Detailing the impacts of grapevine trunk diseases will be important to continued growth of Idaho’s wine industry, researchers say.

University of Idaho plant pathology graduate student Madeline Kinnear and adviser James Woodhall, based at the UI Parma Research and Extension Center, are studying the diseases. The fungal pathogens attack the woody trunk and vine tissue of grapevines after entering through wounds such as pruning cuts. Multiple disease species may infect a single vine.

Grapevine trunk diseases are found around the world. They have caused substantial losses in California, according to a UI news release.

‘A silent killer’

The diseases are “kind of like a silent killer,” Woodhall said. “You can’t really see them, but eventually the whole plant dies over a protracted period. It may take a few years.”

The project is important “so we know what we get here and how the diseases will develop in Idaho conditions.”

Kinnear has taken samples from sick grapevines at several area vineyards, isolating and cultivating the fungi they contain to diagnose which trunk diseases are present.

The project also entails inoculating vines with those fungi, in a greenhouse, to assess which trunk disease species are most aggressive, which may be innocuous and whether certain grape varieties are more or less susceptible.

Kinnear and Woodhall intend to develop assays for the rapid detection of the most economically important trunk diseases they identify. They plan to trap spores throughout growing seasons to pair with weather data; the findings are to be included in modeling used in management guidance.

Sampling vineyards

Kinnear visited 10 vineyards and took samples from 80 individual grapevines that showed signs of decline potentially associated with trunk diseases. A wide variety of diseases, including three of the industry’s top four of concern, was found in cold and warm environments, according to UI.

She grew cultures of about 200 fungi species, 16 of which appear to be pathogenic. Ten were confirmed as known trunk diseases. The rest either affect roots or have not been associated with losses in grape production.

Two of the species Kinnear isolated from several locations in southern Idaho are known to cause problems for grape growers in the Middle East but had not been confirmed in the U.S. previously.

In the fall, she started inoculating grapevine cuttings with many of the trunk disease strains she has isolated to help determine which are most aggressive and pathogenic.

During surveys, the UI researchers have isolated Trichoderma, a genus fungus that has been used for bio control. Rather than using general strains supplied by biological chemical companies, they plan to evaluate local strains that may be more active against trunk diseases.

A final component of the project will involve working with Oregon State University researchers to find better biological control options for combatting trunk diseases.

The project started in July 2022 with a $100,000 grant from the Northwest Center for Small Fruits Research. The UI researchers’ efforts to develop testing assays and best practices have been funded with a $90,000 USDA Specialty Crop Block Grant through the Idaho State Department of Agriculture.