Assessing Grapevine Leafroll Disease Impact in Commercial Vineyards throughout Pennsylvania
Open Access
- Author:
- Varaksa Jr, Alexander
- Graduate Program:
- Plant Pathology
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- February 15, 2022
- Committee Members:
- Carolee Bull, Program Head/Chair
Cristina Rosa, Thesis Advisor/Co-Advisor
Paul David Esker, Committee Member
Michela Centinari, Thesis Advisor/Co-Advisor
Beth Krueger Gugino, Committee Member
Richard P Marini, Committee Member
Flor E Acevedo, Committee Member - Keywords:
- grapevine leafroll disease
GLD
grapevines
Cabernet Franc
vineyards
virus
impact
yield
juice chemistry
growth
weather - Abstract:
- Grapevine leafroll disease (GLD) is an economically damaging viral disease of grapevine that is negatively impacting the wine industry by reducing yields and delaying fruit ripening. Recent studies have indicated that GLD presence has been identified in the northeast U.S. Unfortunately, little information is known on GLD presence and spread in Pennsylvania, the impacts of GLD, and how to properly manage it. GLD impact has been shown to be variable as well, where different factors such as the environment, cultivar, rootstock, virus species, or mixed infection can play a role in disease severity. Additionally, the spread and impact of GLD over time is not well understood, suggesting a need for multi-location and multi-year studies. The goal of this research was to determine GLD spread over time in four vineyards located in different climatic regions in Pennsylvania, determine GLD impact in each location over several years, and correlate disease impact with site-specific weather conditions, which would provide useful information for future GLD studies and for growers. This thesis has three main objectives, and each objective is addressed in a separate chapter of the thesis. The first chapter focuses on identifying GLD presence and spread within four commercial vineyards located in regions with considerable weather variability across Pennsylvania. Within the first chapter, vineyard blocks were tested for GLD each year to determine if the disease was spreading from year to year. Vector scouting was conducted to determine if mealybug vectors are present in the vineyards, which would indicate that disease can continue to spread. I hypothesized that disease spread would occur within vineyards if mealybug vectors were found. At this current time, no mealybug management or scouting practices are conducted in any of the vineyards by growers. The second objective of this thesis was to determine disease impact on vine vegetative growth, production, and fruit quality over the span of three years by evaluating GLD effects at four commercial vineyards and comparing within and across seasons. In Pennsylvania, growers have little to no information regarding the effect of GLD on vine parameters. Through this objective, I identified if vine production and fruit quality differences between healthy and GLD infected vines were consistent or varied across years and regions, and if the results can impact a grower’s production. I hypothesized that GLD-infected vines will have lower yields by having lower cluster weights, reduced pruning weights, and will be less cold hardy due to the viruses’ impact on carbohydrate assimilation and storage in the vines. I also hypothesized that fruit from infected vines will have lower total soluble solids (TSS) and higher titratable acidity (TA) at harvest due to delayed vine maturity caused by GLD. Additionally, GLD impact will vary across sites and regions, as differences in weather conditions may play a role in disease effects. The third objective of this thesis was to identify the influence of weather parameters on GLD impacts on infected vines compared to uninfected. This objective focused on two common weather parameters that heavily influence vine growth, productivity and fruit quality, rainfall and growing degree days (GDD) measured each season at the four commercial vineyards. This objective could help identify if the severity of GLD’s effects on vines vary with seasonal weather conditions (e.g., lower or higher seasonal temperatures). For this objective, I hypothesized that the effect of weather will differ in GLD-infected vines when compared to non-infected vines. Differences between GLD-infected and non-infected vines will be more relevant under unfavorable conditions (i.e., more rainfall, less heat accumulation) for berry development and ripening in the northeastern US. However, GLD-infected vines in areas or seasons with higher GDD and less rainfall might be able to assimilate enough carbon to properly ripen the fruit, leading to similar trends in GLD-infected and non-infected vines. Results from this research can provide useful information for incorporating weather conditions into GLD impact studies that allows for GLD effect correlation with weather. My findings also show the importance of conducting GLD research in several locations over longer periods of time to get proper assessments of GLD effect. Showing that GLD impact is site-dependent would be useful in developing proper management strategies for growers based on the effects in their vineyards.