Eugene K. Blythe

Bioassay-Guided Investigation of Two Monarda Essential Oils as Repellents of Yellow Fever Mosquito Aedes aegypti

As part of an ongoing research program to identify active mosquito repellents, Monarda bradburiana Beck and Monarda fistulosa L. essential oils showed good repellent activity with minimum effective dosages (MED) of 0.055 ± 0.036 and 0.078 ± 0.027 mg/cm(2), respectively, compared to reference standard N,N-diethyl-3-methylbenzamide (DEET) (0.039 ± 0.014 mg/cm(2)). Systematic bioassay-guided fractionation of essential oils of both Monarda species was performed to identify the active repellent compounds, and isolated pure compounds were individually tested for repellency. Of the isolated compounds, carvacrol, thymol, eugenol, and carvacrol methyl ether were found to be the repellent compounds with MEDs in the range of 0.013-0.063 mg/cm(2). Active repellent compounds were also tested for larvicidal activity against 1-day-old Aedes aegypti larvae. Thymol was the best larvicide among the tested individual compounds (LD50 of 13.9 ppm). None of the individual compounds showed cytotoxicity against mammalian cells; however, the essential oils were toxic to all cell lines.

Chemical Composition and Biological Activity of Four Salvia Essential Oils and Individual Compounds against Two Species of Mosquitoes

The chemical compositions of essential oils obtained from four species of genus Salvia were analyzed by gas chromatography with a flame ionization detector (GC-FID) and gas chromatography-mass spectrometry (GC-MS). The main compounds identified from Salvia species essential oils were as follows: 1,8-cineole (71.7%), α-pinene (5.1%), camphor (4.4%), and β-pinene (3.8%) in Salvia apiana; borneol (17.4%), β-eudesmol (10.4%), bornyl acetate (5%), and guaiol (4.8%) in Salvia elegans; bornyl acetate (11.4%), β-caryophyllene (6.5%), caryophyllene oxide (13.5%), and spathulenol (7.0%) in Salvia leucantha; α-thujene (25.8%), viridiflorol (20.4%), β-thujene (5.7%), and camphor (6.4%) in Salvia officinalis. In biting-deterrent bioassays, essential oils of S. leucantha and S. elegans at 10 μg/cm(2) showed activity similar to that of DEET (97%, N, N-diethyl-m-toluamide) in two species of mosquitoes, whereas the activities of S. officinalis and S. apiana essential oils were lower than those of the other oils or DEET. Pure compounds β-eudesmol and guaiol showed biting-deterrent activity similar to DEET at 25 nmol/cm(2), whereas the activity of 13-epi-manool, caryophyllene oxide, borneol, bornyl acetate, and β-caryophyllene was significantly lower than that of β-eudesmol, guaiol, or DEET. All essential oils showed larvicidal activity except that of S. apiana, which was inactive at the highest dose of 125 ppm against both mosquito species. On the basis of 95% CIs, all of the essential oils showed higher toxicity in Anopheles quadrimaculatus than in Aedes aegypti. The essential oil of S. leucantha with an LC50 value of 6.2 ppm showed highest toxicity in An. quadrimaculatus.

Chemical Composition, Larvicidal, and Biting Deterrent Activity of Essential Oils of Two Subspecies of Tanacetum argenteum (Asterales: Asteraceae) and Individual Constituents Against Aedes aegypti (Diptera: Culicidae)

ABSTRACT Water-distilled essential oils from dried aerial parts of Tanacetum argenteum (Lam.) Willd. subsp. argenteum (Lam.) and T. argenteum (Lam.) Willd. subsp. canum (C. Koch) Grierson were analyzed by gas chromatography and gas chromatography-mass spectrometry. In total, 27 and 32 components were identified representing 97.2 and 98.7% of essential oils of subsp. argenteum and canum, respectively. Main compounds of T. argenteum subsp. argenteum were &agr;-pinene (67.9%) and &bgr;-pinene (4.8%), whereas &agr;-pinene (53.6%), 1, 8-cineole (14.8%), and camphor (4.7%) were the major constituents of subsp. canum. Essential oil of T. argenteum subsp. canum at 10 µg/cm2 with Biting Deterrent Index (BDI) value of 0.73 showed activity similar to N,N-Diethyl-meta-toluamide (DEET) at 25 mol/cm2, whereas the activity of essential oil of subsp. argenteum was lower (BDI = 0.47) than subsp. canum and DEET. Based on 95% CIs, activity of ß-caryophyllene (BDI value = 0.54) and caryophyllene oxide (BDI = 0.66) were significantly lower than DEET. In larval bioassays, essential oil of T. argenteum subsp. argenteum showed LC50 value of 93.34 ppm, whereas T. argenteum subsp. canum killed only 40% of the larvae at the highest dose of 125 ppm. Among the pure compounds, &bgr;-caryophyllene (LC50 = 26 ppm) was the most potent compound followed by caryophyllene oxide (LC50 = 29 ppm), which was also similar to (-)-&bgr;-pinene (LC50 = 35.9 ppm) against 1-d-old Ae. aegypti larvae at 24-h post treatment. Compounds (-)-&agr;-pinene and (+)-&bgr;-pinene showed similar larvicidal activity. Activity of (+)-&bgr;-pinene with LC50 value of was similar to the essential oil of T. argenteum subsp. argenteum.

Yellow Nutsedge (Cyperus esculentus) Control and Tomato Response to Application Methods of Drip-Applied Herbicides in Polyethylene-Mulched Tomato

Abstract Drip-applied herbicides provide farmers with a more timely and cost-effective approach for applying PRE herbicides; however, herbicide movement is often limited. Field studies were conducted evaluating drip-application methods for applying PRE herbicides under polyethylene-mulched beds on yellow nutsedge punctures and the corresponding responses of a tomato crop (height and yield). The experiment was a factorial treatment arrangement of three drip application methods and three PRE-applied herbicides [halosulfuron (54 g ai ha−1), S-metolachlor (1.4 kg ha−1), and fomesafen (280 g ha−1)]. Herbicides were applied either immediately following saturation of the planting beds (method A), over an extended period while saturating the beds (method B), or prior to bed saturation (method C). Additional treatments included a commercial standard (S-metolachlor sprayed to the bed surface prior to mulch application) and a nontreated control (polyethylene mulch only). Drip-applied fomesafen, halosulfuron, and S-metolachlor provided similar control of yellow nutsedge, produced comparable yields, and failed to elicit any negative growth responses when compared to our commercial standard. With the exception of nutsedge punctures counted 56 DAT, application method did not influenced measurable outcomes. At 56 DAT nutsedge punctures were significantly lower in treatments applied by method B compared to those applied with method A. Nomenclature: Fomesafen; halosulfuron; S-metolachlor; yellow nutsedge, Cyperus esculentus L; tomato, Solanum lycopersicum L Resumen Los herbicidas aplicados en sistemas de riego por goteo brindan a los productores un sistema más barato y flexible para la aplicación de herbicidas PRE en diferentes momentos. Sin embargo, el movimiento del herbicida es a menudo limitado. Se realizaron estudios de campo para evaluar métodos de aplicación de herbicidas por goteo para aplicar herbicidas PRE bajo camas con coberturas de polyethylene para el control de la perforación causada por Cyperus esculentus y la correspondiente respuesta del cultivo de tomate (altura y rendimiento). El experimento fue un arreglo factorial de tratamientos de tres métodos de aplicación por goteo y tres herbicidas aplicados PRE [halosulfuron (54 g ai ha−1), S-metolachlor (1.4 kg ha−1), y fomesafen (280 g ha−1)]. Los herbicidas fueron aplicados ya fuera inmediatamente después de saturar las camas de siembra (método A), a lo largo de un período extendido durante la saturación de las camas (método B), o antes de la saturación de las camas (método C). Tratamientos adicionales incluyeron un estándar comercial (S-metolachlor asperjado sobre la cama de siembra antes de la colocación de la cobertura) y un testigo sin tratamiento (solamente cobertura de polyethylene). Fomesafen, halosulfuron, y S-metolachlor aplicados por goteo brindaron un control similar de C. esculentus, produjeron rendimientos comparables, y no generaron respuestas negativas en el crecimiento del cultivo cuando se compararon con nuestro estándar comercial. Con la excepción del número de perforaciones causadas por C. esculentus contadas 56 DAT, el método de aplicación no influenció ninguna de los factores medidos. A 56 DAT, las perforaciones de C. esculentus fueron significativamente menores en tratamientos aplicados con el método B al compararse con los del método A.

Alginate Encapsulation of Begonia Microshoots for Short-Term Storage and Distribution

Synthetic seeds were formed from shoot tips of two in vitro grown Begonia cultivars using 3% sodium alginate in Murashige and Skoog medium (MS) salt solution as the gel matrix and 100 mM calcium chloride for complexation. Synthetic seed formation was achieved by releasing the sodium alginate/explant combination into 100 mM calcium chloride (CaCl2 ·H2O) solution for 30 or 45 min. Both control and encapsulated shoots were transferred into sterile Petri dishes and stored at 4°C or 22°C for 0, 2, 4, 6, or 8 weeks. Conversion of synthetic seeds into plantlets for both storage environments was assessed in MS medium or peat-based substrate. No significant difference was found between the 30 and 45 min CaCl2 ·H2O treatments or the two cultivars. Encapsulation of explants improved survival rate over time irrespective of the medium type or storage environment. Survival rates of 88, 53, 28, and 11% for encapsulated microshoots versus 73, 13, 0, and 0% for control explants were achieved in microshoots stored for 2, 4, 6, and 8 weeks, respectively. The best results were obtained when synthetic seeds were stored at 4°C and germinated on MS medium. Regenerated plantlets were successfully established in potting soil.

Turf Tolerance and Virginia Buttonweed (Diodia virginiana) Control with Fluroxypyr as Influenced by the Synergist Diflufenzopyr1

Virginia buttonweed control in warm-season turfgrass species requires high application rates and/or repeated applications of herbicides (or both) with an auxin-type mode of action. These treatments often lead to unacceptable turfgrass injury. Diflufenzopyr functions as a synergist with auxin-type herbicides, and it has been suggested that it may do the same when combined with pyridine herbicides such as fluroxypyr. The objective of this field and laboratory research was to determine whether Virginia buttonweed control could be improved with admixtures of fluroxypyr and diflufenzopyr without unacceptable turf injury. Treatments consisted of fluroxypyr applied alone at 140 and 280 g ae/ha, diflufenzopyr alone at 70 and 140 g/ha, and all possible two-way admixtures. Treatments were applied to a hybrid bluegrass ‘Thermal blue’ infested with Virginia buttonweed. Sod of centipedegrass ‘common’, hybrid bermudagrass ‘Tifway’, hybrid zoysiagrass ‘Emerald’, and St. Augustinegrass ‘Raleigh’, which had been previously established in pots, were treated simultaneously and returned to a greenhouse. Fluroxypyr plus diflufenzopyr at 280 and 70 g/ha, respectively, controlled Virginia buttonweed nearly 40% more than fluroxypyr alone. Turfgrass injury was species-dependent, and was generally either equivalent to or less than that obtained with fluroxypyr alone. Radiotracer studies established that, depending upon the turfgrass species, fluroxypyr absorption was either not influenced or reduced by the addition of diflufenzopyr. Neither root nor foliar absorption of fluroxypyr by Virginia buttonweed was influenced by diflufenzopyr. Translocation of foliar-absorbed fluroxypyr was reduced, but translocation of root-absorbed fluroxypyr was increased by diflufenzopyr. The diflufenzopyr-induced synergism may indicate that a significant portion of the applied fluroxypyr was absorbed by roots or by other subsoil tissues, or both. Nomenclature: Diflufenzopyr 2-(1-[([3,5-difluorophenylamino]carbonyl)-hydrazono]ethyl-3-pyridinecarboxylic acid; fluroxypyr; Virginia buttonweed, Diodia virginiana L. #3 DIQVI; hybrid bermudagrass, Cynodon dactylon Burtt-Davey X C. transvaalensis L. Pers. ‘Tifway’; centipedegrass, Eremochloa ophiuroides (Munro.) Hack. ‘Common’; hybrid zoysiagrass, Zoysia japonica Steud. X Z. tenuifolia Willd. Ex Trin ‘Emerald’; St. Augustinegrass, Stenotaphrum secundatum (Walt.) Kuntze. ‘Raleigh’; hybrid bluegrass, Poa pratensis X P. arachnifera Torr. ‘Thermal Blue’. Additional index words: Auxin herbicides, 14C-fluroxypyr, herbicide translocation, herbicide synergist, pyridine herbicide, warm-season turfgrass. Abbreviations: DAT, days after treatment; LSS, liquid scintillation spectrometry; WAT, weeks after treatment.

Potential for halosulfuron to control Eclipta (Eclipta prostrata) in container-grown landscape plants and its sorption to container rooting substrate

Eclipta is a seed-borne summer annual that is problematic in the production of container-grown landscape plants. Halosulfuron at 70 g/ha is registered as a directed application to landscape areas but not to container-grown landscape plants. Halosulfuron was applied preemergence (PRE) to seeded eclipta and postemergence (POST) to progressively older eclipta seedlings at rates ranging from 0.18 to 100 g/ha. For halosulfuron PRE treatments, eclipta control was determined from the foliage weight of surviving seedlings. For halosulfuron POST treatments, control was determined from the weight of foliage regrowth following the removal of the treated foliage 2 wk after treatment. Nonlinear regression and log-logistic analysis indicated that the rate required for 90% control (I90) for halosulfuron PRE was 45 g/ha. For halosulfuron POST, the I90 was 60 g/ha for plants having five or fewer true leaves and 98 g/ha for plants that had lateral branching from the basal crown. Analysis estimated the I90 for flowering-sized eclipta exceeded 300 g/ha. Selective placement studies revealed that the phytotoxicity resulting from POST treatments occurs by foliar and root uptake, with foliar exposure having greater activity. For POST treatments that were limited to foliage-only contact, a split application increased control up to 25% compared with a single application of the same total dosage. However, control remained inadequate because the rate required for 75% control (I75) was 157 and 121 g/ha for single and split applications, respectively. Halosulfuron sorption by a pine bark–based rooting substrate, as used in container production, was 96% of the amount applied. The propensity for surface-applied halosulfuron to be leached in this substrate was evaluated by eclipta bioassay. After 2 wk, with 23 cm of cumulative irrigation and rainfall, halosulfuron was detected 12 cm below the substrate surface. The propensity for substrate-adsorbed halosulfuron to return to the water phase may also contribute to PRE activity for eclipta control. Nomenclature: Halosulfuron; eclipta, Eclipta prostrata L., #3 ECLAL. Additional index words: Herbicide sorption, log-logistic analysis, organic rooting substrates. Abbreviations: Ix, x% growth inhibition; POST, postemergence; PRE, preemergence; WAT, weeks after treatment.

Nitrogen Requirements for Sweetpotato Following a Crimson Clover Cover Crop

Sweetpotato [Ipomoea batatas (L.) Lam.] is an economically important crop in the southeastern United States, and sustainable production practices that include reducing fertilizer costs and improving soil organic matter are needed. Field studies were conducted in the Spring of 2007 and 2008 to evaluate nitrogen fertilization requirements of sweetpotato. Treatments of 0, 50, and 101 kg·ha−1 nitrogen (from ammonium nitrate applied preplant broadcast) were applied following a crimson clover (Trifolium incarnatum L.) cover crop along with a conventional no cover crop treatment using 101 kg·ha−1 N (from ammonium nitrate). Sweetpotato yields for all rates of N fertilizer following the cover crop were similar (for ‘Beauregard’ in 2007) or greater (for ‘Xushu 18’ in 2008) than yields from plants grown using the conventional treatment. Percentage of dry matter of storage roots was not affected by treatment. Nitrogen fertilization can be reduced or eliminated when sweetpotatoes are produced following a crimson clover winter cover crop.

Management of Plum Curculio and Catfacing Insects on Peaches in Central Alabama: Standard Crop Stage–Based vs. Integrated Pest Management–Based Approaches

ABSTRACT Plum curculio, tarnished plant bug, brown stink bug, and green stink bug are the major insect pests causing fruit damage on peaches grown in the southeastern United States. Insect management aids, monitoring techniques, predictive models, and action thresholds for southeastern peaches are either lacking or they are not robust enough to facilitate industry acceptance of as-needed insecticide applications during the growing season (Horton et al., 2003). In this 3-year study, we compared two approaches to scheduling insecticide applications for control of these pests on three peach cultivars in an established central Alabama orchard: 1) an industry standard, representative of prevailing practice in the southeastern United States, which consisted of scheduled insecticide applications timed to coincide with crop stage; and 2) an integrated pest management (IPM) treatment, which employed limited prescheduled insecticide applications timed to coincide with the crops developmental stage, supplemented with as-needed insecticide applications when preestablished action thresholds were reached. Percentage of insect-damaged fruit from trees under the IPM treatment was similar to, or in some cases greater or less than, that of fruit from trees receiving the standard treatment. Depending on the year, the same or fewer insecticide applications were made under the IPM treatment compared with the standard treatment. The IPM treatment came close to providing acceptable levels of plum curculio control with the early-season cultivar Correll but not with the mid- and late-season cultivars Sunland and Biscoe.

Ambrosia Beetle (Coleoptera: Curculionidae: Scolytinae) Captures Using Colored Traps in Southeast Tennessee and South Mississippi

Abstract Ambrosia beetles (Coleoptera: Curculionidae: Scolytinae) have become a major impediment to profitable nursery production, with proper controls centered around an accurate monitoring program. Whereas the use of semiochemicals by ambrosia beetles is well understood, the potential use of visual cues including colors remains relatively understudied. Field tests were performed in Tennessee and Mississippi to determine response of the ambrosia beetle community to 13 trap colors (black, blue, brown, clear, gray, green, lavender, opaque, orange, purple, red, white, and yellow). Traps consisted of corrugated plastic in the shape of a prism and covered in insect glue (Pestick™ or Tangle-Trap®). All trap colors were analyzed with a spectro-photometer to quantify spectral reflectance, ranging from 6 - 80% reflectance. Mean ambrosia beetle capture from opaque and red traps (60 and 54, respectively) was significantly higher than from yellow or white traps (30 and 28, respectively). However, captures from each of the afore-mentioned 4 colors were not significantly different from the other 9 colors tested. Although further research is needed to explain the efficacy of the opaque traps, we can recommend that industry-standard black traps are an acceptable choice for ambrosia beetle monitoring programs; whereas, yellow or white traps are not recommended.