Scholarly Works, Virginia Agricultural Experiment Station

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VAES faculty are located at 11 Agricultural Research and Extension Centers in Virginia and three colleges at Virginia Tech (CALS, CNRE, and VMRCVM).

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Public, animal, and environmental health implications of aquaculture
Garrett, E. Spencer; dos Santos, Carlos Lima; Jahncke, Michael L. (1997-10)
Aquaculture is important to the United States and the world's fishery system. Both import and export markets for aquaculture products will expand and increase as research begins to remove physiologic and other animal husbandry barriers. Overfishing of wild stock will necessitate supplementation and replenishment through aquaculture. The aquaculture industry must have a better understanding of the impact of the ''shrouded'' public and animal health issues: technology ignorance, abuse, and neglect. Cross-pollination and cross-training of public health and aquaculture personnel in the effect of public health, animal health, and environmental health on aquaculture are also needed. Future aquaculture development programs require an integrated Gestalt public health approach to ensure that aquaculture does not cause unacceptable risks to public or environmental health and negate the potential economic and nutritional benefits of aquaculture.
Mycelial growth, sporulation, and survival of Monilinia fructicola in relation to osmotic potential and temperature
Hong, Chuanxue; Michailides, Themis J. (Mycological Society of America, 1999)
The effects of osmotic potential (Psi) and temperature on mycelial growth, sporulation, and survival of Monilinia fructicola were determined using potato-dextrose agar (PDA) amended with KCI and sucrose. Comparatively, KCl facilitated the sporulation and sucrose facilitated the mycelial growth and survival of the fungus. Optimal mycelial growth occurred at -1 MPa and 25 C and sporulation at -3 MPa and 20 C. Sporulation decreased more rapidly than mycelial growth as osmotic potential and temperature became less conducive. Significant interactions between osmotic potential and temperature were observed on affecting the mycelial growth and sporulation. Monilinia fructicola did not grow in PDA amended with KCl at Psi < -11 MPa (20 and 25 C), -9 MPa (15 and 30 C), or -7 MPa (10 C) after 6-d incubation; it also did not grow in PDA amended with KCl at Psi < -11 MPa nor in PDA amended with sucrose at Psi < -13 MPa even after 60-d incubation at any temperatures tested. Monilinia fructicola survived water stress better at low temperatures than at high temperatures. These results could help in understanding the ecology and epidemiology of brown rot of stone fruit and in development of integrated disease management strategies.
Reduction of bunch stem necrosis of Cabernet Sauvignon by increased tissue nitrogen concentration
Capps, E. R.; Wolf, T. K. (American Society for Enology and Viticulture, 2000)
Field experiments were conducted over three years at two vineyards in northern Virginia to examine relationships between specific nutrients and the incidence of bunch stem necrosis (BSN) of Cabernet Sauvignon. Nitrogen, magnesium, acid calcium were applied alone or in combination. Only one of the vineyards (Winchester) showed appreciable BSN incidence during the study period. During the 1996 season at Winchester vineyard, bloom-time leaf petiole and veraison rachis nitrogen concentration of unfertilized (control) vines were 0.80% and 1.16%, respectively. The corresponding control BSN incidence was 41% at harvest time. Seasonally split application of nitrogen fertilizer at 112 kg/ha actual nitrogen increased bloom-time leaf petiole and veraison cluster stem nitrogen concentration to 1.85% and 1.82%, respectively, in the nitrogen plots. The corresponding BSN incidence was reduced to 14% at harvest time. BSN symptoms were not as pronounced during the 1997 season; however, all treatments, including the control plots had elevated tissue nitrogen levels in 1997. Application of nitrogen fertilizer in 1998 was associated with bloom-time leaf petiole and veraison rachis nitrogen concentrations of 1.18% and 1.34%, respectively. Corresponding BSN was reduced to 3% at harvest time, versus 17% to 23% in treatments that did not receive nitrogen. Magnesium and calcium had minimal (1997) or no impact on BSN incidence. Measures of canopy density, cane pruning weights, crop yield, and fruit chemistry suggest that the ameliorating effects of nitrogen on BSN incidence were directly related to increased tissue nitrogen concentration, and not an indirect effect of vigor stimulation or crop ripening rate. A low incidence of BSN at the second vineyard precluded a definitive explanation of prior BSN expression at that location. We conclude that low tissue [N] may be one cause of BSN, and that vineyards should be examined individually for contributing factors.
Effects of horticultural oils on the photosynthesis, fruit maturity, and crop yield of winegrapes
Finger, Sarah A.; Wolf, Tony K.; Baudoin, Antonius B. (American Society for Enology and Viticulture, 2002)
The effects of horticultural oils on grapevine photosynthesis, fruit maturity, and crop yield components in field experiments were evaluated. Three applications of a 1.5% (v/v) oil/water emulsion were made to Chardonnay and Cabernet Sauvignon vine canopies at 6200 L/Ha (Chardonnay) and 2440 L/Ha (Cabernet Sauvignon) in 1998 using several horticultural oils. Net assimilation rates (NAR) and fruit soluble solids concentrations (SSC) were reduced in both cultivars by all oils, as compared to the control. In addition, berry weights, cluster weights, crop per vine, and vine pruning weights were all reduced by oil treatments to Chardonnay vines. Experiments in 1999 sought to determine if reduced spray volumes or applications to only the fruit zone minimized reductions in NAR and SSC. Chardonnay and Cabernet Sauvignon were treated twice with JMS Stylet-Oil(TM) (1.5%) using 5600 L/Ha or 1870 L/Ha applied to the whole canopy or 930 L/Ha applied only to the fruit zone. The NAR of 5600 L/Ha-treated Cabernet Sauvignon was significantly lower than the NAIR of 1870 L/Ha oil-treated vines on three of four subsequent measurement dates. The NAR of Chardonnay in either the 1870 or 5600 L/Ha whole canopy oil treatments was significantly lower than the NAR of the water treatment at all measurement dates. Oil application to only the fruit zone (930 L/Ha) reduced the negative impact on NAR. Cabernet Sauvignon fruit SSC was consistently reduced by the 5600 L/Ha and 1870 L/Ha treatments, relative to the water-treated control. Similarly, the SSC of Chardonnay fruit in the 1870 and 5600 L/Ha treatments was consistently reduced compared to controls. Oil effects on fruit pH and titratable acidity were occasionally observed. While horticultural oils may serve as effective fungicides, our results highlight the potential negative impacts they can have on fruit composition and fruitfulness if used excessively.
Effects of prohexadione-calcium on grape yield components and fruit and wine composition
Lo Giudice, Danielle; Wolf, Tony K.; Zoecklein, Bruce W. (American Society for Enology and Viticulture, 2004)
Prohexadione-calcium (prohexadione-Ca) was applied to field-grown Cabernet franc, Cabernet Sauvignon, Chardonnay, and Seyval to evaluate rates and timing effects on fruit yield components and on fruit and wine composition. Berries per cluster, berry weight, cluster weight, and clusters per shoot in the subsequent season were all decreased by multiple, prebloom plus postbloom, applications to Cabernet Sauvignon and Cabernet franc. Similar reductions in current season components of yield were observed with Seyval. Application (250 mg/L) to single clusters of Cabernet Sauvignon and Chardonnay at bloom, or in the one-to-two-week prebloom period decreased fruit set, whereas applications one to two weeks postbloom reduced berry weight, with no impact on fruit set. Berry weight reduction correlated to increased color intensity (420 nm + 520 nm), total anthocyanins, total phenols, and phenol-free glycosyl-glucose (PFGG) in Cabernet Sauvignon. In a separate experiment, prohexadione-Ca increased Cabernet franc must color intensity, total anthocyanins, and total phenols, despite having, minimal effects on berry weight or crop yield. Aroma and flavor triangle difference tests did not distinguish treatment differences with young Cabernet franc wines. This study of prohexadione-Ca effects on grape reproductive development illustrated that berry set and berry weight were responsive to application timing, with the one-to-two-week period after bloom most sensitive to reductions in berry weight. The concurrent effects on fruit composition were generally positive, while the full impact on wine quality remains equivocal, but worthy of further evaluation.
Cultural characteristics of Eutypa lata and one unknown isolate on different nutrient media
Aćimović, Srđan G.; Delibašić, Goran (University of Kragujevac, Serbia, 2005-08)
Red imported fire ants (Hymenoptera : Formicidae) increase the abundance of aphids in tomato
Coppler, Laura B.; Murphy, John F.; Eubanks, Micky D. (Florida Entomological Society, 2007-09)
Red imported fire ants, Solenopsis invicta (Buren) (Hymenoptera: Formicidae), are abundant in many agroecosystems in the southern United States and can affect the abundance of arthropods in these systems. We determined the effects of red imported fire ants on the abundance of aphids, other herbivorous insects, and beneficial arthropods in Alabama tomato (Lycopersicon esculentum) by manipulating the density of red imported fire ants in plots of tomato plants and by sampling fresh market tomato farms for two years (2003 and 2004). In both years of our study, aphid abundance was significantly greater in tomato plots with high densities of fire ants than in plots where fire ant densities were suppressed. Further, the abundance of fire ants was positively correlated with the abundance of aphids on intensely managed tomato farms in both years. These aphids included many species that are the primary vectors of economically-important plant viruses of tomato and other vegetable crops. The positive effect of fire ants on aphid abundance was likely due to facultative fire ant-aphid mutualisms. Other studies have demonstrated that fire ants protect honeydewproducing insects from natural enemies, and we found that fire ants reduced the abundance of beneficial arthropods in the second year of our field experiment. However, red imported fire ants did not significantly reduce the abundance of non-aphid herbivores in either year of our field experiment, suggesting that fire ants are not important biological control agents of these insects in tomato. Fire ants may disrupt biological control of aphids in tomato fields and suppression of fire ants on tomato farms may decrease the abundance of aphids.
Effect of vertical shoot-positioned, smart-dyson, and Geneva double-curtain training systems on Viognier grape and wine composition
Zoecklein, Bruce W.; Wolf, T. K.; Pelanne, L.; Miller, M. K.; Birkenmaier, S. S. (American Society for Enology and Viticulture, 2008-03)
Viognier grapes grown in northern Virginia and resultant wines were evaluated as a function of training system. Treatments included vertical shoot-positioned (VSP), Smart-Dyson (SD), and Geneva double curtain (GDC), with vines of all treatments spaced 2.4 m apart in 3.0 m wide rows. In addition to increased cluster numbers and crop yield, GDC training generally increased fruit zone sunlight interception and fruit exposure, while it decreased cane pruning weights per meter of cordon, compared with SD and VSP. Crop adjustments were made between bloom and veraison in six seasons, to result in average yields of 10.5 kg/vine (GDC), 9.9 kg/vine (SD), and 6.0 kg/vine (VSP), with the lower SD canopy bearing 30 to 40% less crop than the corresponding upper SD canopy. Crop loads (yield/cane pruning weight) were generally between 4 and 12; GDC crop load approached 20 in three seasons, while SD approached 14 in one. Leaf area per crop ratio was determined one season and exceeded 1.8 m(2)/kg of fruit for all systems. Fruit was harvested at similar Brix values, with differences in berry weight, pH, titratable acidity, and malic and tartaric acids among treatments generally not significant. Volatile compounds were analyzed using headspace solid-phase microextraction GC-MS. Fruit showed consistent differences in linalool, alpha-terpineol, beta-damascenone, and n-hexanol concentrations among training systems. SD had the highest concentration of most free volatiles quantified in both juice and wines, while GDC wines frequently had the highest concentration of phenol-free glycosides. Triangle difference sensory testing demonstrated differences between GDC and SD in wine aroma and flavor and between VSP and SD in flavor. GDC wines generally had higher fruity and floral aromas compared with the other systems.
Bacterioses of Soybean
Balaž, Jelica S.; Aćimović, Srđan G. (University of Novi Sad, Serbia, 2008-10-01)
Eutypa Dieback and ESCA - Trunk Necrosis and Dieback Diseases of Grapevines in Serbia
Aćimović, Srđan G.; Delibašić, Goran; Schilder, Annemiek; Tanovic, Brankica (University of Novi Sad, Serbia, 2008-12-22)
Erwinia amylovora in Vojvodina and Measures of Control
Balaž, Jelica S.; Keserović, Zoran; Aćimović, Srđan G.; Nikolic, Zorica; Mažić, Jelena (University of Novi Sad, Serbia, 2009-02-10)
Expression of feeding symptoms from pink hibiscus mealybug (Hemiptera: Pseudococcidae) by commercially important cultivars of hibiscus
Vitullo, Justin; Zhang, Aijun; Mannion, Catharine; Bergh, J. Christopher (Florida Entomological Society, 2009-06)
The pink hibiscus mealybug, Maconellicoccus hirsutus (Green), is a highly polyphagous pest that invaded southern Florida in 2002 and is now widely established throughout most of the state. Although Hibiscus rosa-sinensis L. is a preferred and economically important host of M. hirsutus, the susceptibility and expression of feeding symptoms by different cultivars have not been evaluated. Cultivars of H. rosa-sinensis were infested with M. hirsutus and evaluated daily for 40 d for the onset and percentage of terminals expressing feeding symptoms. Under different initial densities of M. hirsutus, the cultivar 'President' showed no difference in the latency to expression of feeding symptoms, which occurred between 7 and 15 d after infestation, but did show significant differences between initial density and percentage of terminals expressing feeding symptoms from 10 d onward. When infested with 20 females, 80% of 'President' terminals exhibited symptoms 30 d after infestation. Four other cultivars initially infested with 10 female M. hirsutus showed significant differences in the onset and severity of feeding symptoms. All plants of the cultivars 'Florida Sunset' and 'Joanne' expressed damage symptoms at 12 +/- 2 SE d and 10 +/- 1 d, respectively, following infestation. Only a single plant of the cultivars 'Double Red' and 'Snow Queen' showed such symptoms at 19 and 30 d after infestation, respectively. Significant differences between cultivar and the percentage of terminals expressing feeding symptoms were observed from 20 d onward. Terminals sampled from all plants after 40 d revealed that egg, nymph, and adult female M. hirsutus were found on all plants, including those that did not exhibit feeding symptoms. These data have shown that hibiscus cultivars differ in their expression of M. hirsutus feeding symptoms, that M. hirsutus can reproduce on cultivars of hibiscus that do not express feeding symptoms, and that feeding symptoms are not a reliable indicator of infestation by M. hirsutus, highlighting the need for further investigation of the mechanisms underlying differences among cultivars.
Some important fungal pathogens of medicinal plants in Južna-Bačka region
Balaž, Jelica S.; Aćimović, Srđan G.; Crnobarac, Jovan; Adamović, Dušan; Jacimovic, Goran (University of Novi Sad, Serbia, 2010-01-01)
Using Microscopy to Assess Chorion Structural Integrity and Parasitoid Oviposition Sites on Stink Bug (Hemiptera: Pentatomidae) Eggs
Koppel, Amanda Leigh; Herbert, D. Ames Jr.; Westbrook, E. W. (Cambridge University Press, 2011-02)
Previous efficacy studies found that many insecticides used by growers could be having an adverse effect on egg parasitoids (Telenomus podisi) developing in the eggs of the brown stink bug (Euschistus servus), while unhatched stink bugs experienced lower levels of mortality. One plausible explanation for this was that insecticides might enter parasitized eggs more readily via oviposition wounds. Parasitized E. servus eggs, as well as nonparasitized stink bug (Acrosternum hilare, E. servus, Murgantia histrionica, and Podisus macoliventris) eggs, were examined using electron microscopy. Egg response to perforation by a tungsten probe served as a control. Microscopy images depicted the chorion surface as characterized by a matrix of ridges and micropylar processes in a ring around the margin of the operculum. Observations of oviposition sites showed a "scab" formed where the ovipositor penetrated the chorion, and at sites penetrated by the probe. These formations appeared to be the result of fluids from inside the egg leaking out, drying, and hardening after oviposition or probe perforation, suggesting that the response was not due to substances secreted by the parasitoid. Further, no open wounds or holes were seen to increase the possibility of insecticides entering parasitized eggs.
Harlequin Bug Biology and Pest Management in Brassicaceous Crops
Wallingford, A. K.; Kuhar, Thomas P.; Schultz, P. B.; Freeman, J. H. (Entomological Society of America, 2011-04-01)
Harlequin bug, Murgantia histrionica (Hahn), is a piercing-sucking pest of brassicaceous crops, particularly in the southern United States. The pest typically completes two to four generations per year, and overwinters as an adult in debris and weeds. Both adults and nymphs feed on aboveground plant tissues, leaving white blotches on leaves. Under heavy feeding pressure, plants can wilt and die. Chemical insecticides such as pyrethroids, organophosphates, carbamates, and neonicotinoids have been used for effective control of harlequin bug adults and nymphs. However, there is potential for cultural control of this pest using trap cropping. This paper reviews the biology and management of harlequin bug.
Cover Crop, Rootstock, and Root Restriction Regulate Vegetative Growth of Cabernet Sauvignon in a Humid Environment
Hatch, T. A.; Hickey, C. C.; Wolf, T. K. (American Society for Enology and Viticulture, 2011-09)
Cover crops, rootstocks, and root restriction were evaluated as means to regulate vegetative growth of Cabernet Sauvignon grapevines in a humid environment. Treatments were arranged as a strip-split-split plot with row-middle and under-trellis cover crop (UTCC) compared to row-middle only cover crop combined with 85 cm weed-free strips in the vine row as main plots. Rootstocks Riparia Gloire (Riparia), 420A, and 101-14 were subplots, while sub-subplots comprised two treatments: vines were either planted in root-restrictive (RR) fabric bags (0.015 m(3)) at vineyard establishment or were planted without root restriction. Root restriction and UTCC were independently effective in suppressing vegetative development as measured by rate and seasonal duration of shoot growth, lateral shoot development, trunk circumference, and dormant pruning weights. Riparia was the most effective rootstock in limiting vegetative development among the three evaluated; vines grafted to Riparia had similar to 25% lower cane pruning weights than did vines grafted to 420A or 101-14. Under-trellis cover crop reduced cane pruning weights by 47% relative to vines grown on herbicide strips. Canopy architecture was generally improved by both UTCC and by root restriction, but generally unaffected by rootstock. Root restriction reduced the discrimination against C-13 assimilation in both berries and leaf laminae tissue as measured by delta C-13, while under-trellis floor management did not affect this measure of chronic water stress. The principal direct effeci of the UTCC and the root-restriction treatments was a sustained reduction in stem (xylem) water potential (psi(stem)). Stomatal conductance and net assimilation rate were depressed by increasing water deficit, particularly for root-restricted vines. Results suggest practical measures can be used to create a more favorable vine balance under conditions of variable rainfall, such as exist in the eastern United States.
Biology, Crop Injury, and Management of Thrips (Thysanoptera: Thripidae) Infesting Cotton Seedlings in the United States
Cook, D.; Herbert, D. Ames Jr.; Akin, D. S.; Reed, J. (Entomological Society of America, 2011-10-01)
Several species of thrips are known to infest cotton seedlings in the United States and constitute one of the most common insect pest challenges for growers. The species complex, species abundance, extent of crop injury, and impact on lint yield varies widely across the cotton states. Cotton seedlings are most susceptible to thrips injury during the first 4 to 5 weeks after plant emergence. Feeding by thrips results in distortion, malformation and tearing of seedling leaves, reduced leaf area and plant height, reduced root growth, and injury to or death of the apical meristem, the latter of which leads to excessive vegetative branching. Plant maturity (i.e., fruit production) can be delayed and in extreme cases, losses of as much a 30-50% of lint yield potential have been reported. To date, no varieties of cotton have resistance to thrips, so controls are based solely on insecticide applications. Treatment thresholds and control practices (e.g., insecticide seed treatments, in-furrow or foliar applied insecticides) vary widely across cotton states. This article provides a brief summary of the various species of thrips present in U.S. cotton, their plant host range and injury to cotton, a general description of thrips biology, and management practices currently available to growers.
Fifty Years of Cereal Leaf Beetle in the U.S.: An Update on Its Biology, Management, and Current Research
Philips, Christopher R.; Herbert, D. Ames Jr.; Kuhar, Thomas P.; Reisig, Dominic D.; Thomason, Wade E.; Malone, Sean M. (Entomological Society of America, 2011-10-01)
Cereal leaf beetle, Oulema melanopus L., is an introduced insect pest of small grains first recorded in the United States in the early 1960s. Since its introduction from Europe or Asia into Michigan, cereal leaf beetle has rapidly spread and can now be found in most states. Cereal leaf beetle feeds on numerous species of grasses and is considered a major pest of oats, barley, and wheat. Although several studies have investigated cereal leaf beetle biology and population dynamics, numerous gaps remain in understanding the mechanisms that influence its spread and distribution, which makes predicting pest outbreaks difficult. Because of the difficulty in predicting when and where pest outbreaks will occur many growers in the southeast apply insecticides on a calendar basis rather than using a threshold-based integrated pest management approach. Our challenge is to develop new information and procedures that will encourage growers to reevaluate the way they are approaching spring-time insect control in wheat, and consider adoption of the integrated pest management approach. This article is a review of cereal leaf beetle biology, past and present management practices, and current research being conducted.
Transcriptomics of shading-induced and NAA-induced abscission in apple (Malus domestica) reveals a shared pathway involving reduced photosynthesis, alterations in carbohydrate transport and signaling and hormone crosstalk
Zhu, Hong; Dardick, Chris D.; Beers, Eric P.; Callahan, Ann M.; Xia, Rui; Yuan, Rongcai (2011-10-17)
Background Naphthaleneacetic acid (NAA), a synthetic auxin analogue, is widely used as an effective thinner in apple orchards. When applied shortly after fruit set, some fruit abscise leading to improved fruit size and quality. However, the thinning results of NAA are inconsistent and difficult to predict, sometimes leading to excess fruit drop or insufficient thinning which are costly to growers. This unpredictability reflects our incomplete understanding of the mode of action of NAA in promoting fruit abscission. Results Here we compared NAA-induced fruit drop with that caused by shading via gene expression profiling performed on the fruit abscission zone (FAZ), sampled 1, 3, and 5 d after treatment. More than 700 genes with significant changes in transcript abundance were identified from NAA-treated FAZ. Combining results from both treatments, we found that genes associated with photosynthesis, cell cycle and membrane/cellular trafficking were downregulated. On the other hand, there was up-regulation of genes related to ABA, ethylene biosynthesis and signaling, cell wall degradation and programmed cell death. While the differentially expressed gene sets for NAA and shading treatments shared only 25% identity, NAA and shading showed substantial similarity with respect to the classes of genes identified. Specifically, photosynthesis, carbon utilization, ABA and ethylene pathways were affected in both NAA- and shading-induced young fruit abscission. Moreover, we found that NAA, similar to shading, directly interfered with leaf photosynthesis by repressing photosystem II (PSII) efficiency within 10 minutes of treatment, suggesting that NAA and shading induced some of the same early responses due to reduced photosynthesis, which concurred with changes in hormone signaling pathways and triggered fruit abscission. Conclusions This study provides an extensive transcriptome study and a good platform for further investigation of possible regulatory genes involved in the induction of young fruit abscission in apple, which will enable us to better understand the mechanism of fruit thinning and facilitate the selection of potential chemicals for the thinning programs in apple.
Persistence of Overseeded Cool-Season Grasses in Bermudagrass Turf
Serensits, Thomas; Cutulle, Matthew; Derr, Jeffrey F. (Hindawi, 2011-11-02)
Cool-season grass species are commonly overseeded into bermudagrass turf for winter color. When the overseeded grass persists beyond the spring; however, it becomes a weed. The ability of perennial ryegrass, Italian (annual) ryegrass, intermediate ryegrass, and hybrid bluegrass to persist in bermudagrass one year after seeding was determined. Perennial ryegrass, intermediate ryegrass, and Italian ryegrass produced acceptable ground cover in the spring after fall seeding. Hybrid bluegrass did not establish well, resulting in unacceptable cover. Perennial ryegrass generally persisted the most one year after seeding, either because of summer survival of plants or because of new germination the following fall. Plant counts one year after seeding were greater in the higher seeding rate treatment compared to the lower seeding treatment rate of perennial ryegrass, suggesting new germination had occurred. Plant counts one year after seeding plots with intermediate ryegrass or Italian ryegrass were attributed primarily to latent germination and not summer survival. Applications of foramsulfuron generally did not prevent overseeded species stand one year after seeding, supporting the conclusion of new germination. Although quality is less with intermediate ryegrass compared to perennial ryegrass, it transitions out easier than perennial ryegrass, resulting in fewer surviving plants one year later.

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