- Winter 1996 "Update" Newsletter Article -
Viticulture study offers variety of data
From CATI Publication #960101
Copyright © 1996. All rights reserved.
Data analysis on a multi-year, comprehensive viticulture research project has been organized and is now available in a new report published by the California Agricultural Technology Institute (CATI).
Plant Science professor Mark Mayse and research scientist Keith Striegler were the lead investigators in a study of sustainable viticulture practices in a commercial Chenin blanc vineyard in California's central San Joaquin Valley.
The study covered three years and addressed an assortment of issues grape growers must face as they move from conventional to more sustainable viticultural practices.
Conventional treatments in the study included cultivating between vinerows and applying nitrogen fertilizer. Sustainable treatments included planting and maintaining cover crops, no fertilizer application, and leaf removal from the base of shoots.
As expected, the density of beneficial organisms such as spiders and parasitic wasps was higher in and around the vines with cover crops, the authors noted. The cover crops (treatments included grasses and legumes) provide shelter, nectar, pollen and moisture that attracts the beneficial, which in turn help to control populations of unwanted, plant-eating pests.
Some of the most significant data relating to cover crops was the incidence of parasitism by a tiny wasp (Anagrus) that feeds on the eggs of the western grape leafhopper (WGLH) and variegated leafhopper (VLH), two of the most serious grapevine pests in California.
"Anagrus parasitism of leafhopper eggs played a major role in reducing nymph populations, as [Anagrus] densities appeared to be enhanced by a legume cover crop," the authors state in the report. The incidence of parasitism of the leafhopper eggs also reached "biologically meaningful levels" several weeks earlier in the cover-cropped vineyard plots compared to the treatments with clear middles, Mayse added.
In terms of plant growth, the study further confirms the impact of legumes in supplying nitrogen. "The choice of cover crop can have a dramatic impact on the nutritional status of the vine," Mayse said. Results showed that grass cover crops reduced nitrogen concentrations as well as yield.
Specific viticultural data collected over the three years of the project included yield, cluster weight, clusters per vine, berry weight, berries per cluster, percentage bunch rot, pruning weight, soluble solids, pH, titratable acidity, and a series of nutrient levels. All findings are explained with brief summaries and most are detailed with tables.
Integrated pest management (IPM) data collection included leaf sampling for leafhoppers and their egg parasitoids, canopy shakecloth sampling for spiders, as well as sweepnet and pitfall trap sampling for herbivores and natural enemies on vineyard floor vegetation.
Mayse described the study as unique in its comprehensive examination of both viticulture and pest management practices. The findings further document and confirm that while cover crops may not offer a dramatic advantage over conventional practices, they help to establish ecological stability in the vineyard. Ecological stability is the key to preventing outbreaks of unwanted pests.
"Chenin blanc grapevines were grown successfully for three years without reliance on synthetic fertilizer, insecticides and herbicides," the authors observe. "Our findings indicate that grape growers have numerous alternative practices which should be considered in developing more sustainable viticulture systems." To obtain a copy of the study, entitled "Sustainable Viticulture Practices in the San Joaquin Valley of California," see the publication request form on Page 7.
For more information on this project, the authors may be contacted through the Viticulture and Enology Research Center, at (559) 278-2089.{ page top }