Technical Yearbook 2024

SEPTEMBER

Leaf symptoms associated with Phomopsis cane and leaf spot.

Abstract This South African wine industry-funded study identified the causal organisms of Phomopsis cane and leaf spot and Phomopsis dieback in Western Cape vineyards. It also assessed the effectiveness of commercially available fungicides against the disease. Results from this research provide critical insights and strategies for managing Phomopsis, ensuring vineyard health and productivity. Understanding and controlling Phomopsis (‘streepvlek’) in Western Cape vineyards By Lucinda Heyns, Palesa Lebenya, Lizel Mostert & Francois Halleen

Introduction The increasing occurrence of symptoms of Phomopsis (‘streepvlek’) in Western Cape vineyards prompted the undertaking of this research project. The primary aim of this project was to identify the specific Diaporthe (= Phomopsis) species responsible for Phomopsis cane and leaf spot (‘streepvlek’) and to assess the efficacy of fungicides currently in use. The research sought to clarify the causal organisms and ensure that registered fungicides are still effective, even under favourable conditions for disease development. This article delves into the findings from the recently concluded, industry-funded research project. Objectives and methods Identification of causal species Detailed surveys were conducted in vineyards with typical ‘streepvlek’ symptoms on green shoots, bleached canes and

dieback symptoms (Phomopsis dieback). The researchers conducted the surveys in vineyards known for high incidences of ‘streepvlek’ symptoms. Each vineyard had 100 grapevines visually inspected for symptoms. During the 2016/2017 season, surveys were conducted in 36 vineyards across 18 regions, representing 33 cultivars in Western Cape vineyards. The focus was on identifying brown-black cracks that typically manifest on the basal internodes of green shoots. Subsequently, during the 2017/2018 and 2018/2019 seasons, surveys on bleached canes were carried out in 108 vineyards spanning 15 areas and 18 grape cultivars. Samples of symptomatic green shoots and bleached canes were collected for laboratory analysis. In addition to these surveys, samples were obtained from grapevine propagation material, dormant grafted nursery vines, and internal wood necrosis associated

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TECHNICAL YEARBOOK 2024