Effects of yield regulation practices on grapevine productivity, health, and economic sustainability

Effects of yield regulation practices on grapevine productivity, health, and economic sustainability

Summary

The overall goal of this project is to research the use of early leaf removal for performance in yield regulation in Vitis vinifera L. ‘Grüner Veltliner’, an overcropping wine grape variety extensively grown in Pennsylvania.  In this study, we proposed to compare early leaf removal at two different phenological stages (trace-bloom and fruit-set) against traditional cluster thinning and un-thinned and non-defoliated control treatments to assess the role of each practice on yield regulation, vine response to carbon assimilation and storage, winter injury, bud fruitfulness in the year following treatment, and berry quality.  We additionally proposed to evaluate the economic costs and price increases per 750 mL bottle associated with each yield regulation tactic.   

Objectives/Performance Targets

Our project had 4 main objectives outlined in the original proposal:

1. To conduct a field trial to assess and compare the effects of cluster thinning (CT) and early leaf removal (ELR) on vegetative growth, yield components, Botrytis bunch rot infections, cluster compactness, bud fruitfulness, and fruit composition.
2. To assess the impact of CT and ELR on parameters associated with vine susceptibility to winter injury, including single-leaf net carbon assimilation, bud and cane cold hardiness, and carbohydrate reserve storage.
3. To perform an economic analysis that estimates the additional price per tonne of fruit and cost per 750 mL bottle of wine needed to maintain grower economic welfare, if CT and ELR practices were adopted compared to if they were not.
4. To provide recommendations to stakeholders for managing high-yielding wine grape varieties for optimal fruit composition and vine health.

Towards our objectives, we properly implemented each canopy management tactic at the appropriate time during the 2016 growing season, and collected much of the necessary data to fulfill our first three objectives.  We are continuing to collect data on winter tissue cold hardiness, having begun our monthly sample collection in November 2016. 

For our fourth objective, I am currently scheduled to present at the Mid-Atlantic Fruit and Vegetable Convention in February 2017 on crop load management practices, as well as present results from 2015-2016 on this project at the Pennsylvania Wine Marketing and Research Board Symposium in March 2017. 

Accomplishments/Milestones

In addition to our data collected from the 2015 growing season, we have successfully applied each of our four field treatments during the summer of 2016 and collected data on:

• Leaf area (vegetative growth)
• Single leaf gas exchange (net carbon assimilation)
• Botrytis rot severity and cluster compactness
• Yields at harvest
• Treatment application times for economic impact assessment

We are currently working towards obtaining data on fruit-set, berry chemical quality, and winter bud cold hardiness.  We will continue collecting bud cold hardiness data through the winter of 2017, as well as work with our grower-collaborator to plan for collecting pruning weight and 2017 bud fruitfulness data as the appropriate time approaches.  Across October and November, we have been working to establish a protocol for carbohydrate extraction and quantification from wood tissue.   We have successfully established detection and quantities of vine storage carbohydrates using liquid chromatography-mass spectroscopy (LC-MS) technology.  Over the coming winter and spring 2017, we plan to begin analyzing our tissue samples for carbohydrate content, continue our winter data collection, and obtain statistical analyses of our collected data from 2016.   

Our project has, for the most part, proceeded as expected.  We have learned that the second season of field work always goes easier than the first season. We have determined ways to make much of our data collection more efficient, and having experience with the equipment and protocols makes for an overall smoother field season.  I, personally, have learned a great deal about two things over the course of the past season:  1) An experiential understanding of our vineyard system and the growth habits of the vines at that site that has improved my ability to manage the vines and 2) Analytical chemistry skills in order to continue progress on quantifying carbohydrates. 

Carbohydrates quantification has been the largest change that has occurred from our original proposed project.  In our attempts to quantify carbohydrates using high-performance liquid chromatography, we realized that the detector that we had planned to use was not sensitive enough for the quantity of material we were trying to detect.  We have since decided to utilize the services provided by the Penn State Metabolomics Center to use LC-MS for our carbohydrates analysis.    

Impacts and Contributions/Outcomes

Our project to date has shown that early leaf removal, especially when performed at trace-bloom, has the potential to reduce yield levels in wine grapes similar to the reduction achieved through traditional cluster thinning.  This project has contributed to sustainability through collecting relevant data that provides evidence for the use of yield regulation in order to achieve optimal vine health and berry quality while improving cost effectiveness for growers.  We hope that our conclusions can influence grower decisions for choosing canopy management practices that best fit their site and vine variety.  In addition to giving presentations at grower meetings and extension events, this data will be presented to academic stakeholders at the American Society of Enology and Viticulture conference, and we plan to pursue peer-reviewed publication for our data at the completion of this project.  Additionally, information on yield regulation will be provided to growers through online publication through our extension blog.

Collaborators: