Video presents results of Riesling early leaf removal

Learn results on Riesling with cluster zone leaf removal around bloom to reduce fruit set and consequently reduce cluster compactness.

Video presents results of Riesling early leaf removal

Viticulture in Michigan is limited by a cool and humid climate, often evidenced by harvest season cluster-rot, poor ripening and reduced technological maturity for economically important wine grape varieties characterized by the compactness of the berries held on the cluster rachis. Thanks to funding from the Michigan Grape and Wine Industry Council, growers can watch a short video on “Leaf removal: A tool to improve crop control and fruit quality in vinifera grapes.” This video presents results on Riesling (the most-planted white wine variety in Michigan) on cluster zone leaf removal around bloom to reduce fruit set and consequently produce a controlled reduction in cluster compactness, improving fruit technological maturity and harvest and reducing bunch rot.

The defoliation treatments were effective in reducing the bunch size, consistently showing a reduced number of berries when compared to the control. The removal of six basal nodes appeared to be a stress threshold above which the vines were no longer able to effectively maintain a supply of resources to the reproductive organs of the vine. The reduction of leaf area, achieved with defoliation of six basal nodes, did not significantly affect the final yield per vine, but did affect the number of bunches per vine. Early removal reduced yield per vine, and such yield reduction corresponded to an increased level of berry sugar accumulation as well as to a reduced fruit acidity.

The development of this project helped growers to better understand using a practical tool in canopy management (leaf removal) that can have a great impact on yield per vine and fruit ripening. Although manual defoliation is a time-consuming operation, the value of its positive effects in improving quality traits is fundamentally important and proved to far outweigh the initial expense by providing drastically improved quality and yield. The positive impact on the formation of looser clusters is also important, especially in wet years, which reduced the incidence of bunch rot and increased the quality of the fruit (basic fruit chemistry, color and skin/flesh ratio).

Early leaf removal proved to be a valid technique for reducing crop, improving fruit quality and decreasing the incidence of bunch rot, taking the place of multiple fungicide applications reducing the amount of chemical sprayed on a vineyard and the labor cost associated with it.

To access “Leaf removal: A tool to improve crop control and fruit quality in vinifera grapes” and other wine grape research videos on a variety of topics, go to the Michigan State University Extension Grapes Research page.

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