In its 2020-21 fiscal year, the Oregon Wine Board of Directors granted $350,000 to researchers for eight projects with the potential to advance quality grape growing and winemaking in Oregon. The update below is part of a series to let industry members know about the status of these projects.
Dr. Walt Mahaffee is a research plant pathologist with the USDA-Agricultural Research Service. He is also a courtesy faculty member with the Department of Botany and Plant Pathology and a core member of Oregon Wine Research Institute at Oregon State University. He is the principal investigator on the project detailed below.
Alexander Wong, graduate research assistant in the Department of Botany and Plant Pathology, has prepared the update below. Cooperators include Dr. Virginia Stockwell, USDA-ARS HCRL and Dr. Rachel Naegele, USDA-ARS SBBRU.
This project also receives funding from the Northwest Center for Small Fruits Research.
Botrytis bunch rot: Who, where, when, and what to use
This project will aid Botrytis bunch rot management by improving our understanding of how and where Botrytis bunch rot disease epidemics start and progress. This study is evaluating the degree of fungicide resistance and the pathogen inoculum sources and spread in vineyards, and how these factors impact disease management practices. The results will be used to develop new integrative pest management programs to reduce and manage the amount of Botrytis and, in turn, delay the development of fungicide-resistant populations.
Our objectives are to:
- Collect and identify Botrytis isolates from vineyards and characterize their resistance to a variety of fungicide classes;
- Monitor bunch rot disease in vineyards to evaluate where and how Botrytis populations originate and change throughout the growing season; and
- Monitor inoculum levels throughout the growing season.
Importance to the Oregon wine community:
Bunch rot in grapes is a significant threat to wine and juice grape production and is mainly controlled using fungicides, which leads to concerns about fungicide resistance emergence. There is also interest in improving identification of where and when Botrytis epidemics start in order to optimize timing of fungicide applications.
Progress so far:
In the 2020 field season, nine field sites from eight different vineyards (seven commercial vineyards and one research vineyard) in the Willamette Valley were sampled for Botrytis from June to September. Grape clusters, vineyard floor debris, and nearby wild blackberries were collected, incubated, and then visually accessed for Botrytis.
Botrytis incidence on clusters over the field season ranged from about 3% to over 30%. Botrytis isolates generated were screened for fungicide resistance. Some level of tolerance was seen in all fungicide classes among isolates, with tolerance to more than one fungicide class observed in 22% of the isolates.
Monitoring for sources of inoculum was done by sampling dead grape rachis and cane tissue from vineyard floors and wild blackberries adjacent to the vineyards. Presence of inoculum on vineyard floor debris decreased as the season progressed, but for field sites with wild blackberries, Botrytis on blackberry flower parts and berries was found throughout the season and at one site increased dramatically near harvest after a significant rainfall.
These results suggest that vineyard Botrytis resistance levels are of concern and should be continued to be monitored along with the changes of Botrytis inoculum to better time applications of fungicides and other integrative pest management tools.
In 2021 we will continue to monitor Botrytis inoculum and bunch rot disease at the same sites as 2020, starting at bud break through harvest to capture a larger window of when inoculum is being produced. The fungicide tolerance assay testing will expand to testing more chemistries against isolates collected from 2020 and 2021. We are preparing to utilize a quantitative polymerase chain reaction to quantify the amount of airborne Botrytis inoculum that could have been collected from spore trapping for powdery mildew samples dating back over a decade.