EAST LANSING, Mich. — Sour rots can be an issue for grape growers at harvest time, but they can also be challenging to manage. A team at Cornell University has just released a “Research Focus” report that highlights results from the last four years of studies led by graduate student Megan Hall working with Wayne Wilcox and Greg Loeb on the disease and insect components of this complex. Full details can be seen in Defining and Developing Strategies for Managing Sour Rot.
The article provides some key management concepts from their research including:
- Inoculation with microbes found in rotten berries was not sufficient to produce sour rot symptoms.
- Sour rot symptoms developed only when Drosophila fruit flies were added to experimental inoculations.
- Field spray trials over three years with antimicrobials targeting the yeast and bacteria alone provided modest reductions in sour rot severity.
- Including insecticides targeting Drosophila fruit flies dramatically reduced sour rot severity.
- High cordon-trained Vignoles had higher severity of sour rot than midwire cordon-trained vines with vertical shoot positioning in 2014, 2015 and 2016.
They summarize the article by highlighting that management of sour rot involves controlling both the microbes and the Drosophila fruit flies. Here in Michigan we have variable risk of sour rot in different growing seasons, and we have both the native fruit flies and the invasive spotted wing Drosophila. Both types of flies can play a role in moving sour rot pathogens between berries and enhancing the level of infection. In our work in Michigan, we have seen higher sour rot levels in vineyards where there are also more vinegar flies, so we expect these results to be applicable to helping manage sour rot in Michigan vineyards too.
— Rufus Isaacs, Michigan State University Extension, Department of Entomology
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