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Early defoliation of Great Lakes wine grapes tested

Date:
December 12, 2011
Source:
American Society for Horticultural Science
Summary:
Economically significant varieties of wine grapes in eastern North America can be susceptible to harvest season cluster rot. Researchers designed experiments to determine whether leaf removal or a temporary reduction in carbon assimilation at the beginning of bloom would reduce fruit set and cluster compactness. Vines subjected to removal of four or six basal leaves had an average fruit set reduction of 45 percent from the control. Cluster weight and berries per cluster were similarly reduced.
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Wine grape production in the Great Lakes Viticultural Region can be a challenging enterprise. Spring frost, winter injury, short and variable growing seasons, and cool, humid growing conditions subject grape vines to disease, including harvest season cluster rot. Tight-clustered wine grape varieties in the region show varying susceptibility to cluster rot; cultivars such as Pinot gris, Pinot noir, Riesling, Seyval, and Vignoles are all susceptible, making it difficult to achieve maximum fruit maturity for these economically important varieties.

Leaf removal in the fruiting zone has been used successfully as a vineyard management practice during the summer season. When used on high-density canopies, leaf removal techniques improve clusters' microclimate, reducing conditions that can cause bunch rot complex diseases and improving fruit quality. However, leaf removal can also affect fruit quality negatively. Excessive leaf removal can lead to overexposed clusters (high light intensity and high temperature) and reduced berry color in red cultivars. Moreover, the effects of leaf removal on yield vary depending on timing and severity.

Paolo Sabbatini and G. Stanley Howell from the Department of Horticulture at Michigan State University conducted experiments to determine whether early leaf removal influences vine performance, or if non-destructive, short-term photosynthesis reduction at the beginning of bloom would influence vine performance in a manner similar to leaf removal. The experiments were conducted at the Horticulture Teaching Research Center in East Lansing and the Southwest Michigan Research and Extension Center in Benton Harbor, Michigan. The research findings were published in HortScience.

Fruit set reduction resulting from early leaf removal, in all the cultivars except Pinot noir, confirmed the importance of carbohydrate supply during the fruit set period. Vines subjected to removal of four or six basal leaves had an average fruit set reduction of approximately 45% from a non-treated control. "Cluster weight and berries per cluster were similarly reduced with a greater effect on the basal than the apical cluster of the shoot. Reduced fruit set was associated with a reduction in cluster compactness and harvest season rot," said Sabbatini. "This was also reflected in yield and basic fruit chemistry parameters associated with the importance of basal leaves to the developing cluster."

The experiments showed a strong negative effect of early leaf removal in year one of the study on vine performance in year two. This "carryover effect" increased shootless nodes per vine, reduced the number of clusters per shoot and per vine, and dramatically reduced fruit set and yield per vine.

"From our data, we cannot assess whether this carryover is related to reduced bud cold hardiness or bud damage resulting from the leaf removal practice," the researchers added. "Unless these negative carryover responses can be ameliorated, this approach to reduce cluster compactness and cluster rot will not be acceptable. We speculate that this could be readily accommodated through retaining non-fruiting shoots at the head with all leaves retained that serve as canes to be retained for production in the next year."


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The above post is reprinted from materials provided by American Society for Horticultural Science. Note: Materials may be edited for content and length.


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American Society for Horticultural Science. "Early defoliation of Great Lakes wine grapes tested." ScienceDaily. ScienceDaily, 12 December 2011. <www.sciencedaily.com/releases/2011/12/111212124553.htm>.
American Society for Horticultural Science. (2011, December 12). Early defoliation of Great Lakes wine grapes tested. ScienceDaily. Retrieved September 1, 2015 from www.sciencedaily.com/releases/2011/12/111212124553.htm
American Society for Horticultural Science. "Early defoliation of Great Lakes wine grapes tested." ScienceDaily. www.sciencedaily.com/releases/2011/12/111212124553.htm (accessed September 1, 2015).

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