THE OCCURENCE AND CONTROL OF PHOMOPSIS SPECIES CAUSING 'STREEPVLEK' SYMPTOMS AND DIEBACK IN WESTERN CAPE VINEYARDS

Researcher: Dr. F. Halleen - 10 Jun 2016

The objective of this study is to develop a better understanding of the organisms responsible for the various symptoms associated with Phomopsis (“streepvlek”) disease, their epidemiology as well as management strategies to effectively control the disease.

Phomopsis (“streepvlek”) cane and leaf spot is a disease of economic importance, especially in certain climatic conditions. It can cause significant damage (i.e. shoots breaking) and crop loss. Clear evidence exists that the incidence of the disease is increasing. Factors that could contribute to this phenomenon include climate change (longer, wet spring) and the significant increase in the diversity of other fruit crops in close proximity to vineyards. These crops pose a threat since they can act as alternative hosts to these pathogens and serve as inoculum sources. Recent research revealed the presence of twelve Phomopsis species in grapevines of South Africa. The efficacy of fungicides against all these newly identified pathogens is unclear and could also be a reason why the occurrence of disease symptoms are observed more frequently.

However, even more important is the fact that Phomopsis species are increasingly associated with severe internal necrosis (trunk disease and wood-rotting symptoms). The disease is therefore not only cosmetic and of minor economic importance, but one of the major factors contributing to the short productive lifespan of South African vineyards.

This study will be an in-depth effort to understand the reasons behind the increase in disease symptoms and lack of control. It aims to provide clarity on the multitude of Phomopsis species associated with grapevines. Their roles and infection pathways in the grapevine trunk and the relation to the cane and leaf blight (“streepvlek”) symptoms will be investigated. The results will hopefully allow researchers to provide scientifically based guidelines to effectively control these pathogens.

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