Tobacco Cyst Nematode Research Articles

The ribosomal intergenic spacer (IGS) in the potato and tobacco cyst nematodes, Globodera pallida, G. rostochiensis and G. tabacum

The potato cyst nematodes Globodera pallida and G. rostochiensis (PCN), and tobacco cyst nematode (TCN), G. tabacum, are the most important parasitic nematodes of potato and tobacco worldwide. Ribosomal DNA provides useful molecular data for diagnostics, the study of polymorphisms and for evolutionary research in eukaryotic organisms including nematodes. Here we present data on the structure and organization of a rarely studied part of the intergenic spacer (IGS) region of the PCN and TCN genome of cyst nematodes. This region has shown potential for diagnostic purposes and population studies in other organisms including nematodes. In nematodes, the ribosomal RNA gene cluster comprises three genes: 5.8S, 18S and 28S rRNA, which are separated by spacer regions: the intergenic spacer (IGS), non-transcribed spacer (NTS), externally transcribed spacer (EST) and the internally transcribed spacer (ITS). The intergenic spacer (IGS) region consists of an external transcribed spacer (ETS) and a non-transcribed spacer (NTS) which is located between the 28S of one repeat and the 18S gene of the next repeat within the rRNA genes cluster. In this study, the first flanking portion of the IGS was amplified, cloned and sequenced from PCN and TCN. Primers were then designed to amplify the whole IGS sequence. PCR amplification of IGS from G. tabacum, G. pallida, and G. rostochiensis yielded respectively: a single amplicon of 3 kb, three amplicons sized 2.5, 2.6 and 2.9 kb, and two amplicons sized 2.8 and 2.9 kb. Results showed that Globodera spp. has more than one variant copy of the IGS, with both long and short repetitive DNA elements. An approximately 400 bp long region without any internal repetitive elements, were identified in a position between the two repetitive regions suggesting that there is a 5S gene in the IGS of these species.

Effect of the trap crop, Solanum sisymbriifolium, on Globodera pallida, Globodera tabacum, and Globodera ellingtonae.

The effect of the nematode trap crop Solanum sisymbriifolium was assessed against three Globodera spp., the potato cyst nematode Globodera pallida (in Idaho), the recently described Globodera ellingtonae (in Oregon), and the tobacco cyst nematode Globodera tabacum (in Connecticut) in field trials. At all locations the ability of S. sisymbriifolium to reduce Globodera encysted second-stage juveniles (J2) in egg densities compared to fallow was considered. For G. ellingtonae, the impact of planting and termination dates of S. sisymbriifolium on final egg densities was also evaluated; and for G. pallida, the ability of the nematode to reproduce on potato (Solanum tuberosum) after exposure to S. sisymbriifolium was determined. Encysted J2 in egg densities of all three Globodera spp. declined from 25 to 68% after trap cropping with S. sisymbriifolium. For G. pallida, S. sisymbriifolium reduced final encysted J2 in egg density by 23 to 50% compared to the fallow treatment, and significantly decreased G. pallida reproduction on potato after exposure to S. sisymbriifolium by 99 to 100% compared to the fallow treatment (P < 0.0001). For G. ellingtonae, the planting date of S. sisymbriifolium in May or June did not impact final egg densities (P = 0.32). Rather, percentage reduction in G. ellingtonae encysted J2 in egg density was most influenced by the length of time to which nematodes were exposed to S. sisymbriifolium, with 30 and 81% reduction after 6 vs 12 wk of exposure, respectively (P < 0.0001). Similar levels of nematode reduction after S. sisymbriifolium were observed for G. tabacum after 12 to 14 wk of exposure to the trap crop; G. tabacum density changes consisted of a 114% increase after susceptible tobacco, a 65% decrease after resistant tobacco, and an 88% decrease after S. sisymbriifolium compared to bare soil. In conclusion, this research demonstrates the widespread applicability of S. sisymbriifolium in reducing a diversity of Globodera spp. present in the USA.

Occurrence of the tobacco cyst nematode subspecies Globodera tabacum subsp. virginiae in France

Tobacco cyst nematode is a sexually diploid species composed of three subspecies, Globodera tabacum subsp. tabacum (Gtt), G. tabacum subsp. virginiae (Gtv) and G. tabacum subsp. solanacearum (Gts). In Europe, only Gtt have been reported to date. Here, we report from a plant in a French tobacco field, the identification of a mixture between cysts of the subspecies Gtt and cysts genetically different. The objective of the present study was to determine the subspecies status of those particular cysts. To this aim, we performed CAPS analyses on two genes and a principal component analysis on microsatellite data. The results obtained with both CAPS and microsatellite markers demonstrate for the first time the occurrence of G. tabacum subsp. virginiae in France.

Human influence on the dispersal and genetic structure of French Globodera tabacum populations

The dispersal abilities and the population genetic structure of nematodes living in soils are poorly known. In the present study, we have pursued these issues in the tobacco cyst nematode, Globodera tabacum, which is responsible of significant yield reductions. Nine microsatellites markers were used to explore the dispersal and genetic structure of 18 French G. tabacum populations. All the populations sampled belong to the “tabacum” subspecies and low level of gene flow was observed among G. tabacum populations in France. Bayesian genetic assignments revealed two distinct genetic groups that matched with the geographic limits of two agricultural cooperative societies. An important part of the genetic variability was observed between these agricultural cooperative societies and also within populations. Those results highlight the impact of the human organization of agricultural practices on the genetic structure of G. tabacum populations and complement previous results obtained on other cyst nematodes, showing the major contribution of human activities and soil transports during harvest in the passive dispersion of these organisms.

Sequence polymorphism of nematode effectors highlights molecular differences among the subspecies of the tobacco cyst nematode complex

Globodera tabacum is a little-known species complex of specialized plant–parasitic nematodes. In this study we investigated for the first time the sequence variability of five effectors: three genes coding for cell wall degrading enzymes (Pel1, Pel2 and ExpB3) and two genes coding for CLE peptides (CLE1 and CLE4) among a set of populations representing the different subspecies described. Substantial variability was observed in the sequence dataset which is consistent with the differential pathogenicity of the G. tabacum subspecies on a range of Nicotiana species. Using these sequence data, we were able (1) to show the presence of a novel CLE-like class in cyst nematodes, (2) to support the existence of most probably three and not four subspecies in this species complex, (3) to reveal that the subspecies G. tabacum tabacum presents the highest diversity and (4) to develop a PCR tool that allows a quick and reliable identification of this subspecies among the species complex.

Registration of ‘B2’ Connecticut Broadleaf Cigar‐Wrapper Tobacco Resistant to Fusarium Wilt, Tobacco Mosaic Virus, Cyst Nematodes, and Blue Mold

‘B2’ Connecticut broadleaf cigar‐wrapper tobacco (Nicotiana tabacum L.) (Reg. No. CV‐124, PI 664300) is a male‐sterile hybrid released by the Connecticut Agricultural Experiment Station and is resistant to Fusarium wilt, Tobacco mosaic virus (TMV), the tobacco cyst nematode [TCN; Globodera tabacum tabacum (Lownsbery and Lownsbery 1954) Stone 1973], and blue mold [caused by Peronospora tabacina de Bary Adam 1933 (= Peronospora hyoscyami de Bary 1863 f. sp. tabacina Skalicky 1964)]. Initial crosses were made in 1987 between VA‐81 and PD4 flue‐cured tobacco and three broadleaf inbreds resistant to Fusarium wilt [caused by Fusarium oxysporum Schlechtend.:Fr. f. sp. nicotianae (J. Johnson) W.C. Snyder &amp; H.N. Hans.] and TMV. F2 selections were backcrossed twice to broadleaf lines, inbred and selected across 12 generations using bulk modified single‐seed descent with 2% of plants (20 plants of 1000) selected most years; selection for TMV and TCN resistance was conducted in greenhouse screens with fewer plants. Lines were field selected for reduced ozone weather fleck. One F12 selection was backcrossed again to the broadleaf cultivar ‘Scantic’ and inbred via pedigree selection across 10 generations with field and greenhouse selection. Progeny testing was used to select F8 plants homozygous for resistance to TCN and for hypersensitive TMV resistance from Nicotiana glutinosa L. A superior male‐fertile inbred (MF‐2) resulting from 27 generations of selection for broadleaf characteristics with 8 cycles of selection each for Fusarium wilt, TMV and TCN resistance was identified and crossed with a male‐sterile CT broadleaf line resistant to TMV and Fusarium wilt (MS‐1) to produce the F1 male‐sterile hybrid B2.

Multiplex Real-Time PCR Assays for the Identification of the Potato Cyst and Tobacco Cyst Nematodes.

TaqMan primer-probe sets were developed for the detection and identification of potato cyst nematodes (PCNs) Globodera pallida and G. rostochiensis using two-tube, multiplex real-time polymerase chain reaction (PCR). One tube contained a primer-probe set specific for G. pallida (pale potato cyst nematode) multiplexed with another primer-probe set specific for G. rostochiensis (golden potato cyst nematode). A second tube consisted of the G. pallida-specific primer-probe set multiplexed with a primer-probe set specific for G. tabacum (the morphologically similar tobacco cyst nematode). This internal transcribed spacer rDNA-based system was specific for the Globodera spp. of interest and successfully identified several populations of PCN. This rapid, sensitive, and specific quantitative PCR assay presents a useful tool for PCN regulatory response and management programs.

Multiplex real-time polymerase chain reaction for identifying potato cyst nematodes, Globodera pallida and Globodera rostochiensis, and the tobacco cyst nematode, Globodera tabacum

Because the potato cyst nematodes (PCNs), Globodera rostochiensis and Globodera pallida, and tobacco cyst nematode (TCN), Globodera tabacum, may occur in the same geographic regions, their accurate identification is essential for implementing appropriate regulatory and crop loss mitigating strategies. Molecular methods for differentiating PCNs based on the internal genomic transcribed spacer (ITS) sequences have been developed but the potential of the many DNA amplification-based test formats have not yet been fully explored and most published work has not included TCN. In our study, the two PCN species and TCN could be distinguished by melting curve analysis of ITS amplicons generated in an EvaGreen-based real-time polymerase chain reaction (PCR) test. However, a multiplex real-time Taqman PCR test, which is also based on ITS sequences, was developed in this study with primers and probes modified with locked nucleic acids and proved to be superior for identification of one or more Globodera spp. in samples containing DNA from cysts and (or) second-stage juveniles. The test was specific for the PCN and TCN species with efficiencies of 0.91, 1.02, and 0.89 for G. rostochiensis, G. pallida, and G. tabacum tabacum, respectively. The multiplex, real-time PCR test was useful for distinguishing PCNs and TCN from other nematodes as well as their identification to species level in a single assay, correctly identifying each species in a DNA template from mixed populations. Key words: potato cyst nematode, golden cyst nematode, pale cyst nematode, tobacco cyst nematode, real-time PCR, melting curve analysis, locked nucleic acid, molecular identification. Étant donné que les nématodes à kystes de la pomme de terre (NKP) Globodera pallida et G. rostochiensis ainsi que le nématode à kystes du tabac (NKT) G. tabacum peuvent être présents dans une même zone géographique, il est essentiel de pouvoir les identifier avec précision afin d'appliquer les mesures adéquates relatives aux stratégies d'atténuation en cas de pertes de cultures. Des méthodes moléculaires permettant de différencier les NKP, basées sur les séquences de l'espaceur interne transcrit (ITS), ont été développées, mais le potentiel des nombreux tests d'amplification de l'ADN n'a pas encore été complètement exploré, et la plupart des travaux qui ont été publiés sur le sujet n'ont pas encore été faits sur les NKT. Dans notre étude, les deux espèces de NKP et les NKT pouvaient être caractérisés par l'analyse de la courbe de fusion des amplicons des ITS générée par PCR en temps réel faisant appel au marqueur EvaGreen. Toutefois, une PCR multiplex en temps réel Taqman basée également sur les ITS, conçue au cours de l'étude et faisant appel à l'utilisation d'amorces et de sondes modifiées à l'aide d'acides nucléiques bloqués (LNA), s'est avérée plus efficace quant à l'identification d'une ou de plusieurs espèces de Globodera dans les échantillons contenant de l'ADN extrait de kystes ou de plantules ayant atteint le deuxième stade de croissance. Le test était spécifique des espèces de NKP et NKT à des taux d'efficacité de 0,91, 1,02 et 0,89 pour G. rostochiensis, Globodera pallida et G. tabacum, respectivement. La PCR multiplex en temps réel s'est avérée utile pour distinguer les NKP et les NKT d'autres nématodes ainsi que pour les caractériser au niveau de l'espèce en effectuant qu'un seul biotest, tout en permettant d'identifier chaque espèce à partir d'une matrice d'ADN constituée d'un mélange de populations. Mots-clés : nématode à kystes de la pomme de terre, nématode doré, nématode blanc, nématode à kystes du tabac, PCR en temps réel, analyse de la courbe de fusion, acide nucléique bloqué, identification moléculaire.

First Report of Globodera tabacum Infecting Tobacco Plants in Quebec, Canada.

The tobacco cyst nematode Globodera tabacum (Lownsbery & Lowns-bery) Behrens is a damaging soilborne pathogen of shade and broadleaf tobacco in the United States (2). Nematode infection of roots can cause dramatic stunting, yield loss, and reduce leaf quality. G. tabacum is considered a complex of three cyst nematodes not distinguishable morphologically including G. tabacum tabacum, G. tabacum virginiae, and G. tabacum solanacearum. During 1998, infested flue-cured tobacco plants were harvested in the Lanaudière Region near Montreal, Quebec. Cysts recovered from roots and soil were identified by morphological and morphometric analysis of mature cysts and unhatched juveniles. Although multiple interceptions on nursery stock entering Quebec from infested nurseries in Hartford County, Connecticut from 1974 to 1986 have been recorded (1), to our knowledge, this is the first record of G. tabacum established in Canadian soil. On the basis of historic nematode infestations in this county, it could be inferred that it was G. tabacum tabacum, but further analysis is necessary for definitive subspecies determination. The infested tobacco plants were stunted in the field when compared with noninfested plants. Recently, the production in that area has been abandoned. Because cysts may survive for years in absence of host and also because potato, also a host of G. tabacum, is being introduced on these tobacco farms, it is believed that the distribution of this nematode could expand in the future in this part of the country.

The promoter of the Arabidopsis thaliana Cel1 endo‐1,4‐β glucanase gene is differentially expressed in plant feeding cells induced by root‐knot and cyst nematodes

SUMMARY Transgenic tobacco and Arabidopsis thaliana carrying the Arabidopsis endo-1,4-beta-glucanase (EC 3.2.1.4) Cel1 promoter fused to the beta-glucuronidase (GUS) reporter gene were infected with the root-knot nematode, Meloidogyne incognita, and either the tobacco cyst nematode, Globodera tabacum (tobacco), or beet cyst nematode, Heterodera schachtii (Arabidopsis). Cel1-driven GUS expression was detected in cell elongation zones of noninfected plants and within feeding sites (giant-cells) induced in roots of both plant hosts by M. incognita. The first detectable signs of Cel1 expression within developing giant-cells occurred at the onset of giant-cell formation and continued throughout the M. incognita life cycle. UidA (Gus) transcripts were detectable within giant-cells induced in tobacco roots at 11-13 days postinoculation with M. incognita as determined by in situ mRNA hybridization. By contrast, expression of the Cel1 promoter was not detected within developing syncytia induced in tobacco or Arabidopsis roots by G. tabacum and H. schachtii, respectively, at any time point. The results demonstrate specific regulation of cell wall-degrading enzymes that may be required for cell wall modifications during feeding cell formation by sedentary endoparasitic nematodes. Differential expression of Cel1 by cyst and root-knot nematodes further supports underlying mechanistic differences in giant-cell and syncytium formation.

Inheritance of Resistance to Tobacco Cyst Nematode in Flue‐Cured Tobacco

The tobacco cyst nematode [Globodera tabacum solanacearum (Miller and Gray) Behrens] is an important pathogen affecting flue‐cured tobacco (Nicotiana tabacum L.) in Virginia and North Carolina and type 32 tobacco in Maryland. The objective of this study was to determine the mode of inheritance of resistance to G. t. solanacearum in the flue‐cured tobacco cultivars Coker 371 Gold and Kutsaga 110. Each cultivar was crossed to the susceptible cultivar K 326 and F1 progeny were backcrossed to each parent. Plants from each parent and F1, F2, BC1Ps, and BC1Pr progeny were evaluated for G. t. solanacearum resistance in the greenhouse. Six‐week‐old transplants were inoculated with 6000 G. t. solanacearum eggs from crushed cysts. Eight weeks after inoculation, a 1‐g sample of fibrous root was stained and vermiform, swollen, pyriform, and adult nematodes were counted. The number of cysts and eggs per 400 000 mm3 of soil were counted from each transplant. Generation means analyses were performed. Additive and dominance gene action play an important role in resistance to G. t. solanacearum in Coker 371 Gold and Kutsaga 110. F2 progeny data from the Coker 371 Gold cross fit a 3:1 (resistant:susceptible) segregation ratio and BC1Ps generation data fit a 1:1 segregation ratio, indicating that resistance to G. t. solanacearum is conferred by a single dominant gene. A continuous range of variation was observed among the F2 progeny for the K 326 × Kutsaga 110 cross, indicating resistance in Kutsaga 110 is quantitative. Globodera tabacum solanacearum resistance in Coker 371 Gold and Kutsaga 110 may be derived from different sources.

Intra-species DNA polymorphism in the tobacco cyst – nematode complex (Globodera tabacum) using AFLP

Amplified fragment length polymorphism (AFLP) was used to obtain information on the within-species genetic variability of the tobacco cyst-nematode (TCN) complex. AFLP was found to be well suited to this type of study. The current classification of TCN was confirmed. Results indicate that the Globodera tabacum solanacearum group, believed to be restricted to the U.S.A., also occurs in Mexico. The within-species variability of TCN is considerable. Populations from Mexico may form a new subgroup. AFLP group-specific markers were identified for two of the TCN subgroups: Globodera tabacum tabacum and Globodera tabacum solanacearum.

Evaluation of Tobacco Accessions for Resistance to Tobaco Cyst Nematode and Wildlife

Control of tobacco cyst nematode (Globodera tabacum solanacearum Miller and Gray) is of major concern to growers of flue‐cured tobacco (Nicotiana tabacum L.) in Virginia. A diverse geographic array of accessions including cultivars of several classes of tobacco, flue‐cured type tobacco introductions, and Nicotiana species were evaluated during 1993 and 1994 in the greenhouse to identify new sources of resistance to tobacco cyst nematode (TCN). Six‐week‐old transplants were inoculated with 6000 TCN eggs from crushed cysts. An average of eight weeks after inoculation, a 1‐g sample of root was stained and vermiform, swollen, pyriform, and adult nematodes were counted. Accessions were also evaluated for response to wildfire (Pseudomonas syringae pv. tabaci Wolf and Foster) to determine if resistance to these two pathogens was correlated. The underside of a single 10‐ to 15‐cm leaf from 6‐wk‐old transplants was inoculated with a suspension of wildfire bacteria by means of a CO2 air brush. Leaves were rated for disease severity 5 d after inoculation. Several accessions had significantly reduced nematode reproduction including TI 1597, TI 1625, ‘Burley 64’, ‘MD 40’, ‘Pennbell 69’, and ‘Kutsaga Mammoth 10’. Although wildfire resistance was highly correlated with TCN resistance, some accessions had no resistance relationship to the two pathogens. Nicotiana miersii Ramy was susceptible to wildfire while supporting very low nematode populations and both TI 551 and ‘KY 190’ were resistant to wildfire but were susceptible to TCN. Evaluation of accessions for wildfire resistance may not be a reliable method of screening for TCN resistance and would result in alternate sources of TCN resistance being overlooked.

Evaluation of Tobacco Germ Plasm for Resistance to the Tobacco Cyst Nematode,Globodera tabacum solanacearum

Twenty-four tobacco genotypes were evaluated in the greenhouse for resistance to a North Carolina isolate of the tobacco cyst nematode Globodera tabacum subsp. solanacearum. The experimental design was a split-plot with eight replications. The experiment was repeated three times. Genotypes were assigned to whole plots, and nematode infestation levels (0 or 10,000 eggs per 1,300 cm 3 of soil) were assigned to subplots. Fresh stalk and root weights of all plants were recorded. Two new variables were created based on these measurements: percent stalk weight [%SW = (SW of infected plant + SW of uninfected plant) x 100] and percent root weight [%RW = (RW of infected plant + RW of uninfected plant) x 100]. Nematode reproduction, measured as number of cysts and eggs per pot, and reproduction factor (final number of eggs + initial number of eggs), was determined for each genotype. Significant differences (P ≤ 0.05) were observed among tobacco genotypes for nematode reproduction. Low levels were detected in the cultivars Burley 21, PD 4, VA 81, NC 567, Speight G-80, Kutsaga Mammoth 10, Kutsaga 110, and in the flue-cured breeding lines Cyst 913 and 9025-1. Differences in vegetative growth among genotypes grown in nematode-infested soil were detected only between those with the highest and lowest %SW and %RW. Genotype shoot and root weight were not correlated with nematode reproduction. Nevertheless, results from these experiments indicate that nematode reproductive parameters may be used to evaluate tobacco germ plasm for resistance to G. t. subsp. solanacearum in the greenhouse.

Aphid and Flea Beetle Control on Tobacco Grown in Fumigated Soil, 1994

Abstract This experiment was conducted to evaluate various combinations of soil insecticides and foliar treatments for TA and TFB control and the resulting effects on the yield and price of fluecured tobacco grown in fumigated soil. Seven treatments and an untreated control were established in a randomized complete block design with 4 replications at the VPI &amp; SU Southern Piedmont Agricultural Research and Extension Center, Blackstone, VA. Plots, 4 × 40 ft (2 rows × 24 plants), were separated by single border rows. The entire test site was fumigated for control of the tobacco cyst nematode, Globodera solanacearum. Telone C- 17 was applied broadcast at 19.1 gal/acre on 12 Apr. Most treatments of liquid formulations were applied broadcast with a CO2-pressurized, tractormounted boom sprayer that delivered at 30.4 gal/acre and 40 psi through 8003LP tips on 29 Apr. Treatments were immediately incorporated by double disking. The Temik treatments were applied in a 14 inch band using a tractor-mounted Gandy granular applicator and treatments were immediately covered with 6 inches of soil at bed formation on 17 May. The soil was in excellent condition for both the pretransplant soil and bedding treatments. Foliar applications of Orthene and Dipel were applied with a CO2-pressurized sprayer that delivered 30 gal/acre through 3 TX-12 nozzles at 60 psi. ‘K- 326’ flue-cured tobacco was transplanted into experimental plots in a Chesterfield-Mayodan-Bourne sandy loam soil on 18 May. Virginia Cooperative Extension recommendations were followed for production of the crop. TA populations were estimated on the upper 4 leaves of 10 plants/plot about once a week from 6 to 11 wks after transplanting. TFB and TFB feeding holes in the most damaged leaf were counted on 10 plants/plot during late May and early Jun. On 26 Aug, aphid damage was rated on a scale of 0 to 10 where 0 = no damage and 10 = very severe injury. Tobacco was harvested as it ripened, weighed, graded by a USDA/AMS inspector, and yield and price were calculated. Data were analyzed by ANOVA and significantly different means were separated by WD (K-ratio = 100). Aphid count data were transformed to Log,0(x + 1) before analysis.

Induction Patterns of an Extensin Gene in Tobacco upon Nematode Infection.

When sedentary endoparasitic nematodes infect plants, they induce complex feeding sites within the root tissues of their host. To characterize cell wall changes induced within these structures at a molecular level, we studied the expression of an extensin gene (coding for a major structural cell wall protein) in nematode-infected tobacco roots. Extensin gene expression was observed to be induced very early upon infection. This induction was weak, transient, and probably due to wounding during penetration and migration of the tobacco cyst nematode Globodera tabacum ssp solanacea-rum. In contrast, high extensin gene expression was observed during the whole second larval stage (an ~2-week-long phase of establishment of the feeding site) of the root knot nematode Meloidogyne javanica. During later stages of this interaction, expression gradually decreased. Extensin gene expression was found in at least three different tissues of the gall. We propose that distinct mechanisms lead to induced expression in these different cell types. The significance of these results for the understanding of plant-nematode interactions as well as the function of structural cell wall proteins, such as extensin, is discussed.

Insecticidal Activity of Products Applied for Control of Tobacco Cyst Nematodes, 1988

Abstract Experimental plots consisting of 1 border row and 1 40-ft test row (24 plants) were established on 4-ft centers in a field infested with a tobacco cyst nematode, Globodera tabacum subsp. solanacearum (Miller and Gray) Stone, at the Southern Piedmont Agricultural Experiment Station, Blackstone, Va. The soil was an Appling sandy loam (pH 6.1, 2-7% slope, 1.2% organic matter). Plots were arranged in a randomized complete block design with 4 replicates. Liquid nematocides were applied on 29 Apr (air temperature 64°F, soil temperature 55°F, 25% soil moisture) using a tractor-mounted sprayer equipped with 8003LP nozzles spaced 20 inches apart. Sprayed treatments were applied at 25 psi to attain a delivery volume of 32 gal/acre. Liquid nematocides were incorporated by disking immediately after treatment. Temik 15 G treatments were applied using a Gandy apparatus mounted to a pushcart. Preplanting Temik treatments were applied 2 May and incorported by bedding the soil immediately after treatment. Temik sidedress treatments were applied on 19 May and incorporated immediately by cultivation of the bed. ‘Coker 319’ tobacco was transplanted into the field on 3 May. Supplemental irrigation was applied 69 and 78 d after transplanting. Fertilizer and other cultural and pest control practices conformed to recommendations of the Virginia Cooperative Extension Service. Five plants/plot were examined 24 d after transplanting for number of flea beetles and number of flea beetle holes on the most damaged leaf.

Soil Insecticides for Control of Insects Feeding on Flue-Cured Tohacco Foliage, 1987

Abstract The effectiveness of various soil insecticides was evaluated for the control of insects feeding on tobacco foliage at Southern Piedmont Agricultural Experiment Station, Blackstone, Va. Eleven treatments and an untreated check were arranged in a randomized complete block design replicated 4 times. Flue-cured tobacco was transplanted 1 in plots of 40 × 12 ft (3 rows) on 19 May. The soil was a Chesterfield-Mayodan-Bourne sandy loam (pH 5.8, 3% organic matter). Pretransplant soil treatments were applied, incorporated by double disking, and bedded up on 7 May (ambient temperature, 90-95°F; soil temperature 82-88°F). Granular formulations were broadcast with a Gandy granular applicator mounted on a push cart. The liquid formulations were applied with a COa-pressurized backpack sprayer that delivered 26 gal/acre through Spraying Systems 8002LP tips at 25 psi. Temik treatments were applied over the bedded row in a 12-inch band with a Gandy applicator and incorporated with a rotary tiller on 15 May. The season was dry (0.34, 1.10, 1.95, and 1.72 inches for May, June, July, and August, respectively), but the crop was irrigated 5 times (1.3 inches, 24 Jun and 15 Jul; 1.5 inches, 23 and 28 Jul; and 1 inch, 7 Aug) to maintain proper growth. Moderate populations of the tobacco cyst nematode, Globodera tabacum solanacearum were present in all test plots. Every 1-2 wk from transplanting to the completion of harvest, the most abundant insect pests were sampled in the center row of each plot. Counts included tobacco flea beetles on 10 plants/plot; flea beetle feeding holes on the most damaged leaf of 10 plants/plot on the first 2 observation dates and on the top leaf at least 6 inches long on the 3rd and 4th dates; green peach aphids between the 4th and 6th lateral veins on the right side of 4 upper leaves at least 6 inches long on 10 plants/plot; and tobacco and tomato hornworms together on all plants on the center row of each plot. Tobacco was harvested from each plot, cured, weighed, and graded to determine return in $/acre. Aphid counts were transformed to log10(X + 1) before analysis, but actual means are shown. Data were analyzed by ANOVA, and significant means were separated by DMRT.