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May 2016 WINES&VINES 85 WINE EAST GRAPEGROWING Furthermore, performing pre- bloom leaf removal in years when percent of fruit set is natu- rally reduced by unfavorable weather conditions could result in excessive crop reduction. Bunch rot research at the LERGREC Bunch rot research at the Lake Erie Regional Grape Research and Extension Center (LER- GREC) in North East, Pa., ini- tially utilized Vitis interspecific hybrid Vignoles, a highly suscep- tible white hybrid that produces small, compact clusters. In fun- gicide trials, rot control in this variety was often mediocre at best, even after the application of full season programs of highly active Botrytis spp.-specific fun- gicides such as Vangard, Switch and Rovral. After véraison, as Vignoles berries began to soften in overcrowded clusters, fruit on the insides of clusters would be- come crushed, and fruit on the outside would split or be par- tially pushed off of their stems. Damaged fruit rotted quickly, spreading rot extensively within the most compact clusters. In 2001, the LERGREC began research to determine the role that cluster compactness played in bunch rot development in Vi- gnoles, and to what extent the alleviation of compactness would reduce rot development in this variety. The results indicated strongly that the adoption of cluster loosening methods would increase the effectiveness of bunch rot control programs on this cultivar and possibly others (Hed et al. 2009). Over the next several years, researchers examined a number of methods for their efficacy at reducing cluster compactness and bunch rot, with varying lev- els of success. The application of mineral- and vegetable-based oils and anti-transpirants just before bloom—in an attempt to mimic the effects of pre-bloom leaf removal by temporarily im- pairing photosynthesis during bloom and the early fruit-set pe- riod—met with limited success. Removal of the bottom third of each Vignoles cluster at pre-clo- sure (clipping) was extremely effective at reducing rots, but also extremely unpractical. We also examined the effects of gib- berellin applications, either pre- bloom (aimed at lengthening clusters to reduce compactness) or during bloom (to reduce com- pactness by reducing fruit set), the latter of which seemed to provide more consistent control of bunch rots than pre-bloom gibberellin (Hed et al. 2011) or oils and anti-transpirants. How- ever, no method matched that of pre-bloom leaf removal in terms of consistent reduction in com- pactness and bunch rots. Researchers at LERGREC ini- tiated a long-term trial in 2007 with the two most successful of the cluster loosening treat- ments: fruit-zone leaf removal at trace bloom (when the first caps fall off at the beginning of bloom) and bloom applications of gibberellin (Hed et al. 2015). They compared these treat - ments with no leaf removal/no gibberellin (check) and with two other, later timings of leaf removal: just after fruit set (the currently recommended tim- ing) and véraison. Field trials were carried out using vigorous, six-year-old grapevines of clone 96 of Vitis vinifera Chardonnay grafted onto 3309C rootstock. Vine spacing was established at 1.8 meters within rows by 2.8 meters be- tween rows. During dormant pruning, four canes were left: two canes at ~1 meter and two canes at 1.3 meters. Shoots were trained vertically between catch wires, and overcrowding of shoots was avoided by adjusting shoot number to between 16.4 and 19.7 shoots per meter row during early June. The experi- ment was set up in randomized complete blocks with four repli- cations. No nitrogen fertilizer was applied, as vigor was more than adequate, and all experi- mental plots (12 vines each) re- ceived Botrytis spp.-specific fungicide applications at pre- closure and véraison. Leaf removal research yields results Researchers at LERGREC found that the earlier leaf removal was performed, the greater the reduction in Botrytis bunch rot, though the improvement was not always statistically signifi- cant (see table on page 84). For example, leaf removal at trace bloom, post-fruit set or véraison reduced Botrytis severity by an average of 71%, 47% or 14%, respectively, compared to no leaf removal. Leaf removal at trace bloom significantly re- A Chardonnay canopy is shown before fruit-zone leaf removal (top photo) and after fruit-zone leaf removal (bottom photo), which exposes clusters of pea- sized berries to air, sunlight and pesticide, reducing the bunch rot risk.