Can you spot the trunk disease on this infected grapevine?

A grapevine trunk cross section with trunk diseases,
though the typical symptoms are barely visible.
Photo: Annie Klodd

The photo below shows a cross section of a Marquette grapevine trunk. Looking at this photo, would you think that there was anything wrong with it? As it turns out, this grapevine has five different trunk diseases responsible for grapevine decline including "dead arm," Esca, and Eutypa, revealed by expert laboratory analysis.

Often in online resources, plant diseases are demonstrated in photos that clearly show the symptoms. This is so that farmers can accurately identify them out in the field with as little ambiguity as possible. However, sometimes diseases can be present even if the tell-tale symptoms are not yet visible, such as in this example.

The Marquette grapevine pictured was not producing well in 2018 and parts of its cordons had begun to die. We were curious whether this declining grapevine was infected with grapevine trunk diseases, which are known to cause vine decline and loss of productivity. Cutting into the vine, it was hard to see any classic symptoms of trunk disease, like brown pie slice shaped cankers and brown or yellow markings inside the wood.

Of course, we still sent the sample in to the diagnostic lab to learn more. We wanted to demonstrate that grapevine trunk diseases can be present even without obviously presenting themselves. Sure enough, the results came back showing five different trunk disease species in the wood, along with the common bunch rot-causing fungus Botrytis. We are aware of the presence of trunk disease-causing pathogens in Minnesota vineyards, and we hope to determine how widespread they are and how much they are contributing to grapevine decline.

If grapevines are declining and showing dead cordons and trunks, the best practice is to remove that dead wood and re-train new cordons and trunks from healthy shoots or suckers, respectively. This will interrupt the spread of any potential trunk diseases present and increase the productivity and health of the vine.

Pending grant funding, we hope to sample vines throughout Minnesota in 2019 and 2020, to learn how widespread grapevine trunk diseases are and how much they are contributing to grapevine decline. We will also be developing region-specific recommendations for managing grapevine trunk diseases that are most appropriate for our cold climate. Currently, most recommendations were developed in warmer climates and need to be adapted for Minnesota's climate and varieties. To learn more about grapevine trunk disease, please see: http://treeandvinetrunkdiseases.org/

Author: Annie Klodd, Extension Educator-Fruit and Vegetable Production. Kloddann@umn.edu