Keith Striegler and Tammy Jones, University of Missouri
Leaf removal in vertical shoot positioning (VSP) system (L) and in Chambourcin grapes. Photos by Andy Allen, University of Missouri.
Leaf removal is the process of removing leaves from the vine in the area around the fruit clusters, usually immediately above and immediately below the fruit. This is often called basal leaf removal on vertically shoot positioned canopies or simply cluster-zone leaf removal. Proper leaf removal can accomplish the following:
- Improve air circulation
- Increase fungicide/insecticide spray penetration
- Expose the fruit to more sunlight
- Improve flavor compounds, color, and bud fertility
- Decrease titratable acidity, pH, and potassium
- Reduce herbaceous or vegetative aromas in some cultivars
An adequate number of leaves must remain on the shoot to produce carbohydrates to support vine growth, fruit development and ripening, develop overwintering reserves and to allow vine shoot and bud winter hardiness. In many circumstances, the removal of two to three leaves around the fruiting zone is adequate to achieve proper cluster-zone leaf removal.
Achieving the desired outcomes of leaf removal will depend on timing and intensity of leaf removal as well as climate. Removal of too many leaves in warm climates can lead to sun-burned fruit. In warm grape growing regions where there is high sunlight intensity coupled with high heat, leaves are removed on the morning-sun side of the canopy and leaves remain on the afternoon-sun side. Timing is also important as the risk of sun-burned fruit is increased if the leaves are removed after veraison. Over-exposure of fruit can also lead to reduced anthocyanin production, delaying ripening and diminishing wine quality in warm climates. Maximum benefits can generally be achieved when leaf removal occurs after bloom but well before veraison. In general, more leaf removal and cluster exposure is tolerated in cool climates in comparison to warm grape growing regions.
Leaf removal can be performed manually or with mechanical leaf removers. There are a number of different makes and models of leaf removers available commercially. It is critical to time the use of mechanical leaf pullers so as not to damage flowers and/or fruit.
Recommended Resources
Ozark Mountain Vineyard Sustainability Assessment Workbook, University of Missouri
Canopy Management, North Carolina State University
Midwest Grape Production Guide, Ohio State University
Wolf, T. K. (Ed.). (2008). Wine grape production guide for eastern North America. Ithaca, New York: NRAES.
Reviewed by Patty Skinkis, Oregon State University and Jim Wolpert, UC Davis