Effects of Red-leaf Disease on Cabernet Sauvignon at the Oakville Experimental Vineyard and Mitigation by Harvest Delay and Crop Adjustment

Download or read book Effects of Red-leaf Disease on Cabernet Sauvignon at the Oakville Experimental Vineyard and Mitigation by Harvest Delay and Crop Adjustment written by Benjamin L. Calvi and published by . This book was released on 2011 with total page 77 pages. Available in PDF, EPUB and Kindle. Book excerpt: Grapevines with foliar symptoms similar to leafroll or corky bark infections, but testing negative for the presence of known grape viruses, are often referred to as having "red-leaf" disease. In 2008, a block at the Oakville Experimental Vineyard in Napa Valley, California was observed to express symptoms fitting this description. The progression of red-leaf symptoms was mapped in 2008 and 2009 identifying symptomatic and asymptomatic vines. In 2010, this study aimed, firstly, to determine if Cabernet Sauvignon grapevines with red-leaf disease also expressed delayed maturation symptoms characteristic of the above viruses, and secondly, to test if those symptoms could be mitigated by harvest delay or crop adjustment. Effects of this red-leaf disease on both vegetative and fruit components were observed. Fruit on vines with red-leaf symptoms showed reduced sugar accumulation of 2.3 Brix compared to healthy controls, and the severity of red-leaf symptoms was directly correlated to a reduction in Brix. Photosynthesis, stomatal conductance, pruning weight, berry weight, and berry anthocyanin levels were also lower in diseased vines. Reduced sugar accumulation was somewhat mitigated by delaying harvest and adjusting crop to 50%, with early thinning having a greater impact than late thinning. When imposing a desired sugar level of 25 Brix, harvest was delayed in the early thinned, late thinned, and fully cropped diseased vines by 6, 9, and 15 days, respectively. Midday leaf water potential, juice acidity, and pH were unaffected by red-leaf symptoms or mitigation treatments. A lower ratio of leaf: petiole potassium and higher berry potassium levels in diseased vines support the theory of vascular blockage at the leaf-petiole boundary, and both translocation of solutes as well as berry metabolism appear to be affected by the suspected viral pathogen.