VERC - Optimal Viticulture Systems Comparison

- Research Note -

Optimal Viticulture Systems Comparison
by
Mark A. Mayse and R. Keith Striegler

CATI Publication #970402
© copyright April 1997, all rights reserved

INTRODUCTION

This joint project includes two primary research components: 1) a study comparing conventional and organic practices in a Barbera vineyard at the California State University, Fresno Farm Laboratory; and 2) a study comparing conventional, biologically-intensive, and organic practices in a new Merlot vineyard in Mendocino County (Fetzer Vineyards).

The overall goal of this research is to comparatively evaluate over several years the relative strengths and limitations of three distinct and dynamic systems of viticultural production and protection: 1) conventional, 2) biologically intensive, and 3) organic.

Specific objectives for the optimal viticulture systems comparison project include the following:

To identify and monitor the principal microbiological and nutrient features of the soil rhizosphere as it evolves in each of the three treatment systems;
To evaluate important viticultural and ultimately enological parameters which develop among the treatments;
To carefully study and elucidate prevalent population patterns of key destructive and beneficial arthropods (insects, spiders, mites, etc.) over a series of seasons among the system treatment plots; and
To conduct summary comparisons of economic analyses (e.g., energy budgets, input costs, production and quality output values) for each treatment system.
As mentioned previously, the study described above is being conducted in a new Merlot planting at Fetzer Vineyards in Mendocino County. Due to vineyard space and research staffing constraints, the study being conducted in the new Barbera planting at California State University, Fresno is limited to the two more extreme production system treatments (i.e., conventional and organic).

Relatively few research projects as comprehensive in scope as the work described in this Research Note have been conducted in perennial cropping systems. However, with the pro-active role already being played by key members of the wine-grape industry in moving toward development of more sustainable viticulture systems, such a long-term comparison of viable but demonstrably different sets of grape production and protection practices seems like a natural step to take.

Perhaps the greatest challenge in the ultimate execution and evaluation of this long-term research project will be to maintain objectivity, and to minimize biases with respect to the different treatment programs (three in Mendocino County, two at California State University, Fresno) which could otherwise undermine the integrity of the research findings. Thus, we must consistently achieve the goal of farming all plots within the constraints of each treatment system in the most productive and efficient ways possible. If we are successful in this pursuit, then the long-term results generated from this project should help elucidate an optimal system of comprehensive vineyard production and management.

REVIEW OF RELEVANT LITERATURE

In 1991 we initiated plans for a study to be conducted in a new Barbera vineyard located on the California State University, Fresno Farm Laboratory. The Barbera block was established during 1992 and 1993, and two viticultural system treatments (organic and conventional) were implemented in 1994. Field data (both viticulture and plant protection) were gathered for the first time during the 1995 season. The Barbera study was instrumental in providing the original impetus and interest in the portion of this project to be conducted in Mendocino County.

To our knowledge, there have been no other similarly comprehensive research projects conducted in vineyard agro-ecosystems. However, wine grapes would appear to be a natural and logical choice for this type of study. As mentioned in a California Agriculture article (Auburn 1994), the "Senate Agriculture Committee has recently reported that California growers using IPM on wine grapes have cut their insecticide and fungicide use by at least 50 percent."

For several years, scientists at UC Kearney Ag Center have been conducting a long-term study of optimal production and protection practices in stone fruit orchards. Among the researchers involved in this perennial agro-ecosystem work are horticulturist Scott Johnson, plant pathologist Themis Michaelides, and entomologist Kent Daane.

One specific part of the project which became the focus of graduate student Hugo Ramirez's M.S. thesis work at California State University, Fresno (major professor, Mayse) involved a comprehensive examination of the effects of host tree fertility on the occurrence and severity of specific disease-producing organisms (Ramirez 1993).

In 1988, researchers at UC Davis initiated a 12-year project to compare conventional, low-input, and organic farming systems using a four-year, five-crop rotation of processing tomatoes, safflower, corn and wheat followed by double-cropped dry beans. Although the Davis study solely involves annual cropping systems, several observations to date should be helpful in implementing the vineyard research described in this proposal. For example, the UCD researchers have found that non-chemical weed control, along with development and utilization of implements to better manage cover crops, can pose substantial challenges. Other key issues facing the interdisciplinary group as they move through the second rotational cycle of the project include "identifying the best cover crops for each system/season combination and observing phenomena that have an impact on soil fertility and plant nutrition, particularly the season-long monitoring of cover-crop- derived nitrogen fertility, crop growth and yield" (Temple et al. 1994).

A wealth of general information and specific guidelines for monitoring vineyard pests is provided by the UC Grape Pest Management Manual (Flaherty et al. 1992). Perhaps of greater relevance to the multidisciplinary research proposed here, however, is a chapter by Mayse and co-workers (1997) which documents the critical roles played by cultural practices (including overall vineyard management, cover crops, trellising systems, fertilizer and irrigation practices, etc.) in grape pest management situations.

STUDY AREAS AND METHODS

The site for the Mendocino County study component of this project is a new 21-acre planting of Merlot (clone 3) on 5C rootstock at the Fetzer Vineyards' Eagle Peak Ranch in Mendocino County. Due to some variation in length of vine rows at the edges of the vineyard, the study plots are comprised of rows 12-112, a layout which provides the desired total of nine plots, each consisting of about 11 vine rows. This vineyard is planted in a 10 ft. x 7 ft. spacing pattern, with vine rows running in an east-west orientation.

At California State University, Fresno, the new 13-acre planting (east-west) of Barbera on Harmony rootstock has already been set up as six treatment plots (about 12 rows each) which includes three replicates of each of the two production system treatments (conventional and organic).

The nine treatment plots in Mendocino County are laid out in a regular pattern to minimize confusion about treatment patterns and to prevent effects of adjoining same-treatment plots resulting from fictional doubling of plot size. The three distinct treatments (details below), each replicated three times, represent our best efforts to simulate the following three prevalent approaches to grape production/protection: 1) conventional practices, 2) biologically- intensive practices, and 3) organic farming practices.

Each treatment pattern includes an optimal and generally accepted array of practices representing that particular type of system. Relatively large individual plot size in this study (about two acres each) should allow for harvested grapes from each plot to be carried through to wine and evaluated independently by plot, which is an uncommon advantage in this kind of research.

Conventional Treatment
Practices generally follow a conservative, calendar-based approach to vineyard management and decision-making. Resident vegetation is allowed to develop between vine rows during the winter, but row middles are clean cultivated from budbreak through the rest of the season. Synthetic fertilizers (N, P, K-based) are soil-applied (i.e., placed under drip emitters) at typical, recommended rates on a calendar basis, whether they are needed or not. A spring application of fertilizer is made at berry set. Irrigation in conventional plots follows a standard program of drip applications.

With respect to pest control, an approach often described as "Best Management Practices" is followed. This approach involves some level of preventive treatments for insect pests, and certainly for potential disease problems. Any registered pesticides may be used according to label rates and frequency in the conventional plots.

Biologically-intensive Treatment (Mendocino County study only)
Practices for the bio-intensive treatment and the organic treatment resemble each other in a number of ways. Most importantly, viticultural practices in these blocks generally follow a more functional, not strictly calendar-based program, which involve management actions taken as needed. During the first three years of the project, winter legume cover crops (e.g., rose clover, three species of subterranean clover, birdsfoot trefoil) will be planted (drilled in bio-intensive plots, broadcast under vines in organic plots) to build soil organic matter. Winter cover crops are mowed at budbreak.

In the bio-intensive treatment plots, neither synthetic, soil-applied synthetic fertilizers nor compost are used. Nitrogen is supplied from the winter cover crops, and foliar feeds based upon petiole analysis for other nutrients are used. Irrigation in biologically-intensive plots is a standard program of drip applications.

A true, as-needed style of Integrated Pest Management is followed in the bio-intensive treatment. Materials selected for application are primarily "soft" pesticides (e.g., soaps, oils) whenever possible. Thus, in bio-intensive plots preventive pesticide treatments are used only for diseases (i.e., not insects, nematodes, vertebrates), although any registered materials could be used at label rates and frequency if monitoring data indicate that an incipient pest problem is developing.

Organic Treatment
Use of cover crops in the organic treatment is very similar to the pattern for bio-intensive plots. However, cover seed will be broadcast under vines in organic plots for the first three years of the project. Compost is applied to organic plots at two tons per acre in the fall, with additional nitrogen provided by the subsequent winter cover crop. In addition, foliar feeds are applied in organic plots as needed, based upon petiole analysis results. Irrigation in organic plots involves a standard program of drip applications. Pest management activities in the organic treatment, although based upon sound IPM principles, must be restricted materials which are allowed under Organic Farming regulations. Thus, treatments for pest problems are used primarily on an as-needed basis, and only "organically allowed" pesticides can be ultimately applied in these plots. By simply verifying organic status (through informal inspection) in this treatment rather than trying to market the products as certified organic, it will not be necessary to include the formally mandated buffer areas which would otherwise quickly take large portions of the vineyard block out of the experimental project.

RESEARCH OUTLINE

Treatment parameters for the Mendocino County study as described above were first instituted during fall 1994. Formal data collection in the California State University, Fresno Barbera study began in 1995. The extensive program of data collection and evaluation from experimental plots at both study sites over the next several years is the primary topic of this section of the Research Note.

Objective 1: Characterize and monitor the microbiological and nutrient components of the soil rhizosphere.
The co-principal investigators have arranged for a cooperative agreement with broadly experienced soil microbiologist Dr. Ethelynda Harding of the California State University, Fresno Biology Department to help coordinate the soil quality/nutrient/pathogen aspects of the long-term study.

There are three primary components of this portion of the project: soil characteristics, microbial tests, and pests/pathogens. Among the soil physical and chemical features being monitored are the following: improved texture, improved water filtration rates (checked spring, mid-season, fall), improved cation exchange capacity (CEC), pH and buffering capacity, and mineral profile. For the general microbial tests, samples are collected three times a season on relative population levels (dilution plate method), relative activity levels (dehydrogenase activity levels), and a qualitative test for actinomycete population levels. Pests and pathogens being investigated in this portion of the project include grape phyloxera population levels and plant parasitic nematode population levels.

Objective 2: Evaluate viticultural and enological parameters.
The following crop/product measurements are made: 1) cover crop growth - percent of soil surface occupied by cover crop plant is subjectively assessed during the season; 2) vine nutritional status - petiole samples are collected at bloom, berry set, and veraison, and levels of nitrate (N, P, K, Zn, Mg, Mn, Na, Cl, and B) will be measured; 3) fruit composition - berry samples (100 berries per lot) are collected for analysis at harvest, and from these samples berry weight, percent soluble solids, titratable acidity, and pH are determined; 4) yield data are collected; 5) dormant season pruning weights are collected; 6) severity of Botrytis bunch rot is determined at harvest; and 7) standard wine composition and organoleptic analyses will be conducted by Fetzer personnel for wine lots from grapes produced in each of the nine individual treatment plots (after vineyard productivity becomes sufficient).

Objective 3: Monitor and investigate population patterns of key destructive and beneficial arthropods above ground.
Throughout the growing season, population counts for several important insects and related arthropods are taken in all treatment plots: 1) western and variegated grape leafhopper nymph counts; 2) counts for western grapeleaf skeletonizer, omnivorous leafroller, and orange tortrix larvae; 3) leaf examination (presence/absence technique) for herbivorous mites; 4) spider counts using pitfall traps and canopy shake sampling; 5) parasitism of leafhopper eggs by the wasp parasitoid Anagrus; and 6) generalist insect predators (e.g., lacewings, lady beetles, damsel bugs, big-eyed bugs) sampled by canopy shake. Also, routine field sampling activities generally allow the detection of incipient problems from any pests other than the key groups mentioned here.

Objective 4: Comparison of economic analyses.
With the cooperation of Associate Dean Dennis Nef of California State University, Fresno's School of Agricultural Sciences and Technology, we plan to comprehensively compare input/output costs associated with each of the three treatment patterns. Included among the economic parameters to be analyzed are 1) cover crop materials and activities, 2) pest management monitoring and treatment costs (e.g., preventive vs. as-needed), and 3) soil and plant monitoring costs. Comparisons will naturally be approached from both short-term and long-term perspectives in order to most accurately determine the optimal system of vineyard production and management.

ACKNOWLEDGMENTS

The authors wish to acknowledge the involvement and technical assistance of William O'Keefe, Debra Dexter-Mendez, Greg T. Berg, Chris B. Lake and Mark Salwasser in this project.

Funding has been provided by the California Agricultural Technology Institute (CATI), the American Vineyard Foundation (AVF) and Fetzer Vineyards.

LITERATURE CITED

Auburns, J.S. 1994. Society pressures farmers to adopt more sustainable systems. Calif. Agric. 48(5): 7-10.

Flaherty, D.L., L.P. Christensen, W.T. Lanini, J.J. Marois, P.A. Phillips, and L.T. Wilson (eds.). 1992. Grape Pest Management (2nd ed.). Univ. of Calif. Div. Agric. and Nat. Res. Publ. #3343. 400 pp.

Mayse, M.A., P. Trichillo, C. Pickett, and M. McKenry. 1997. Cultural Control of Arthropods and Nematodes in Vineyards. In L.T. Wilson, T.J. Dennehy, and N.J. Bostanian, eds. Arthropod and Nematode Management in Vineyards with Emphasis on North America and Western Europe, Pergamon Press. [In press].

Ramirez, H. 1993. Effects of nitrogen fertilization on brown rot disease caused by Monilinia fructicola on nectarine (cv. fantasia). M.S. Thesis, California State University, Fresno. 103 pp.

Temple, S.R., O.A. Somasco, M. Kirk, and D. Friedman. 1994. Conventional, low-input and organic farming systems compared. Calif. Agric. 48(5): 14-19.

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