Using Nectar Cover Cropping in Vineyards for Sustainable Pest Management

Using Nectar Cover Cropping in Vineyards for Sustainable Pest Management

Summary

Research investigating the use of cover crops in southern California vineyards for pest control has demonstrated that access to floral resources greatly increases natural enemy fitness, buckwheat is likely to be a better cover crop for use, cover crops may positively affect natural enemy numbers, irrigation required by the cover crop may lead to increased vine vigor and pest populations, cover crops may harbor pathogens (Xylella), which could be transmitted to vines by sharpshooters, and cover crops may impact fruit yields and quality because of the additional irrigation needed to keep cover crops alive over summer.

Objectives/Performance Targets

1. Determine if buckwheat flowers and cahaba vetch extrafloral nectaries increase longevity and fecundity of key natural enemies.
   Determine when to sow cover crops to maximize nectar availability for natural enemies.
   Determine if buckwheat and cahaba vetch, sown in alternate rows of grapes, enhances natural enemy populations and reduces pest populations below economic thresholds at study sites over a two year period.
   Determine if buckwheat and cahaba vetch influence grape yield and quality.
   Determine if buckwheat and cahaba vetch affect vine vigor.
   Verify that buckwheat and cahaba vetch do not provide refuge for grape pathogens (e.g., Xylella) or pathogen vectors (e.g., sharpshooters).
   Determine if buckwheat and vetch out compete and suppress unwanted weed species.
   Determine the rate of dispersal of natural enemies from buckwheat and cahaba vetch plots.
   Extend the information gained from this research to the Californian grape community through outreach and education.
   Promote increased adoption of nectar cover cropping practices in Temecula, Lodi and Coachella Valley if research results merit application.

Accomplishments/Milestones

Laboratory trials were proposed to investigate if buckwheat flowers and cahaba vetch extrafloral nectaries increase longevity and fecundity of three natural enemies, G. ashmeadi (glassy-winged sharpshooter parasitoid), Anagrus epos (grape leafhopper parasitoid), and Anagyrus pseudococci (vine mealybug parasitoid). We have completed these studies for A. pseudococci. Results showed that female A. pseudococci provided with vetch and buckwheat plants survived 4 and 5 days longer, respectively, compared with those females provided water only (Fig. 1). Similarly, the total number of offspring produced by female A. pseudococci was up to 4-fold higher when females were provided vetch and buckwheat compared with water only (Fig. 1). This suggests that vetch and buckwheat may be a suitable food source for A. pseudococci for enhancing longevity and fecundity in the field when sown as a cover crop. Increased fitness because of access to floral resources, could in turn, enhance biological control of mealybugs through increased parasitism.
For G. ashmeadi, studies have been completed for the buckwheat and water treatments. Results to date showed that providing G. ashmeadi with buckwheat enhanced G. ashmeadi longevity by 9 days and increased offspring production more than 2-fold compared with water only (Fig. 2). Investigating the effect of vetch on G. ashmeadi longevity and fecundity has proved difficult during 2008 since cahaba vetch is a winter cover crop making it very difficult to synchronize nectar production of greenhouse plants with the G. ashmeadi and glassy-winged sharpshooter (GWSS) colonies. GWSS and G. ashmeadi colonies were not maintained in 2009 due to the intensive labor requirements of the 2009 field trial and counting and identifying insects on sticky traps from the 2008 field trial. The vetch treatment is therefore scheduled to be completed in spring 2010 when the 1st generation of GWSS and G. ashmeadi occurs.
Finally, trials with the leafhopper parasitoid, A. epos, have not been conducted. Efforts to establish A. epos and A. erythroneurae (variegated leafhopper parasitoid) colonies in 2008 were unsuccessful. In 2009, we were unable to attempt to establish Anagrus sp. colonies since labor was concentrated on insect monitoring and maintainance of the 2009 field trial and processing 2008 sticky traps. We will conduct longevity and fecundity trials with Anagrus sp. this spring.

In June 2007, the cover crop phenology trial was set up at Ag. Ops., UCR. This trial involved sowing five buckwheat and vetch plots in the middle of each month for one year and measuring every six weeks plant height, the sowing to flowering times, and length of the flowering period. Preliminary results showed that mean six week height varied with sowing date for both plant species, with shorter plants occurring during the winter months (Fig. 3). Such height information may be useful when selecting cover crops for crops that require an open canopy for prevention of moisture-loving diseases.
Fig. 4 shows that the number of days required from sowing to flowering for buckwheat was shorter during the warmer summer months of July-August. From April through to September it took buckwheat under 30 days from sowing to produce nectar-producing flowers. This information is important for growers intending to synchronize buckwheat nectar production to the phenology of natural enemies of key pests. Vetch took between 0.6-28 days longer each month to start producing nectar compared with buckwheat. This indicates that buckwheat may be a better cover crop for growers that require a quick growing plant that provides nutrition for natural enemies that are likely to contribute to the suppression of an identifiable pest problem. This is particularly important in the summer months (June-August) where buckwheat produced nectar 17-28 days faster than vetch. Conversely, once extrafloral nectaries were present on vetch plants, they produced nectar for up to 146 days longer than buckwheat flowers throughout the year (Fig. 5). There is a trade off here, speed to floral production vs. longevity of floral production. This result suggests that mixed species sowings may be useful to simultaneously take advantage of quick flowering species and those that have long flowering periods.
Consequently, information on days to nectar production and the length of nectar producing period can be used to construct guides to assist growers with cover crop sowing decisions. For example, Fig. 6 portrays a guide growers can use for strategizing buckwheat plantings. Growers could select a month along the x-axis where they require increased biological control for a particular pest problem, then the duration of flowering information could be used to determine which month the grower would need to sow buckwheat to maximize nectar production for natural enemies when the pest occurrs.

In 2009, we aimed to replicate the 2008 cover crop field study at Bella Vista, Temecula, which investigated the effect of buckwheat and vetch cover crops on natural enemy and pest populations. Trials conducted in 2008 at Bell Vista and Agricultural Operations, UCR demonstrated that cahaba vetch was a very poor competitor with common agricultural weeds, struggled to germinate and survive the warm spring conditions in southern California and was prone to high infestations of aphids, thrips, mites and other pests that severely impeded the growth of plants. Additionally, we were unable to purchase cahaba vetch seeds for our 2009 field trial since the only supplier in the U.S.A. lost their entire crop to mildew fungal disease and had no cahaba vetch seed in stock! Consequently, cahaba vetch was not trialed at Bella Vista in 2009.
For the 2009 field trial, seven buckwheat and six control plots were allocated randomly at Bella Vista vineyard. Control plots included cultivation between rows and mechanical weeding within the rows to remove unwanted weed vegetation. Buckwheat seeds were sown on April 1st, April 29th, June 17th and July 2nd. Sprinkler irrigation was installed on the existing grower’s grape irrigation in the buckwheat plots. Each buckwheat plot was irrigated for two hours the day after each sowing to ensure good germination, then approximately every 7-10 days. Additionally, irrigation was supplemented with 16 gal of water per plot, applied via water sprayer and 4WD motorbike approximately three times a week. Rabbit scram was deployed around susceptible buckwheat plots throughout May and June to deter rabbit feeding on tender seedlings. Despite all these efforts we encountered a number of problems with establishing and maintaining a cover crop during this trial and no replicated plots of buckwheat were established in the 2009 field trial. Poor establishment of cover crops in 2009 was due to a batch of poor quality seed with a low germination rate (just 10-33% in greenhouse studies) that was brought from suppliers, irrigation issues (including sprinkler head blockages and flooding), birds eating seeds before they germinated, rabbits eating large patches of germinated seedlings, extreme summer temperatures killing seeds and seedlings, and severe damage to cover crop plants from tractor and vineyard workers during routine vineyard maintenance.
Monitoring of insects using weekly transparent sticky traps and bi-weekly 30 second funnel beat samples were conducted between May through until late-July, 2009. Leafhopper visual counts and 1 min sweep net samples were conducted every two weeks during June until late-July 2009. Double-sided sticky tape was placed around the trunk and canes of two vines per plot and changed every two weeks during June until late-July 2009 to monitor mealybugs and spiders. In late-July 2009, it was apparent that establishment of buckwheat replicates was unattainable, therefore we ceased all insect monitoring and concentrated labor resources on identifying and counting insects from the 2008 sticky traps stored in the freezer.

Sticky trap and visual count results from the 2008 field trial:
During the 2008 trial, four replicates of the cover crop treatment were established with buckwheat (cahaba vetch did not establish and this side of the row was cultivated on June 11th, 2008 and re-sown with buckwheat). The other three allocated ‘cover crop plots’ had irrigation installed, but since buckwheat did not establish, these plots were reassigned as an ‘irrigated treatment’. Consequently, the three treatments for this study were: (1) buckwheat cover crop with irrigation; (2) irrigation with no buckwheat cover crop; and (3) a cultivated control with no buckwheat cover crop or irrigation. Including an ‘irrigated treatment’ will help determine whether effects of buckwheat cover crop on insect fauna, grape yield, fruit quality, and vine vigor was due to the buckwheat cover crop or the irrigation required by the cover crop plants.
Two sticky traps were placed on the north and south side of the middle row of each plot, 12 ft apart. Traps were collected and replaced weekly. The number of pests and natural enemies were recorded separately for each side of the sticky trap as this will provide information on whether insects were flying towards or away from the grape canopy and buckwheat cover crop. Identifying and counting insects from the 2008 sticky traps was a mammoth task. We have completed processing sticky traps deployed between June 10th, 2008 and August 19, 2008. Results pooled over all sticky traps sides (foliage versus open side), row directions (north or south) and dates show that the abundance of pestiferous leafhoppers was 81% and 36% higher in the irrigated and buckwheat treatments compared with controls (Fig. 7). We speculate that these results may be due to the irrigation in the buckwheat and irrigated treatments increasing vine vigor, which made these vines more attractive to leafhoppers. Mean cane weight was 63-69% higher for vines in the buckwheat and irrigated treatments compared with controls (see Objective 5 below; Fig. 11). Buckwheat plots resulted in 27% less pestiferous leafhoppers compared with the irrigated treatment lacking buckwheat (Fig. 7) which may be attributable to higher numbers of predators, such as predatory beetles, lacewings, ladybugs, big-eyed bugs and spiders, in buckwheat plots compared with the irrigated treatment lacking buckwheat (Fig. 8). Predatory wasps, predatory thrips, predatory beetles, lacewings, ladybugs, minute pirate bugs and big-eyed bugs captured on sticky traps were up to 1100% higher in buckwheat plots compared to controls (Fig. 8). However, buckwheat plots also had higher populations of pestiferous thrips, aphids, sharpshooters and false chinch bug (up to 174% higher) compared with controls (Fig. 7). Statistical analyses are currently being conducted to determine whether these differences are significant, and to investigate the effect of date, treatment, row direction, trap side and their interaction on the abundance of each insect species.
Results from visual counts data obtained every two weeks from June 5th, 2008 until August 21st, 2008 supported sticky trap data in that the number of pestiferous green and variegated leafhoppers counted per leaf was up to 2-fold higher in the buckwheat and irrigated plots when compared with controls (Fig. 9). There was no significant difference between cover crop plots and irrigated plots. The number of predators counted per leaf was more than 5-fold higher on grapes in buckwheat plots compared with controls, while there was no difference in the number of lacewing eggs between treatments (Fig. 9).
Pest and beneficial insects from sweep net, double-sided tape and funnel beat samples are currently being identified and counted. Statistical analyses will be conducted to determine effect of treatment on abundance of pests and natural enemies. Results from the different methods of measuring insect populations (sticky traps, visual counts, sweep netting, double-sided tape and funnel beat sampling) will strengthen final conclusions drawn about the strengths and weaknesses of cover cropping in arid southern California.

On September 18th, 2008, the number of grape clusters present within a 3 m section of vine in the center of each plot was counted, and 10 clusters were harvested from each section and transported to the laboratory for grape yield and quality measurements. The mean weight per cluster was 26% and 39% higher for those harvested from buckwheat plots and the irrigated treatment, respectively, compared with controls (Fig. 10). There was no difference in number of clusters or number of berries per cluster between treatments (Fig. 10). Mean Brix content was 2.9 and 2.5 degrees higher in control plots compared with the buckwheat and irrigated treatments, respectively (Fig 10). This was probably attributable to the extra irrigation the buckwheat and irrigated treatments received which may have diluted sugars in the berries or caused excess vine vigor, thereby decreasing the amount of sunlight reaching the berries.
Berries from each of the 10 harvested clusters were removed and the number of ‘shriveled berries’ and berries damaged by feeding insects were counted. Additionally, 25 berries were randomly selected from each cluster and berry diameter was measured using calipers. The percentage of berries scarred through insect feeding damage and those stained with leafhopper excreta was calculated. Results showed that the number of berries that were shriveled due to dehydration was 450-452% higher in control plots compared with the buckwheat plots and irrigated treatment (Fig 10). This illustrates the effect of extra irrigation grapevines received at berry maturity in the buckwheat and irrigated plots. The number of berries with broken skin from insect damage was 1811% and 1358% higher in buckwheat plots compared with controls and the irrigated treatment (Fig. 10) suggesting that the nectar provided by the buckwheat plots may have attracted insects, such as bees and yellow jackets, which then fed on ripened berries. Bees and yellow jackets were observed feeding from berries in buckwheat plots during harvest. Berry size was equivalent for all treatments (Fig. 10). The percentage of scarred berries was 38% higher in buckwheat plots compared with controls (Fig. 10). Feeding by thrips adults and larvae can scar immature berries and scar damage becomes noticeable as berries mature. Aesthetic damage resulting from thrips feeding may not be important for wine grapes when compared with table grapes. The number of thrips counted on sticky traps were 43% higher in buckwheat plots compared with controls.

The influence of cover crops on vine vigor was investigated in October 2008 by measuring the weight of winter prunings from three randomly selected vines in the center of each treatment plot. For each vine, the number of canes growing from each arm was recorded. All canes were removed from the vine with clippers and any remaining leaves and secondary shoots growing from the primary cane removed. Canes from each vine were placed into Ziplock bags and labeled with treatment and replicate. The average weight per cane was calculated for each vine by weighing the contents of each bag and dividing the weight by the number of canes. Figure 11 shows that mean weight was 63% and 69% higher in the irrigated and buckwheat treatments, respectively, compared with the control plots. This difference can be attributed to the extra irrigation the vines received in the buckwheat and irrigated treatments.

Approximately twenty-five buckwheat and vetch plants were needle-inoculated in the laboratory with X. fastidiosa and tested with ELISA kits after four weeks to determine whether these plants could act as a host for X. fastidiosa, the causative agent of Pierce’s Disease (PD) in grapes. Results from the buckwheat needle inoculations showed that 63% and 53% of plants became infected with X. fastidiosa as detected by ELISA and culture tests, respectively (Table 1). This demonstrates that X. fastidiosa can successfully infect and replicate in buckwheat. Results from the vetch needle inoculations showed that 45% and 15% of plants became infected with X. fastidiosa as detected by ELISA and culture tests, respectively (Table 1). This demonstrates that X. fastidiosa can also successfully infect and replicate in vetch.
Since both plants tested positive to X. fastidiosa, further testing was conducted to determine whether GWSS could acquire X. fastidiosa from buckwheat or vetch and successfully transmit the pathogen to grape vines. If GWSS can transfer the pathogen from the cover crop plants to grapes then cover crop plants may act as a potential reservoir of X. fastidiosa and be detrimental to grape growers. This is an important question that needs addressing. Consequently, the ability of GWSS to transmit X. fastidiosa from the cover crop to grapes, and then from grapes to the cover crop was investigated. For this work, forty GWSS (to allow for mortality) were released into cages containing cover crop plants infected with X. fastidiosa. Insects were left for a 48-hour feeding and acquisition period, then insects were collected and 5 GWSS were placed into a sleeve cage on each of 5 grape plants. The insects were left to feed for 48 hours, after which the insects were collected into individually labeled 1.5mL microcentrifuge tubes and frozen at -80?C for processing. Following the 48 hr feeding period, the grape test plants were grown in a greenhouse and tested for X. fastidiosa infection 8, 12 and 16 weeks post-feeding using ELISA and plate culturing techniques. Using the same protocols, GWSS transmission from cover crop to cover crop, and grapevine to grapevine (controls) were tested. Preliminary results show that GWSS can transmit X. fastidiosa from buckwheat plants to buckwheat plants, and from buckwheat plants to grapevines (Table 2). The grapevine to grapevine controls were also positive. Results for vetch are pending.
Finally, trials that investigated natural inoculation of buckwheat and vetch under field conditions were conducted at Agricultural Operations, UCR where X. fastidiosa is known to occur. Buckwheat and vetch was sown in the field in August 2008 and after 3 weeks, 10 buckwheat and 10 vetch plants were randomly selected and individually covered with acetate cages. Acetate cages were 12” tall and 4” in diameter, with 2 x 4” ‘windows’ on opposites covered with nylon mesh organdy. The top was also covered with nylon mesh organdy. The seam of the acetate and the fabric were glued using a hot glue gun. Cages were secured in place over plants with a 3 foot long length of 1” diameter PVC pipe positioned in the ground directly east of the plant and the cage was placed over the plant and fastened to the PVC using a size 32 rubberband (114g or 0.25lb) to prevent the cage from being blown over by afternoon winds.
125 adult GWSS were collected from the field and placed in a bug dorm with a potted grapevine (variety Redglobe). The grapevine had been needle-inoculated and infected with Xylella fastidious subspecies fastidiosa (Temecula strain of PD). Insects were left to feed for a 48-hour acquisition access period (AAP) then live GWSS were aspirated into plastic 40-dram vials (5 per vial). One vial was placed into each cage for each plant. Four potted grapevine controls (non-infected) were placed beside the buckwheat and vetch plants and fitted with nylon organdy sleeve cages. One vial of GWSS was released onto each potted grapevine. All GWSS were given a 96-hour inoculation access period (IAP), after which, insects were collected and plants labeled. Grapevine controls were returned to the greenhouse.
Buckwheat plants started dying at 2-3 weeks post-IAP, so all plants were collected at 3 weeks post-IAP and tested for PD. Four plants were too dry for culture testing, so these were tested with ELISA only in case dead cells could be detected. The remaining 6 buckwheat plants were tested with ELISA and culture. The vetch plants were sampled at 4-weeks post-IAP by collecting a small branch from the base of the plant. Lowest leaves from each branch of the grapevine controls were collected and the lowest 2cm of petiole tissue from each leaf was used. Results show that transmission from grapevine to buckwheat and grapevine to vetch were successful in the field (Table 3).

The ability of buckwheat and vetch to outcompete weeds was not investigated in the 2008 field trial because vetch was such a poor competitor that plots needed to be weeded by hand to ensure establishment of vetch for the trial. Vetch is a winter cover crop and did not perform well in hot weather. This objective could also not be examined in the 2009 field trial because replicated buckwheat plots could not be established and vetch was not investigated in 2009 field trial (see Objective 3).

In July 2008, insects were triple marked with yellow fluorescent SARDI pigment and a 80% milk: 20% egg white mix by spraying plants with this mixture via a 2-stroke backpack sprayer. Marking insects in this manner by spraying the plants they are visiting and living on was intended to investigate the dispersal of natural enemies from cover crop plots into the vineyard. This dispersal information will help determine how many rows of cover crops growers would require for adequate dispersal of biological control agents from resource-providing plants. Control plots were untreated to investigate the natural gradient of unmarked insects captured on sticky traps, and to investigate the efficiency of buffer zones used to separate treatments by determining whether protein-marked insects are detected in the controls. An additional 6 transparent sticky traps were placed on the 1st, 3rd, 6th and 10th row adjacent to the center of 4 replicates of each treatment, Cards were placed in each cardinal direction. Sticky traps were collected and replaced three and six days after marking to determine how long insects remained marked under prevailing field conditions. Sticky traps have been placed in the freezer waiting processing. In the laboratory, sticky traps will be scanned with a UV light to determine the presence of the yellow fluorescent pigment on beneficial insects and approximately 1,000 beneficial insects (marked with the fluorescent pigment and unmarked) will be removed from sticky traps across all treatments and replicates for each sampling date (2,000 insects in total). Insects will be removed using a toothpick, placed into individual 1.5 ml microcentrifuge tubes, labeled and frozen. Samples will be sent to James Hagler (USDA-ARS Phoenix Arizona) for ELISA testing to detect milk and egg proteins.
The number of marked and unmarked beneficial insects will be compared between treatments, distances and dates using three-way ANOVA. Data from this experiment will be used to determine: (1) how far marked beneficial insects disperse from cover crop refuges, (2) how many cover crop rows are required to assist natural enemy dispersal in vineyards, (3) whether control plots contained marked insects from neighboring cover crop treatments (i.e., how efficient the 36 m buffer zones were).

The outreach originally proposed for this project is outlined in Table 4. Outreach scheduled in 2008 was not conducted since the project leader went on maternity leave in October 2008. The scheduled outreach for October 2008, November 2008 and February 2009 was delayed until the following year. A demonstration field day, including pre-planted buckwheat at the Bella Vista experimental site was scheduled for July 2009, however, this was not conducted due to the difficulties encountered with establishing a buckwheat cover crop (see Objective 3). Results were not extended to grape growers in 2009 and 2010 via several planned presentations at grower meetings and conferences, and the production and distribution of an informative color leaflet (see Table 4) because preliminary data showed potential negative attributes of cover crops and we felt it was important to finish processing sweep net, double-sided tape and funnel beat samples before drawing final conclusions and extending pros and cons of this technology to grape growers. Preliminary results suggest that cover cropping may not prove to be a viable option for grape growers in southern California due to the difficulty of establishing cover crops in southern California climate, cost of irrigation water, and both cover crops testing positive for harboring Xylella. Additionally, preliminary results from sticky trap and visual counts data showed that additional irrigation required by the cover crop may lead to increased populations of pestiferous leafhoppers, thrips, aphids and sharpshooters. Sweep net, double-sided tape and funnel beat samples need to be processed before we can drawn final conclusions. Processing of these insect samples will be completed by March-April and data will be analyzed in May-June. Once analyses have been conducted we will decide whether results from this research justify production of a chapter for Code of Sustainable Winegrowing Workbook as planned for May 2010.
As part of this project’s outreach, a survey (reviewed and approved by Western SARE in an earlier progress report) was mailed out in June 2007 and it was planned that this survey be repeated in June 2010 after this research and associated outreach were completed to measure the rate of adoption and percentage reduction of pesticide use resulting from utilization of our study cover crop plants. In June 2007, the survey was mailed to 100% of growers located in Ventura (5 growers; funding was awarded from Hansen Trust to extend outreach efforts to Ventura grape growers), Lodi (740 growers), Coachella Valley (30 growers) and Temecula (45 growers) with help of cooperative extension specialists Phil Phillips and Carmen Gispert, and Cliff Ohmart (Lodi Woodbridge Winegrape Commission) and Linda Kissam (Temecula Winegrowers Association). Information about the cover crop project was posted online in June 2007 (http://www.biocontrol.ucr.edu/irvin/Research/WSARE.html) and growers could download the survey and return it via email. We had 225 replies from growers which is a 27.4% response rate. Since planned outreach was not conducted in 2008 and 2009, the mail survey aimed at assessing adoption rate of buckwheat ad vetch cover cropping will not be conducted in June 2010.
Although cover cropping may not prove to be a viable option for southern Californian growers, this project is making significant contributions to our understanding of the potential that cover crops offer when used as a pest management tool in vineyards in southern California by investigating the strengths and limitations of cover cropping under the unique growing conditions representative of grape producing areas of southern California. In June 2010, we will develop a website on cover crops for Southern California growers outlining the results of our research and listing the pros and cons of cover cropping in arid Southern California. It is important to extend the results of our project to grape growers throughout California, especially since results demonstrate that cover crops may act as reservoirs of Xylella which can be transmitted to grapevines by GWSS. We will summarize our research for incorporation into UCIPM Pest Management Guidelines (Joyce Strand, Associated Director for Communications, UCIPM), a key resource for grape growers and pest control advisors, and present results at upcoming grower meetings by contacting UC Viticulture and Enology Farm Advisors in Kern County (Jennifer Hashim-Buckey), Mendocino County (Glenn McGourty), Coachella Valley (Carmen Gispert), Napa County (Monica Cooper), Sonoma County (Rhonda Smith) and San Luis Obispo County (Mark Battany), and applicable Chapters of the California Association of Pest Control Advisors (CAPCA) including Cathy Ellis (President of the Southern California Chapter). Additionally, we will publish results from this project in two manuscripts submitted to leading journals and write a report outlining the results of this research for distribution to leading grower advisers and UC extension specialists who supported this project (Carmen Gisbert [UC Cooperative Extension Specialist, Coachella Valley], Ben Drake [PCA, Temecula Valley], Nick Toscano [Extension Specialist & Area-Wide GWSS Management Team, Temecula Valley], Cliff Ohmart [IPM Director, Lodi Woodbridge Winegrape Commission; now works at SureHarvest], Peggy Evans [Executive Director, Temecula Winegrowers Association] and Phil Phillips [UC Cooperative Extension Specialist, Ventura County]. This projects end date is still June 30, 2010.

• Finish investigating the effect of vetch on longevity and fecundity of G. ashmeadi.
  Conduct trials investigating the effect of buckwheat and vetch on the longevity and fecundity of Anagrus sp..
  Finish constructing guides based on days to nectar production and the length of nectar producing period to assist growers with cover crop sowing decisions.
  Identify and count the number of pest and beneficial insects from sweep net, double-sided tape and funnel beat samples from the 2008 field trial.
  Contact Daniel Jeske, (UC Satistics Department) regarding experimental design and statistics of each experiment and conduct most applicable statistical analyses for each objective.
  Finish GWSS/Xylella transmission studies with vetch.
  Process insects from dispersal study and send samples to James Hagler (USDA-ARS Phoenix Arizona) for ELISA testing to detect milk and egg proteins.
  Calculate the amount of water applied to cover crop plots and estimate the cost of irrigating the cover crop.
  Write information for incorporation in the Code of Sustainable Winegrowing Workbook.
  Develop a website on cover crops for Southern California growers outlining the results of our research and listing the pros and cons of cover cropping in arid Southern California.
  Summarize our research for incorporation into UCIPM Pest Management Guidelines
  Present results at upcoming grape grower meetings throughout California.
  Write two manuscripts for submission to leading journals.
  Write a report outlining the results of this research for distribution to leading grower advisers and UC extension specialists who supported this project.

Impacts and Contributions/Outcomes

Work completed and reported here is the first significant set of studies that have investigated the strengths and limitations of cover cropping under the unique growing conditions representative of grape producing areas of southern California. Consequently, this project is making significant contributions to our understanding of the potential that cover crops offer when used as a pest management tool in vineyards in southern California. The contributions this work had delivered here in this progress report are:

1. Identification of cover crop species that can be used in southern California

• Growth time required to flowering and duration of flowering and how this host plant phenology can be manipulated and used by growers during different times of the year
  Improved understanding of how cover crops influence pest and natural enemy abundances
  Identification of the risk cover crops pose in relation to harboring Xylella and insects that vector this pathogen
  Quantification of the effects cover crops have on grape yield, fruit quality and vine vigor.

1. The economic and practical feasibility of cover crops for pest control in vineyards in southern California will be quantified. This is particularly important with respect to water usage. The amount of water applied to cover crop plots was recorded during each year’s field trial and the grower’s water bills are currently being used to calculate the cost of irrigating the cover crop.
   The vineyard-wide effect cover crops have on natural enemy activity and pest suppression as spillover occurs from resource rich areas with cover crops into resource poor areas devoid of cover crops.

Collaborators: