- Cool weather during fruit initiation and bloom can cause wide yield fluctuations in Oregon vineyards. These fluctuations in clusters per vine, flowers per cluster, and berries per cluster make yield prediction difficult. Over- or underestimates of yield have caused problems in marketing grapes and viticultural decision making. Oregon State University has been testing methods of estimating yield for the last three years. A system we developed appears to work well for Pinot noir and, with some modification, should work for other varieties. Growers interested in trying this system should collect data this season, as long term records are important. The system requires a grower to measure or estimate four factors each season: 1) bearing vines per block, 2) clusters per vine, 3) cluster weight at the lag phase of berry growth, and 4) cluster weight at harvest. These data will allow a grower to make two crop estimates each season. The first is pre-bloom, early enough for sales and winery planning. The second is pre-veraison, still early enough to revise sales plans and to make crop adjustments through cluster thinning. Each factor will be discussed below and will be followed by examples of how yield estimates can be developed from this information.