Short- and Long-Term Effects of Leaf Removal and Gibberellin on Chardonnay Grapes in the Lake Erie Region of Pennsylvania

Abstract

Over six seasons from 2007 to 2012, the effects of the timing of cluster zone leaf removal and bloom gibberellin applications on Botrytis bunch rot, cluster morphology, yield, and juice composition were evaluated on Vitis vinifera Chardonnay grapevines. All experimental plots received Botrytis-specific fungicide applications at preclosure and veraison. Leaf removal at veraison, postfruit-set, or trace bloom reduced Botrytis severity by an average of 14, 47, or 71%, respectively, compared to no leaf removal. Leaf removal at trace bloom (LRTB) reduced Botrytis incidence and severity in five and four seasons, respectively, and was as effective as (2007 to 2010), or more effective than (2011 and 2012) two additional fungicide applications (at bloom and at preharvest), suggesting potential to reduce fungicide inputs. Gibberellin was less effective than LRTB, but reduced the incidence of Botrytis in 2008 at 5 mg/L and the severity of Botrytis in 2010 at 25 mg/L. Botrytis development increases with number of berries per cluster and berries per centimeter of cluster (compactness). Berries per cluster was reduced by LRTB in 2007, 2010, and 2011, and by 10 mg/L gibberellin in 2007 and 25 mg/L in 2011. Berries per centimeter was reduced by LRTB and gibberellin in 2007, 2008, and 2011. Leaf removal at postfruit-set produced the most noteworthy effects on juice composition, reducing titratable acidity in 2007, 2011, and 2012. Yields were reduced by LRTB in 2008, but no significant yield effects were observed in subsequent seasons. The efficacy of LRTB for reducing Botrytis bunch rot was highest in years with the most compact clusters, suggesting that the value of this treatment increases with increasing potential for bunch rot development.