Table Grape Vineyards Research Articles

Effectiveness of pre- and post-veraison calcium applications to control decay and maintain table grape fruit quality during storage

A two year research was carried out on a table grape vineyard, cv. Italia, to evaluate the effectiveness of pre- and post-veraison calcium applications for controlling postharvest table grape rots and maintaining high fruit quality during cold storage. Two calcium application timings (from fruit set to veraison and from veraison to harvest) were compared to an untreated control. Clusters were sprayed with calcium chloride as Ca EDTA 44%. After each calcium application, bunch samples were collected and Ca2+ concentration was measured in berry compartments (skin, flesh and seeds). The main mechanical and chemical characteristics were measured on bunch samples at harvesting and during storage. In addition, the incidence of Botrytis cinerea rots, computed as McKinney index, was evaluated in field on natural inoculum and after harvesting on bunches artificially inoculated and maintained at room temperature. The highest Ca2+ concentrations were detected in skin tissues and after pre-veraison applications. Calcium accumulation in skin and flesh tissues stopped after veraison, whereas it continued up to ripening in seeds since the axial flow, differently from the peripheral, remains functional. In both years, calcium applications to bunches were effective both in maintaining postharvest fruit quality, as shown by flesh firmness and berry breaking force, and in reducing B. cinerea rots during storage. The applications were particularly efficacious if carried out between fruit set and veraison when stomata are functional and the re-translocation of calcium not directly absorbed by the bunches may occur via xylem transport.

The distribution and symptomatology of grapevine trunk disease pathogens are influenced by climate

Grapevine trunk diseases, caused by a range of phytopathogenic fungi, represent a serious impediment to wine and table grape production wherever these crops are cultivated. Previous studies have shown that the distribution of these pathogens is influenced by climate and that they are associated with a variety of internal wood decay symptoms. Little was known, however, about the influence of climate on the disease symptomatology of the different pathogens in a specific area. To address this, a survey was conductedin 30 wine and table grape vineyards in summer, marginal and winter rainfall regions of South Africa. Apart from Eutypa lata , which occurred only in the winter rainfall region, Phaeomoniella chlamydospora , species of Phaeoacremonium , Botryosphaeriaceae and Phomopsis occurred in all regions surveyed. The incidence of the fungal genera and species associated with trunk disease varied between regions, with overlapping symptom profiles that differed based on the climatic region. These findings suggest that symptom-based disease diagnosis alone is unreliable and that distribution and symptomatology of grapevine trunk pathogens are strongly influenced by climatic conditions in a specific production region.

Temporal susceptibility of grapevine pruning wounds to trunk pathogen infection in South African grapevines.

Grapevine trunk diseases, caused by a range of phytopathogenic fungi, represent a serious impediment to wine and table grape production wherever these crops are cultivated. Previous studies have shown that the distribution of these pathogens is influenced by climate and that they are associated with a variety of internal wood decay symptoms. Little was known, however, about the influence of climate on the disease symptomatology of the different pathogens in a specific area. To address this, a survey was conducted in 30 wine and table grape vineyards in summer, marginal and winter rainfall regions of South Africa. Apart from Eutypa lata , which occurred only in the winter rainfall region, Phaeomoniella chlamydospora , species of Phaeoacremonium , Botryosphaeriaceae and Phomopsis occurred in all regions surveyed. The incidence of the fungal genera and species associated with trunk disease varied between regions, with overlapping symptom profiles that differed based on the climatic region. These findings suggest that symptom-based disease diagnosis alone is unreliable and that distribution and symptomatology of grapevine trunk pathogens are strongly influenced by climatic conditions in a specific production region.

Effectiveness of Insecticides in Controlling the First and Second Generations of the Lobesia botrana (Lepidoptera: Tortricidae) in Table Grapes

The moth Lobesia botrana (Denis & Schiffermüller) (Lepidoptera: Tortricidae) is a key pest of table and wine grape (Vitis spp.) varieties in Cyprus. Many different insecticide combinations were applied for three consecutive years (2006-2008) in a Sultana seedless table grape vineyard, aimed at controlling the first and second generations of this pest under warm and dry Mediterranean climatic conditions. In Cyprus, Sultana is the main early maturing table grape variety grown in the country. L. botrana has two generations and a partial third on this export variety, of which the first two generations are the most destructive. Applications were made according to pheromone trap captures of males. One application was used against the first and two applications against the second generation of L. botrana. A high rate of bunch damage was observed in the untreated rows during all years, reaching 56.7, 62.5, and 69.2% in 2006, 2007, and 2008, respectively. Differences between insecticide treatments and the untreated control were statistically significant. The treatment combination of lufenuron, spinosad, and indoxacarb as well as the combination of chlorpyrifos, spinosa and indoxacarb, used against the first and second generations of L. botrana, were the most effective compared with the untreated control. Satisfactory control of the pest also was observed with other combinations such as lufenuron, cypermethrin, and Bacillus thuringiensis; chlorpyrifos, cypermethrin, and B. thuringiensis; and lufenuron, deltamethrin, and azadirachtin.

Evapotranspiration of grapevine trained to a gable trellis system under netting and black plastic mulching

The evapotranspiration (ET c) of a table grape vineyard (Vitis vinifera, cv. Red Globe) trained to a gable trellis under netting and black plastic mulching was determined under semiarid conditions in the central Ebro River Valley during 2007 and 2008. The netting was made of high-density polyethylene (pores of 12 mm2) and was placed just above the ground canopy about 2.2 m above soil surface. Black plastic mulching was used to minimize soil evaporation. The surface renewal method was used to obtain values of sensible heat flux (H) from high-frequency temperature readings. Later, latent heat flux (LE) values were obtained by solving the energy balance equation. For the May–October period, seasonal ET c was about 843 mm in 2007 and 787 mm in 2008. The experimental weekly crop coefficients (K cexp) fluctuated between 0.64 and 1.2. These values represent crop coefficients adjusted to take into account the reduction in ET c caused by the netting and the black plastic mulching. Average K cexp values during mid- and end-season stages were 0.79 and 0.98, respectively. End-season K cexp was higher due to combination of factors related to the precipitation and low ET o conditions that are typical in this region during fall. Estimated crop coefficients using the Allen et al. (1998) approach adjusting for the effects of the netting and black plastic mulching (K cFAO) showed a good agreement with the experimental K cexp values.

A Survey of Scale Insects (Hemiptera: Coccoidea) and Tending Ants in Tunisian Vineyards

In 2009, two mealybug species Planococcus ficus (Signoret) and Planococcus citri (Risso) and an armoured scale species, Hemi- berlesia lataniae (Signoret) were recorded throughout Tunisian table-grape vineyards. P. ficus was by far the most widespread scale insect species within the investigated grape growing areas and was also recorded on fig trees. Among 31 inspected vineyards, 8 were non-infested, 16 slightly to moderately infested, and 7 highly infested by mealybugs. Therefore, the latter are principal pests in vine- yards and should be sustainably managed to avoid major crop losses on grapevine. Six ant species were found in Tunisian mealybug- infested table-grape vineyards. They are Tetramorium semilaeve Andre, Plagiolepis schmitzii (Forel), Tapinoma nigerrimum (Nylander), Crematogaster schmidti (Mayr), Pheidole pallidula (Nylander) and Pheidole teneriffana Forel. The four latter species were reported tending mealybugs on grapevines. T. nigerrimum was found to be the ant most associated with the pseudococcid mealybugs. Our findings are new data for Tunisian grape-growing areas and will contribute to enhance Integrated Pest Management programs in vineyards.

Dimensioning the Irrigation Variables for Table Grape Vineyards in Litho-soils

The pedo-climatic and farm characteristics of Bari’s hinterland have allowed for the diffusion of prestigious table viticulture. The typical “tendone” vineyard structure is set up after managing the surface of the soil. The karstic nature of the region and the thermo-rainfall trend during the vegetative season impede the vineyard from producing adequately without irrigation. Given the importance of water contributions to table grapes, it is necessary to correctly measure the water variables for economic and environmental reasons. Farmers often irrigate according to “fixed” turns and volumes, against the rules of “good irrigation practice” which consider monitoring the water status of the soil or plant as a prerequisite of irrigation scheduling. During this experiment, two methods of irrigation management were compared: “fixed-turn” and “on demand”. For “on demand” irrigation, the irrigation volume is calculated on the basis of the soil water status (estimated according to the “water balance” method described in the “Paper n. 56 FAO”) and the irrigation is scheduled on the basis of the experimental relationship between “pre-dawn” leaf water potential and the water available in the soil. For this comparison, data from a 2-year “on farm” experimentation, in an area typical of table grape cultivation in Southern Italy, have been used. The results obtained show that, in respect to the “fixed-turn” management, the “on demand” management allows for a 20% reduction in water volumes, without compromising production. The water balance method proved to be a promising criterion for irrigation scheduling in these shallow soils, rich in stones (litho-soils). This only held true when the depth of the soil layer explored by the root system was defined by the “equivalent depth” and not by the actual soil’s depth.

EFFECT OF SOIL APPLICATIONS OF KCL PLUS CACL2 ON TABLE GRAPES

Plants have developed physiological mechanisms to adapt to high soil salinity, such as stomatal closure and osmoregulation. The latter allows maintenance of water flux because of an increased internal osmotic pressure. We carried out an experiment in a commercial 'Thompson Seedless' table grape vineyard in central Chile (34°20' S, 71°17' W) where concentrated solutions of CaCl 2 and KCl were applied to the soil regularly during December and January of the 2005/06 and 2006/07 growing seasons. Soil analyses showed that, where the salt solutions were applied, chloride (Cl) levels and electrical conductivity (EC) were higher, but K and Ca levels were similar to the control. Foliar and fruit analyses showed that Cl concentrations were higher in both seasons in leaves and fruits from vines exposed to the applied salts. Shoot, bunch and berry weight did not differ between treatments. Berry firmness at harvest and 30 days postharvest was higher in the salt treatment while berry dry matter percentage was lower. Cell area was measured in histological sections of berries from both treatments, and larger cells were found in fruit from the salt treatment. These results suggest that grapes have osmoregulation mechanisms that respond to high amounts of Cl in soil.

Antifungal efficacy of Aloevera in vitro and its use as a preharvest treatment to maintain postharvest table grape quality

Aloe vera gel was added at several concentrations on potato dextrose agar (PDA) to test its efficacy on inhibiting mycelium growth of two common fungi responsible for fruit decay ( Penicillium digitatum and Botrytis cinerea). For both fungi, the inhibition of mycelium growth rate increased with Aloe concentration, although to gain the same inhibition the necessary A. vera gel concentration was 3-fold higher for B. cinerea than P. digitatum. Overall, the dose of 250 mL L −1 led to 4- and 2-log reductions of mycelium growth for P. digitatum and B. cinerea, respectively. Based on these results, A. vera gel at 250 mL L −1 was applied as a preharvest treatment to table grape vineyards 1 or 1 and 7 days before harvesting. Fruit were cold-stored for 35 days and sampled weekly. Respiration rate and weight loss were significantly reduced in treated samples, while ripening parameters such as colour and fruit firmness were significantly delayed. Both mesophilic aerobics and mould and yeasts counts were significantly lower at harvest in treated samples, the effect being persistent during storage. At the end of the experiment, the percentage of rotted berries was significantly lower in treated than in control fruit. From these results it could be inferred that A. vera could be considered as a promising preharvest treatment to maintain table quality during postharvest storage.

Control of Lobesia botrana (Lepidoptera: Tortricidae) in vineyards in Cyprus using the Mating Disruption Technique

The Isonet-L pheromone dispensers were applied in 2004–2006 in an organic table grape vineyard aiming to control the European Grapevine moth Lobesia botrana (Den.&Schiff.) (Lepidoptera: Tortricidae). Laboratory analysis showed that almost 50% of the pheromone in the dispensers was released during April and May, while another 25% was released in June alone. A high rate of bunch damage in the untreated vineyard was observed throughout the trial, reaching 40.8, 59.6 and 64.4% in 2004, 2005 and 2006, respectively. At the same time, bunch damage in the treated field was 6.8, 6.0, and 10.4% for the same years, respectively. Damage caused by L. botrana in the treated vineyard was significantly lower compared to the damage in the control field. In 2004, bunch damage was estimated at 0.68 ± 0.36 and 4.08 ± 0.36 in the treated and the control vineyards, respectively. Significant differences were also observed in 2005, where damage was estimated at 0.6 ± 0.32 in the treated and 5.96 ± 0.32 in the untreated plot, while in 2006, these values were 1.04 ± 0.33 and 6.44 ± 0.33 in the treated and the control vineyards, respectively. Significant statistical differences were observed regarding bunch damage in the border and centre of the treated vineyard in 2004 and 2006, where the bunch damage values were estimated at 0.52 ± 0.13 and 0.8 ± 0.17 in the border, and 0.16 ± 0.07 and 0.24 ± 0.08 in the centre of the treated vineyard, respectively. Statistical differences ( P < 0.0001) were also obtained when bunch damage was assessed between the treated and untreated vineyards across the trial years, where damage was estimated at 0.77 ± 0.20 and 5.49 ± 0.20 in the treated plot and the control, respectively.

Incidence and Distribution of Grapevine Leafroll‐associated viruses in Tunisian Vineyards

AbstractSurveys were carried out in Tunisian table grape vineyards for assessing the occurrence and distribution of grapevine leafroll‐associated viruses (GLRaVs). Leafroll symptoms were commonly observed in most of the surveyed vineyards. Samples were randomly collected from 712 individual vines for laboratory testing. Enzyme‐linked immunosorbent assay (ELISA) tests showed that 81.5% of the vines were infected by one (35.7%) or more (45.8%) viruses. GLRaV‐3 was the most widespread virus (76.3%), followed by GLRaV‐5 (38.5 %), GLRaV‐6 (13.2%), GLRaV‐1 (9.1%), GLRaV‐2 (6.3%), and GLRaV‐7 (0.9%). GLRaV‐3 and GLRaV–5, two mealybug‐transmissible Ampeloviruses, were present in mixture in 35.9% of samples. The highest infection rate was found in Cape Bon region (81.7 %), where cv. Italia had an infection rate of 79.5%. Superior seedless, the main cultivar in Sidi Bouzid, had 75% infection. GLRaV‐6 and ‐7 were detected for the first time in Tunisia.

Effect of Irrigation Amount and Preharvest Irrigation Cutoff Date on Vine Water Status and Productivity of Danlas Grapevines

An irrigation study was conducted in a <i>Vitis vinifera</i> L. (cv. Danlas) table-grape vineyard in Morocco with vines receiving no applied water (NI treatment) or one of two applied water amounts with subplots composed of three irrigation cutoff dates: early cutoff (EC) at berry set, late cutoff (LC) at veraison, and no cutoff (traditional irrigation, TI; based on grower practice). Midday leaf water potential (Ψ_l), canopy temperature (T_C), and soil water content were measured in several of the treatments. Midday Ψ_l was significantly correlated with soil water content (r = 0.89), ambient temperature (r = −0.71), and vapor pressure deficit (r = −0.62). The highest yield and berry weights were measured in TI vines followed by LC vines. NI vines had the lowest soluble solids at harvest. No significant differences were observed for fruit pH and titratable acidity among treatments. A comparison of NI and TI treatments indicated that yields increased as T_C - T_A (ambient temperature) and Ψ_l increased. Under the conditions of this study, an average T_C - T_A of −2.5°C or a Ψ_l of −1.0 MPa would be sufficient to maintain yield and fruit quality, while a Ψ_l value of −1.2 MPa would indicate water stress. Estimated vineyard evapotranspiration was much greater than the amount of water normally applied to vines in this region, and values of Ψ_l and temperature differentials indicated such. However, since grapes produced in this region are destined for the early table-grape market, results indicate that vines could be deficit irrigated or water applications could be terminated at veraison without a significant yield loss.

Direct and indirect methods to simulate the actual evapotranspiration of an irrigated overhead table grape vineyard under Mediterranean conditions

AbstractTwo methods, indirect and direct, for simulating the actual evapotranspiration (E) were applied to an irrigated overhead table grape vineyard during summer, situated in the Mediterranean region (south Italy), over two successive years. The first method, indirect but more practical, uses the crop coefficient (Kc) approach and requires determination of the reference evapotranspiration E0 (FAO (Food and Agriculture Organization) method). This method underestimated on average by 17% the daily values of the actual evapotranspiration E. The analysis in this paper shows that the values of Kc for the table grapes determined by the FAO method seem to not be valid in our experimental conditions. Similar conclusions can be found in the literature for the table grape cultivated under different experimental conditions and using different training systems. The second method, is a direct method for estimating the evapotranspiration. It requires development of a model for the overhead table grape vineyard E, following the Penman–Monteith one‐step approach, and using standard meteorological variables as inputs for the determination of the canopy resistance. This method, which needs a particularly simple calibration, provided a better simulation of the hourly and daily evapotranspiration than the indirect method. In additon, the standard error of the daily values for the direct method ( ± 0 · 41 mm) was about 50% lower than that obtained for the indirect method, also when the indirect method used a locally calibrated coefficient Kc instead of a generic Kc. Both, for practical application and theoretical issues, the advantages and disadvantages linked to the use of each tested method are discussed in detail. Copyright © 2007 John Wiley &amp; Sons, Ltd.

Current control of phytosanitary insect pests in table grape vineyards of the Hex River Valley, South Africa

Phlyctinus callosus (Coleoptera: Curculionidae), a key phytosanitary pest of South African table grapes, is controlled using sticky Plantex® trunk barriers, while Epichoristodes acerbella (Lepidoptera: Tortricidae), another important phytosanitary pest, is controlled using DiPel® (Bacillus thuringiensis var. kurstaki). Other less important pests are Gonocephalum simplex (Coleoptera: Tenebrionidae), Dysdercus fasciatus (Hemiptera: Pyrrhocoridae) and Gryllus bimaculatus (Orthoptera: Gryllidae). Bunches of grapes in vineyards were sampled for all phytosanitary pests during the 2003/2004 season, by both direct inspection and by shaking individual bunches to collect insects that fell. Insects moving up the vine trunk were collected with cardboard collars. The heads and bases of vines were also inspected. Cover crops and surrounding habitats were sampled by sweep netting. Pheromone traps, using E. acerbella pheromone capsules, were placed in vineyards. Abundance of pests was related to presence or absence of st...

First Report of Anthracnose Caused by Elsinoë ampelina on Grapes in Michigan.

In 2001, dark brown-to-purple, sunken lesions were observed on shoots and berries of 5-year-old 'Mars' and 'Marquis' table grapes (Vitis spp.) in Onondaga, MI. The disease affected >90% of the vines. Many leaves were curled and distorted and some shoot tips had died back. Older wood showed crater-like indentations. No fruit was harvested due to poor fruit quality. Lesions (at least 10 per sample) were surface-disinfested with 1% sodium hypochlorite, placed on potato dextrose agar (PDA), and kept at 23 to 25°C under ambient light. Sphaceloma ampelinum de Bary (teleomorph Elsinoë ampelina Shear) was isolated from shoots, leaves, and clusters (4). Colonies appeared as slow-growing, dark red mounds. Conidia were hyaline, ovoid, and measured 2.5 to 5 × 5 to 12.5 μm (average 3.5 × 7.4 μm). While grape anthracnose is usually considered a southern disease, occasional outbreaks have been reported in Ohio (1) and it appears to have become more common in Michigan in recent years. Several old herbarium specimens and records of the fungus on grapes in Michigan exist (2,3), but pathogenicity was not proven. In 2004, the disease was confirmed in eight table grape vineyards (three 'Marquis', two 'Concord Seedless', two 'Mars', and one unknown variety), one juice grape ('Niagara'), and one wine grape vineyard ('Vidal') in various locations in Michigan. To determine pathogenicity, shoots of two potted 'Mars' plants were sprayed until runoff with a suspension of 106 conidia/ml of an isolate from 'Marquis' grapes in Lawton, MI. The plants were covered with clear plastic bags for 48 h and kept at 23 to 25°C on the lab bench for 2 weeks. Shoots sprayed with water served as controls. After 4 days, numerous brown spots appeared on inoculated young leaves, petioles, internodes, and tendrils. Lesions continued to enlarge and coalesce into large necrotic areas. The fungus was successfully reisolated on PDA using the procedure described above. ITS1F/ITS4 amplification of three isolates from 'Marquis' vineyards in St. Joseph, Lawton, and Onondaga, MI produced a product of approximately 1,040 bp. The sequences most closely matched that of E. banksiae I. Pascoe & P. Crous from Banksia prionotes Lindl. in GenBank, but no E. ampelina sequences were available for comparison. The sequences of the three isolates in this study were submitted to GenBank (Accession Nos. AY826762, AY826763, and AY826764). The disease in the vineyard in Onondaga may have been present on the plants which originated in Arkansas. Additional evidence for nursery stock as a source of inoculum was the discovery of anthracnose on 'Concord Seedless' plants at a retailer in Okemos, MI in 2004. Anthracnose was also found on riverbank grape (Vitis riparia Michx.) in Holland, MI, indicating the potential of wild hosts to be an inoculum source. However, nothing is known about the ability of isolates from wild grapes to infect cultivated grapes. Control methods, such as the use of disease-free plants, pruning, and effective fungicides are necessary to avoid serious losses in susceptible varieties, particularly in years with heavy rainfall.

Microclimate and plant water relationship of the “overhead” table grape vineyard managed with three different covering techniques

The effect of three vineyard cover types on the microclimate, plant water relations and vineyard evapotranspiration (ET) of an overhead table grape vineyard (cv. “Italia”) is characterised in this study. Two covering techniques, thin net (V2) and thin plastic film (V3) were compared with an uncovered vineyard (V1). The trial was carried out in southern Italy. Global ( R g), net ( R n) and photosynthetically active radiations (PAR) were attenuated by the covers. R g was reduced 8% by the thin net and 14% by the plastic film; PAR was reduced 17% by the thin net and 32% by the plastic. R n was reduced 20% by the thin net and 25% by the plastic film. The air temperature at the height of the grape clusters was 1 °C higher (average diurnal value) in the uncovered vineyard than in the covered ones. Air humidity was 20% lower for the uncovered vineyard. In the uncovered vineyard, predawn leaf water potential ( Ψ b) decreased more rapidly following irrigation than in the other two systems and reached a minimum in a few days. On the day following irrigation uncovered vineyards had higher diurnal stomatal conductance ( C s) values than the other two systems. However, at 7 days after irrigation the uncovered vines had lower C s values than the other treatments. In the uncovered vineyard actual evapotranspiration was high (6.4 mm per day) after irrigation, then it decreased rapidly until reaching its minimum value (about 4 mm per day) after 9 days. In the vineyard covered by plastic, ET was lower (3 mm per day) after irrigation and its decrease was very slow, taking 24 days to reach its minimum value (1.9 mm per day). The ET of the vineyard covered by the thin net was intermediate between the other two systems. From these results, it was possible to demonstrate a close relationship between the crop coefficient and the predawn leaf water potential, well-differentiated in the three treatments. Suggestions for the correct management of irrigation water were also proposed and are based on the calculation of the crop coefficient.

Eight-Year Nematode Study from Uniformly Designed Rootstock Trials in Fifteen Table Grape Vineyards

Ten grape rootstocks were evaluated in 15 fumigated replant settings for their resistance to nematode build-up. Ramsey, Harmony, Freedom, VR O39-16, Teleki 5C, 5BB, 101-14 Mgt, 1103P, 3309C, and own-rooted vines were planted into various soil textures in a completely randomized block design with five replications for each rootstock. Each site was planted to a single scion variety and farmed commercially. Own-rooted control vines at all sites were sampled during spring 1992, 1993, and 1994 to determine nematode infestation. All rootstocks were then sampled from eight infected sites until 1998. Nematode counts differed among rootstocks, but <i>Xiphinema index</i> populations performed similarly at seven sites as they increased, peaked, and then declined within several years. Based on nematode densities, Harmony, Freedom, and VR O39-16 were rated resistant to <i>X. index</i>. In two vineyards <i>Xiphinema americanum</i> multiplied equally well on all rootstocks and exhibited minimal population decline thereafter. No single rootstock performed optimally with any consistency. Annual fruit yields (marketable + cull fruit) over a six-year interval (1993 to 1998) were accumulated to obtain average yield. Among the best rootstocks was 1103P, but it also supported highest population levels of <i>X. index</i>. Harmony and 101-14 Mgt were generally the lowest yielding, but other rootstocks performed poorly within specific scion and field settings. This study provides information on two dagger nematode species, their population dynamics after soil fumigation, and their interactions with selected grape rootstocks. It also raises questions about field trial designs for rootstock studies.

New closterovirus in ‘Redglobe’ grape causes decline of grafted plants

In California, first-generation table grape vineyards were planted on their own roots. But in recent years growers have been replanting onto acreage previously in grapes more often. Grafted plants are being sought to overcome nematodes and other site-related problems. We investigated the etiology of the decline and death of ‘Redglobe’ table grape scions propagated on different rootstocks, using a series of greenhouse and field experiments, and reverse transcriptase-polymerase chain reaction (RT-PCR) assays. We determined that a specific graft-transmissible agent was closely associated with declining young grapevines. The ‘Redglobe’ closterovirus that we identified was given the trivial name Grapevine rootstock stem lesion associated virus (GRSLaV).

Grape growers report losses to black-foot and grapevine decline

Sporadic but increasing incidence of two new diseases, which we have named “black-foot disease” and “Phaeoacremonium grapevine decline,” are taking a toll in California's table and wine grape vineyards (Scheck et al 1998a, 1998b). Although the full scope of the problem is not yet measured, grape growers throughout major production regions in California have reported economic losses from replanting costs. Symptoms of these diseases are almost indistinguishable from each other; the diseases are in fact the same that have occurred in grapevines in other places in the world and in older grapevines here. Our research reveals that black-foot is caused by Cylindrocarpon obtusisporum, and grapevine decline is caused by Phaeoacremonium species (P. aleophilum, P. chlamydosporum, or P. inflatipes).

Influence of ground cover on spider populations in a table grape vineyard

1. Cover crops and/or resident ground vegetation have been used in California vineyards to increase the number of predators and decrease the number of pestiferous herbivores. The most common resident predators in vineyards are spiders (Araneae). Several observational studies suggest that the addition of cover crops results in an increase in spider density and a decrease in insect pest densities.2. To test experimentally the effects of cover crops and/or resident ground vegetation (hereafter collectively referred to as ground cover) on spider populations, a 3‐year study was undertaken in a commercial vineyard. Large, replicated plots were established with and without ground cover during the growing season. Spider species diversity was analysed on the vines and on the ground cover.3. On the vines, there was no significant difference in spider species richness or the total number of spiders in plots with and without ground cover. There were differences in the relative abundance of two spiders between treatments, with one species (Trachelas pacificus [Chamberlin &amp; Ivie]) more abundant in plots with ground cover and another (Hololena nedra Chamberlin &amp; Ivie) more common on vines in plots with no ground cover. Annual variation in spider abundance was greater than variation due to ground cover treatment.4. On the ground cover, the spider species diversity was considerably different from that found on the vines above, suggesting that there is little movement of spiders between the ground cover and the vines. Enhancement of T. pacificus populations on vines with ground covers may be a result of prey species movement between the ground cover and the vines. Spider abundance was sparse on the bare ground.5. The maintenance of ground cover increased spider species diversity in the vineyard as a whole (vine and ground cover). However, the relatively small changes in spider abundance on the vines indicate there are limitations in the use of ground covers for pest management with respect to generalist predators.