Whole-farm Impact of Converting Conventionally Managed Eastern Vineyards to Organic Management Practices
Because of increasing public concern over the use of pesticides in agriculture, growers in general are showing more interest in organic management practices. Eastern grape growers, confronted with loss of synthetic pesticides due to pest resistance and government and processor restrictions, are no exception. However, before a grower converts his entire operation to organic management practices, he needs to understand the consequences of this action in terms of pest problems, crop yield, produce quality and production costs and returns. We propose to determine pest populations and problems, vine vigor, yield, fruit composition, and juice and wine quality, as well as production costs in conventionally and organically managed vineyards. Vintner’s International, Inc., one of the largest grower-winery operations in the eastern US, has committed 30 acres of vineyards and significant manpower to a five-year study of the conversion of conventionally managed vineyards to organic management practices.
Studies will be conducted in 10-acre blocks of the varieties Concord, Elvira and Seyval. In each 10-acre block, one half will be managed organically and the other half will be managed conventionally. Because grape is a perennial crop and the effects of conversion to organic practices may not be obvious in the first years of the study, observations must be made over several seasons. Therefore, conversion to organic practices will be initiated in 1990 and the study will continue for five years. Information from this study will have a substantial impact upon the development of organic viticulture in the northeastern United States. The systematic evaluation of organic management practices (a poorly researched area), and the comparison of these practices to conventional management, may provide a model for conversion of eastern vineyards if conventional management becomes unsustainable in the near future. The results of this study will be communicated to growers through field tours, meetings, and published reports.
(1) Determine the impact of vineyard conversion on vine nutrition, soil fertility and moisture, vine vigor, capacity and yield.
(2) Determine the impact of vineyard conversion on disease incidence and severity.
(3) Compare the efficacy and survival of beneficial biological control fungi under conventional and organic management programs.
(4) Determine the contribution of dormant eradicant treatments to seasonal disease control under conventional and organic management programs.
(5) Demonstrate the efficacy of a non-pesticidal insect pheromone for control of grape berry moth; determine the long-term effects of eliminating conventional insecticides from vineyards; and develop risk assessment methods for management of grape leafhopper.
(6) Determine the impact of vineyard conversion on fruit and wine quality.
(7) Determine the impact of vineyard conversion on production costs and profitability.
(8) Relay results of the study to growers using current Cooperative Extension methods.
Results to Date
This section summarizes the third year’s (1992) activities and responses.
Soil and petiole analyses indicate that conventionally and organically managed vineyards are similar in overall nutritional status. Differences in yield and yield components between the culture methods were less in 1992 than in previous years. The very wet growing season reduced the impact of any differential weed competition between the two systems. At the same statistical crop level, conventionally managed vines had higher soluble solids, which may indicate that the late season canopy of these vines was more functional.
Differences in competition and water use were seen when alternative cover crops were used between rows. The higher soluble solids at similar crop loads may indicate improved canopy function when legumes are planted between rows. In-row weed management with propane weed burners appears to be as effective as paraquat, and in 1992 experience was gained using this method instead of paraquat to burn down grapevine suckers.
This was the first year of significant disease, due largely to the excessively wet growing season. Phomopsis was common in both Concord management systems, whereas downy mildew and black rot were severe in the organically-managed blocks. Powdery mildew and Botrytis bunch rot were common in both Seyval management systems, but powdery mildew was more severe on fruit of organically-managed vines. Diseases were not a problem in either management system of Elvira. The application of a biocontrol agent, Ampelomyces quisqualis, to an Aurore vineyard reduced the severity of powdery mildew and treatment with another biocontrol agent showed promise in controlling downy mildew.
Insect damage was less severe in 1992 due in part to unseasonably cool temperatures and rain. Grape berry moth damage exceeded the threshold in one portion of the organically-managed Concord vineyard. No conventional blocks received insecticide treatments. Foliar damage due to leafhopper was insignificant in all conventional and organic areas. Anagrus epos, an egg parasite of leafhoppers, was abundant and effective in preventing an estimated 80% of leafhopper eggs from hatching.
Concord grapes grown conventionally in 1992 were slightly riper in sugar and acid content than those farmed organically, yet there was no difference in juice color. There was no difference in the juice quality of Elvira grapes from either management system. Seyval grapes from the conventionally-farmed vines were also more mature with higher Ph and sugar content.
Growing costs, such as fertilization and mechanical weed control, for the organic vineyards were greater than for the conventional vineyards. Yield was higher for Concord and Seyval grapes grown conventionally, but lower for Elvira grapes. Nevertheless, returns to management, a measure of profitability, were greater for the conventional management system regardless of cultivar.
Because we are still in the early stages of this long term project, most extension efforts are limited to informing growers of the nature of the study. As individual components of the project, such as results from insect studies and ground cover management, come into fruition, growers are informed through publications and meetings.