This project will aid Botrytis bunch rot management by improving our understanding of how and where Botrytis bunch rot disease epidemics start and progress. First, it will identify when inoculum is available and infects fruit to optimize disease management practices. Second, it will determine the extent of fungicide resistance in Oregon vineyards to mitigate the further spread of resistant populations. Together, the results from this project will allow Oregon grape growers to make better-informed integrative pest management decisions to control bunch rot.
- Characterize fungicide tolerance of Botrytis isolates from vineyards
- Monitor potential sources of inoculum in and around vineyards.
- Monitor inoculum levels throughout the growing season.
Importance to the Oregon wine community
Grape bunch rot (Botrytis spp.) is an important grape pathogen that can greatly affect crop quality. This causes to vineyards with bunch rot issues to rely heavily on fungicide applications, which in turn, increases the risk of fungicide tolerance emergence. The outcome from the project will improve on how bunch rot is controlled to manage and mitigate the development of fungicide resistance. To achieve this outcome, we need to advance our understanding of Botrytis epidemiology. Combining this with a survey of fungicide tolerance of Botrytis will allow for the development rational mitigation approaches to managing disease pressure and fungicide tolerant populations of Botrytis.
Walt Mahaffee, Research Plant Pathologist in the Horticultural Crops Disease and Pest Management Research Unit at the USDA-ARS, and Alexander Wong, Graduate Research Assistant at Oregon State University Department of Botany and Plant Pathology, are the principal investigators on the project. Cooperators include Virginia Stockwell, Research Plant Pathologist in the Horticultural Crops Disease and Pest Management Research Unit at the USDA-ARS, and Rachel Naegele, Research Geneticist, USDA-ARS SBBRU
2020-21: Year 1 Update
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.
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.
2021-22: Year 2 Update
In its 2021-22 fiscal year, the Oregon Wine Board of Directors granted $289,000 to researchers for six 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.
Progress so far
In 2020 and 2021, nine and eleven vineyards, respectively, in the Willamette Valley, Oregon were sampled for Botrytis from June to September. Grape clusters, vineyard floor grapevine debris (rachis), and nearby wild blackberries were collected, incubated, and visually assessed for Botrytis. Bunch rot incidence on clusters throughout the field season ranged from about 3% to over 30% in 2020 and around 1% to 11% in 2021. Botrytis incidence on vineyard floor debris in 2021 decreased as the season progressed in all but one location having greater than 75% in late April and under 25% by September. For field sites where wild blackberries were present, Botrytis on blackberry flower parts and berries was found at low levels throughout the season. Botrytis isolates generated from these grape, debris, and blackberry samples were screened for fungicide tolerance to Benomyl (FRAC 1), Iprodione (FRAC 2), Difenoconazole, Myclobutanil, Tebuconazole (FRAC 3), Boscalid, Fluopyram (FRAC 7), Cyprodinil (FRAC 9), Azoxystrobin and Trifloxystrobin (FRAC 11), Fenhexamid (FRAC 17), and Polyoxin-D (FRAC 19). There was some level of tolerance to all fungicide classes tested, with tolerance to more than one fungicide class observed in 26% of the >200 total isolates tested so far. Airborne Botrytis conidia from impaction spore traps were assessed from April to September by qPCR assays. Spore trap qPCR assays have shown that there can be surges of conidia being released during grapevine bloom when temperatures (15-25°C) and humidity (>70%) are favorable. These results taken together suggest that fungicide tolerance levels of vineyard Botrytis are of concern and should continue to be monitored, along with the seasonal and environmental changes of Botrytis inoculum to better time applications of fungicides and other integrative pest management tools.
These results indicate that botryticide modes of action should be only used once a season due to presence resistance to most current modes of action and applications should be focused around bloom, when inoculum is most prevalent, and the environment is favorable for colonization of susceptible host tissues.
The above results from 2020 and 2021 collections are available online with the qPCR results of airborne inoculum trends to be published by August 2022. The next steps of the project will be continuing to sample sites for Botrytis in 2022, characterizing isolates for fungicide tolerance, and tracking inoculum trends using qPCR assays. Results will be published online when they become available.
This project also received funding from the Northwest Center for Small Fruits Research
2023: Final Report
From 2020-2022 eleven sites from nine different vineyards in Oregon and four Washington vineyard sites were surveyed for Botrytis by sampling grape inflorescence and fruits, vineyard floor debris (prior year rachis) and nuisance blackberry. Botrytis on grape inflorescence and fruit varied from site to site and year to year likely due to yearly disease pressure differences and unique site microclimates. Amount of prior year dead grape rachis on the vineyard floor sporulating with Botrytis infestations varied from year to year but generally declined as the season progressed. Incidence of Botrytis on vineyard floor debris in all but one site in 2021 was over 75% in late April and all sites sampled decreased over time to under 25% by September. Wild nuisance blackberry flowers and fruits adjacent to the vineyard were also found to be potential sources of Botrytis inoculum throughout the season, Historical spore trap DNA samples from the Willamette Valley were re-assayed for presence of Botrytis cinerea spores and showed that Botrytis inoculum is nearly continually present in the vineyard. Increases in inoculum were correlated with the bloom to fruit set period and temperatures around 13-22°C (55-72°F). These results suggest that bunch rot risk can be reduced by focusing fungicide applications to periods before berry touch and reducing the amount of bunch trash. Single spore Botrytis isolates collected from vineyard survey samples were assayed for fungicide tolerance to Benomyl (FRAC 1), Iprodione (FRAC 2), Myclobutanil, Tebuconazole, Difenoconazole (FRAC 3), Fluopyram, Boscalid (FRAC 7), Cyprodinil (FRAC 9), Trifloxystrobin, Azoxystrobin (FRAC 11), Fludioxonil (FRAC 12), and Fenhexamid (FRAC 17). In the over one hundred isolates tested so far, there has been fungicide tolerance seen in all FRAC groups mentioned (except Fludioxonil) with multiple fungicide group tolerance seen in 10% of the isolates tested. These results indicate a fungicide group for Botrytis management should not be used more than once in season and there is possible carryover of resistant inoculum from the prior year on rachis debris. This year’s fungicide use and rotation decisions should consider what fungicide were used the previous year. All the results from 2020-2022 seasons are publicly available at http://gall-id.cgrb.oregonstate.edu:3838/grunwald/wonga4/