Restoring Plant Diversity and Soil Health in Napa and Sonoma Vineyards: scaling up an agroecologically based pest management strategy

Restoring Plant Diversity and Soil Health in Napa and Sonoma Vineyards: scaling up an agroecologically based pest management strategy

Summary

The Agroecology Research Group at the University of California Berkeley initiated a two-year on-farm research and extension project with the goal of defining in a participatory process with vineyard growers, plant diversification strategies that optimize the soil food web and native biological control services by creating a functional ecological infrastructure within and around vineyards. The target is that in 5 years, we would have a minimum of 50 farmers testing or fully adopting the new agroecological schemes on their vineyards. In the 2009 growing season the project involved seven vineyards located in nine separate research sites in Napa and Sonoma counties. The project involved one (1) Certified Organic, two (2) Certified Biodynamic and six (6) IPM-managed/integrated production systems. The project was designed to assess the effectiveness of flowering non-crop vegetation (e.g., winter and summer cover crops) on the enhancement of functional biodiversity for insect pest suppression in California vineyard agroecosystems. This year’s research has allowed us to further define the key cover crop species composition and the management of such plants to successfully sponsor cost-effective biological control of key wine grape pests and improve soil quality.

In the nine vineyards we compared insect parameters between treatment blocks under agroecological management versus neighboring control blocks under farmer’s standard management (FM). Given the two-year drought affecting the region, in some vineyards cover crop germination and establishment was erratic thus many growers were not able to implement the complete agroecological treatments. In many cases erratic winter and early spring weather affected cover crop establishment and conditioned very low pest densities in some sites. For this reason data were at times inconsistent across vineyards and therefore the need to extend the project one more season thru 2010. Nevertheless, preliminary results from the 2009 growing season are showing a fairly consistent reduction in leafhopper nymph densities across all vineyards where experimental blocks represented the optimal cover crop treatment designs. Although preliminary, these results appear to support the hypothesis that cover crop diversification is a key strategy to sponsor the internal regulation of arthropod pests without the use of synthetically compounded and/or OMRI-listed pest control material inputs.

As planned, we conducted training of farmworkers in Spanish on how to monitor key pests and natural enemies in vineyards. The intention of this was to provide them the training necessary so that they can assist their vineyard management in data collection and interpretation for future on-site pest management decision making. We made special efforts for extensive grower involvement via organization of several cross-visits among participants to share information and experiences, and also one field day open to the wider farming community which took place in Rutherford on July 7, 2009 ( see http://www.napavalleyregister.com/articles/2009/07/08/news/local/doc4a54330c8dd83273635507.txt) .

We have established a project website (http://agroecology.berkeley.edu) where we are starting to post all relevant information regarding the project, including sections on preliminary findings, relevant research articles in vineyard agroecology and a manual on agroecological vineyard diversification, which we hope to finish by the beginning of 2010.

Introduction to topic

As vineyard acreage in the North Coast continues to grow, concerns have been raised about how the expansion of vineyard monocultures and the continued fragmentation of natural habitats will negatively impact biodiversity and the natural control of agricultural pests. As habitat and other essential resources for natural enemies are further reduced, the possibilities for pest outbreaks increases as biological control and other important ecosystem services (e.g. water purification, soil quality, biodiversity conservation) are significantly diminished (Altieri and Nicholls, 2004)

Over the last three years the Agroecology Research Group at UC Berkeley has been collaborating with viticulturists in re-designing vineyard systems through habitat manipulation for conservation biological control of key wine grape pests, in particular grape leafhopper (Erythroneura elegantula) and vine mealy bug (Planococcus ficus). Despite the use of Integrated Pest Management (IPM) techniques and OMRI-listed pest control inputs, many vineyards continue to experience high levels of pest pressure. Such recurring pest problems in vineyards (and other monocultures) is a predictable ecological phenomena, which results from the absence of on-farm plant diversity and simplified or degraded natural habitats that often surround vineyard systems. These simplified ecosystems contain limited habitat and resources for beneficial organisms (e.g. generalist predators and parasitoids) and thus reduce the capacity for the internal regulation (biological control) of pest populations

The proposed project is an exceptional opportunity to scale-up the agroecological approaches that our group has been experimentally testing for the last ten years (Altieri et al, 2005). Our research has consistently shown that reducing vineyard monoculture structure through the use of winter and summer cover crops, establishment of hedgerow corridors and/or protection and restoration of surrounding vegetation can be a highly effective means of enhancing conservation biological control and preventative pest management in vineyards (Altieri and Nicholls, 2004). Further, such ecosystem management practices are neither reliant on synthetically compounded pest control materials nor OMRI listed broad-spectrum pesticides known to negatively impact populations of beneficial insects and other beneficial arthropods. If properly designed and implemented, such alternative pest management strategies could potentially result keep pest densities beneath economically acceptable thresholds while significantly reducing pest management costs.

Objectives/Performance Targets

As stated in the original proposal, the project is, via a participatory process involving vineyard growers, to jointly test plant diversification strategies that optimize the soil food web and native biological control services by creating a functional ecological infrastructure within and around vineyards. Since the 2008 season we have been assessing the effectiveness of specific agroecological management strategies (e.g., winter and summer cover crops and native plant hedgerow corridors) 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 further define 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 proposal is that it be participatory in nature so that farmers and key farm workers are engaged in the design, 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.

Accomplishments/Milestones

It is important to note that sampling of the vineyards ended on September 15, 2009, and given the amount of data collected and still being processed we only have preliminary results to report, featuring cumulative leafhopper nymphal densities. Data on diversity and abundance trends of general predators, parasitization rates, etc. will be available by the end of December

Nymphal densities

Most growers informed us that the 2008-2009 was an unusual growing season, especially because of a two-year drought associated with low winter rainfalls, early spring frosts and cool spring which affected vine growth as well as insect populations. As a result, leafhopper densities were unusually low in some vineyards, never reaching more than 2/nymphs per leaf (thresholds that warrant control actions range from 10-20 nymphs/leaf).

Given these low numbers it was not possible to detect significant differences in nymphal densities between agroecological and farmer management blocks at many sites. In some vineyards this trend in low leafhopper abundance was furthered because farmers sprayed organically allowed pesticides, such as Pyganic (Quintessa). For 2010 we have planned establishment of no-pesticide control blocks in order to assess the true population potential of leafhoppers in farmers monocultures, so that we can compare such values with densities reached in the agroecological blocks. Nevertheless, preliminary results from the 2009 growing season are showing a fairly consistent reduction in cumulative leafhopper nymph densities across four vineyards where experimental blocks represented the optimal cover crop treatment designs.

Outreach

Growers have played a central role in the development of the proposed research project from the very beginning and have played an influential role in determining plot designs as well as appropriate cover cropping practices used in the experimental plots. Some growers have also worked collaboratively with researchers to define the species composition and location of multifunctional hedgerows. We also conducted several insect monitoring training sessions including growers and selected farm laborers on insect monitoring sampling methods, allowing them the opportunity to subsequently collaborate with the management at their vineyard in the monitoring and assessment of insect populations and soil and crop health parameters that could potentially help provide valuable data, observations and feedback to researchers in future studies.

Producers and managing viticulturists have also played a central role during the outreach and extension field days organized in association with the project. By exhibiting their experimental plots to the wider grower community, produces are serving as disseminators of best management practices and provide technical information to other farmers 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, producers are helping us gather information and review/edit written materials produced by us for wide-scale distribution. Much of this information is been made available on our website (http://agroecology.berkeley.edu). In addition to publication in technical journals, findings derived from the 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 is being produced after we have analyzed two years of accumulated data.

Impacts and Contributions/Outcomes

Our preliminary findings suggest several conclusions:

1. Although pest pressure was low in many vineyards, in the agroecological blocks leafhopper densities were maintained at densities below growers’ economic thresholds and comparable to those attained in farmer management blocks where chemical or organic pesticides were used. It is important to test these treatments under high pest pressure conditions and for this reason we will establish new experiments in five new vineyards that have historically experienced high leafhopper pressure. A control treatment under farmer management with no pesticide applications is crucial to determine the population development potential of key pests in the absence of disturbance.

2. Winter cover crops and establishment of spring and summer flowering cover crops enhanced the diversity and abundance of natural enemies (predators and parasitoids) but we need to study more carefully the functional mechanisms that explain how natural enemies best control target pests in the presence of flowering ground covers. For example, we know that spiders are key predators in the vineyard agroecosystem but one of the limitations on early season spider establishment in vineyards is the availability of sufficient prey. Other limiting factors faced by spiders are desiccation and intra-guild predation. The ability of floral resources to support a broad range of neutral non-pest organisms is likely to increase the availability of alternate prey for spiders both earlier in the growing season and throughout its entirety. The presence of flowering ground cover throughout the growing season is also likely to create a variety of new microhabitats beyond those already provided by the vine canopy, bark and detritus on the vineyard floor. Increasing the diversity of alternate habitats has in some cases also been proven to reduce intra-guild predation through niche partitioning. In a vineyard this could potentially allow multiple spider species to more effectively control target pest organisms. Moreover, flowering ground covers will likely reduce spider mortality from desiccation by providing them with some protection from temperature fluctuations and maintaining an environment with higher relative humidity.

3. For the 2009-2010 growing season we will continue to test the 4 species of flowering ground cover, which include purple tansy (Phacelia tanacetifolia), sweet alyssum (Lobularia maritime), wild carrot (Daucus carota) and buckwheat [Fagopyrum esculentum]) sown with over-wintering cover crops, beneath vine rows, strip tilled into the center of no-till alternate rows, and sown into over-wintering cover crops following their spring incorporation, respectively. We have also chosen to include a fifth species (Ammi majus) of flowering ground cover in next season’s trials. The different flowering periods of the five plant species being trialed will work in combination to ensure that floral resources (e.g., nectar and pollen) are available throughout the growing season. These species have been chosen based on their successful use in previous trials, adaptation to a Mediterranean climate and compatibility with modern vineyard management.

4. For a third season we will continue implementing agroecological treatment blocks in 12 commercial vineyards in Napa and Sonoma counties. At each site, one 5-acre (minimum) agroecological treatment plot will be established in October and November of 2009, and compared with similar sized control blocks of standard farmer’s management (split plot design). In order to ensure statistical accuracy and better control over treatment variables to conduct mechanistic studies 2 large-scale replicated trials will be established. One trial will consist of a 12-acre randomized block with 3 replications, another will consist of a 10-acre randomized block with 5 replications. These trials will compare:
a. a combination of 5 floral resource provisioning plant species (purple tansy [Phacelia tanacetifolia], sweet alyssum [Lobularia maritima], wild carrot [Daucus carota], bishop’s weed [Ammi majus], and buckwheat [Fagopyrum esculentum]) sown with over-wintering cover crops, beneath vine rows, strip tilled into the center of no-till alternate rows, and sown into over-wintering cover crops following their spring incorporation, respectively;
b. a grower standard management practice (synthetic herbicides for weed management);

The project is already fostering the widespread adoption of organic farming practices by first familiarizing the seven growers participating in the study (collectively controlling over 10,000 acres of wine grapes) with the implementation and assessment of alternative agroecological production practices. We organized two cross visits among the seven participating growers to observe the treatments implemented at other vineyards, to discuss the effectiveness of the practices, and to exchange relevant management considerations for the efficient implementation and scaling up of such strategies. We also organized a public field day featuring two experimental blocks showcasing the success of the agroecological production practices to the wider viticulture community. As a result of these efforts additional farmers joined the project for the 2009-2010 season (MacRostie, Beckstoffer, Griffin’s Lair and others) and have started sowing cover crops in experimental plots at their properties.

References

Altieri, M.A. and CI Nicholls 2004 Biodiversity and pest management in agroecosystems,. Haworth Press, New York.

Altieri, MA, L. Ponti and CI Nicholls (2005) Manipulating vineyard biodiversity for improved insect pest management: Case studies from northern California. International Journal of Biodiversity Science and management 1: 191-203

Daane KM, Costello MJ. (1998) Can cover crops reduce leafhopper abundance in vineyards? California Agriculture; 52(5):27-33.

Ingells, CA, R.L. Bugg, G.T. McGourty and L.P.Christensen 1998 Cover cropping in vineyards: a growers handbook. UC DANR Publication 3338, Oakland, CA.

Nicholls, CI, MA Altieri, A Dezanet and M Lana (2004) A rapid, farmer-friendly agroecological method to estimate soil quality and crop health in vineyard systems. Biodynamics 250: 33-34.

Nicholls C, Parrella MP, Altieri MA.(2000) Reducing The Abundance Of Leafhoppers And Thrips In A Northern California Organic Vineyard Through Maintenance Of Full Season Floral Diversity With Summer Cover Crops. Agricultural And Forest Entomology 2(2):107-113.

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