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Grapevine red blotch virus (GRBV) causes red blotch disease and is transmitted by the three-cornered alfalfa hopper, Spissistilus festinus. GRBV isolates belong to a minor phylogenetic clade 1 and a predominant clade 2. Spatiotemporal disease dynamics were monitored in a 1-hectare 'Merlot' vineyard planted in California in 2015. Annual surveys first revealed disease onset in 2018 and a 1.6% disease incidence in 2022. Ordinary runs and phylogenetic analyses documented significant aggregation of vines infected with GRBV clade 1 isolates in one corner of the vineyard (Z = −4.99), despite being surrounded by clade 2 isolates. This aggregation of vines harboring isolates from a non-prevalent clade is likely due to infected rootstock material at planting. GRBV clade 1 isolates were predominant in 2018–2019 but displaced by clade 2 isolates in 2021–2022, suggesting an influx of the latter isolates from outside sources. This study is the first report of red blotch disease progress immediately after vineyard establishment. A nearby 1.5-hectare 'Cabernet Sauvignon' vineyard planted in 2008 with clone 4 (CS4) and 169 (CS169) vines was also surveyed. Most CS4 vines that exhibited disease symptoms one-year post-planting, likely due to infected scion material, were aggregated (Z = −1.73). GRBV isolates of both clades were found in the CS4 vines. Disease incidence was only 1.4% in non-infected CS169 vines in 2022 with sporadic infections of isolates from both clades occurring via secondary spread. Through disentangling GRBV infections due to the planting material and S. festinus-mediated transmission, this study illustrated how the primary virus source influences epidemiological dynamics of red blotch disease. [ABSTRACT FROM AUTHOR]

The threecornered alfalfa hopper (Spissistilus festinus) is a pest of grapevine, with damage caused by transmission of grapevine red blotch virus. Because grapevine is not a preferred host of the threecornered alfalfa hopper, abundance in vineyards depends on proximity to source habitats and presence of preferred hosts in vineyard understories. The potential for alfalfa fields and pastures in the Central Valley of California to serve as sources of threecornered alfalfa hopper was evaluated by quantifying parameters associated with threecornered alfalfa hopper reproductive and nutritional status. Laboratory studies determined that the threecornered alfalfa hopper is synovigenic, emerging as an adult prior to initiation of oogenesis and that females have multiple rounds of egg production. Alfalfa fields, irrigated pastures, and vineyards were sampled monthly. Adults were observed year-round in alfalfa fields and pastures, with populations peaking in fall. Gravid females were observed from February through November. While rare, adult threecornered alfalfa hoppers were collected from 2 of 4 sampled vineyards. In spring, adults were observed in samples collected from vineyard ground cover. In fall, adults were observed in samples collected from vineyard ground cover and foliage samples. Samples collected from pastures and vineyards were male biased, whereas equal numbers of males and females were observed in alfalfa fields. Adults collected from alfalfa fields were larger, heavier, and had greater estimated energetic reserves than adults collected from pastures. Adults collected from vineyards were of above average size and had relatively high estimated energetic reserves. Results suggest that alfalfa fields are more likely to serve as sources of threecornered alfalfa hoppers than irrigated pastures and that differences in male and female behavior may affect rates of pathogen transmission. [ABSTRACT FROM AUTHOR]

Grapevine trunk diseases (GTDs) are caused by multiple unrelated fungal pathogens, and their management remains difficult worldwide. Biocontrol is an attractive and sustainable strategy given the current need for a cleaner viticulture. In this study, twenty commercial vineyards were sampled across California to isolate endophytic and rhizospheric bacteria from different grapevine cultivars with the presence and absence of GTD symptoms. A collection of 1344 bacterial isolates were challenged in vitro against Neofusicoccum parvum and Diplodia seriata, from which a subset of 172 isolates exerted inhibition levels of mycelial growth over 40%. Bacterial isolates were identified as Bacillus velezensis (n = 154), Pseudomonas spp. (n = 12), Serratia plymuthica (n = 2) and others that were later excluded (n = 4). Representative isolates of B. velezensis, P. chlororaphis, and S. plymuthica were challenged against six other fungal pathogens responsible for GTDs. Mycelial inhibition levels were consistent across bacterial species, being slightly higher against slow-growing fungi than against Botryosphaeriaceae. Moreover, agar-diffusible metabolites of B. velezensis strongly inhibited the growth of N. parvum and Eutypa lata, at 1, 15, and 30% v/v. The agar-diffusible metabolites of P. chlororaphis and S. plymuthica, however, caused lower inhibition levels against both pathogens, but their volatile organic compounds showed antifungal activity against both pathogens. These results suggest that B. velezensis, P. chlororaphis and S. plymuthica constitute potential biocontrol agents (BCAs) against GTDs and their application in field conditions should be further evaluated. [ABSTRACT FROM AUTHOR]

The seasonal abundance of Diatrypaceae spores was studied in southern California's desert table grape-growing region of Coachella Valley. Glass microscope slides covered with petroleum jelly were placed in a mature cv. Mid-Night Beauty® vineyard, and collected weekly from September 2006 to May 2009 (1400 samples for 140 consecutive weeks). Overall, Diatrypaceae-like colonies were recorded from Petri plates after processing spore traps in 93 (66%) of 140 weeks. Phylogenetic analyses showed Eutypella citricola and Eutypella microtheca to be the Diatrypaceae spp. captured from the spore traps. Though spores were captured throughout each year, their incidence varied among the different seasons. The greatest number of Eutypella spores were captured in autumn (38.7% of the total) followed by winter (30.6%), summer (19.7%), and spring (11%). The greatest numbers of spores were captured in October each year (15.7%) and least in June (1%). Eutypella spore release was correlated with rainfall only in 26 (28%) of the 93 weeks that spores were captured during the study. Analysis of diseased samples collected from the cv. Mid-Night Beauty® vineyard showed that E. citricola, E. microtheca and E. scoparia were the most prevalent fungi isolated from cankers. A pathogenicity study showed that E. citricola and E. microtheca isolates collected from spore traps caused larger vascular necrosis than the non-inoculated controls, indicating their role as pathogens on grapevines. This study has demonstrated Eutypella spp. to play an important role in grapevine health under desert growing conditions of southern California. In addition, and contrary to what it is largely accepted, results from this research suggest that Diatrypaceae spore release can occur in the absence of precipitation. This study expands current knowledge on epidemiology of Diatrypaceae spp. other than Eutypa lata, and provides important information for enhancing control strategies against grapevine trunk diseases under desert growing conditions. [ABSTRACT FROM AUTHOR]

Summary: Xylella fastidiosa subsp. fastidiosa causes Pierce's disease of grapevine (PD) and has been present in California for over a century. A singly introduced genotype spread across the state causing large outbreaks and damaging the grapevine industry. This study presents 122 X. fastidiosa subsp. fastidiosa genomes from symptomatic grapevines, and explores pathogen genetic diversity associated with PD in California. A total of 5218 single‐nucleotide polymorphisms (SNPs) were found in the dataset. Strong population genetic structure was found; isolates split into five genetic clusters divided into two lineages. The core/soft‐core genome constituted 41.2% of the total genome, emphasizing the high genetic variability of X. fastidiosa genomes. An ecological niche model was performed to estimate the environmental niche of the pathogen within California and to identify key climatic factors involved in dispersal. A landscape genomic approach was undertaken aiming to link local adaptation to climatic factors. A total of 18 non‐synonymous polymorphisms found to be under selective pressures were correlated with at least one environmental variable highlighting the role of temperature, precipitation and elevation on X. fastidiosa adaptation to grapevines in California. Finally, the contribution to virulence of three of the genes under positive selective pressure and of one recombinant gene was studied by reverse genetics. [ABSTRACT FROM AUTHOR]

Phaeomoniella chlamydospora and wood‐rotting basidiomycete fungi, namely Fomitiporia spp., are known esca pathogens. However, the effect of their mixed infections and the sequence of infection on disease development is unclear. To determine the effects of single and co‐inoculations on symptoms, potted Vitis vinifera 'Crimson Seedless' was inoculated with P. chlamydospora either alone or in combination with one of four basidiomycetes: Coprinellus radians, Fomitiporia langloisii, F. polymorpha and the novel species Tropicoporus texanus. Basidiomycetes were isolated from vines with foliar symptoms of esca in California and Texas. In sequential co‐inoculations, the effects of different sequences of infection (P. chlamydospora first, basidiomycete 6 months later; and vice versa) were tested, compared to simultaneous co‐inoculations. Plants inoculated with P. chlamydospora either alone or in combination with a basidiomycete (in any sequence) did not differ significantly in the length of black‐streaking lesions. In plants inoculated only with a basidiomycete, the appearance of large brown lesions, coupled with the absence of this wood symptom from control plants, suggests that C. radians, F. langloisii and T. texanus are pathogenic. Foliar symptoms resembling those of esca in the field (marginal and/or interveinal scorching, combined with red and/or yellow discoloration) were statistically more frequent among plants inoculated with F. polymorpha or T. texanus, either simultaneously or following P. chlamydospora, compared to single inoculations. Sequential co‐inoculations of a basidiomycete before or after P. chlamydospora were associated with similar lesion lengths, suggesting that basidiomycetes may not require infection by P. chlamydospora in order to extensively colonize the wood. [ABSTRACT FROM AUTHOR]

Botryosphaeria dieback, caused by species of Botryosphaeriaceae, is an important grapevine trunk disease in Australia. Inocula produced by the pathogens are primarily dispersed by rain splash and wind and infect pruning wounds leading to cankers, dieback. and eventually death of vines. The objective of this study was to develop molecular tools to detect and quantify Botryosphaeriaceae inocula from the environment. These tools are essential for investigating spore dispersal patterns of Botiyosphaeriaceae pathogens in Australian vineyards. DNA extraction protocols were evaluated and one modified protocol was found suitable for extracting Botiyosphaeriaceae DNA from artificially and naturally inoculated Burkard volumetric spore sampler tapes. Multispecies primers and a hydrolysis probe for quantitative PCR (qPCR) were further developed to detect and quantify Botryosphaeriaceae inocula from environmental samples. Specificity tests showed that the multispecies primers were able to amplify the DNA of 10 Botiyosphaeriaceae species (58 isolates) found in Australia while none of the 27 nontarget fungal species (90 isolates) tested were amplified. The qPCR assay was suitable for amplifying purified DNA, synthetic DNA fragments (gBlocks). and mixed DNA from spore trap tapes. The qPCR method developed in this study was shown to be rapid and sensitive in detecting Botryosphaeriaceae inocula from the environment using spore traps. [ABSTRACT FROM AUTHOR]

Brown spot, caused by Cladosporium spp., is becoming a problematic postharvest disease of late season table grape (Vitis vinifera) in the California central valley, and management is hindered by knowledge gaps in disease etiology and epidemiology. Brown spot is herein described as a pre- and postharvest diy rot typified by an external brown to black spot or black mycelium which encases the placenta. Isolates in the Cladosporium herbarían and C. cladosporioides species complexes were recovered from 85 and 5% of brown-spot affected berries, respectively. Five isolates in the C. herbarían species complex, representing three phylogenetically distinct species (C. limoniforme, C. ramotenellum, and C. tenellum), and one C. cladosporioides isolate all caused brown spot symptoms under cold-storage conditions, with and without mechanical wounding. Isolate virulence was similar (P > 0.05) based on disease incidence and severity on intact berries but severity varied on wounded berries (P < 0.001). Surface disinfestation reduced severity of cluster rot development following 2 weeks in cold storage (P = 0.027) but incidence was not affected (P = 0.17). This work provides foundational information on brown spot pathosystem etiology and biology in late-harvest table grape, which can be used to improve management. [ABSTRACT FROM AUTHOR]

Some diseases manifest as one characteristic set of symptoms to the host, but can be caused by multiple pathogens. Control treatments based on plant symptoms can make it difficult to effectively manage such diseases, as the biology of the underlying pathogens can vary. Grapevine leafroll disease affects grapes worldwide, and is associated with several viral species in the family Closteroviridae. Whereas some of the viruses associated with this disease are transmitted by insect vectors, others are only graft-transmissible. In three regions of California, we surveyed vineyards containing diseased vines and screened symptomatic plants for all known viral species associated with grapevine leafroll disease. Relative incidence of each virus species differed among the three regions regions, particularly in relation to species with known vectors compared with those only known to be graft-transmitted. In one region, the pathogen population was dominated by species not known to have an insect vector. In contrast, populations in the other surveyed regions were dominated by virus species that are vector-transmissible. Our survey did not detect viruses associated with grapevine leafroll disease at some sites with characteristic disease symptoms. This could be explained either by undescribed genetic diversity among these viruses that prevented detection with available molecular tools at the time the survey was performed, or a misidentification of visual symptoms that may have had other underlying causes. Based on the differences in relative prevalence of each virus species among regions and among vineyards within regions, we expect that region and site-specific management strategies are needed for effective disease control. [ABSTRACT FROM AUTHOR]

An outbreak of Pierce's disease of grapevine in the Temecula Valley in the late 1990s was one in a decades-long series of sporadic appearances of this infection in California. However, the new outbreak was qualitatively different because of the rapidity with which it spread in the vineyard and its appearance almost simultaneously at distant locations. The causative agent of Pierce's disease is the bacterium Xylella fastidiosa, and the distinct characteristics of the Temecula Valley outbreak were traced to the establishment of a new insect vector in California, the glassy-winged sharpshooter. Intensive and collaborative efforts among government agencies, industry and research institutions over 15 years have successfully contained the disease, and given scientists time to discover promising long-term potential solutions through genetic resistance. [ABSTRACT FROM AUTHOR]

Obscure mealybug is a pest of grapes in the cool climate regions of coastal California, is found on some vineyard weeds, and is tended by the Argentine ant. A study was conducted at a vineyard in Arroyo Grande, CA, to evaluate the impact of weeds on ant activity on grapevines, and the role that ants and weeds have on obscure mealybug infestation in grape clusters. The incidence of the fungus Botrytis cinerea was recorded as well. Treatments were weed exclusion versus the presence of weeds, and ant exclusion versus the presence of ants. Ant activity was evaluated weekly using sugar-based monitoring stations, and mealybug infestation and Botrytis incidence of clusters were evaluated at harvest. Ant exclusion reduced the overall number of ant visits by 82%, and ants increased mealybug infestation of clusters by 53%. Ant activity was 33% higher in the weeds treatment, but there was no impact of weeds on mealybug infestation. We suggest that the higher ant activity recorded in the weeds treatment may have been an artifact of the sugar-based sampling method. Botrytis incidence was three times higher with ants, but did not differ between weeds and weed exclusion treatments. The study supports other research showing a relationship between mealybug infestation and the presence of ants, as well as the lack of impact of floor vegetation on mealybug infestation of grape clusters. It is the first report of a relationship between ants and Botrytis, although it is more likely that the higher Botrytis incidence found here is a result of increased mealybug density than a direct effect by ants. [ABSTRACT FROM AUTHOR]

Field surveys recently conducted in California and in other grape-growing regions in the United States showed Phomopsis viticola to be one of the most prevalent fungi isolated from grapevine perennial cankers in declining vines. The current study has not only confirmed the presence of P. viticola from grapevine cankers in California but also has for the first time revealed the occurrence of Diaporthe ambigua, D. eres, and D. neotheicola in symptomatic grapevine wood in California by means of morphological studies and multigene sequence analysis. Pathogenicity trials conducted on mature cordons of Vitis vinifera 'Syrah' and 'Red Globe', as well as on lignified Syrah dormant canes, showed P. viticola isolates from California to be capable of causing perennial cankers. Lengths of vascular discoloration caused by P. viticola were similar to those caused by Eutypa lata and several Botry-osphaeriaceae spp., which are well-known grapevine trunk disease pathogens. Additionally, a lack of spring growth was commonly observed in dormant canes inoculated with P. viticola spore suspensions in two pathogenicity trials. As part of this study, V. vinifera 'Cabernet Sauvignon' and 'Zinfandel' wood was shown to be more susceptible to infection by P. viticola than 'Barbera', 'Chardonnay', 'Merlot', and 'Thompson Seedless' wood. After more than 40 years overlooking P. viticola as a grapevine wood pathogen, this study provides strong evidence of the role of P. viticola as a canker-causing organism, and suggests its addition to the fungi involved in the grapevine trunk disease complex. Results from this study suggest D. ambigua and D. neothe-icola to be saprophytes or weak pathogens on grapevine wood. [ABSTRACT FROM AUTHOR]

Epidemics of powdery mildew, the most important disease of grape-vines in California, are driven by moderate temperatures (21 to 30°C). High temperatures can delay or stop the growth and sporulation of Erysiphe necator. Using controlled conditions, we investigated the response of the pathogen's colony growth, conidiospore production, and germination to eight temperatures (30 to 44°C) at 12 exposure times (0.25 to 24 h). The pathogen survived, grew, and reproduced at higher temperatures than previously reported; exposure time was as important as temperature in defining lethal and sublethal effects. Lethal effects started at 36 to 38°C. Lethal exposure times decreased with increasing temperature. Based on this new information on the patho-gen's biology, we tested revisions to the high-temperature threshold of the UC Davis Powdery Mildew Risk Index in field settings. No differ-ences in the total number of fungicide applications resulted from the use of either the original or the revised models. However, use of the 38°C for 2 h threshold consistently showed equal (leaves) or better (fruit) disease control compared with the original model, as well as equal disease control compared with a calendar schedule, but with five fewer applications over the 2 years of the study. [ABSTRACT FROM AUTHOR]

Xylella fastidiosa (Xf) causes diseases in many agricultural, horticultural, and landscape crops, including Pierce's disease (PD) of grapevines. PD has been a serious problem in scattered table, wine and raisin grape growing regions throughout California, as well as in Texas for more than 100 years. In this study, we evaluated the genetic variation in diversity and structure of Xf associated with PD of grapevines in California and Texas using simple sequence repeat (SSR) markers. The analysis revealed a high level of genetic diversity across the populations of Xf isolated from the grapevines from different viticulture locations or counties in California and Texas. Overall genetic diversity of Xf was detected comparatively high in Texas (0.835) than that in California (0.662). Hierarchical analysis of molecular variance (AMOVA) showed a significant genetic structure of Xf population between California and Texas. UPGMA clustering analysis and the Bayesian clustering algorithm using STRUCTURE consistently placed California and Texas Xf populations into two major genetic groups with no clear population structure within each state. [ABSTRACT FROM AUTHOR]

Seasonality plays an important role in the dynamics of infectious disease. For vector-borne pathogens, the effects of seasonality may be manifested in the variability in vector abundance, vector infectiousness, and host-infection dynamics over the year. The relative importance of multiple sources of seasonality on the spread of a plant pathogen, Xylella fastidiosa, into vineyards was explored. Observed seasonal population densities of the primary leafhopper vector, Graphocephala atropunctata, from 8 years of surveys in northern California were incorporated into a model of primary spread to estimate the risk of pathogen infection under different scenarios regarding seasonality in vector natural infectivity (i.e. constant or increasing over the season) and grapevine recovery from infection (i.e. none or seasonal recovery). The extent to which local climatic conditions affect risk estimates via differences in vector abundance was investigated. Seasonal natural infectivity, seasonal recovery, and especially the combination, reduced (up to 8-fold on average) within-season and cumulative yearly estimates of pathogen spread. Estimated risk of infection also differed greatly among years due to large differences in vector abundance, with wet and moderate winter and spring conditions favouring higher G. atropunctata abundance. Seasonal variation of the pathogen-vector interaction may play an important role in the dynamics of disease in vineyards, reducing the potential prevalence from what it could be in their absence. Moreover, climate, by affecting sharpshooter leafhopper abundance or activity, may influence Pierce's disease dynamics. [ABSTRACT FROM AUTHOR]

We conducted studies in a Paso Robles, CA, grape (Vitis vinifera L.) vineyard in 2002 and 2003 to estimate the impact of regulated deficit irrigation (RDI) intensity and duration on western grape leafhopper, Erythroneura elegantula Osborn. Treatments were based on deficit intensity, 50 and 25% of standard irrigation (moderate and severe deficits, respectively), and deficit duration, 3 or 6 wk time, initiated at the grape phenological stage of berry set. The standard irrigation served as the control, and was intended to be as close to 100% of evapotranspiration (1.0 ETc) for grape in this area. Each week we took counts of leafhopper nymphs and estimated stomatal conductance, and at the end of each leafhopper generation we counted live, hatched and parasitized leafhopper eggs. Second generation leafhopper nymphal density was lowered by about 38 and 70% in 2002 and 2003, respectively, but in 2003 only the severe deficit had a negative effect on the third generation. This same pattern was seen in oviposition: second generation egg density was reduced by about 44% in the deficit treatments, but in the third generation only the severe deficit was lower than the control. There was little difference between the 3 vs. 6 wk duration in nymphal or egg density. The differences among treatments in second generation peak nymphal density were greater than the differences in second generation hatched eggs, suggesting that in addition to egg mortality, the deficits also affected nymphal mortality. Management strategies for maintaining leafhopper density low in the second generation and third generations include maintaining a sub-1.0 ETc irrigation strategy after the main RDI period, or reinstating the RDI to correspond to the third generation. [ABSTRACT FROM AUTHOR]

Background: Grapevine leafroll-associated viruses are a problem for grape production globally. Symptoms are caused by a number of distinct viral species. During a survey of Napa Valley vineyards (California, USA), we found evidence of a new variant of Grapevine leafroll-associated virus 3 (GLRaV-3). We isolated its genome from a symptomatic greenhouse-raised plant and fully sequenced it. Findings: In a maximum likelihood analysis of representative GLRaV-3 gene sequences, the isolate grouped most closely with a recently sequenced variant from South Africa and a partial sequence from New Zealand. These highly divergent GLRaV-3 variants have predicted proteins that are more than 10% divergent from other GLRaV-3 variants, and appear to be missing an open reading frame for the p6 protein. Conclusions: This divergent GLRaV-3 phylogroup is already present in grape-growing regions worldwide and is capable of causing symptoms of leafroll disease without the p6 protein. [ABSTRACT FROM AUTHOR]

In Northern California, surveys of several vineyards planted to Vitis vinifera cv. Pinot noir (PN) clones 02A, 667, 777, and UCD 04 grafted onto the rootstock V. berlandieri x V. rupestris 110 Richter (110R) revealed 2 to 45% of vines showing solid red leaf canopies and two distinct disease stages, i.e., full canopied plants with normal grape clusters (designated as acute) or stunted shoots and straggly bunches (designated as chronic). In addition, the scion-rootstock junction of symptomatic grapevines had developed a necrotic union; hence, the name 'grapevine necrotic union' (GNU). Also, two white fruited cultivars, Chardonnay (clone 04, vineyard in Yolo county) and Pinot gris (clone 152, vineyard in Monterey county), exhibited GNU-associated symptoms, with an exception of pale yellowed leaves. A detailed survey, from 2004 to 2009, was made in a subblock containing 664 grapevines (8 rows x 80-85 grapevines) in a PN 02A vineyard (planted in 1997) located in Sonoma county. The initial incidence of GNU was 2.1% in 2004 and rose to 21.9% by 2009 suggesting secondary spread. Molecular assays (RT-PCR and PCR) for grapevine viruses, phytoplasmas, and Xylella fastidiosa, failed to detect a putative causal agent. Likewise, bud-chip inoculations of test plants of Cabernet sauvignon scions on different rootstocks, including 110R, were inconclusive. However, several bench-grafts of collections of PN 02A, PN 91 and Chardonnay 04 onto 110R produced plants that developed GNU symptoms in a research plot. Based on the results obtained so far, GNU is being regarded as an emerging disease of unknown etiology in California vineyards. [ABSTRACT FROM AUTHOR]

Vitis and non-Vitis spp. surrounding nine Napa Valley vineyards were surveyed for Grapevine leafroll-associated virus (GLRaV)-1 to -5 and -9, Grapevine virus A (GVA), Grapevine virus B (GVB), and Grapevine virus D (GVD). Vitis spp. from three riparian areas not adjacent to vineyards were also included. DNA fingerprinting and probability analyses indicated that the Vitis samples consisted primarily of Vitis californica followed by V. californica x V. vinifera hybrids. Single and mixed infections of GLRaV-2, -3, GVA, or GVB were detected by conventional or quantitative reverse-transcription polymerase chain reaction in 6 of the 66 V. californica and 11 of the 19 V. californica x V vinifera hybrids. GLRaV-l, -4, -5, -9, and GVD were not detected. Phylogenetic analysis of GLRaV-2 and -3 partial coat protein gene nucleotide sequences indicated that the isolates from V californica and V. californica x V. vinifera hybrids were closely related to isolates from V. vinifera. [ABSTRACT FROM AUTHOR]

Diatrypaceous fungi have been isolated from cankered wood of grapevines (Vitis vinifera) in California. However, the pathogenicity of these fungi and their potential to cause diseases in grapevine was unknown. A series of pathogenicity tests were conducted to determine if these fungi were grapevine pathogens. In all experiments, species of the family Diatrypaceae were re-isolated from the margins of developing lesions, although frequency of re-isolation and average length of vascular discolorations varied among isolates. Cryptovalsa ampelina, Diatrype stigma, and Eutypa leptoplaca were capable of colonizing dormant canes and causing vascular necrosis. Cryptosphaeria pullmanensis, C. ampelina, D. stigma, Diatrype whitmanensis, and E. leptoplaca infected and caused lesions in green shoots of the new vegetative growth. Diatrype oregonensis and Diatrypella verrucaeformis isolates did not produce lesions that were significantly different from those produced in the control shoots and canes. This suggests that D. oregonensis and D. verrucaeformis fungi may be saprophytic rather than pathogenic to grapevine. [ABSTRACT FROM AUTHOR]

Pierce's disease and almond leaf scorch disease have been chronic problems for California grape and almond growers, respectively. Both diseases are caused by the xylem-limited, bacterial pathogen Xylella fastidiosa, which is transmitted by xylem-feeding insects. We evaluated the potential for alfalfa to serve as a source of vectors and inocula in California. Analysis of Geographic Information Systems maps on the distribution and abundance of grape, almond, and alfalfa plantings determined that 94,521 ha of almond and grape were planted within 1.6 km of an alfalfa field. Seasonal trends of X. fastidiosa detection were monitored outdoors and in the greenhouse in five needle-inoculated alfalfa cultivars (CUF101, Moapa69, WL342, WL530HQ, and WL625HQ) over 2 years. Results suggest that cool winter temperatures reduced X. fastidiosa populations to undetectable levels but did not eliminate infections. Sampling of alfalfa fields to assess incidence of X. fastidiosa corroborated this result, with positive samples detected in summer only. Incidence of X. fastidiosa in alfalfa during summer was low, with only 6 positive samples out of 1,156 samples collected over 3 years. Insect trapping in alfalfa fields over 3 years found that the green sharpshooter (Draeculacephala minerva) was the most abundant vector. Within alfalfa fields, green sharpshooter abundance was highest in weedy areas, suggesting a preference for weeds over alfalfa. These results confirm that weedy alfalfa fields can serve as an important source of vectors. Incidence of X. fastidiosa in alfalfa was low, possibly due to preference of vectors for weeds over alfalfa. [ABSTRACT FROM AUTHOR]

Shriveled fruit in vineyards has several origins including sunburn, dehydration, bunchstem necrosis and the recently described sugar accumulation disorder. These disorders are often confused with one another, but they can easily be distinguished by the location or composition of shriveled fruit and the condition of the rachis (the stem structure of a cluster). Sunburn is typically exhibited only on berries that are exposed to direct sunlight, and bunchstem necrosis is typified by necrotic rachis tissue. Berries with sugar accumulation disorder exhibit low sugar concentration, whereas berries with late-season dehydration typically have above-normal sugar concentration. Berries with sugar accumulation disorder and bunchstem necrosis exhibit the sugar content when sugar accumulation ceases or stem necrosis occurs, respectively. In tests, berries with sugar accumulation disorder exhibited lower berry weight, pH and anthocyanins, as well as differences in many nitrogenous compounds compared to normally developing fruit. In one location, sugar accumulation disorder was expressed at the whole-vine level, but none of the commonly known pathogenic organisms were found. [ABSTRACT FROM AUTHOR]

The seasonal abundance of Botryosphaeriaceae spp. spores was studied in California vineyards by using glass microscope slides covered with petroleum jelly placed on grapevine cordons and Burkard volumetric spore traps at seven and two different locations, respectively. Correlation analysis was used to determine which meteorological variables (precipitation, relative humidity, temperature, and wind speed) influenced Botryosphaeriaceae spp. spore release. Among all variables, regression analysis resulted in a strong relationship between spore release and precipitation. Additionally, a positive relationship between irrigation and spore release was also observed in the Riverside County vineyard. During the study period, spore discharge of Botryosphoeriaceae spp. occurred from the first fall rain through the last spring rains, coinciding with September to April. However, based on the results obtained from the spore traps, most spores (over 60%) were trapped following rain events during the winter months of December, January, and February, which coincides with the grapevine pruning season. Botryosphacriaceae spp. spore release was much lower in fall and early spring (22%) and very few or no spores were trapped in late spring and summer (3%). This work suggests that a delay of pruning time in California may. be warranted to reduce grapevine infection because the current timing coincides with the greatest period of spore discharge. [ABSTRACT FROM AUTHOR]

Dieback, or "dead arm," in noncoastal California grapevines is most commonly caused by Botryosphaeria spp. Using Koch's postulates, we demonstrated that isolates of B. obtusa are pathogenic on grapevines. We initiated studies to investigate the life cycle of B. obtusa and ways to control it with cultural practices. Fungal spores disseminated by rainstorms were collected in traps in an Arbuckle vineyard from December 2006 through spring 2007. The data suggests that B. obtusa was rain-disseminated throughout winter and spring, and that pycnidia on deadwood in the vines is a major source of inoculum for new infections. Transmission may also be possible via vegetative propagation, pruning shears and insects. Durable latex paints were investigated for protecting pruning and surgical wounds; a self-priming latex paint was shown to be an effective barrier and was nonphytotoxic. [ABSTRACT FROM AUTHOR]

In the 1930s and 1940s, little was known about viruses, and in formation on plant diseases caused by viruses was just beginning to appear in the scientific literature. Problems with grapevines in California, first referred to as "red leaf," were initially attributed to inexperience in viticultural techniques and poor growing conditions. However, the problem was later identified as lea froll disease, which causes red leaves, and poor yields and fruit quality. We evaluated its rate of spread for 5 years in a Napa Valley vineyard, and found an average rate of more than 10% per year. Lea froll disease can be vectored by low-level populations of grape mealybugs, and is now spreading rapidly in at least one Napa Valley vineyard for unknown reasons. Using stock for planting vines that is certified as virus-free is a key strategy in preventing the spread of grapevine lea froll disease. [ABSTRACT FROM AUTHOR]

Botryosphaeria spp. recently have been identified as important grapevine pathogens worldwide. To date, Botryosphaeria rhodina has been the only species associated with cankers on Vitis vinifera in California. A field survey of 166 vineyards in 21 counties was conducted in order to determine the occurrence of other Botryosphaeria spp. in California. In all, 1,735 samples of cankered trunks, cordons, and spurs were collected. Botryosphaeria spp. were the most common fungi isolated from grapevine cankers in California. Morphological identification along with phylogenetic analysis of the internal transcribed spacer region (ITS 1-5.8S-ITS2) of the nuclear ribosomal DNA (rDNA) and a partial sequence of the β-tubulin gene showed that at least seven Botryosphaeria spp. occur on grapevines in California: B. australis, B. dothidea, B. lutea, B. obtusa, B. parva, B. rhodina, and B. stevensii. Botryosphaeria spp. were found in grapevine cankers in all grape-growing regions surveyed in California, whereas incidence and distribution varied with location. Grapevine cankers in California have been associated mainly with Eutypa dieback. However, the frequent recovery of Botryosphaeria spp. from cankers in this study indicates that the role of these fungi in grapevine health needs to be more carefully considered. [ABSTRACT FROM AUTHOR]

Xylella fastidiosa is a xylem-limited bacterium that causes almond leaf scorch (ALS), Pierce's disease of grapevines, and other plant diseases. We surveyed ground vegetation in ALS-infected almond orchards in California's Central Valley for the presence of this bacterium. Plant tissue samples were collected throughout a 2-year period and processed for the presence of X. fastidiosa using restriction enzyme digestion of RST31 and RST33 polymerase chain reaction (PCR) products and bacterial culture on selective media. Overall disease incidence was low in the ground vegetation species; only 63 of 1,369 samples tested positive. Of the 38 species of common ground vegetation tested, 11 tested positive for X. fastidiosa, including such common species as shepherd's purse (Capsella bursa-pastoris), filaree (Erodium spp.), cheeseweed (Malva parvifolia), burclover (Medicago polymorpha), annual bluegrass (Poa annua) London rocket (Sisymbrium irio), and chickweed (Stellaria media). There was a seasonal component to bacterial presence, with positive samples found only between November and March. Both ground vegetation and almond trees were most commonly infected with the almond strain of X. fastidiosa (six of seven surveyed sites). ALS-infected almond samples had an X. fastidiosa concentration within previously reported ranges (1.84 × 106 to 2.15 × 107 CFU/g); however, we were unable to accurately measure X. fastidiosa titer in sampled ground vegetation for comparison. These results are discussed with respect to ground vegetation management for ALS control. [ABSTRACT FROM AUTHOR]

The population structure of Botrytis cinerea was investigated by using transposable elements, DNA fingerprinting generated by microsatellite primed-polymerase chain reaction (MP-PCR), and sensitivity to the hydroxyanilide fungicide, fenhexamid, for 234 isolates collected from fig, grape, kiwifruit, pea, and squash in California. Among 234 isolates tested, 195 had two transposable elements, Bozy and Flipper (transposa type), 38 had only the Boty element (Boty type), and one had neither of these elements (vacuma type). Four of these 234 isolates, which belonged to hie Bosy type, were resistant to fenhexamid. A phenogram generated based on MP-PCR mark- ers showed that the isolates were not clustered based on their source hosts or the presence of transposable elements. Analysis of molecular variance (AMOVA) showed that there were no significant genetic differentiations among isolates collected from grape, kiwifruit, pea, and squash at the Kearney Agricultural Center. A more detailed analysis based on AMOVA partition of the total genetic variance indicated that 96% of the variation occurred within populations. The parsimony tree length permutation (PTLPT) and index of association (IA) analyses of MP-PCR data set were consistent with absence of sexual recombination in sampled populations of this pathogen. [ABSTRACT FROM AUTHOR]

This study investigated phylogenetic divergence, morphological difference, and pathogenic variation among Cytindrocarpon species isolates associated with black foot disease of grapevine (Vitis sp.) in California. To assess phylogenetic divergence, we sequenced the internal transcribed spacer (ITS) of the nuclear ribosomal DNA (rDNA), partial beta-tubulin (BT) gene introns and exons, and the small subunit mitochondrial rDNA. Isolates associated with black foot disease belonged to two paraphyletic species, Cylindrocarpon destructans and C. macrodidymum. The morphology of these isolates was in agreement with published descriptions of both species. We found that C macrodidymum isolates were reliably distinguishable from C destructans isolates in culture by a unique orange-dark brown colony color on 2% malt extract agar and genetically by a species-specific 52-bp DNA insertion in the BT region. Selected isolates of each species inoculated onto grapevine rootstock 5C caused typical black foot disease symptoms. This is the first report of C. macrodidymum in California. [ABSTRACT FROM AUTHOR]

The fate of Xytella fastidiosa, the bacterium that causes Pierce's disease of grape, was assessed in 29 species of plants associated with vineyards in California's San Joaquin Valley. Bacterial populations and movement in greenhouse-grown plants were measured 1. 3, and 9 weeks after mechanical and insect inoculation. X. fastidiosa was recovered in 27 of 29 species in greenhouse tests, with common sunflower (Helianthus annuus), cocklebur (Xanthium strumarium), annual bur-sage (Ambrosia acanthicarpa), morning glory (Ipomoea purpurea), horseweed (Conyza canadensis), sacred datura (Datura wrightii), poison hemlock (Conium maculatum), and fava bean (Vicia faba cv. Aquadulce) being infected in more than 50% of inoculation attempts. Twenty-three species supported bacterial populations in excess of 104 CFU/g of plant tissue. X. fastidiosa populations increased for 9 weeks after inoculation in six species, and were static or declined in 16 species. Although the blue-green sharpshooter (Graphocephala atropunctata) was more efficient than mechanical inoculation for infecting plants, median populations and systemic movement for the two methods did not differ significantly. X. fastidiosa colonization of greenhouse and field-grown plants was compared in five alternate hosts. X. fastidiosa was recovered from 23 and 34% of field-grown plants, compared with 49 and 67% of greenhouse grown plants, in the winter and summer, respectively, with at least 10 times fewer bacteria in field plants in the winter. Although X. fastidiosa has a wide host plant range, its fate in most species is variable and heavily influenced by field conditions. [ABSTRACT FROM AUTHOR]

Xylella fastidiosa is a xylem-limited bacterium that causes Pierce's disease (PD) of grapevines. A variety of plant species found near a severe outbreak of PD in vineyards in the Temecula Valley of California were tested using enzyme-linked immunosorbent assay, culture on media, and polymerase chain reaction to identify potential inoculum sources in the area. Species that consistently tested positive for X. fastidiosa were the known hosts, grape, almond, and oleander, and two new hosts, Spanish broom (Spartium junceum) and wild mustard (Brassica spp). Sequence analysis of the 16S-23S rRNA spacer region found that strains isolated from grapevine, Spanish broom, wild mustard, and almond clustered with previously sequenced PD strains. Thus, these species could serve as sources of inoculum for infection of grapevines and should be removed or monitored for signs of infection. Sequences from oleander isolates from Temecula formed another cluster with a previously published oleander strain sequence. Oleander strains do not infect grapevines and thus do not appear to cause a direct threat to grapevines. Two additional isolates from almond were determined to be genetically different from PD strains, and the ability of these strains to infect grapevine is not known. Greenhouse transmission studies indicate that the glassy-winged sharpshooter was able to transmit a PD strain of X. fastidiosa to Spanish broom, black mustard, and other hosts. [ABSTRACT FROM AUTHOR]

The yeast Metschnikowia fructicola, ethanol, and sodium bicarbonate (SBC), alone or in combinations, were applied to table grapes on vines 24 h before harvest to control the incidence of postharvest diseases. In four experiments, all significantly reduced the total number of decayed berries caused by Botrytis cinerea, Alternaria spp., or Aspergillus niger after storage for 30 days at 1 °C followed by 2 days at 20°C. In three experiments, a mean gray mold incidence (caused by B. cinerea) of 34.2 infected berries per kilogram among untreated grape was reduced by Metschnikowia fructicola at 2 × 10[sup 7] CFU/ml, ethanol at 50% (vol/vol), or SBC at 2% (wt/vol) to 12.9, 8.1, or 10.6 infected berries per kilogram, respectively. Ethanol, SBC, and SO[sub 2] generator pads were similarly effective. M. fructicola effectiveness was not improved when combined with ethanol or SBC treatments. Ethanol and yeast treatments did not harm the appearance of the grapes. M. fructicola and SBC left noticeable residues, and SBC caused some visible phytotoxicity to the rachis and berries. Ethanol applied at 50% (vol/vol) reduced epiphytic fungal and bacterial populations by about 50% compared with controls. M. fructicola populations persisted on berries during storage when applied alone or after ethanol treatments, whereas SBC reduced its population significantly. [ABSTRACT FROM AUTHOR]

Abstract. The analysis of disease incidence data when diseased plants are aggregated in clusters is discussed. The logistic-normalbinomial distribution provides a basis both for analysing experiments according to their factor structure and for describing the observed frequency distribution of affected plants per sampling unit. These analyses are illustrated with data from disease assessments of Eutypa dieback of grapevine in Californian vineyards. A comparison of the results of this study with those of a previous one suggests that clustering of Eutypa dieback may occur on different scales, dependent on the presence ofperithecia ofthe causal organism, Eutypa lata , in a vineyard. [ABSTRACT FROM AUTHOR]

Grape phylloxera, Daktulosphaira vitifoliae Fitch, is a parthenogenetic, aphid-like pest which attacks the roots and leaves of many Vitis L. species. Feeding on the roots of V vinifera L. cultivars leads to decreased plant productivity and eventual death. Isolates of phylloxera have been grouped into 'biotypes' based on the aggressiveness of their feeding behaviour, relative reproductive rates, and abilities to cause decline on V vinifera and the grape rootstock AXR1. The goal of our research was to determine whether these biotype definitions were reflected in the genetic diversity among laboratory-cultured colonies of Californian phylloxera. Thirteen phylloxera isolates, encompassing biotypes A, B and non-A or -B types based on their feeding and reproduction, were analysed using the RAPD-PCR method. Results indicate that there were genetic differences among isolates and that there was as much polymorphism within biotypes as among biotypes. This is surprising in a parthenogenetic organism and leads us to suggest that there have been multiple introductions of phylloxera into California, that phylloxera are not obligately parthenogenetic, or that there are other mechanisms whereby phylloxera may evolve relatively rapidly. [ABSTRACT FROM AUTHOR]

Simple Summary: In California, grape cultivation for wine, juice, fresh and raisin markets is one of the most profitable agricultural sectors. Pathogens, weeds and insect pests cause millions in crop loss and result in additional costs through the use of pesticides and other control tools. Here, we report on the emergence of a new California grape pest, the carpentermoth Givira ethela (Neumoegen and Dyar, 1893). This paper also aimed at the moth's identification through molecular and morphological features and updates the distribution of G. ethela in California. Furthermore, the presence of G. ethela larval galleries appears to facilitate the mealybug pest Planococcus ficus Signoret, 1875, providing better access to vine sap and protection from natural enemies, environmental stresses, and pesticide treatments. We propose that management practices against G. ethela should include the correct identification of the pest and of its damage, but also the investigation of monitoring methods, economic thresholds, biological controls, and a better understanding of the relationship between G. ethela and P. ficus or other mealybug pest species. Grape cultivation is a billion-dollar agricultural sector in California, where invasive or novel pest species can disrupt management practices. We report herein on a new pest associated with California vineyards, the carpentermoth Givira ethela (Neumoegen and Dyar, 1893). Rather than an invasive species, G. ethela appears to be a newly recognized wood-boring pest of Vitis vinifera (L.) in regions of California's Central Valley, where its initial occurrence has been dated back to, at least, the beginning of the 2000s. The habitus of adult, genitalia and pupa is illustrated. Givira ethela distribution in California is updated including published records and new data. Carpentermoth galleries seem to facilitate the access of Planococcus ficus Signoret, 1875 to vine sap and protection from natural enemies, environmental stresses, and pesticide treatments. Notes on pest status, life history, monitoring practices, natural enemies, and management options on grapes are also discussed. Tools for the Integrated Pest Management of G. ethela should include the correct identification of the insect and its damage, a full understanding of its biology and ecology, the application of monitoring methods, and the identification of economic thresholds and injury levels. [ABSTRACT FROM AUTHOR]

In California's Mediterranean climate, management of grapevine trunk diseases (Botryosphaeria dieback, Eutypa dieback, Phomopsis dieback, Esca) focuses on protecting vines during the dormant season, when pruning coincides with rain-induced spore dispersal of the causal fungi ('trunk pathogens'). Applying protectants (fungicides, toxic barriers, sealants, biocontrol agents) after pruning can minimize infection of pruning wounds. For the dormant seasons of 2017–2019, in a 2-year-old Vitis vinifera 'Scarlet Royal' vineyard in the southern San Joaquin Valley, we evaluated tractor-spray applications of the following protectants labeled for table grapes: fluopyram + tebuconazole, pyraclostrobin + boscalid, thiophanate-methyl + myclobutanil, and Bacillus amyloliquefaciens. A comprehensive set of virulent and widespread trunk pathogens, including Diaporthe ampelina , Eutypa lata , Neofusicoccum parvum , and Phaeomoniella chlamydospora , were inoculated to pruning wounds post-application, with detection attempts after a 3 to 4-week incubation period (before budbreak). Consistently high efficacies of pyraclostrobin + boscalid (68–100% and 56–100%, respectively) and thiophanate-methyl + myclobutanil (64–77% and 91–100%, respectively) against Botryosphaeria-dieback pathogen N. parvum and Phomopsis-dieback pathogen D. ampelina suggest spray applications of these protectants could minimize infection by these common trunk pathogens. Low and variable detection rates of slow-growing Eutypa-dieback pathogen E. lata and Esca pathogen P. chlamydospora suggest that the incubation period should be longer or that more replication is needed. Low efficacy of B. amyloliquefaciens , especially with only 4 days in 2017 before pathogen inoculation, suggests this biological-control agent may need more time and/or repeated applications to become established on pruning wounds before being challenged by a pathogen. • Trunk diseases impact table grapes, but most research is done on wine grapes. • Pruning-wound protectants were tested in a California table-grape vineyard. • Two protectants were effective against Botryosphaeria and Phomopsis-dieback fungi. • A 1-month incubation may be too short for Phaeomoniella chlamydospora and Eutypa lata. • Biological-control agent Bacillus amyloliquefaciens may require repeated applications. [ABSTRACT FROM AUTHOR]

• First detection of grapevine virus T (GVT) in California. • Characterization of four diverse GVT isolates via high-throughput sequencing. • Identified degenerate PCR primers that overcome the known genetic diversity of GVT. Grapevine virus T (GVT) is a new member of the genus Foveavirus and has been reported to infect grapevines in several European countries. In 2018, GVT was detected for the first time in California in a domestic selection of wine grape, cv. Lambrusca di Alessandria, via high-throughput sequencing (HTS). To further investigate the presence of GVT in other grapevine plants, a two-step reverse transcription (RT)-PCR assay involving degenerate primers was developed. In order to cover the high genetic diversity of GVT, the sequences of available isolates were aligned to identify a conserved region in the coat protein gene that was a suitable target for the assay. The results of the RT-PCR assay showed that GVT was present in three additional grapevine selections among 416 plants integrating the Foundation Plant Services introduction pipeline; all were later confirmed by HTS. A complete and three near-complete genomes of the four GVT isolates were characterized and found to be divergent, sharing an overall 81 % pairwise identity in their nucleotide sequences. This suggested that the new RT-PCR assay was effective in detecting a broad range of GVT variants. The RT-PCR detection method developed in this study would be useful for routine virus testing. [ABSTRACT FROM AUTHOR]

The article focuses on the findings of a study on pomace and its potential to reduce spread of vine mealybugs among coastal vineyards in California. It found that to reduce the risk of contaminating vineyards with the mealybugs, growers must avoid spreading the waste around the plantation unless it has been covered with plastic for 1 week. Sanitation is commended to avoid spreading any species of the bug. Containers used to haul grapes and waste should be cleaned with a high-pressure sprayer.

The article offers information on the discovery of Pierce's disease bacterium in 1974 which could destroy grapevines (Vitis vinifera cv) in California. Topics discussed include the disease has been studied with the belief that it was caused by a virus, a study reports on the isolation of a rod-shaped, gram-positive bacterium from disease-spreading leafhopper (Draeculacephala minerva), and experiments have showed that a gram-positive bacterium is the cause of the disease in grapevines.

The article reports on the needed research on containing the spreading of leafroll disease in vineyards in California. The need for research on leafroll disease is in response to the result of a mapping of leafroll distribution in a Cabernet Sauvignon vineyard in Napa County which documented an increase in infection rate of about 10% per year over five years. It is recommended that research should focus on grapevine leafroll viruses and understanding leafroll transmission.

Reports on the case of melting decay of "Red Globe" grapes in cold storage facilities in California and in grapes stored for export. Presence of numerous yeast and bacterial cells under the skin; Bacillus subtilis; Cryptococcus laurentii; Aureobasidium pullulans.