Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 19, 2009
Publication Date: June 1, 2009
Citation: Blom, P.E., Tarara, J.M. 2009. Trellis tension monitoring improves yield estimation in vineyards. HortScience. 44:678-685. Interpretive Summary: The Trellis Tension Monitor (TTM) technology, which was described in an earlier report, offers grape growers a way to estimate yield automatically and dynamically, which until now was not possible. Longstanding, currently practiced approaches to estimating yield are expensive and labor intensive, tending to rely on only one to two early- to mid-season snapshots of the crop, which are derived from hand sampling fruit clusters. Predictions of grape yields are highly sought by juice processors and wineries because of finite processing capacity and the need for immediate processing of the perishable fruit. As the vine and grapes grow, the TTM detects the change in weight that is being supported by the trellis. TTMs were operated in 10 commercial vineyards in Washington State where major juice processors historically have made yield estimates. The TTM tended to produce more accurate estimates of yield in each vineyard than did the standard processor protocol. No subjective inputs were allowed, which otherwise would be the case in commercial practice. The TTM method could replace traditional, manual methods of yield estimation or could be used in conjunction with processors' and wineries' traditional approaches to increase the amount of real-time information and provide data for revising yield estimates right up to harvest.
Technical Abstract: The preponderance of yield estimation practices for commercial vineyards is based on longstanding but individually variable industry protocols that rely on hand sampling fruit on one or a small number of dates during the growing season. Limitations associated with the static nature of yield estimation may be overcome by deployment of Trellis Tension Monitors (TTMs), systems that provide dynamic measurement of changes in the tension of the main trellis support wire. TTMs were installed in 10 commercial vineyards from which 2 commercial juice processors annually collect data to derive yield estimates. Processor and TTM data were subjected to three permutations of the basic linear computational approach to estimating yield, and their accuracies evaluated, given known harvested yield at various spatial scales. On average, TTM data produced more accurate estimates of actual yield than did the established computational protocols of the juice processors. There was high vineyard to vineyard variability in the accuracy of the estimate under all approaches, even from those permutations designed to match the spatial scale of the data collected for yield estimation with the spatial scale of the actual harvested yield. The processor protocols appear to be more sensitive than the trellis tension approach to the selection of the antecedent years used for comparison with the current year's data. Trellis tension monitoring may be useful to supplant traditional, labor-intensive yield estimation practices or to supplement longstanding practices with real-time information that can be applied to dynamic revision of static yield estimates.