Management of Riparian Woodlands for Control of Pierce’s Disease

AVF Proj. ID: 9524 / /Cat.: ,
Primary Investigator(s): Alexander H. Purcell, Joe R. McBrideby

This is a continuing project to develop new methods of managing Pierce’s disease (PD) of grapevines by managing the plant habitats of the principal insect vector of PD, the blue-green sharpshooter (BGSS). Populations of BGSS would be reduced by replacing plants such as wild grape, blackberry, and others with plants that are not favored by the BGSS for reproduction or feeding. We are also testing buffer strip plantings of redwood and Douglas fir between vineyards and riparian woodlands as a barrier to reduce the influx of BGSS into vineyards during spring. The second goal is to reduce the percentage of BGSSs that are infective with the Pierce’s disease bacterium {Xylella fastidiosa) by replacing plants that support the multiplication, within-plant movements, and year-round survival of A”. Fastidiosa with plants that do not. Managing riparian woodlands to reduce the threat of PD also must meet requirements to maintain good habitats for fish and wildlife, prevent water contamination, and not degrade other public uses or values of this ecosystem. During 1995-96 we monitored populations of BGSS before and after the management treatments. We also estimated that about 6%of BGSS in the study site were infected with Z Fastidiosa in September, 1995. Sticky trap catches of BGSS along both sides of the study site along Conn Creek, Napa County, verified that BGSS was common along the entire study site. Trap catches in vineyards were much lower than in adjacent riparian vegetation (10%or less of riparian catches). During the fall, selected plants were removed from treatment plots by cooperating growers using California Conservation Corps work crews. Replantings and buffer strip plantings were made during February-March. Additional plantings to replace trees that died will be made after September, 1996, depending on rainfall. As expected, trap catches of BGSS were drastically reduced in plots where riparian vegetation was removed. Two additional experimental sites should be added in 1996. Approval from California Dept. Of Fish and Game for these experiments was given for a Napa River site. Permission will be sought to establish a Sonoma County site on Maacama Creek if BGSS activity proves to be sufficient based on our sampling of BGSS populations. Future replications of this experiment on other sites will give more realistic short term estimates of the effectiveness of the vegetation management approach because not as many large trees will be removed. A mix of University and AVF funding is planned to support this complex, multi-year project. This year funding (>$20,000/year) for 2 or 3 years shared funding has been awarded through a competitive grant from the California Department of Pesticide Regulation.

Nematode Evaluation of Eight Rootstocks Present in Existing Field Trials

AVF Proj. ID: 9525 / /Cat.: ,
Primary Investigator(s): Michael McKenryby

Selected grape rootstock trials from 5 to 22 years in age were evaluated around California. In these trials mixtures of nematode species had built up giving us an opportunity to validate our previous data from microplot settings. Data from four to five replicates were collected from each site. Many trials had at least 10 rootstocks. A few had only two or three but were older, thus making them worthwhile to sample. We eventually collected samples from 15 sites in Kern County, three in Fresno County, three in Monterey County, one each from Sonoma, Mendocino and Merced counties, and will be sampling one from San Joaquin County. The nematode data from more than 1,100 soil samples are still being analyzed but attached are two charts showing our method for comparing field data with existing microplot data in sites where Xiphinema index was present. This work is tedious and expensive and my concern is that the payoff may not be as great as other studies we hope to conduct in the future. The major problem is that even when rootstock trials are 5 years old and the nematodes are not yet evenly distributed across replicates, resulting in false negatives. Nonfumigated sites such as the field in Mendocino on Chart 2 did not help to clarify. The Mendocino field did not have an own-rooted comparison but we are able to “guesstimate” based on the populations on 3309. There were also advantages to this work. The primary advantage was the opportunity to sample sites with mixed populations where nematodes may be competing with one another or other soil microbes. We have learned that 1103P is too good a host for X. index but remain unclear on 110R and 101-14. Root knot nematode resistance in Freedom and Harmony was nonexistent in two of three older trials in Fresno County, although their tolerance to the nematode and extreme vigor has kept them from declining below the own-rooted. The field-derived data do appear to validate our previous microplot work. VR 039-16 is supporting X. index in one replicate of Kern County and at a separate field site in Monterey. This needs further investigation.

Pierce’s Disease Epidemiology and Management

AVF Proj. ID: 9529 / /Cat.: ,
Primary Investigator(s): Alexander Purcellby

This continuing project studied what happens to the Pierce’s disease (PD) bacterium {Xylella fastidiosa) in various plant species. We selected plants that are preferred by the principal insect vector of PD in coastal California, the blue-green sharpshooter (BGSS). We used infective BGSSs to inoculate plants in the lab with X. Fastidiosa. After keeping the plants in a greenhouse or waiting for mechanically inoculated plants in the field to develop infections, we attempted to isolate the bacterium from the plants. We recovered X. Fastidiosa for both types of inoculation from buckeye, valley oak, elderberry, and big leaf maple. We recovered bacteria from ash, coast live oak and bay laurel from BGSS-inoculated plants in the greenhouse but not from field-inoculated plants. We did not recover bacteria from alder, black walnut, arroyo willow, red willow, or sandbar willow that had been inoculated by either method or from cottonwood that had been mechanically inoculated. We recovered X. fastidiosa from mechanically-inoculated wild plum, which was not tested using BGSS inoculation. We kept all greenhouse-infected plants outdoors at Oakville during winter, 1995-96 and returned them to the greenhouse to hold for retesting (culture) later this summer. Many normally deciduous species (oaks, for example) kept their leaves throughout the very mild winter. We have reisolated X. fastidiosa from overwintered California blackberry. An analysis of DNA differences among 29 strains from grape or almond grouped strains into 3 clusters: north coast strains (no almond tested), most almond strains (Central Valley), and southern and central California strains (almond and grape).

Seasonal Development and Control of Mealybug Species in Central Coast Vineyards

AVF Proj. ID: 9531 / /Cat.: ,
Primary Investigator(s): Mary Lee Bianchi, Phil Phillips, Kent Daane, Walt Bentleyby

Survey sites were established and monitored for mealybug, ant, and beneficial species. Obscure and long-tailed mealybugs were identified at all survey locations. No positive identification of grape mealybug has been made from any affected vineyards, although its presence is suspected due to recovery of parasite species known to parasitize grape mealybug. There does not seem to be a pattern of conditions that preselect the predominance of mealybug or ant species at any of the survey sites. Although predation was found at all sites it was not important as a control factor. Parasitism was found at three of the five sites, in very low levels. Determination of the seasonal development of each species under coastal conditions was not achieved during the 1995 growing season for three reasons. It was not considered prudent to release these species until positive identification of each was made. Obscure and long-tailed have been positively identified. In addition, pure colonies of the mealybug species were not available for release. Wet, cold weather conditions during the spring and early summer in the Edna Valley were also not conducive to a successful release. Due to the inability to complete objective 2 in 1995 the trial was amended to look at the efficacy of delayed dormant applications and inseason applications of short and long residual insecticides as well as a newly registered material reported to be effective in controlling mealybugs (Table 1). Timing of insecticide applications may be more critical than type of insecticide used when working with multiple species having different developmental cycles during the season. Dormant applications of chlorpyrifos have been successful in controlling grape mealybug populations in the San Joaquin Valley because it overwinters either as eggs or as newly hatched crawlers (Walt Bentley personal communication May 1996). In severely infested vineyards some in-season applications are also necessary. The most successful in-season treatments have been timed to a predominance of the early crawler stage of grape mealybug. In this trial monitoring of sticky tapes on canes indicated an early peak of crawler emergence in the first week of July. Treatments were applied the last week of June. Pre and post counts of leaves indicated significant reductions in mealybug numbers immediately after treatment with dimethoate and methomyl. Only dimethoate was consistent in being significantly different from the control in the number of crawlers captured on sticky tapes during the remainder of the season, and in significantly reducing the infestation of mealybugs in the clusters at harvest as compared to the unsprayed control.

Spiders in Vineyard Agro-Ecosystems

AVF Proj. ID: 9532 / /Cat.: ,
Primary Investigator(s): Mark A. Mayse, Simon Gravesby

The overall goal of this research project is to continue to elucidate the ecological roles and potential economic value of spiders in vineyard agro-ecosytems. Specific objectives include: 1) To determine key behavioral habits and to study prey selection of both Cheiracanthium and Trachelas spiders, 2) To further investigate the diversity and abundance of spiders in vineyards, and 3) To develop a color field guide to important spiders in California vineyards. During 1995, spider research was conducted both in vineyards near Ripperdan (Grenache) and at CSU Fresno (Barbera, conventional and organic plots). Direct observation sampling in the grapevine canopy was conducted during evening hours (peak hunting activity periods for Cheiracanthium and Trachelas) using headband-mounted lights with red filters to avoid disturbing normal spider behavior. Another spider sampling technique used in 1995 involved placing corrugated cardboard bands around the base of vine trunks (particularly effective for Trachelas). Near the band locations, canopy shake samples were also conducted. Direct observation sampling involved a total of 26 hours viewing time in 1995. Only 8.3% of the total sampling time resulted in successful sighting of a Cheiracanthium or Trachelas spider. Frequency of occurrence data for the two spider genera mirrored results from 1994, in that 92% spider sightings were Cheiracanthium with the remaining 8% being Trachelas. Also similar to 1994 patterns, juvenile spiders were observed more frequently than were adults. Behavioral activities of Cheiracanthium spiders were rather diverse: adults hunting (25%), adults resting (25%), adults with egg sac/molting sac (8.3%), and juveniles hunting (54.2%). No Cheiracanthium were directly observed in the act of feeding on prey in 1995. Trachelas spiders were found in only two behavioral categories: juveniles resting (50%), and juveniles hunting (50%). Band trapping results at CSUF revealed the highest numbers of Trachelas adults in conventional plots in late January 1995, while Trachelas juveniles peaked in organic plots on the same date. Both adult and juvenile Cheiracanthium reached highest densities in late January in the organic plots. Band traps at the Ripperdan Ranch produced peak Trachelas adults and juveniles in late February 1995. Cheiracanthium adults at Ripperdan peaked throughout February, while juveniles reached highest densities in late February. Joint CSUF/UC collaboration (co-authors Mark Mayse, Michael Costello, Billy O’Keefe, Kent Daane, Curtis Sisk) on a color-illustrated field guide entitled, “Spiders in San Joaquin Valley Grape Vineyards” came to fruition in late 1995 with the guide’s publication. In addition, we are completing a translation of the guide’s text and caption information into Spanish to further expand the circle of effective contact for this publication; the translation will ultimately be included as a simple insert included in the basic color field guide.

Testing Zinfandel Selections for Fanleaf Virus

AVF Proj. ID: 9533 / /Cat.: ,
Primary Investigator(s): James Wolpertby

A previous clonal evaluation trial was terminated with the conclusion that the certified clones of Zinfandel showed few differences in yield components, such as berries/cluster and berry size. The former is desired for contributing to lower rot potential and the latter for better color development. Over the past few years, efforts were made to identify new Zinfandel clonal selections from old, healthy-appearing vineyards with reputations for wine quality. Selections were made on the basis of observed fruit characteristics such as cluster shape and compactness as well as berry size. While vines were visually selected for freedom from disease, it was important to test for grapevine fanleaf virus (GFLV) to prevent the spread of that disease into the test site. Other costs for plot establishment were and will be borne by other sources of funding. The trial was established at the OakviUe Experimental Vineyard. St. George rootings were planted in spring of 1995 and 52 selections were chip-budded in September with an additional 11 selections scheduled to be spring-budded in 1996.

Transmission of grapevine leafroll associated viruses

AVF Proj. ID: 9432 / /Cat.: ,
Primary Investigator(s): Deborah Golino, Adib Rowhaniby

1995 FINAL REPORT – Evidence is strong that leafroll disease has spread from infected vines to uninfected vines in the disease-tested, true-to-variety collection of grapevines at the Foundation Plant Material Service facility in Davis. The collection is the core of the California Grapevine Registration and Certification Program. This disease spread has serious implications for the grape clean stock program and commercial vineyards in California. Reports do exist of field transmission of viruses in the leafroll group by mealybugs in other areas of the world. Due to the success of early transmission experiments in the Golino laboratory with mealybugs, this aspect of the research has recieved additional attention in 1995. Four populations of mealybugs were collected, identified and increased: one of the obscure mealybug, Pseudococcus affinis, a mealybug species commonly found in California; one of the citrus mealybug, Planococcus citri; and two cultures of the long tail mealybug, P. longispinus, also common in California vineyards. In the last year, experiments were done using the obscure mealybug to transmit leafroll types I, II, m (isolates 109 and 101), IV and corky bark isolate 100. Isolate 109 is a very severe strain of leafroll type III, the most important leafroll type in California. By 8 months after inoculation 30%of inoculated plants were infected. We are in the process of repeating these experiments to determine whether this rate of transmission is consistent. This is the first evidence that the obscure mealybug can act as a vector for grapevine leafroll virus. The obscure mealybug did not transmit leafroll type II virus in any of three experiments involving 87 Cabernet Franc and LN-33 test plants. Preliminary results indicate the the obscure mealybug transmits grapevine corky bark virus, a related closterovirus, at a low rate; tests with LR type I are in progress. ELISA tests have been successful in detecting leafroll type III in the bodies and honeydew of the obscure mealybug . Initial results with the citrus mealybug indicate it cannot transmit leafroll III. Preliminary results with the long tail mealybug indicate it can transmit corky bark. Future studies will concentrate on the long tail mealybug.

Spiders in Vineyard Agro-Ecosystems

AVF Proj. ID: 9428 / /Cat.: ,
Primary Investigator(s): Mark A. Mayseby

Two workgroup sessions on “Spiders in Vineyards” were held during 1994 (CSU Fresno-March, UC Kearney Ag Center-October), providing outstanding opportunities for information exchange and research coordination. Round-the-clock spider sampling studies (6A, 12N, 6P, 12M) conducted near Madera indicated that overall, spiders as a group were collected (canopy shake technique) equally well at any time of day. Spiders were sampled during the unorthodox fall / winter season of 1993-94 at Ripperdan (Madera County) using pitfall traps and cardboard banding (to our knowledge, no other researchers in California have sampled spiders using this field protocol during the winter). Studies focusing on direct observation of Trachelas and Cheiracanthium behavioral ecology in vineyards provided 31 hours of nocturnal field viewing time, only 20%of which resulted in successful spider sightings. Of this total spider viewing time, over 92% involved Cheiracanthiunr, Trachelas comprised only 8%. Daytime leaf sampling data revealed that the small theridiid spider Theridion constituted over 2/3 of all spiders observed during 1994. Field researchers were mildly surprised to find the well-known clubionid spider Cheiracanthium frequenting malaise traps placed on vineyard trellis crossbars which were designed primarily to sample populations of parasitic insects. A total of 10 Cheiracanthium spiders (7 females and 3 juveniles) were found in the malaise traps; no other spider species were found in the malaise traps at any time during 1994.

Pierce’s disease epidemiology and management

AVF Proj. ID: 9426 / /Cat.: ,
Primary Investigator(s): Alexander Purcellby

The aim of this project is to evaluate the fate of the Pierce’s disease (PD) bacterium (Xylella fastidiosa) in various plant species to enable vegetation management for control of PD. Plant species that are preferred hosts of PD vectors are being tested first, but we are also screening plants to identify plants that are not hosts and thus are potential replacements for plants that are good hosts of the bacterium. Of 4 woody perennials inoculated with PD bacteria in late summer, 1994, we detected survival and multiplication of the bacterium in live oak and maple but not in spice bush or bay laurel. Survival over the last winter will be estimated in late summer, 1995. There was some indication of systemic movement of bacteria in maple; further tests are underway in greenhouse and field trials. The bacterium multiplied and spread in French broom, was transmitted from broom to grape in insect vector trials, and was recovered from naturally-infected broom near vineyards. Multiplication without systemic (within-plant) spread was detected in coyote brush, elderberry (more tests needed to evaluate spread), ivy, and mugwort. No bacterial multiplication was detected in 8 additional plant species evaluated in the lab. Fifteen perennial plant species located in riparian vegetation along a stream in Napa Valley were mechanically inoculated (40-60 sites for each species) with X. fastidiosa in April-May, 1995 and will be tested in late summer for bacterial multiplication, within-plant movement, and overwinter survival. Greenhouse-grown seedlings of these and other plant species were inoculated in the lab with infective sharpshooters for greenhouse studies. Strains of X. fastidiosa that were isolated from throughout California in the first 6 months of this project now are being examined for genetic differences by isolating bacterial plasmids and by using molecular probes that have been widely useful in distinguishing strains of other Gram-negative bacteria. The most genetically divergent strains will be inoculated into a range of plant host species to assess possible host range differences among strains of X. fastidiosa.

Development of Methodologies for Rapid Detection

AVF Proj. ID: 9410 / /Cat.: ,
Primary Investigator(s): Adib Rowhani, Deborah Golinoby

The efficiency of ELISA for detecting grapevine leafroll associated viruses was compared with bioassay index on field indicator Cabernet Franc. The test results indicated a good correlation between ELISA and field index. To overcome the shortage of polyclonal antibodies for grapevine leafroll associated viruses (GLRaV) types (T) Til, Till and TIV, viruses have been isolated and purified and Rabbits have been immunized. The preliminary evaluation of these antisera indicated that the antiserum to Till has a relatively high titer, to TIV has low titer and no specific titer was found for Til. A polymerase chain reaction (PCR) technique which is a very sensitive and reliable method for the detection of plant viruses has been developed for the detection of grapevine fanleaf virus (GFLV) in grapevine tissue. This technique was able to detect GFLV in a sample when one infected grapevine leaf was mixed with 200 healthy ones. We have modified and simplified the PCR methodology by combining immunology and PCR (immunocapture-PCR, IC-PCR) for the detection of GFLV, GLRaV Till and grapevine virus A (GVA). In this technique the lengthy process of nucleic acid extraction required for PCR has been eliminated. The results showed that this modification works quite well for the detection of these 3 viruses. Attempts are underway to develop PCR for the detection of GLRaV Til and TIV.