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Performance of prebloom leaf removal for the control of Botrytis bunch rot of grapes in Pennsylvania.
B. HED (1), H. Ngugi (2). (1) Lake Erie Regional Grape Res & Ext Ctr, North East, PA, U.S.A.; (2) Pennsylvania State University, Biglerville, PA, U.S.A.

The severity of bunch rot disease caused by <i>Botrytis cinerea</i> is strongly related to cluster compactness. For two seasons, we evaluated cluster zone leaf removal at trace bloom (TBLR) for effects on cluster compactness and Botrytis bunch rot development on <i>Vitis vinifera</i> ‘Chardonnay’ in seven vineyards in Pennsylvania. The vineyard trials compared a ‘grower standard’ bunch rot management program (GS) to GS plus TBLR. TBLR reduced cluster compactness, measured as the number of berries per cm, by 11 and 10 % in 2010 and 2011, respectively, when averaged across all vineyards. However, significant reductions (<i>P</i> < 0.05) were achieved in only one vineyard in 2010 and three vineyards in 2011. TBLR reduced bunch rot severity by 37 % in 2010 and 55 % in 2011, when compared to GS with no leaf removal, but the reductions were significant in just one vineyard in 2010 and two vineyards in 2011. When compared to GS with leaf removal after fruit set, TBLR reduced bunch rot severity by an average of 20 % in 2010 and 30 % in 2011, but the reductions were significant in just one vineyard in each year. Over both seasons, TBLR reduced cluster weights in all but one vineyard, with reductions averaging 13 and 11 % in 2010 and 2011, respectively. There were no significant effects of TBLR on return fruitfulness (clusters per shoot) after year one. TBLR may represent an important option for integration into bunch rot management programs. <p><p>Keywords: Fungus, Fruits-Nuts, Grape

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