Technical Yearbook 2024

Blackening at the base of the shoot is associated with Phomopsis cane and leaf spot. These shoots become brittle and may break, especially if the wind blows.

according to manufacturers’ guidelines, fungicides provided excellent Phomopsis cane and leaf spot control. Key conclusions from the results Diaporthe ampelina is the causal organism of Phomopsis cane and leaf spot and bleached canes. It is found exclusively on grapevines. While other Diaporthe species have been identified in South African grapevines, they are linked to Phomopsis dieback, a different manifestation of the disease. This form most likely infects pruning wounds, leading to internal necrosis. Effective Phomopsis dieback management involves pruning wound protectants to prevent these infections. Commercially available fungicides effectively control Phomopsis cane and leaf spot in vineyards. However, they must be used as part of a preventative spray program and according to manufacturers’ guidelines. Diaporthe life cycle and disease spread Diaporthe ampelina overwinters in pycnidia (flask-shaped fruiting bodies) on canes, spurs, petioles and other dead or diseased grapevine parts. During wet conditions, spores are released from mature pycnidia and spread via rainwater to shoots or other susceptible tissues, leading to new infections. Bleached canes are formed when pycnidia, produced in abundance on these infected shoots, push through the cane surface, allowing air to enter. Practical recommendations for the industry Sanitation practices Remove pruning debris from vineyards, especially bleached canes that harbour Diaporthe fruiting bodies, to reduce

inoculum levels. Alternatively, chip the debris finely and incorporate it into the soil. Management of alternative hosts Remove dead wood to extend sanitation practices to surrounding woody hosts. This will help prevent Diaporthe species from infecting grapevines and causing Phomopsis dieback. Fungicide application Apply registered fungicides against Phomopsis cane and leaf spot as recommended, especially if it frequently rains during bud break and the early growth stages in spring. Pruning wound protection Treat Phomopsis dieback as a grapevine trunk pathogen, with pruning wound protection as a key, integrated strategy.

Conclusion The research highlights the critical need for

ongoing surveillance, effective sanitation practices, and the correct use of appropriate fungicides to manage Phomopsis in Western Cape vineyards. By understanding the specific Diaporthe species involved and their pathogenicity, vineyard managers can implement more targeted and effective control measures, ensuring the health and productivity of their vineyards. 

Reference https://www.wineland.co.za/understanding-and-controlling-phomopsis-streepvlek-in-western-cape-vineyards/

For more information, contact Francois Halleen at fhalleen@villacrop.co.za.

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TECHNICAL YEARBOOK 2024