Fresno Counties Research Articles

Identification and Characterization of Citrus tristeza virus Isolates Breaking Resistance in Trifoliate Orange in California.

Most Citrus tristeza virus (CTV) isolates in California are biologically mild and symptomless in commercial cultivars on CTV tolerant rootstocks. However, to better define California CTV isolates showing divergent serological and genetic profiles, selected isolates were subjected to deep sequencing of small RNAs. Full-length sequences were assembled, annotated and trifoliate orange resistance-breaking (RB) isolates of CTV were identified. Phylogenetic relationships based on their full genomes placed three isolates in the RB clade: CA-RB-115, CA-RB-AT25, and CA-RB-AT35. The latter two isolates were obtained by aphid transmission from Murcott and Dekopon trees, respectively, containing CTV mixtures. The California RB isolates were further distinguished into two subclades. Group I included CA-RB-115 and CA-RB-AT25 with 99% nucleotide sequence identity with RB type strain NZRB-G90; and group II included CA-RB-AT35 with 99 and 96% sequence identity with Taiwan Pumelo/SP/T1 and HA18-9, respectively. The RB phenotype was confirmed by detecting CTV replication in graft-inoculated Poncirus trifoliata and transmission from P. trifoliata to sweet orange. The California RB isolates induced mild symptoms compared with severe isolates in greenhouse indexing tests. Further examination of 570 CTV accessions, acquired from approximately 1960 and maintained in planta at the Central California Tristeza Eradication Agency, revealed 16 RB positive isolates based on partial p65 sequences. Six isolates collected from 1992 to 2011 from Tulare and Kern counties were CA-RB-115-like; and 10 isolates collected from 1968 to 2010 from Riverside, Fresno, and Kern counties were CA-RB-AT35-like. The presence of the RB genotype is relevant because P. trifoliata and its hybrids are the most popular rootstocks in California.

Detection and Establishment of Aedes aegypti and Aedes albopictus (Diptera: Culicidae) Mosquitoes in California, 2011-2015.

In 2011, a thriving population of Aedes albopictus (Skuse), the Asian tiger mosquito, was discovered within three cities in Los Angeles County over an estimated 52-km2 urban area. Two years later in 2013, Aedes aegypti (L.), the yellow fever mosquito, was detected within several urban areas of Madera, Fresno, and San Mateo counties. State and local vector control agencies responded with an aggressive effort to eradicate or interrupt the spread of these two invasive mosquitoes; however, known populations continued to expand outward and new infestations were identified at an accelerated pace in central and southern California. By the end of 2015, one or both species had been detected within the jurisdictional boundaries of 85 cities and census-designated places in 12 counties. Herein we report on the discovery and widespread establishment of Ae. aegypti and Ae. albopictus in urban areas of coastal, central, and southern California between 2011 and 2015 and discuss the subsequent rapid changes to the activities and priorities of vector control agencies in response to this unprecedented invasion.

How many workers are employed in California agriculture?

In 2014, the average employment of hired workers in California crop and livestock agriculture, counting all occupations, rose by 10% to 410,900. However, although the state reports the number of jobs on farms regularly, it does not report the number of workers who fill these jobs. We analyzed all Social Security numbers reported by farm employers in 2014 and found two workers for each average or year-round equivalent farm job, making the total number of farmworkers employed in agriculture 829,300, or twice average employment. Approximately 83% of farmworkers had their maximum earnings with an agricultural employer in 2014, and almost 80% of those primary farmworkers were employed by crop support firms (392,000) or fruit and nut farms (154,000). Over 60% of all workers had only one farm employer, followed by 27% with two or more farm employers, and 35% were employed in Kern (116,000), Fresno (96,000) and Monterey (82,000) counties. These data show that California has a remarkably stable farm workforce: most farmworkers are attached to one farm employer, often a labor contractor who moves them from farm to farm.

Use of Spatial Epidemiology and Hot Spot Analysis to Target Women Eligible for Prenatal Women, Infants, and Children Services

We used a geographic information system and cluster analyses to determine locations in need of enhanced Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) Program services. We linked documented births in the 2010 California Birth Statistical Master File with the 2010 data from the WIC Integrated Statewide Information System. Analyses focused on the density of pregnant women who were eligible for but not receiving WIC services in California's 7049 census tracts. We used incremental spatial autocorrelation and hot spot analyses to identify clusters of WIC-eligible nonparticipants. We detected clusters of census tracts with higher-than-expected densities, compared with the state mean density of WIC-eligible nonparticipants, in 21 of 58 (36.2%) California counties (P < .05). In subsequent county-level analyses, we located neighborhood-level clusters of higher-than-expected densities of eligible nonparticipants in Sacramento, San Francisco, Fresno, and Los Angeles Counties (P < .05). Hot spot analyses provided a rigorous and objective approach to determine the locations of statistically significant clusters of WIC-eligible nonparticipants. Results helped inform WIC program and funding decisions, including the opening of new WIC centers, and offered a novel approach for targeting public health services.

FIRST REPORT OF LASIODIPLODIA CITRICOLA ASSOCIATED WITH STEM CANKER OF PEACH IN CALIFORNIA, USA

In July 2009 and October 2012, stems of young peach (Prunus persica) trees with cankers from Kings, Fresno and Yuba Counties, respectively, in California were submitted to our diagnostic laboratory. The cankered areas were discoloured brown in comparison with the creamy healthy bark and covered with gum galls. More than 30 trees were killed in Fresno and Kings Counties, and 6 trees in Yuba County. Scraping the cankers revealed large black pycnidia and brown discoloured wood. A fungus consistently isolated from the cankers was identified as Lasiodiplodia citricola based on morphological characteristics (Abdollahzadeh et al., 2010) and analyses of ITS, and TEF-1α gene regions. The sequence showed high identity (ITS, 100%; TEF-1α, 99%) with reference sequence (isolate: IRAN 1522C = CBS 124707, ex-type of L. citricola; accession Nos.: ITS, GU945354; TEF-1α, GU945340; β- tubulin, not available) for L. citricola (Abdollahzadeh et al., 2010). Sequences were deposited to GenBank (isolates: 7F93, 7F94 and 7F95. Accession Nos.: ITS, KC357262–KC357264; TEF-1α, KC357268–KC357270; β-tubulin, KC357265–KC357267). Pathogenicity of L. citricola in P. persica variety nectarina cv. Summer Fire was tested using three isolates. Ten two-year-old branches for each isolate were inoculated. Inoculations were made in late Oct. 2012 as described by Chen et al. (2013). Lesion length was measured 3 weeks after inoculation. The three isolates of L. citricola produced 60–67-long lesions within 3 weeks, while wounds were covered with callus tissue in the control inoculations. L .citricola was reisolated from the inoculated branches and no fungus was re-isolated from the control branches. These results indicate the pathogenicity of L. citricola to P. persica.

Pesticide and Nitrate Trends in Domestic Wells where Pesticide Use Is Regulated in Fresno and Tulare Counties, California.

The California Department of Pesticide Regulation initiated regulations on pesticide use in 1989 to mitigate groundwater contamination by atrazine [6-chloro--ethyl-'-(1-methylethyl)-1,3,5-triazine-2,4-diamine] and subsequently for simazine (6-chloro-,'-diethyl-1,3,5-triazine-2,4-diamine), diuron ['-(3,4-dichlorophenyl)-,-dimethylurea], bromacil [5-bromo-6-methyl-3-(1-methylpropyl)-2,4(1,3)-pyrimidinedione], and norflurazon [4-chloro-5-(methylamino)-2-[3-(trifluoromethyl)phenyl]-3(2)-pyridazinone]. Annual water samples from 2000 to 2012 were obtained from domestic wells in Fresno and Tulare counties in regulated areas designated either as leaching groundwater protection areas (GWPAs), where residues move downward in percolating water, or runoff GWPAs, where residues move offsite in rain or irrigation runoff water to sensitive sites such drainage wells. Concentrations decreased below the reporting limit, so maximum likelihood estimation methodology for left-censored data was used. Decreasing trends in concentration were measured in both GWPA designations for simazine, its breakdown products desisopropyl atrazine (ACET, 2-amino-4-chloro-6-ethylamino--triazine) and diamino chlorotriazine (DACT, 2,4-diamino-6-chloro--triazine), and diuron. Bromacil crop use was predominant in runoff GWPAs, where decreases over time were also measured. In contrast, increased trends were observed for norflurazon and its breakdown product desmethyl norflurazon [DMN, 4-chloro-5(amino)-2-(α,α,α trifluorometa-tolyl] in runoff GWPAs. Use of simazine, diuron, and bromacil was regulated before norflurazon, so patterns of detection represent a shift to use of unregulated products. For NO, 22 of 67 wells indicated linear decreases in concentration coinciding with decreases in pesticide residues in those wells. Concentration of ACET, DACT, diuron, and NO in well water was two to five times greater when located in runoff GWPAs. Greater amounts of herbicide were applied to crops grown in runoff GWPAs, but high concentrations in runoff water entering ponds or drainage wells could also be a factor for increased well water concentration. Initial regulatory measures appear to have been effective in reducing groundwater concentrations, but continued monitoring is needed to evaluate changes made to the regulatory approach in 2004.

Lagophylla diabolensis(Compositae–Madiinae), a New Hare-Leaf from the Southern Diablo Range, California

Lagophylla diabolensis is a new hare-leaf from the southern Diablo Range of Fresno, Monterey, and San Benito counties, California. Plants of the Diablo Range hare-leaf were previously included within L. dichotoma, which is treated here in a restricted sense to comprise plants from the Sierra Nevada foothills and eastern Great Central Valley. Lagophylla diabolensis differs morphologically from L. dichotoma by having consistently glandular distal foliage (glands clear to dark-purple), narrower cauline leaves, generally uniformly tawny stems, and smaller heads. The taxonomic significance of those morphological differences is corroborated by other evidence that L. diabolensis is more closely related to the widespread L. ramosissima than to L. dichotoma sensu stricto. The Diablo Range hare-leaf occurs as scattered colonies, often in clayey soils of grassy openings in oak-pine woodland below 1100 m elevation. Extreme rarity and paucity of recent collections of L. diabolensis and L. dichotoma in the current sense indicates that both species warrant conservation concern.

Helianthus winteri (Asteraceae), a New Perennial Species From the Southern Sierra Nevada Foothills, California

Helianthus winteri is described from Fresno and Tulare Counties in the southern Sierra Nevada foothills of California. It is distinguished from H. annuus by its woody trunk, year-round blooming, and morphological characteristics. It occurs in open, ungrazed foothill woodlands and annual grasslands on well-drained, granitic soils, generally on lower-elevation, south-facing foothill slopes east of the San Joaquin Valley.

Distribution and phenology of Rhagoletis fausta (Osten Sacken 1877) and Rhagoletis indifferens Curren 1932 (Diptera: Tephritidae) in California

Abstract We determined the distribution of Rhagoletis fausta (Osten Sacken 1877) and Rhagoletis indifferens Curren 1932 (Diptera: Tephritidae) in California outside the state interior quarantine area. Our data confirmed the historical records of R. fausta in Alpine, Amador, El Dorado, Fresno, Kern, Mariposa, Mendocino, Modoc, Mono, Nevada, Placer, Plumas, Sierra, Tehama, Tulare, and Tuolumne counties and we trapped R. fausta for the first time in Butte, Calavaras, Glenn, Inyo, Lassen, Madera, and Yuba counties. We confirmed the historical records of R. indifferens in Amador, El Dorado, Fresno, Mendocino, Modoc, Nevada, Placer, Plumas, and Sierra counties and we trapped R. indifferens for the first time in Butte, Calaveras, Lassen, Madera, Mariposa, Tulare, Tuolumne, and Yuba counties. No R. fausta were trapped in Lake, Los Angeles, or San Bernardino counties and no R. indifferens were trapped in Alpine, Glenn, Inyo, Lake, Mono, or Tehama counties. The lower altitude at which we trapped both flies increase...

High degree of single nucleotide polymorphisms in California Culex pipiens (Diptera: Culicidae) sensu lato.

Resolution of systematic relationships among members of the Culex pipiens (L.) complex has important implications for public health as well as for studies on the evolution of sibling species. Currently held views contend that in California considerable genetic introgression occurs between Cx. pipiens and Cx. quinquefasciatus Say, and as such, these taxa behave as if they are a single species. Development of high throughput SNP genotyping tools for the analysis of Cx. pipiens complex population structure is therefore desirable. As a first step toward this goal, we sequenced 12 gene fragments from specimens collected in Marin and Fresno counties. On average, we found a higher single nucleotide polymorphism (SNP) density than any other mosquito species reported thus far. Coding regions contained significantly higher GC content (median 54.7%) than noncoding regions (42.4%; Wilcoxon rank sum test, P = 5.29 x 10(-5)). Differences in SNP allele frequencies observed between mosquitoes from Marin and Fresno counties indicated significant genetic divergence and suggest that SNP markers will be useful for future detailed population genetic studies of this group. The high density of SNPs highlights the difficulty in identifying species within the complex and may be associated with the large degree of phenotypic variation observed in this group of mosquitoes.

Taking ownership of climate change: participatory adaptation planning in two local case studies from California

Interest in adaptation among local and state governments in the USA is on a steep incline since about 2007. Yet, place-specific vulnerability and adaptation research in the USA is still sparse, the public in many regions is still skeptical about the reality of climate change, and model adaptation planning processes are not well-known among practitioners. Against this backdrop of growing interest in adaptation, there is a great need to chronicle and critically assess emerging adaptation planning processes to learn broader lessons and share them widely both in the science and in the practice communities. This paper describes and critically evaluates a pilot project tested in two California local communities—San Luis Obispo and Fresno Counties—to illustrate how active engagement of local government and other stakeholders with experts can advance adaptation planning. The approach taken in this project proved to be an effective “conversation opener” in communities not previously engaged in adaptation planning or where political support to address climate change is low. It created a sense of expectation and accountability among local leaders and stakeholders. It also gave local leaders a chance to take ownership of the process and of the issue; it succeeded in raising interest in adaptation planning and increasing understanding of adaptation and that it is needed as much as mitigation. It helped develop an initial set of adaptation strategies for key climate-sensitive sectors, but to be taken up into ongoing policy processes and implemented by localities, requires state and federal funding.

Etiology and Management of a Mandarin Rind Disorder in California.

Recent reports of a preharvest rind disorder of Satsuma mandarin fruit resulted in severe crop losses in some growing areas of California (Butte, Fresno, Tulare, and Kern Counties). Symptoms were more frequently observed on fruit on the outer perimeter of the tree and on the exposed side of the fruit. Fungal isolations from affected fruit were inconsistent among orchard sites and growing seasons. Isolations resulted in species of Alternaria, Fusarium, Macrophomina, Ulocladium, and Cladosporium. In laboratory studies, mandarin fruit that were soaked in water for 6 h at 15 to 35°C, air dried, and incubated at 20°C for 3 days developed lesions similar to those observed in the field. When fruit were treated with an agricultural summer spray oil or the antitranspirant di-1-p-menthene prior to water soaking, the incidence and severity of the disorder were significantly reduced. Similar results were obtained in 2 years of field trials at two sites using one to three preharvest applications with the agricultural antitranspirant or summer oil starting after fruit color break. In most trials, a single application of these treatments at 1 or 2 weeks after color break was highly effective. Fungicides were inconsistent in their efficacy, whereas trees that were physically protected from rain did not develop the disorder. These data suggest that this mandarin rind disorder is a physiological, abiotic disorder rather than a pathological problem caused by fungi and can be economically managed with water-repellant treatments.

Canine heartworm (Dirofilaria immitis) in Fresno and Madera Counties, California: Prevalence differences between foothill and valley habitats

The aim of this study was to assess the prevalence of heartworm in domestic dogs in Madera and Fresno Counties, California, dependent on habitat and other host and environmental factors. Dogs were screened for presence of heartworm antigen using the PetChek® ELISA on blood samples (N=519) collected at seven sites during April-July 2009. Eighteen dogs were heartworm antigen positive. Pearson Chi-square analyses were conducted testing the presence of heartworm antigen against the following independent variables: elevation range, percentage of time spent outdoors during the day, percentage of time spent outdoors during the night, pet coat length, weight class, prevention status, and sex. Dogs that spent at least 50% of their time outdoors during the day were significantly more likely to have heartworm that those who spent less time outside (N=519, df=1, p=0.031). Overall prevalence (3.47%) was lower than expected, with Madera County having 3.8% positive samples and Fresno County 3.5%; this prevalence is lower than in many previous studies. The effect of time spent outdoors on heartworm prevalence was similar to previous studies. The impact of elevation on infection, though not significant, requires further investigation, as does the prevalence and viability of larval stages in mosquitoes.

Assessing Some Potential Environmental Impacts from Agricultural Anticoagulant Uses

This study was designed to give us a better understanding of the relationship between agricultural anticoagulant ro denticide uses and related occurrence of these materials in raptor tissues. The project utilized data from raptor carcasses collected, both in urban San Diego County and in largely agricultural Fresno, Kern, and Madera Counties, as part of the public health surveillance programs of the County Veterinarian(s) and/or Departments of Environmental Health. Most raptors contained detectible levels of secondgeneration anticoagulants, which are registered only for commensal rodent control in and around structures; very few contained firstgeneration anticoagulants, which are the only anticoagulants registered for use in agricultural production in California. This suggests that secondary hazards to raptors and other wildlife from anticoagulants stems primarily from retail sale of commensal rodent baits, particularly in residential areas, and not from anticoagulant rodenticide uses in agricultural regions.

Bryum chryseumMitt. (Musci: Bryaceae) New to North America North of Mexico

Abstract. Bryum chryseum Mitt, is reported new to the moss flora of North America north of Mexico from three counties in California. The first new record was found in the Mayacmas Range of eastern Mendocino County and more recently it was found in the San Joaquin River watershed in Fresno and Madera Counties. Predominantly a species of the Neotropics, it is also known from Chile, where a Mediterranean-type climate exists very similar to that of California. An illustration of the species is included.

Swap Meets and Socioeconomic Alternatives for Mexican Immigrants: The Case of the San Joaquin Valley

Swap meets have a long tradition in California's San Joaquin Valley. These are markets of different sizes and characteristics that have changed and adapted to demographic changes in the Valley. This article has two interrelated objectives. The first is to describe swap meets' main characteristics and how they have changed, paying special attention to changes introduced by Mexican vendors and consumers. The second is to discuss the different strategies implemented by men and women of Mexican origin in order to open a business at the swap meets. This article is based on qualitative data gathered during four months of field work in southern Central Valley. Seventeen swap meets were studied in Kern, Tulare, Kings and southern Fresno Counties.

PESTICIDES: Double Exposure Heightens Parkinson Disease Risk

Vol. 117, No. 7 NewsOpen AccessPESTICIDES: Double Exposure Heightens Parkinson Disease Risk Cynthia Washam Cynthia Washam Search for more papers by this author Published:1 July 2009https://doi.org/10.1289/ehp.117-a295Cited by:2AboutSectionsPDF ToolsDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InReddit Approximately 1 million U.S. residents and more than 4 million people worldwide have been diagnosed with Parkinson disease (PD), a chronic motor system disorder that usually strikes people over age 60 and triples in those over 85. Epidemiologic studies have consistently found that pesticide exposures heighten the risk of developing PD, a connection further strengthened by rodent studies. However, most studies to date have relied on self-reports and recall of chemical usage, bias-prone mechanisms that make it hard to accurately estimate exposure. A team of researchers led by epidemiologist Beate Ritz of the University of California, Los Angeles (UCLA) may have overcome that hurdle with a new exposure model.Their study, published 15 April 2009 in the American Journal of Epidemiology, suggests that two commonly used pesticides increase PD risk, especially in people exposed at an early age. The UCLA team focused on the combined effects of the herbicide paraquat and the fungicide maneb. When used either alone or in combination with maneb, paraquat had been found in several rodent studies to cause neuronal degeneration and symptoms like those seen in PD patients.The researchers compared pesticide exposures for 368 California residents diagnosed with PD between January 1998 and January 2007 and 341 randomly selected local controls. The subjects lived in agricultural regions in Fresno, Tulare, and Kern counties; most were white, over age 60, and had no family history of PD.Exposure estimates came from maps of land use and from a geographic information system incorporating pesticide application records from the California Department of Pesticide Regulation. “We found a way to assess historic pesticide exposure without relying on subject recall,” says first author Sadie Costello, now a postdoctoral research fellow in the Department of Environmental Health Sciences at the University of California, Berkeley, School of Public Health. Both data sets were linked to subjects’ current and former addresses within the three-county region.The researchers examined subjects’ exposure from 1974 to 1989, from 1990 to 1999, and for the entire time period. Subjects were considered exposed if one or both pesticides were applied within 500 m of their homes while they lived there. Exposure to both pesticides during the 25-year period was associated with a 75% increase in PD risk.Yet associations varied depending on subjects’ age and the timing of exposure. In participants aged 60 or younger at diagnosis (cases) or interview (controls), estimated relative risks of PD with exposure to one or both pesticides were similar regardless of whether exposure occurred between 1974 and 1989 or 1990 and 1999. However, among participants over 60 years of age, associations with PD appeared to be limited to pesticide exposures during the earlier (1974 –1989) time period.Freya Kamel, an NIEHS epidemiologist who has studied the suspected link between pesticides and PD, cautions against assuming that age at exposure can explain the different PD risks. “I don’t think I’d want to speculate until I saw it in more studies,” she says. She notes that the basic precept that developing brains are more vulnerable to neurotoxicants usually applies to prenatal and infant exposures, not to exposures in childhood or young adulthood.Kamel predicts future studies will move toward determining how genetics affects individuals’ susceptibility to environmental toxicants. “Assessing gene–pesticide interactions is a goal of our research,” Costello says. “We have a couple of papers on the topic coming out shortly.”FiguresReferencesRelatedDetailsCited by Huang J, Xiong N, Chen C, Xiong J, Jia M, Zhang Z, Cao X, Liang Z, Sun S, Lin Z and Wang T (2011) Glyceraldehyde-3-phosphate dehydrogenase: activity inhibition and protein overexpression in rotenone models for Parkinson's disease, Neuroscience, 10.1016/j.neuroscience.2011.06.050, 192, (598-608), Online publication date: 1-Sep-2011. Bartolini M and Andrisano V (2010) Strategies for the Inhibition of Protein Aggregation in Human Diseases, ChemBioChem, 10.1002/cbic.200900666, 11:8, (1018-1035) Vol. 117, No. 7 July 2009Metrics About Article Metrics Publication History Originally published1 July 2009Published in print1 July 2009 Financial disclosuresPDF download License information EHP is an open-access journal published with support from the National Institute of Environmental Health Sciences, National Institutes of Health. All content is public domain unless otherwise noted. Note to readers with disabilities EHP strives to ensure that all journal content is accessible to all readers. However, some figures and Supplemental Material published in EHP articles may not conform to 508 standards due to the complexity of the information being presented. If you need assistance accessing journal content, please contact [email protected]. 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Site Characteristics Determine the Success of Prescribed Burning for Medusahead (Taeniatherum caput-medusae) Control

AbstractMedusahead is one of the most problematic rangeland weeds in the western United States. In previous studies, prescribed burning has been used successfully to control medusahead in some situations, but burning has failed in other circumstances. In this study, trials were conducted using the same protocol at four locations in central to northern California to evaluate plant community response to two consecutive years of summer burning and to determine the conditions resulting in successful medusahead control. During 2002 through 2003 large-scale experiments were established at two low-elevation, warm-winter sites (Fresno and Yolo counties) and two higher elevation, cool-winter sites (Siskiyou and Modoc counties). Plant species cover was estimated using point-intercept transects, and biomass samples were taken in each plot. After 2 yr of burning, medusahead cover was reduced by 99, 96, and 93% for Fresno, Yolo, and Siskiyou counties, respectively, compared to unburned control plots. Other annual grasses were also reduced, but less severely, and broadleaf species increased at all three sites. In contrast, 2 yr of burning resulted in a 55% increase in medusahead at the coolest winter site in Modoc County. In the second season after the final burn, medusahead cover remained low in burned plots at Fresno and Yolo counties (1 and 12% of cover in unburned controls, respectively), but at the Siskiyou site medusahead recovered to 45% relative to untreated controls. The success of prescribed burning was correlated with biomass of annual grasses, excluding medusahead, preceding a burn treatment. It is hypothesized that greater production of combustible forage resulted in increased fire intensity and greater seed mortality in exposed inflorescences. These results demonstrate that burning can be an effective control strategy for medusahead in low elevation, warm-winter areas characterized by high annual grass biomass production, but may not be successful in semiarid cool winter areas.

Distribution and Management of Citrus in California: Implications for Management of Glassy-Winged Sharpshooter

The epidemiology of Pierce’s disease of grape (Vitis spp.) in California has changed over the past 10 yr due to the introduction of an exotic vector, Homalodisca vitripennis (Germar), the glassy-winged sharpshooter. Although this insect is highly polyphagous, citrus (Citrus spp.) is considered a preferred host and proximity to citrus has been implicated as a significant risk factor in recent epidemics of Pierce’s disease in southern California. Consequently, a detailed knowledge of the distribution and management of citrus in relation to grape is needed to improve insect and disease management. Analysis of data on the area planted to these two commodities indicates that only five counties in California concomitantly grow >1,000 ha of grape and >1,000 ha of citrus: Riverside, Kern, Tulare, Fresno, and Madera counties. Comparison of the distribution of grape and citrus within each of these counties indicates that the percentage of grape that is in proximity to citrus is greatest for Riverside County, but the total area of grape that is in proximity to citrus is greater for Fresno, Kern, and Tulare counties. The use of carbamates, neonicotinoids, organophosphates, and pyrethroids as part of the citrus pest management program for control of key insect pests was compared among the same five counties plus Ventura County from 1995 to 2006. Ventura County was included in this analysis as this county grows >10,000 ha of citrus and has established glassy-winged sharpshooter populations. The use of these broad-spectrum insecticides was lowest in Riverside and Ventura counties compared with the other four counties. Analysis of historical trapping data at the county scale indicates a negative association of broad-spectrum insecticide use with glassy-winged sharpshooter abundance. These results are used to retrospectively analyze the Pierce’s disease outbreaks in Kern and Riverside counties.

Distribution and Management of Citrus in California: Implications for Management of Glassy-Winged Sharpshooter

The epidemiology of Pierce's disease of grape (Vitis spp.) in California has changed over the past 10 yr due to the introduction of an exotic vector, Homalodisca vitripennis (Germar), the glassy-winged sharpshooter. Although this insect is highly polyphagous, citrus (Citrus spp.) is considered a preferred host and proximity to citrus has been implicated as a significant risk factor in recent epidemics of Pierce's disease in southern California. Consequently, a detailed knowledge of the distribution and management of citrus in relation to grape is needed to improve insect and disease management. Analysis of data on the area planted to these two commodities indicates that only five counties in California concomitantly grow >1,000 ha of grape and >1,000 ha of citrus: Riverside, Kern, Tulare, Fresno, and Madera counties. Comparison of the distribution of grape and citrus within each of these counties indicates that the percentage of grape that is in proximity to citrus is greatest for Riverside County, but the total area of grape that is in proximity to citrus is greater for Fresno, Kern, and Tulare counties. The use of carbamates, neonicotinoids, organophosphates, and pyrethroids as part of the citrus pest management program for control of key insect pests was compared among the same five counties plus Ventura County from 1995 to 2006. Ventura County was included in this analysis as this county grows >10,000 ha of citrus and has established glassy-winged sharpshooter populations. The use of these broad-spectrum insecticides was lowest in Riverside and Ventura counties compared with the other four counties. Analysis of historical trapping data at the county scale indicates a negative association of broad-spectrum insecticide use with glassy-winged sharpshooter abundance. These results are used to retrospectively analyze the Pierce's disease outbreaks in Kern and Riverside counties.