Plant growth regulators (PGRs) are powerful tools that can dramatically influence vine performance, but they also come with complexity and risk. In this episode, Fritz welcomes back Dr. Matthew W. Fidelibus of UC Davis to explore how these compounds are used across table, raisin, and wine grape production. Dr. Fidelibus explains that PGRs include both naturally occurring plant hormones and synthetic compounds that mimic hormonal effects. While they've long been foundational in table grape production, their use in winegrapes is far less common and more nuanced. The conversation highlights how sensitivity to timing, rate, and variety is critical, with even small misapplications potentially affecting fruit set, bud development, or yields across multiple seasons. Fritz and Dr. Fidelibus dig into specific compounds like gibberellic acid, abscisic acid, and ethephon, discussing how they can influence berry size, cluster architecture, color development, and ripening. They also explore emerging research on improving color in virus-affected vineyards, delaying ripening in warm climates, and even modifying aroma profiles. A key takeaway is that PGRs are not a one-size-fits-all solution. They require careful evaluation, regulatory compliance, and, ideally, small-scale trials before broader use. For growers facing challenges like poor fruit set, uneven ripening, or compact clusters, these tools may offer targeted solutions — but only when used with precision and a strong understanding of vine physiology. Listeners will walk away with a clearer understanding of both the potential and the pitfalls of incorporating PGRs into vineyard management. In this episode, you will hear: Overview of plant growth regulators and how they influence vine physiology Historical use of PGRs in table and raisin grape production Key compounds like gibberellic acid, abscisic acid, and ethephon Applications for cluster thinning, berry sizing, and color development Challenges and risks of using PGRs in winegrapes Emerging research, including virus mitigation and ripening control Follow and Review: If you enjoyed this episode, be sure to follow the podcast and leave a 5-star review on Apple Podcasts! Your support helps us reach more listeners. 💜 Click the '+' in the top right corner of Apple Podcasts to follow now. Resources: Come grow with Fritz through https://www.virtualviticultureacademy.com! Save $75 off your first year of membership with the code Underground at checkout. Have a vineyard question? Go to VineyardUndergroundPodcast.com and click the Ask Fritz button. Today's Guest: Dr. Matthew W. Fidelibus is an extension specialist in the Department of Viticulture and Enology, UC Davis. Connect with Matthew and view his research – https://wineserver.ucdavis.edu/people/matthew-fidelibus#/ or follow him at https://bsky.app/profile/viticulture.bsky.social Episode Sponsor: Today's episode was brought to you by Clemens Technologies and SensorInsight. Thank you to Clemens Technologies for sponsoring today's episode. Clemens Technologies is the market leader in machinery for all elements of vineyard management. Visit https://www.clemens-online.com/us/ and provide the code UNDERGROUND to receive 5% off your order of in-stock machinery. Or reach out to Thomas Clemens directly at thomas@clemens-america.com with any questions. Thank you to SensorInsight for sponsoring today's episode. SensorInsight is a leader in vineyard soil moisture and weather monitoring. SensorInsight designs state-of-the-art, remote satellite monitoring of soil moisture and weather, bringing actionable information for your vineyard operations straight to your phone, with real-time data so you can best decide when to turn on your irrigation, how long to run the system, and learn how the dynamics of soil moisture can change over a given season. Visit them today at https://sensorinsight.io. And don't forget to mention the code Underground to receive a discount on your SensorInsight solution. Episode Credits If you like this podcast and are thinking of creating your own, consider talking to my producer, Emerald City Productions. They helped me grow and produce the podcast you are listening to right now. Find out more at https://emeraldcitypro.com. Let them know we sent you.
