Bunch Stem Necrosis – Also known as BSN, is a physiological disorder causing rachis and connected berries to abort. Cabernet Sauvignon and Cabernet Franc are more susceptible than other varieties to late season BSN. Exact cause of BSN is not identified, but many studies demonstrated that pathogens are not involved in BSN.
Black Rot – Guignarda bidwellii, is a fungal pathogen cause infection on leaves, berries as well as the shoots and rachis of grapevines. The leaf symptom of black rot is characterized by brown lesion with dark edges, containing dark fungal fruiting bodies. On shoots and rachis, it causes dark necrotic lesion that contains the fungal fruiting bodies. On fruit, the fugal fruiting bodies develop in a concentric “bull’s eye” pattern, and the infected berries eventually mummify. In some cases, black rot is mistaken for Phomopsis and vice versa, where infection on the rachis cause berries to drop.
Grape Cane girdler – Grape cane girdler (Ampelogylpter ater) is an insect punctures the green shoots, and the stems become prone to breakage. Tissue above the girdle will die eventually.
Mechanical breakage- damage to rachis may cause portions of cluster to shrivel and mummify