Mississippi study finds one trellis system lifts yields for several hybrid grape cultivars

Researchers and extension specialists at the American Society for Enology and Viticulture’s national conference on Thursday outlined new findings and practical guidance that could affect how U.S. vineyards are planted, managed and regulated, from trellis design in Mississippi to federal pesticide labeling changes and training aimed at slowing fungicide resistance.

The session, held from 3:45 p.m. to 4:45 p.m. in Grand Ballroom 100B, brought together work from Mississippi State University, Penn State Extension and the University of California Cooperative Extension.

Haley Williams of Mississippi State University presented results from a study comparing high wire bilateral cordon, or HWBC, with vertical shoot-positioning, or VSP, in six interspecific hybrid bunch grape cultivars grown at the Mississippi Agricultural and Forestry Experiment Station’s South Mississippi Branch in Poplarville. The cultivars were Ambulo blanc, Black Spanish, Lomanto, Mamont noir, MidSouth and Victoria Red.

The study used fruit harvested in 2024 and 2025 and measured yield per hectare and per vine, cluster and berry weights, clusters per vine, berries per cluster, total soluble solids, titratable acidity and juice pH. According to the research team, significant cultivar-by-trellis interactions appeared across all yield components, while fruit quality differences were driven mainly by cultivar.

Black Spanish, Lomanto and MidSouth produced higher yields on HWBC. Black Spanish and Victoria Red also showed greater cluster weights under that system. Berry weight was higher on HWBC for Ambulo blanc but higher on VSP for MidSouth. Lomanto, Mamont noir and MidSouth had more clusters per vine on HWBC, while Black Spanish had more berries per cluster on HWBC.

Across cultivars, Black Spanish, Victoria Red and Ambulo blanc recorded the highest total soluble solids. Black Spanish had higher titratable acidity than all but MidSouth, while Victoria Red and Ambulo blanc had the highest juice pH. The researchers said trellis type showed no apparent effect on fruit quality in this trial, but HWBC may be better suited to maximizing yield in these cultivars.

That finding could matter beyond vineyard layout. For wine producers working with southern-adapted hybrids, trellis choice can shape crop volume without necessarily changing basic fruit composition, which may influence planting decisions and long-term supply planning.

Megan Luke of Penn State Extension focused on regulatory changes tied to Environmental Protection Agency efforts to revise pesticide labels in response to concerns about human exposure risks and environmental risks under the Endangered Species Act. She said the EPA finalized its Herbicide Strategy in 2024 and released the final Insecticide Strategy in 2025. The agency’s Fungicide Strategy is expected by 2027.

Luke described the changes as the first major shift in pesticide labeling since the Worker Protection Standards were introduced. Her presentation centered on how extension staff, growers and winery managers can prepare for compliance by understanding new label language and using EPA tools such as Bulletins Live! 2 and the Mitigation Menu website.

She said the new framework includes a points system as well as drift and runoff calculators and site-specific risk mapping. The presentation also covered examples of products commonly used in grape production that already fall under the new requirements or are expected to do so soon. Luke also addressed guidance on wastewater outflow for operations using antimicrobial products, including wineries.

For beverage producers, those changes could affect both vineyard spray programs and winery sanitation practices. Compliance demands may shape input choices, recordkeeping and water management at a time when growers are also trying to limit operational risk.

Malcolm Hobbs of the University of California Cooperative Extension presented work on fungicide resistance mitigation based on surveys and interviews conducted from 2018 through 2025 with winegrape industry professionals in California and Washington. The project examined barriers to adopting pest and disease management practices, how knowledge resources are used and where educational gaps remain.

Hobbs said the findings were used to develop and evaluate outreach activities designed to improve communication and collaboration skills, strengthen educational resources and engage social networks across the grape industry. The approach calls for equipping key educators with tools to build local peer networks, tailoring materials to specific audiences and improving interpersonal skills that support communication on industry-wide issues.

The researchers said more coordinated education could increase adoption of evidence-based practices for pest and disease management while supporting a more resilient agricultural sector. In practical terms for wine production, wider use of resistance-mitigation practices could help preserve fungicide effectiveness, support vineyard sustainability and reduce disease pressure that can affect grape quality and supply.

The Mississippi trellis study was supported by the Mississippi Agricultural and Forestry Experiment Station, the National Institute of Food and Agriculture through Hatch project accession number 440157, and the U.S. Department of Agriculture’s Agricultural Research Service under number 59-6062-6-003. Hobbs’s work was supported by the American Vineyard Foundation through grants #2023-2746 and #2024-2746 and by a Specialty Crop Research Initiative award from the U.S. Department of Agriculture’s National Institute of Food and Agriculture, award No. 2024-51181-43184. Luke said no specific funding supported her review of EPA guidelines, tools, webinars, strategies and interviews with state-level compliance staff.