|Mlikota Gabler, Franka|
Submitted to: Plant Disease Management Reports
Publication Type: Research Notes
Publication Acceptance Date: 7/15/2009
Publication Date: 8/18/2009
Citation: Hashim-Buckey, J., Smilanick, J.L., Mansour, M., Mlikota Gabler, F., Margosan, D.A. 2009. Evaluation of cluster position on decay, bird-caused injuries, color, and quality of ‘Redglobe’ table grapes, 2008. Plant Disease Management Reports. 3:SMF036. Interpretive Summary: Table grapes rot before and after harvest unless actions are taken to retard this process; approaches used to reduce these losses include the use of fungicides and pruning. In this work, we evaluated a difference in the location of the developing grapes clusters in the vine, namely, whether it touched the vine branches or not when it was mature, on its quality. We found that if the clusters touched these branches, many aspects of their quality (number of rotten berries, bird pecking injured grapes, and adequate berry color) were inferior. Instructions to vineyard pruning crews should include removal of clusters that contact, or that will later grow and contact, the branches of the vines.
Technical Abstract: This trial was conducted in a 25-year old commercial table grape vineyard near Delano, CA. The vines were bilateral cordon trained, spur pruned on a standard “T” trellis system and spaced 7 ft. between vines and 12 ft. between rows. Vines were drip irrigated in the vine row and furrow irrigated in alternating row middles at a level of approximately 80% ET. A mature almond orchard was adjacent to the vineyard. When the berries were approximately 4 to 8 mm in size they treated by hand-dipping the clusters in a 40 mg l-1 solution of gibberellic acid (GA3) to increase berry length and weight, and theclusters were tipped and berries were thinned according to standard grower practices by commercial crews. Powdery mildew was controlled with micronized and dusting sulfur. When the grapes reached commercial maturity (soluble solids contents of 18 to 19%), observations of the influence of cluster position (whether they touched the vine cordons or not) on the number of decayed berries, berries with bird pecking injuries, whether the clusters had sufficient red color to be acceptable for harvest, and whether the cluster was judged free of all defects (‘perfect’) were recorded. Within each row observed, observations of the first twenty five clusters encountered were recorded, three vines were bypassed, and observations resumed for the next 25 clusters, for a total of 50 clusters examined per row. In 2008, the rows examined differed from those examined in 2007. In 2007 and 2008, a total of 175 and 250 clusters were evaluated, respectively. The data were summarized and the significance of their interactions analyzed by Spearman’s coefficient. If the clusters touched the vines cordons, the percentage of decayed berries or those with bird pecking injuries increased, while those with acceptable color or judged to be ‘perfect’ was markedly lower. Most of the decay observed was sour rot. The birds present in the vineyard were primarily song sparrows (Melospiza melodia), and the adjacent mature almond orchard may have influenced their number by providing additional cover and forage. We speculate the primary reasons for the poor quality of the clusters that contact cordons is that they are more accessible to birds that cause injuries and spread the inoculum responsible for sour rot, and because these clusters are generally deeper within the vine canopy so the interception of sunlight is inadequate for them to develop acceptable berry color. Instructions to workers that manage ‘Redglobe’ table grape vineyards should include elimination clusters that contact vine canes or cordons, including clusters that will later contact cordons as they grow.