AWRI Webinar: Bunch stem necrosis – causes and management
Date(s) - 29 Oct 2015
11:30 AM - 12:30 PM
The Australian Wine Research Institute
Email: [email protected]
Presenter – Bruno Holzapfel (National Wine & Grape Industry Centre)
Description – The incidence of bunch stem necrosis (BSN) showed a dramatic spike in the 2014-15 season across many Australian regions. BSN is a physiological disorder of bunches that usually becomes obvious post-veraison. It occurs at low levels in most seasons, especially in susceptible varieties such as Cabernet Sauvignon. Bunches with BSN break easily from the vine and the affected part of the bunch can dry out or drop off ahead of the harvester. In BSN-susceptible cultivars the xylem development is restricted just past each node or branch from in the peduncle (bunch stem); these restrictions create a bottle neck and prevent the flow of nutrients through to the developing berries which becomes apparent post-veraison. The large seasonal variation suggests that environmental conditions have an important role in the development of BSN. Vine and berry nutrition is another factor involved with BSN, which is potentially caused by a deficiency in calcium and/or magnesium. Most management for BSN centres on mineral nutrition. The application of calcium as a foliar fertiliser has occasionally been effective at reducing BSN symptoms; however magnesium has given far more consistent results. Normally multiple applications of magnesium Sulfate (Epsom salt) are used in the flowering and fruit set period.
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