Andrew Harner, Assistant Professor of Viticulture and Extension Specialist, Virginia Tech

Grape producers, like many other specialty fruit crop growers, face a range of challenging environmental conditions during the growing and dormant seasons. Increasingly variable conditions during the wintertime and spring have increased the risk of crop loss, while warmer, wetter growing seasons are intensifying disease pressure and leading to advanced phenological development and ripening. It’s important to understand how this variability impacts grapevine biology and fruit chemical composition and how common management practices influence these interactions. As an Assistant Professor in Viticulture and extension specialist at Virginia Tech, it is my goal to assess how vine physiology and grape chemistry is influenced by management practices, grape genotype, and environmental conditions so that growers can tailor the practices they implement to their specific production goals and produce quality fruit.

A small group of Vitis vinifera cultivars comprise the bulk of wine grape production in the U.S., including in Virginia, but there is increasing interest in newly released and older interspecific Vitis cultivars. These cultivars typically have greater resistance to major grapevine pathogens like downy and powdery mildew than V. vinifera,largely due to the inclusion of various North American Vitis species within their parentage that are more tolerant of these diseases. Breeding of interspecific Vitis hybrids is not a new phenomenon, but the increasing interest in low impact farming methods and increasing regulatory oversight of fungicides and other chemicals commonly used in grape and other fruit systems is spurring both the release and planting of novel cultivars. However, many of these genotypes have not been rigorously tested under variable field conditions and little is known about the optimal management practices and their grape and wine chemical composition. This is something that I hope to directly address.

Here, at the Alson H. Smith, Jr., AREC in Winchester, VA, we have a variety trial planted out to a mixture of novel V. vinifera cultivars and interspecific hybrids, with varying degrees of fungal (downy mildew, powdery mildew) or bacterial (Pierce’s disease, caused by Xylella fastidiosa) resistance. To streamline the field trialing of novel material and concurrently evaluate best-practices, we initiated a small fruit-zone leaf removal study on four white-fruited cultivars (Itasca, Soreli, Fleurtai, and Petra). Fruit-zone leaf removal is an intentional defoliation practice commonly implemented to reduce disease prevalence, improve spray efficacy, and alter fruit chemical composition. We subjected vines to either no leaf removal (control), to truly test their disease resistance potential, leaf removal performed on the east side, or leaf removal performed on both the east and west side (Figure 1). Over the next few years, we will assess the performance of these vines and the fruit composition, with a particular focus on linking variation in fruit-zone microclimate with juice volatile composition, a long-standing research interest of mine.

Control (no leaf removal)
East side leaf removal
East + west side leaf removal

Figure 1. Examples of leaf removal treatments applied to Fleurtai grapevines at fruit-set in June 2024.

Aside from testing novel genotypes and viticultural practices, a major component of my planned work will involve assessing the ecophysiological responses of commonly planted grapevine cultivars to both biotic and abiotic stressors. The goal of this work is to eventually develop recommendations for their mitigation in conjunction with our pathology and entomology personnel at Virginia Tech, including Drs. Mizuho Nita and Doug Pfeiffer. In the short-term this will chiefly focus on the Spotted lanternfly (SLF), a Fulgorid planthopper species introduced to the U.S. in 2014, given its increasing presence in Virginia. While we know from past and ongoing work at Penn State University led by Drs. Michela Centinari and Flor Acevedo that sustained exposure to SLF sap-feeding can negatively impact carbon assimilation and storage, reduce grape ripeness, and impair color development in red-fruited cultivars, there is much we do not know. Planned experiments for this season will investigate the impacts of SLF sap-feeding on various aspects of photosynthesis across the grapevine canopy (Figure 2) and how SLF influences macro- and micronutrient concentrations and partitioning between different vine organs in interspecific hybrid varieties.

A CIRAS-4 portable gas exchange unit with a chlorophyll fluorescence module that will be used for measurement of foliar photosynthesis and chlorophyll fluorescence in projects involving grapevine response to Spotted lanternfly and other biotic and abiotic stressors.

Figure 2. A CIRAS-4 portable gas exchange unit with a chlorophyll fluorescence module that will be used for measurement of foliar photosynthesis and chlorophyll fluorescence in projects involving grapevine response to Spotted lanternfly and other biotic and abiotic stressors.

Over the next few years, I plan to play an active role in efforts investigating SLF’s impacts on grapevines and fruit/wine chemistry and developing targeted management methods, as part of multiple partnerships with Virginia Tech faculty and neighboring land-grant and federal institutions, including Penn State University, the USDA-ARS, Cornell University, and others. I hope to use this as a foundation to eventually explore other grapevine-pest and -pathogen systems relevant to Virginia and the Southern U.S., including grape root borer and Xylella fastidiosa, among others. Ultimately, my aim is to have my program contribute to improved knowledge of the physiological, biochemical, and anatomical traits that can influence cultivar-specific responses to different stresses and robustly assess how these interactions impact grapevine production parameters and fruit and wine chemistry. I am eager to continue familiarizing myself with the Virginia grape and wine industries and begin traveling throughout the southern region to learn more about its diverse fruit crop systems and the challenges that they face. I can always be reached via my email (dharner@vt.edu) or phone (540-232-6050) for any questions or suggestions, and I plan to keep my lab website updated with recent research and extension developments as my program develops.

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