:00 p.m. in three of four site–years. No consistent time-of-day effect was observed on treated grass weeds. Soybean yield was unaffected by treatments, and was similar to the weed-free control. In a greenhouse study, both barnyardgrass and velvetleaf biomass were as much as 25 to 80% greater when glyphosate was applied at 8:00 p.m. vs. 2:00 p.m. Examination of individual components of the time-of-day effect for velvetleaf indicated that leaf angle and time of application accounted for 82 and 18%, respectively, of the biomass change. This research suggests that diurnal changes in leaf movement of velvetleaf account for much of the time-of-day effect, with the remainder likely due to an unknown physiological component. Nomenclature: Glyphosate, barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG, velvetleaf, Abutilon theophrasti Medicus ABUTH, soybean, Glycine max (L.) Merr., ‘Asgrow 3601 RR*STS’ or ‘Asgrow 3701 RR’

Dogfennel (Eupatorium capillifolium) Size at Application Affects Herbicide Efficacy

Abstract Dogfennel is one of the most problematic weeds in Florida pasturelands and its control can become inconsistent as the plant matures. A premix of triclopyr + fluroxypyr has been recently introduced for weed control in pastures and rangeland; however, little published information exists concerning the control of dogfennel in pastures with this herbicide combination. Therefore, experiments were initiated to determine the efficacy of triclopyr + fluroxypyr compared with commonly used pasture herbicides on dogfennel at three heights. All herbicides utilized in this study are commonly used for dogfennel control. Dogfennel control was affected by both herbicide treatment and dogfennel height. In general, 0.80 + 0.28 kg ai/ha of 2,4-D amine + dicamba resulted in inconsistent control, especially as dogfennel plants increased in size. Increasing the rate of 2,4-D amine + dicamba to 1.21 + 0.42 kg/ha increased the consistency. Triclopyr + fluroxypyr provided similar levels of control as that of 1.21 + 0.42 kg/ha 2,4-D amine + dicamba. In all locations, control of 154-cm dogfennel was signficanatly lower than that of 38-cm dogfennel. These data indicate that triclopyr + fluroxypyr is an effective option for dogfennel control, but dogfennel height at the time of application is an important factor for optimizing control. Nomenclature: 2,4-D Amine; dicamba; fluroxypyr; triclopyr; Dogfennel, Eupatorium capillifolium L.

Herbicidal Control of Largeleaf Lantana (Lantana camara)

Abstract Largeleaf lantana is a perennial shrub that commonly infests pastures, roadsides, and natural areas. Many experiments have been conducted to manage this weed, but few successful herbicides have been found. Little information is available for the effectiveness of fluroxypyr, aminopyralid, or aminocyclopyrachlor on largeleaf lantana. Experiments were conducted in central Florida on dense, natural infestations of largeleaf lantana. Aminopyralid (0.12 kg ha−1), fluroxypyr (0.56 kg ha−1), and aminocyclopyrachlor (0.2 kg ha−1) were either applied in the fall (approximately 2 mo before frost) or in the fall followed by a spring application. Aminopyralid was ineffective on largeleaf lantana, and neither one nor two applications resulted in > 20% control 1 yr after treatment (YAT). Fluroxypyr applied once in the fall resulted in 12% control at 1 YAT, but two applications resulted in 80% control after 1 yr. The combination of fluroxypyr + aminopyralid, applied twice, resulted in approximately 90% control 1 YAT. A single application of fluroxypyr + aminopyralid failed to provide greater than 20% control. Conversely, aminocyclopyrachlor applied once in the fall provided 98% control of largeleaf at 1 YAT. Where aminocyclopyrachlor was applied twice, largeleaf lantana control was 100%. From these data, largeleaf lantana can be effectively controlled by two applications of fluroxypyr, two applications of fluroxypyr + aminopyralid, or a single application of aminocyclopyrachlor. Individual plant treatments were also investigated using herbicides applied as basal or cut surface applications. At 1 YAT, only triclopyr + aminopyralid provided > 90% control as a basal application. The other herbicide combinations appeared to be effective earlier, but significant regrowth had occurred by 1 YAT. Cut surface applications were similar with triclopyr + aminopyralid and triclopyr + fluroxypyr providing effective control. Neither triclopyr alone nor imazapyr provided effective control for 1 YAT with basal or cut surface applications. Nomenclature: Aminocyclopyrachlor; aminopyralid; fluroxypyr; imazapyr; triclopyr; largeleaf lantana, Lantana camara L. LANCA.

Influence of Herbicide and Application Timing on Blackberry Control

Abstract Blackberry is a troublesome species across much of the southeastern United States. Control of blackberry with the pyridine herbicides is often variable among different locations. Experiments were conducted to determine whether application timing, either spring or fall, affected efficacy of the pyridine herbicides triclopyr, fluroxypyr and picloram, and metsulfuron. The pyridine herbicides provided greater control when applied in the fall. At 12 mo after treatment, fluroxypyr plus picloram and fluroxypyr plus triclopyr provided 83% control when applied in the fall and 65% when applied in the spring. Conversely, metsulfuron provided 85% control, and application timing was not significant. Although metsulfuron effectively controls blackberry, it is also highly injurious to bahiagrass. Therefore, chlorosulfuron was tested to determine whether it would provide blackberry control while not injuring bahiagrass. Blackberry control with chlorosulfuron was similar to metsulfuron. These data indicated blackberry control in bahiagrass pastures can be effectively accomplished with chlorosulfuron. Nomenclature: Chlorosulfuron; fluroxypyr; metsulfuron; picloram; triclopyr; blackberry, Rubus spp.; bahiagrass, Paspalum notatum Flüggé, ‘Pensacola’.

Effects of Environmental Factors on Seed Germination and Emergence of Smutgrass (Sporobolus indicus) Varieties

Abstract Smutgrass is an invasive warm-season perennial bunch-type grass native to tropical Asia. The two varieties of smutgrass prevalent in Florida are small smutgrass and giant smutgrass. Laboratory seed germination experiments were conducted on both smutgrass varieties to determine the effect of various environmental factors on germination and emergence. The average germination rate for both varieties was 88% at 30/20 C day/night temperatures. Seed germination for both varieties was greater under simulated temperature flux than at constant temperatures. Seed of both varieties germinated at four simulated Florida temperature fluxes (22/11, 27/15, 33/24, and 29/19 C day/night), although the germination of small smutgrass and giant smutgrass was reduced at 33/24 and 22/11 C, respectively. Germination of small and giant smutgrass under dark conditions was 27 and 53%, respectively. Both smutgrass varieties germinated over a wide range of pH values. Small and giant smutgrass germination was inhibited at water potentials below −0.2 MPa and when small smutgrass seed was placed below the soil surface. Emergence of giant smutgrass seed did not occur below 3 cm. Both smutgrass varieties germinated over a broad range of environmental conditions, indicating their capability of year-round germination; however, germination is only likely to occur under field conditions during the summer growing season when rainfall is prevalent. These results indicate that both species have the ability to germinate over a wide range of environmental conditions but that germination is inhibited by moisture stress and depth of burial. Considering that giant smutgrass prefers higher temperatures than small smutgrass, the advent of rainfall from June through September is conducive for germination. Practices that focus on the germination pattern of smutgrass could lead to better long-term management of smutgrass in Florida. Nomenclature: Smutgrass, Sporobolus indicus (L.) R. Br. SPZIN; small smutgrass, Sporobolus indicus (L.) R. Br. var. indicus; giant smutgrass, Sporobolus indicus (L.) R. Br. var. pyramidalis (P. Beauv.) Veldkamp.

Aminopyralid soil residues affect rotational vegetable crops in Florida

BACKGROUND Bahiagrass (Paspalum notatum Flueggé) is a poor host of several soilborne pests of vegetable crops; therefore vegetable crops are commonly grown in a rotation with bahiagrass pastures in Florida. The herbicide aminopyralid provides foliar and soil residual weed control and increases forage production in bahiagrass pastures; however, the soil residual activity of aminopyralid makes carryover injury likely in subsequent sensitive vegetable crops. Field research was conducted to determine the sensitivity of five vegetable crops to soil residues of aminopyralid. RESULTS At an aminopyralid soil concentration of 0.2 µg kg(-1) (the limit of quantitation for aminopyralid in this research), crop injury ratings were 48% (bell pepper), 67% (eggplant), 71% (tomato), 3% (muskmelon) and 3% (watermelon), and fruit yield losses (relative to the untreated control) at that concentration were 61, 64, 95, 8 and 14% in those respective crops. CONCLUSIONS The crops included in this research were negatively affected by aminopyralid at soil concentrations less than the limit of quantitation (0.2 µg kg(-1) ). Therefore, it was concluded that a field bioassay must be used to determine whether carryover injury will occur when these crops are planted on a site where aminopyralid has been previously applied.

Seed Production and Control of Sicklepod (Senna obtusifolia) and Pitted Morningglory (Ipomoea lacunosa) with 2,4-D, Dicamba, and Glyphosate Combinations

Sicklepod and pitted morningglory are two of the most important weed species in row-crop production in the southeastern United States. The upcoming introduction of soybean and cotton varieties resistant to 2,4-D and dicamba will increase the reliance on these auxinic herbicides. However, it is not clear how these herbicides will affect sicklepod and pitted morningglory control. Field experiments were conducted in 2013 and 2014 in Jay, FL to determine whether 2,4-D (560 and 1,120 g ae ha−1), dicamba (420 and 840 g ae ha−1), and glyphosate (1,060 g ae ha−1) alone or in combination applied when weed shoots were 11 (early POST [EPOST]) and 22 (late POST [LPOST]) cm long effectively control and prevent seed production of sicklepod and pitted morningglory. LPOST provided more effective control of sicklepod than EPOST. This was attributed to emergence of sicklepod seedlings after the EPOST application. When glyphosate was tank mixed with 2,4-D or dicamba, sicklepod control was higher (78 to 89% and 87 to 98% in 2013 and 2014, respectively) than for single-herbicide treatments (45 to 77% and 38 to 80% in 2013 and 2014, respectively) 6 wk after treatment (WAT). Pitted morningglory control was not affected by application timing, and 2,4-D provided 91 to 100% 6 WAT, which was equivalent to treatments with tank mixtures containing glyphosate. Dicamba applied at 420 g ha−1 had the lowest pitted morningglory control (44 to 70% and 82 to 86% in 2013 and 2014, respectively). Sicklepod and pitted morningglory plants that survived and recovered from herbicide treatments produced the same number of viable seeds as nontreated plants in most treatments. The results of the present study indicated that the use of 2,4-D and dicamba alone will not provide adequate extended control of sicklepod, and the use of tank mixtures that combine auxinic herbicides with glyphosate or other POST herbicides will be necessary to manage sicklepod adequately in 2,4-D- or dicamba-resistant soybean and cotton. Because sicklepod plants that survived a single herbicide application are capable of producing abundant viable seeds, integrated approaches that include PRE herbicides and sequential POST control options may be necessary to ensure weed seed bank reductions. Nomenclature: 2,4-D; dicamba; glyphosate; pitted morningglory, Ipomoea lacunosa L. IPOLA; sicklepod, Senna obtusifolia (L.) H.S. Irwin & Barneby CASOB. Senna obtusifolia e Ipomoea lacunosa son dos de las especies de malezas más importantes en la producción de cultivos en hileras en el sureste de los Estados Unidos. Próximamente, la introducción de variedades de soja y algodón resistentes a 2,4-D y dicamba aumentará la dependencia en estos herbicidas auxínicos. Sin embargo, no está claro cómo estos herbicidas afectarán el control de S. obtusifolia e I. lacunosa. En 2013 y 2014, se realizaron experimentos de campo en Jay, FL para determinar si 2,4-D (560 y 1,120 g ae ha−1), dicamba (420 y 840 g ae ha−1), y glyphosate (1,060 g ae ha−1) solos o en combinación, aplicados cuando la parte aérea de las malezas alcanzó 11 (POST temprana [EPOST]) y 22 (POST tardía [LPOST]) cm de largo, controlan efectivamente S. obtusifolia e I. lacunosa y previenen la producción de semilla. LPOST brindó un control más efectivo de S. obtusifolia que EPOST. Esto fue atribuido a la emergencia de plántulas de S. obtusifolia después de la aplicación EPOST. Cuando glyphosate fue mezclado en tanque con 2,4-D o dicamba, el control de S. obtusifolia fue superior (78 a 89% y 87 a 98% en 2013 y 2014, respectivamente) que tratamientos con un solo herbicida (45 a 77% y 38 a 80% en 2013 y 2014, respectivamente) 6 semanas después del tratamiento (WAT). El control de I. lacunosa no fue afectado por el momento de aplicación, y 2,4-D brindó 91 a 100% de control 6 WAT, lo cual fue equivalente a los tratamientos con mezclas en tanque que contenían glyphosate. Dicamba aplicado a 420 g ha−1 tuvo el menor control de I. lacunosa (44 a 70% y 82 a 86% en 2013 y 2014, respectivamente). Las plantas de S. obtusifolia e I. lacunosa que sobrevivieron y se recuperaron de los tratamientos de herbicidas produjeron el mismo número de semillas viables que las plantas sin tratamiento en la mayoría de los tratamientos. Los resultados del presente estudio indicaron que el uso de sólo 2,4-D y dicamba no brindará un control adecuado extenso de S. obtusifolia, y el uso de mezclas en tanque que combinen herbicidas auxínicos con glyphosate u otros herbicidas POST será necesario para manejar adecuadamente S. obtusifolia en soja y algodón resistentes a 2,4-D o dicamba. Debido a que las plantas de S. obtusifolia que sobrevivieron a aplicaciones sencillas de herbicidas son capaces de producir una abundante cantidad de semillas viables, estrategias integradas que incluyan herbicidas PRE y seguidos de opciones de control POST podrían ser necesarias para asegurar reducciones en el banco de semillas de malezas.