In collaboration with wine grape growers in Napa and Sonoma County, the project evaluated the strategy of floral resource provisioning (FRP) to enhance biological control of two key vineyard pests: grape leafhopper and vine mealybug. FRP species included annual buckwheat, lacy phacelia, sweet alyssum, bishops weed and wild carrot. While overall findings support the hypothesis that FRP can enhance populations of natural enemies and contribute to pest regulation and the maintenance of soil quality, additional research will be necessary to better understand the specific ecological mechanisms that lead to reduced pest densities in the presence of flowering ground covers.
Pest management in wine grape production frequently depends upon the use of synthetic chemical control strategies (UC IPM 2009). Many of the commonly used insecticides are known to have significant and negative environmental quality and human health risks. In addition, the long-term viability of pesticide use is uncertain due to decreasing pesticide effectiveness resulting from the development of genetic resistance to pesticides by arthropod pests, increasing pesticide costs for growers and an increasingly restrictive regulatory environment (Van Driesche et al. 2008). To systemically address these pressing social and environmental issues, new approaches to pest management must be continuously tested and developed.
This project was developed in response to the expressed interest of California wine grape growers for new ecologically-based pest management strategies for wine grapes, many of whom are responding to increased consumer demand for wines made from organically and/or “sustainably” grown grapes (Wine Institute 2007). Building upon prior research in conservation biological control, this project has been the first comprehensive study of the effects of annual flowering intercrops in multiple sites in Napa and Sonoma county wine grape vineyards.
Local habitat manipulation in crop fields, such as cover crops that provide floral resources, can enhance arthropod pest management (Landis et al. 2000, Altieri and Nicholls 2004, Andow 1991). A review of prior research showed that in over 50% of cases studied, localized (field-scale) habitat diversification led to reduced pest populations, reduced crop damage and/or increased yields. In contrast, results from the other habitat diversity studies showed pest populations remained unaffected (15%) or increased (35%) (Andow 1991). While habitat diversity per se can potentially enhance biological control, inconsistent results have led researchers to conduct studies on more specific types of on-farm habitat provisioning in order to isolate which plant species may convey the greatest functional benefit (Wäckers et al. 2005). Multiple mechanisms can determine the success of habitat manipulation for biological control, including overwintering habitat requirements, dispersal patterns and the availability and influence of floral nectar and pollen (Thomas et al. 1991, Landis et al. 2000, New 2005)
Although use of ground covers and floral resource provisioning in vineyards has shown some reduction in pest densities (Nicholls et al. 2001, Costello and Daane 2003, English-Loeb et al. 2003, Berndt et al. 2006), no single habitat management program has been developed that consistently reduces pests below thresholds growers consider economically significant. Such inconsistencies in research findings have limited adoption of conservation biological control and resulted in continued reliance on conventional pest management practices. This is partially due to previous studies not clearly identifying causation for the observed reductions in pest densities (Cullen et al. 2008).
Widespread adoption of novel pest management practices occurs best when the information is conveyed to growers in a practical format. Towards this goal, we plan a series of field days to extend information on the research progress and receive feedback from participating growers. From past experience, we anticipate 30 – 50 participants at each field day, and some of these growers will be interested in adopting all or some of the management practices highlighted. Through our research, at grower-participatory discussions at field days and with the grower-collaborators, we can better develop sustainable pest management tools that are practical and economical – resulting in greater adoption.
The research and extension components of this project were integrated to derive cost-effective applications of floral resource provisioning for vineyards. To date, no other published study analyzes large-scale alley cropping of floral resources for pest management in Napa and Sonoma County wine grape agroecosystems, although there has been considerable interest in this management tool.
California, Oregon and Washington wine grapes represent one of the larger and more valuable specialty crops in the western U.S. – with an estimate annual crop value over $4 billion and even more value to the region’s economy through associated employment and tourism. Many of these wine grape regions are recognized internationally for fine wines and a burgeoning agricultural tourism industry. Major wine grape grower organizations are already seeking to demonstrate the wine-grape industry’s commitment to more sustainable farming (CAWG 2008). Their stated objectives are to improve the environmental quality of grape growing practices and develop management strategies that are more sensitive to the environment, responsive to the interests of society-at-large and economically feasible to implement and maintain (WGA 2008; CSWA 2008). This project intended to provide a scientific basis for new environmental stewardship and pest management initiatives for wine grapes.
As stated in the original proposal, the project was to be developed and implemented via a participatory process involving wine grape growers to test plant diversification strategies that may enhance the soil food web and native biological control services by creating a functional ecological infrastructure in and around vineyards. Since the 2008 season, we have been assessing the effectiveness of specific agroecological management strategies (e.g., flowering summer cover crops) on the improvement of soil quality and the enhancement of functional biodiversity for pest regulation in California vineyard agroecosystems. The ultimate goal of the research is to contribute to the scientific understanding of the requisite ecological design components (e.g., landscape structure, cover crop species composition and the management of such plants) needed to stimulate soil biological activity, enhance and sustain soil quality and sponsor cost-effective ecological management of key wine grape pests.
A key objective of the project has been to construct a study that is participatory in nature, so that farmers are engaged in the management and evaluation of the agroecological treatments. Another objective is to incorporate an extensive outreach and education component of the project to assure ample sharing, distribution and accessibility of the research findings among farmers, thus facilitating the widespread adoption of agroecological management practices.
Changes in objectives as the project unfolded:
With additional funding from The California Department of Food and Agriculture (CDFA) in 2009, we added a fully replicated research site at the UC Kearney Agriculture Research Center (KAC) in Fresno County. The addition of this research site allowed researchers to study the impact of floral resource provisioning on biological control of vine mealy bug (VMB) and to conduct a series of related laboratory studies to measure the ecological processes theorized to be enhanced through FRP. In 2010, the research project expanded further to include a fully replicated research design in Lodi, California.
All sites used in this study were selected for their uniform cultivar and rootstock combinations, vine age, soil and fertilization conditions, irrigation infrastructure and pest management history. FRP plant species were selected based on their ability to influence pest densities or enhance the longevity, fecundity or sex ratios of parasitoids in previous studies (Begum et al 2006; Burndt et al. 2006; English-Loeb et at 2003; Irvin et al 2007; Lee and Heimpel 2008; Nicholls et al. 2000; Winkler et al 2006).
From 2008-2010, experimental treatments were established each fall and spring by participating growers in Napa and Sonoma County. The flowering species tested included ‘Annual Buckwheat’ (Fagopyrum esculentum), ‘Lacy Phacelia’ (Phacelia tanacetifolia), ‘Sweet Alyssum’ (Lobularia maritima), ‘Bishops Weed’ (Ammi majus) and ‘Wild Carrot’ (Daucus carota) (see Appendix, photos 1-4).
“Grower Trials” in Napa and Sonoma County
In 2008 we established single-replicate split-block trials (“Grower Trials”) in eight commercial vineyards in Napa and Sonoma County (see Figure 1 for an example plot design). In 2009, there were a total of 10 Grower Trials (GT) in Napa and Sonoma County.
“Primary Research Block” at UC Kearney Agricultural Center (Fresno County):
As mentioned, with the addition of funding from the CDFA we were able to establish and monitor a Primary Research Block (PRB) located at the UC Kearney Agricultural Center (KAC) in Fresno County. The PRB consisted of a fully replicated randomized block design with five replicates of the FRP-Treatment and Control (see Figure 2a and 2b). The PRB experiment was designed to test four FRP species that bloom in an overlapping sequence (Sweet Alyssum, Lacy Phacelia, Annual Buckwheat and Wild Carrot).
Similar sampling methodologies were used to monitor the GT and PRB plots. All sampling was conducted from April 15 – October 1 (2008-2009) using standard methods developed for Erythroneura leafhoppers and Planococcus mealybug and their key natural enemies (Daane and Costello 1998, 2003; Nicholls et al. 2004; Walton et al 2006; Daane et al. 2004, 2006, 2007; UC IPM 2008).
Due to the geographic distribution of pest species, monitoring at the GT sites in Napa and Sonoma County focused exclusively on assessing densities of Erythroneura elegantula, Anagrus wasps and generalist predator species. At the KAC site we evaluated the impact of FRP on population densities of vine mealy bug and Erythroneura leafhoppers and their key generalist and specific natural enemies, Anagyrus pseudococci and Anagrus sp., respectively.
All sampling data taken to evaluate seasonal changes in pest and beneficial population densities are being analyzed through repeated measures ANOVA. All annual sampling data taken to analyze single sample occurrences will be calculated using a linear regression model ANOVA. Data will be transformed for any abnormalities.
An important component of this two-year study was the outreach and extension efforts. Throughout the duration of this SARE-funded project, public field days and grower cross-visits played a central role in educating both growers and researchers on the cost-effective use of flowering ground covers in North Coast vineyards. This project has led to the development of a grower network that continues to collaborate with researchers to develop and refine the use of flowering ground covers in vineyards. Grower input has led to improved design of flowering ground cover treatments, which has led to increased grower adoption of these practices. For example, growers have been responsible for identifying new species of flowering plants that are inexpensive, can be fall sown (with winter cover crops) and do not require additional irrigation. Growers have also played a large role in advising producers new to the project on how best to establish the experimental treatments. This led to a greater rate of successful treatment establishment in the 2009 growing season when compared to 2008 (the first year of the project). A similar pattern was seen in the 2010 season, in which we again had seven sites with well-established flowering ground covers, largely due to grower interaction and sharing of technical knowledge. For the 2011 season, 14 growers will now be establishing a total of 17 split-block trials. Further, some growers have now been collaborating with researchers for four growing seasons and have attended our outreach events every year.
Dissemination of Project Results:
By exhibiting their experimental blocks to the wider wine grape grower community, growers are serving as disseminators of best management practices and providing technical information to other growers interested in adopting similar management practices. In order to assure the relevancy and accessibility of educational and extension literature developed in association with the project, growers are helping us gather information and review and edit written materials produced by us for wide-scale distribution. Much of this information is now available on our website (http://agroecology.berkeley.edu). In addition to publication in technical journals, findings derived from this study will be published in industry periodicals and newsletters most commonly read by wine grape producers (e.g. Practical Winery and Vineyard, California Agriculture, etc). Finally, in order to assure the wide spread distribution and accessibility of the findings and practices used in the study, a manual of agroecological vineyard diversification has recently been produced. (See the following URL for the complete publication: http://agroecology.berkeley.edu/resources/Altieri_2010_habitat_management_in_vineyards.pdf.)
Grower Cross-visits (see Photo 5):
These events provide growers participating in this project with an opportunity to share information and experiences related to the implementation and management of flowering ground covers in vineyards. At each site visit, the vineyard manager explained the establishment and management of the treatment to other growers and researchers. Researchers also discussed in more detail their approaches to evaluating the experimental treatments and elaborated on the theory informing the research design.
The objective of the Grower Cross-Visit is to facilitate social learning amongst growers, as well as receive feedback and assess the potential of the experimental practices to fit within current vineyard management practices and to evaluate the relative costs of this pest management strategy. Such participatory discussions enable researchers to better define research objectives that address grower concerns and reflect realistic management constraints.
Public Field Days:
Growers have also played a central role in the outreach and extension field days organized in association with this project. As part of our efforts to encourage grower involvement, we hold an annual Public Field Day in which the wider wine grape growing community is invited to visit an experimental block in order to see the flowering ground covers. These Field Days provide an opportunity for people outside of the project to learn about the research that is being conducted and the experiences of participating growers with the use of these practices.
Farm-worker Training Sessions (Photos 6 and 7):
These training sessions allowed researchers and growers to collaborate in the monitoring and assessment of insect populations as well as soil and crop health parameters throughout the duration of the study. These training sessions allow growers and workers to make better observations of insect populations in their vineyards and thereby provide valuable feedback to researchers.
Establishment of Napa and Sonoma County Field Sites:
In 2008 and 2009, we compared insect population between selected vineyard plots under the FRP-Treatment and a Control plot under normal farmer’s management (FM). No insecticides were used in any of the FRP-Treatment and their Control plots. Due to the separation of a graduate student from the project, soil parameters were compared between FRP-Treatment and Control plots in 2008 only.
Most growers informed us that the 2008 growing season was marked by very unusual weather – low winter rainfalls, early frosts and cool spring temperatures are all thought to have contributed to reduced or delayed vine development and lower overall pest densities. This resulted in a number of field trials in which pest and natural enemy densities were so low that they could not be meaningfully compared. Weather in the 2009 growing season followed more typical patterns, and insect densities were high enough to provide useful comparisons of pest and natural enemy populations between treatment and control plots.
Data collection in 2008 was further limited by growers’ inexperience with establishing and managing flowering ground covers in their vineyards. For many growers, this was their first time sowing these flowers in a vineyard. This resulted in a number of participating vineyards with poorly established stands of flowering ground covers, and subsequently reduced the total number of field sites with a functional FRP treatment to monitor over the entire growing season. While a total of eight split-block trials were planned, only four established well enough to constitute a correctly timed FRP treatment. Additionally, pest response data from one site was thrown out due to an observed pest density gradient overlapping with our research plots (Quintessa). The experimental block at this site was relocated to another area of the vineyard for the 2009 season.
The four sites in 2008 that did not initially establish an early-season FRP treatment were eventually able to sow a flowering ground cover later in the growing season (approximately May 15 – June 1). While early-season pest and natural enemy response data was unusable from these sites (due to lack of treatment), these sites were able to be included in some of the natural enemy response and soil quality assessments conducted later in the 2008 season.
While all of this was detrimental to research objectives, both growers and researchers gained valuable knowledge about the establishment and management of flowering ground covers in vineyards. The Public Field Days and Grower Cross-Visits held throughout this project helped to facilitate grower exchange of information about the use of flowering ground covers in vineyards. For instance, those growers that successfully established the flowers in the 2008 season were able to provide other participants with information about their practices (e.g., timing of sowing, seed rates, equipment used). As mentioned, growers had a much higher rate of successful treatment establishment in subsequent growing seasons. Our research group continues to hold annual outreach and extension events as part of our on-going collaboration with growers to better develop and refine the management of flowering ground covers in vineyards.
Summary of Project Results:
Despite the aforementioned environmental conditions and setbacks, the study produced the following information on pest and natural enemy response to the experimental treatments.
Note: Analysis of data for the entire project (2008-2010) is ongoing. Final data analysis is to be completed by May 2011, at which time multiple public forums will be held to present and discuss results with grower-collaborators, the broader wine grape growing community and the general public.
Grower Trials (Napa and Sonoma County) 2008-2009:
1. In 2008, pest densities at all research sites were so low that no significant differences in pest densities could be detected between Treatment and Control plots. In 2009, 1st generation leafhopper nymph densities were significantly lower in all Treatment plots with high overall pest pressure when compared Control plots. At sites with low overall pest pressure, we found no significant difference in pest densities between FRP/Treatment and Control plots.
2. Treatment and Control plots showed no significant differences in early-season density of Anagrus sp. (a key leafhopper egg parasitoid) in both years of the study.
3. Where assessed, no significant difference in leafhopper egg parasitism rates were observed between Treatment and Control plots in 2009.
4. Significantly higher abundance and diversity of arthropod natural enemies (especially predators) were found on the ground covers in all Treatment plots in both 2008 and 2009.
5. The early-season abundance of arthropod natural enemies (predators and parasitoids) found in the vine canopy varied in Treatment plots over each growing season and no significant pattern was observed.
6. Flowering ground covers appeared to enhance key indicators of soil quality in 2008.
Primary Research Block (Kearney Agriculture Center – Parlier, CA) 2009:
7. In 2009, an enhanced rate of vine mealy bug parasitism/mortality was observed in the FRP-Treatment plots at KAC.
8. In 2009, late-season spider abundance was ~80% higher in the FRP-Treatment plots.
Laboratory Trials (University of California, Berkeley, CA):
9. Laboratory studies showed that, under controlled conditions, floral nectar feeding led to enhanced longevity of Anagyrus psuedococci (a key parasitoid of vine mealy bug).
Although the overall findings of the study do support the hypothesis that incorporating flowering cover crops into vineyard monocultures can support diverse and abundant populations of natural enemies, contribute to pest regulation and maintain soil fertility, additional research is necessary. Ongoing research in 2010-2012 will provide longer-term data on field and landscape heterogeneity influence on bio-control and other ecosystem services in vineyards.
Results from the Grower Trials in 2008
As already reported, leafhopper densities in the 2008 growing season were unusually low in most vineyards, generally never surpassing more than two nymphs per leaf, which is far below normal pest thresholds (the UC IPM recommended treatment threshold for grape leafhoppers is 20 nymphs/leaf [UC IPM 2008]). Given these low numbers, it was not possible to detect significant differences in nymph densities between FRP-Treatment and Control plots at any of the sites (Figure 3).
Natural enemies in the vine canopy:
Natural enemy abundance was measured by predator abundance per yellow sticky-trap (YST). Predator abundance in the vine canopy varied amongst sites in 2008. At two sites we observed more predators per YST in the FRP-Treatment plot, while at the other two sites we found more predators in the Control plot (Figure 4).
Natural enemies on the ground covers:
At one site (Quintessa), flowering summer ground covers in the FRP-Treatment plot were found to attract a greater overall abundance of generalist predators than the resident vegetation (over-wintering cover crops and spring-summer weeds) found in the Control plots (Figures 5a and 5b).
Early-season Anagrus densities:
In 2008, there were no significant differences in early-season Anagrus densities (“early-season” is approximately May 1 – 30, which coincided with peak 1st generation leafhopper oviposition at all sites). Anagrus densities at this time did not exceed more than one per YST at any of the sites.
Leafhopper egg parasitism rate:
A late-season (~August) parasitism study was conducted at one of the field sites with a well-established FRP treatment (Quintessa). Egg parasitism rates were Treatment and Control plot were 24% and 21%, respectively. The 3% difference in leafhopper egg parasitism by Anagrus wasps between the FRP-Treatment and Control plots is statistically and practically insignificant.
We applied the methodology developed by Nicholls et al. (2004) to assess soil quality in July 2008. We constructed ”amoeba” diagrams allowing us to compare soil quality indicators in the FRP-Treatment and Control plots at three vineyard sites. In the case of Oakville Ranch, the FRP-Treatment plot exhibited higher values in most indicators than the Contol plot (Figure 6), and similar trends could be observed at Quintessa, where the FRP-Treatments appear to exert substantial effects in improving soil structure, biological activity, compaction and amounts of organic residues (Figures 7 and 8). Winter cover crops and FRP treatments also appeared to improve soil quality indicators at Wappo Ranch (Figure 8).
As observed in Figure 9, which exhibits the mean soil quality indicators for all surveyed farms, with the exception of Saintsbury, seven out of eight FRP-Treatment plots exhibited higher soil quality values than the Control plots, suggesting that winter and flowering ground covers can enhance key indicators of soil quality.
Results from the Grower Trials in 2009
Leafhopper nymph densities:
In the 2009 Grower Trials (GT), grape leafhopper nymph densities were found to be on average 39% lower in the FRP-Treatment plots when compared to Control plots. These differences were especially noticeable at three research sites where background pest densities were highest (Figure 10).
Natural enemies in the vine canopy:
Predator response to the ground covers was again mixed. Higher predator abundance was observed in FRP-Treatment plots at four of the seven vineyards (Figure 11). Many of the predators detected in the vine canopy of the treatment plots were also found in the FRP treatments.
Natural enemies on the FRP treatments:
At two of the seven sites, sweep netting showed that the FRP treatments attracted a significantly greater diversity and abundance of generalist predators when compared to resident vegetation in control plots. Predator species guilds attracted to the FRP treatments significantly changed in both abundance and diversity with the phenology of the flowers (Figures 12a, 12b and 13).
Early-season Anagrus densities:
As in 2008, overall early-season densities of Anagrus were very low (>4 wasps per trap) and no significant differences between FRP-Treatment and Control plots were observed (Figure 14).
Results from the Primary Research Block in 2009 (Kearney Agriculture Center – Parlier, CA)
Leafhopper nymph densities:
In 2009, overall leafhopper densities were very low and therefore no differences were detected between treatments.
Vine mealybug parasitism:
Mealybug parasitism by the beneficial wasp Anagyrus pseudococci was found to be approximately 20% higher in the FRP plots than in the control plot (Figure 15). Laboratory tests of the impact of FRP on the biology of natural enemies revealed that Ammi majus and Fagopyrum esculentum significantly extended the longevity of A. pseudococci relative to other flowers and the control (water only treatment) (Figure 16). Note: Longevity studies on a wide range of FRP species are ongoing and are to be completed by August 2011.
Spiders in the vine canopy:
Spider abundance in the vine canopy did not vary between Treatment and Control plots over most of the growing season – although around August 1 canopy spider densities in the Treatment plots were consistently 80% higher than in Control plots (Figure 17)
Results from the 2010 Growing Season
As mentioned above, the securing of additional research funding from the California Department of Food and Agriculture has allowed for the expansion of the original research. 2010 data is currently being analyzed and will be available on our website in late spring 2011: http://agroecology.berkeley.edu/.
Conclusions and Discussion:
The addition of flowering ground covers to vineyard plots did not produce consistent trends in pest regulation or natural enemy response over the course of this two-year study. The effects of the FRP treatments and findings were confounded by erratic weather patterns and grower inexperience with the management of flowering ground covers.. These two factors led to both unusually low pest densities and poor establishment of the flowering cover crops in many research sites.
In 2008, leafhopper nymph response to the FRP-Treatment was not detectible, while in 2009 all FRP-Treatment plots were found to have lower nymph densities than Control plots. There appears to be a significant treatment effect, especially at research sites with high pest pressure and good treatment establishment.
Early season abundance of Anagrus wasps did not appear to be influenced by the FRP treatment. Our data indicate that the Anagrus population is most likely influenced by leafhopper abundance itself, suggesting a density-dependent relationship which has been previously suggested by other researchers (Wackers 2005).
Flowering ground cover treatments did attract and retain a significantly greater diversity and abundance of generalist natural enemies over the course of both growing seasons. Although not substantiated in this study, it is likely that these predators move between the flowering ground covers and the vines and may be impacting early- and mid-season leafhopper abundance. More detailed analysis of this data should reveal species specific relationships between natural enemies and FRP species (e.g., Orius predominantly found on D. carota but rarely on P. tanacetifolia) and how such relationships might be further manipulated to increase biological control.
Unusually low insect pest abundance observed in both years of the study along with poor or inconsistent treatment establishment at multiple research sites limited the amount of useful arthropod response data obtained through this project. Consistently lower leafhoppers densities were observed in all cases where flowering ground covers were established at research sites with high overall leafhopper pressure. However the lack of a consistent response across all research plots suggests the need for both longer-term and fully replicated research combined with a range of mechanistic studies to substantiate the causes of observed changes in pest population densities. In addition, recently published studies in the conservation biological control literature suggest that the non-crop vegetation surrounding vineyards and other cropping systems may influence the effects of FRP at the field scale. Such landscape level analyses have been integrated into our research agenda in the 2010 and 2011 growing seasons.
The data obtained from this project suggests the use of flowering ground covers in vineyards may enhance biological control of leafhoppers and vine mealy bug. Perhaps more importantly, the project allowed researchers to establish the foundation (e.g. increased grower contacts, interest and participation, FRP species selection, increased knowledge of treatment implementation and management) for more comprehensive studies of FRP in vineyards. Appendix I depicts the treatment establishment guidelines for growers interested in incorporating flowers into their vineyards, with practical recommendations on seeding rates, planting times, spatial distribution in the field etc.
Educational & Outreach Activities
We have developed a project website (http://agroecology.berkeley.edu/) through which growers can access a number of publications relevant to habitat diversification and sustainable viticulture. Results from this study and our future vineyard research will be posted to this website.
Vineyard Habitat Diversification Manual: “Habitat Management in Vineyards”:
We have recently drafted a set of guidelines for wine grape growers interested in the use of on-farm floral resource provisioning to enhance biological control in vineyards. The manual is based on the findings of our on-going research collaboration with Napa and Sonoma County growers and also includes relevant information from other vineyard diversification studies. This manual will be updated accordingly as new information becomes available. The manual can be viewed online through our project website: http://agroecology.berkeley.edu/index.html.
Please see the following URL for manual:
Popular and Scientific Press:
To further extend our findings, we anticipate publications in popular magazines (e.g., San Francisco Chronicle, Saveur Magazine Wine Spectator), which will raise grower and consumer awareness of ecologically based pest management, as well as industry and scientific journals (e.g., Environmental Entomology, Practical Winery and Vineyard, California Agriculture).
Outreach Activities in 2008:
We held three insect monitoring training sessions (February 28, May 5 and July 22, 2008) that introduced both growers and selected farm laborers to some of the more common insect sampling methods used in this research. Researchers also gave a lecture (in Spanish) on the principles of agroecology and conservation biological control. Each training session took place at one of the participating grower trial sites (Ridge Wine – Healdsburg, CA; Constellation Wine – Wappo Hill)
A Grower Cross-visit took place on June 3, 2008 at Saintsbury vineyards and at Constellation Wine’s Wappo Hill site. Growers discussed establishment of the flowering ground covers with particular attention paid to the sowing of sweet alyssum underneath the vine row. Researchers provided growers with information on the biology of Anagrus spp. and how floral resource provisioning could potentially improve biological control of leafhoppers by this wasp.
Following harvest, a public presentation was held on October 11, 2008 at the Napa Public Library. Preliminary findings from the 2008 research were presented to the larger wine grape grower community and additional growers were recruited for the ongoing study.
As a result of all these efforts, four additional growers joined the project and established experimental blocks at their properties for the 2009 growing season. Many other growers requested that they be invited to future public field days held by our research group.
Outreach Activities in 2009:
We conducted training (in Spanish) of farm workers from participating vineyards on February 25 and June 10, 2009. These training sessions were held at two participating vineyards in Oakville, CA (Constellation Wine and Joseph Phelps). The intention was again to provide workers with the overall logic for the research being done in their vineyards and further train them in insect identification and data collection.
We held a Grower Cross-Visit on May 15, 2009 at a participating vineyard in Sonoma County. Researchers and growers came together to view treatment establishment at one of the participating vineyards and discuss implementation and management of the flowering ground covers. A summary of the data from the 2008 study was also presented to growers. Growers provided researchers with feedback about criteria for future selection of flowering ground cover species.
A Public Field Day was held on June 29, 2009. At this event the larger wine grape growing community was invited to visit one of the on-farm trials in Rutherford, CA. With over 30 growers in attendance, researchers presented project goals and objectives while participating growers shared information about their experience and involvement with the project to date. This field day was reported in the Napa Valley Register:
Working collaboratively with commercial growers in Napa and Sonoma County, we were able to identify and trial multiple flowering spring/summer ground covers that could potentially enhance biological control of pests and be readily integrated into commercial vineyard operations. Not all vineyards are managed alike, and the cost-effectiveness of these practices will vary according to a vineyard’s location, climate, market conditions and the grower’s pest management philosophy. The site-specific nature of ecologically-based pest management strategies implies that specific practices may not produce the same effect equally for all growers. In order to foster greater adoption and scaling up of ecologically-based pest management, it is necessary to develop not just one specific set of habitat management practices but rather educate growers about the key concepts informing these practices in order to better facilitate and guide their own experimentation. Through our research and outreach work over the past three growing seasons, we have established strong working relationships with a significant number of influential wine grape growers and producer organizations in Napa and Sonoma County. These ties have led to a number of successful collaborations as well as valuable discussions on the challenges and opportunities for growers interested in the use of on-farm habitat diversification to enhance biological control. Our goal is to ensure that the objectives of our study remain relevant and applicable to the commercial growers with whom we collaborate. The outreach and extension activities of this study provided a venue for researchers and growers to continually review project goals and objectives and redevelop research priorities as needed.
This project contributed to grower understanding of conservation biological control in vineyards, in particular the use of floral resource provisioning. By participating in this project, grower-collaborators were introduced to the ecological theory that informs the hypotheses of this project. In order to explain why floral resource provisioning may effectively increase biological control in their vineyards, growers were also informed of the basic biology of vineyard pests and their key natural enemies. This information provided growers with guidelines for the selection of flowering plants to enhance biological control. While our Western SARE-funded project was to test a specific suite of flowering summer ground covers, many growers continue to experiment with a variety of other flowering plants according to guidelines that we discussed.
All grower-collaborators were directly involved in the selection, establishment and management of the flowering ground covers used in this project. Some growers have now been experimenting with the use of these flowers for three growing seasons and regularly provide assistance to new grower-collaborators who are establishing flowering ground covers for the first time. As each grower continues to develop and refine the establishment and management of these flowers in their vineyard, they gain new knowledge on the use of FRP and are able to provide valuable feedback on this ecologically-based pest management practice to both researchers and other growers alike.
Additionally, all of our outreach activities included a broad overview of the research process in order for growers to better understand the activities and objectives of our study. Growers were made more aware of the necessary time and amount of data required to provide definitive answers about the use of vineyard habitat diversification to enhance biological control.
Grower-collaborators have certainly benefitted the most from participation in this project. While public field days did provide an opportunity for the wider wine grape growing community to learn about this study and its progress to date, we are planning to publish the results of this project in 2011 in popular and scientific journals in order to deliver the benefits of this project to a much wider audience.
Proposals and Considerations for Future Research in Conservation Biological Control in California Vineyards:
The following are general guidelines and specific proposals for research in California viticulture that would serve to advance the science and practice of conservation biological control. Proposals include both natural and social science studies, with several specific examples provided from the ongoing UC Berkeley vineyard biological control research.
To effectively evaluate the influence of a habitat diversification on biological control, future research must consider the influence of non-crop habitats that lie beyond the individual field or vineyard. Broad-scale studies that correlate landscape heterogeneity and natural enemy and pest densities must be conducted along with a detailed evaluation of the key ecological processes theorized to influence biological control. Field evaluations should observe trends for minimum of two years and include fully replicated studies at the field- and landscape-scale. Field-scale assessments of diversified cropping systems should ideally assess both natural enemy and pest densities along with empirical tests of parasitism and/or predation (Bianchi et al. 2006). In addition to herbivore density, measures should be taken to determine the impact of the herbivore population on crop damage, yield and crop quality. With studies of in-field diversification plantings, the influence of non-crop vegetation on plant nutrient status/vigor should be considered along with impacts to natural enemy fitness (Altieri and Nicholls 2003, Daane and Costello 1998).
To fully understand the positive and negative impacts of vineyard diversification on biological control and to develop more cost-effective control strategies, multi-trophic interactions must also be considered. For example, increased diversity and abundance of natural enemy associated with enhanced field-scale habitat diversity can lead to increased intra-guild predation and subsequent release of pests from biological control (Finke and Denno 2004, Straub et al. 2008). Alternately, studies have shown that increased natural enemy diversity can facilitate prey capture (Wilby et al. 2005, Finke and Snyder 2008), thus enhancing biological control of pests. Similarly, multiple landscape-scale studies have shown increased densities of pests in more heterogeneous landscapes, though intra-guild predation was not discussed (Roschewitz et al. 2005, Ostman et al. 2001).
Correlations between field and landscape diversity and pest densities may not always be the result of top-down control by natural enemies. The reduced resource concentration characteristic of diversified farming systems and complex agricultural landscapes could impact pest densities by interfering with the colonization of the crop environment, thus leading to a bottom-up effect on pest densities (Root 1973, Andow 1991, Altieri 1999). Conservation biological control studies involving habitat manipulation should therefore evaluate both the natural enemies and resource concentration hypotheses. Natural enemy exclusion studies, for example, are a simple way of determining the relative influence of predators and parasitoids on pest densities (Gardiner et al. 2009). Invertebrate response to landscape heterogeneity should be evaluated in a way that can address both of these hypotheses. At a minimum, this would require separately examining insect response to the relative area, diversity and connectivity of both natural habitat and agricultural land at the landscape scale. The high probability of idiosyncratic and species specific response to the landscape will require that observed trends be evaluated relative to a number of alternate measures of landscape heterogeneity, including perimeter-to-area ratio, mean patch size and distance to non-crop habitats (Concepcion et al. 2008). Further, non-crop habitats cannot be assumed to serve only as source habitat for predators and parasitoids and are just as likely support herbivorous insect pests (van Emden 1965, Baggen et al. 1999, Roschewitz et al. 2005). Even if non-crop habitats do support only beneficial insects, the poor quality of a simplified crop environment at the field level may deter natural enemy dispersal from natural habitats (Nicholls et al. 2001, Tscharntke et al. 2008).
The effect of landscape heterogeneity on local invertebrate populations will likely influence the impact of field-scale habitat diversification on biological control (Griffiths et al. 2008, Bianchi et al. 2006, Tscharntke et al. 2007). To evaluate diversified cropping systems along a gradient of landscape heterogeneity, key causal mechanisms responsible for any observed landscape influence must be explored. Although much remains unknown about the response of invertebrates to changes in landscape heterogeneity, the presence and suitability of over-wintering habitat for key natural enemies remains an important, albeit inadequately, researched area of biological control science (Hunter 2002).
As habitat diversity will influence insect movement at both the field- and landscape-scale, researchers are encouraged to consider the movement and distribution of arthropods in relationship to the elements of heterogeneity under study (Corbett 1998, Dover and Settele 2009). The surprising results of Corbett and Rosenheim (1996) demonstrate the importance of empirical assessments of parasitoid dispersal from non-crop habitats. Quantifying insect movement between in-field habitat and crop and from non-crop habitats into cropping systems, especially comparing dispersal into simplified versus diversified cropping systems, will be critical to developing a more nuanced understanding of the impact of heterogeneity at multiple scales on biological control.
Controlled laboratory trials are essential to determining the physiological influence of non-crop vegetation on key pests and natural enemies, especially in the case of FRP (Wackers 2005). The ongoing UC Berkeley study, for example, quantifies the influence of multiple species of floral nectar on parasitoid longevity, fecundity, parasitism rates and sex ratios of the key biological control agents, thus forming the basis for understanding any observed impacts on biological control in field trials. To further substantiate nectar feeding, researchers should consider anthrone or HPLC testing to determine changes in parasitoid gut-sugar levels in the presence of flowers (Heimpel et al. 2008, Stepphun and Wackers 2004). Although challenging, such research on the impact of FRP on the longevity and fecundity of arthropods would ideally be conducted under conditions most resembling the vineyard/field environment (Lee and Heimpel 2008).
It is important for applied research in conservation biological control to include on-farm trials in collaboration with commercial vineyard settings. Such dialog with growers encourage the development of practices suitable for large-scale implementation and facilitate important social learning processes between researchers and growers that may improve the relevancy of research and advance grower adoption of successful practices (Warner 2007, Rolings 1998). Cost-benefit analysis, including data on impact to other ecosystem services (e.g. soil quality, etc) will provide a more holistic basis for grower decision-making regarding the true costs and benefits of vineyard diversification (Fiedler et al 2008; Gurr et al 2003; Jackson et al 2007).
Future research must also include relevant economic and social evaluations in order to develop ecologically-based pest management practices that are suitable for commercial adoption and provide better formulation for public policy in agriculture and conservation (Kleijn et al. 2007, Cullen et al. 2008). To date, very little work has been done to evaluate the impacts of public policy on vineyard habitat management or the ability of public institutions to adequately respond to grower research needs and coordination of agricultural diversification/restoration efforts at the regional scale.
It will also be important to gather information on consumer perception of product quality and price premiums associated with agricultural goods produced using ecologically-based farming practices (Howard and Allen 2010). In addition to farming practices, a recent study has shown that landscape heterogeneity itself can influence perceptions of wine quality (Tempesta et al. 2010).
Finally, habitat diversification tactics as described above may be successfully combined with the many new chemical ecology (e.g. pheromone) approaches to further enhance biological control (Daane et al 2008). “Attract and reward” strategies, for example, combine the use of herbivore-induced-plant-volatiles (HIPVs) with in-field FRP and has shown much promise in enhancing the effectiveness of diversification schemes (Khan et al. 2008, James 2005, Zhang 2005). One such HIPV is methyl-salicylate (MeSA) that has shown to increase abundance of some natural enemies in grape vineyards as well as in other cropping systems ((James and Price 2004; James 2006; Lee 2010). The ongoing UC Berkeley FRP project is currently trialing use of a “Predalure” (AgBio, Westminster, CO) in wine grape vineyards to assess the effectiveness of MeSA to enhance biological control of grape leafhoppers in simplified and diversified FRP plots.
Ongoing and Future UC Berkeley Research on the Impact of FRP and Landscape Heterogenity on Biological Control in California wine grapes:
With the above considerations in mind, our UC Berkeley research group has recently initiated the first comprehensive, multi-scale study of the impact of floral resource provisioning (FRP) and landscape diversity in Napa, Sonoma, San Joaquin and Fresno County wine grapes. The two-year research project will advance the science and practice of conservation biological control in California wine grapes by evaluating the influence of landscape composition – the quality and quantity of non-crop habitats – and floral resource provisioning on pest regulation and pollination services in vineyards and almond orchards. The study will identify over-winter habitat and assess dispersal of key insects from adjacent plant communities, as well as monitor bat and bird species and their contribution to pest control. The study will quantify the impact of FRP species on longevity and fecundity of key pests and parasitoids, as well as maintenance of pollinator species. The study will evaluate the impact of FRP on key soil quality indicators and their relation to drought tolerance. The study will assess consumer and grower support for new ecologically-based farming practices and the development of living wage standards for farm workers.