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Maria Smith

My research focuses on how intensity and timing of cluster-zone leaf removal impact crop production, cold hardiness, and carbohydrate assimilation relative to an un-thinned and cluster thinning treatments.

Cold injury is a major concern for wine grape producers in Pennsylvania.  Critically low temperatures during dormancy as well as late spring frost events during active growth have the potential to drastically decrease yield while the former may also act as an impediment for growing high-value European grapevine varieties (V. vinifera L.).  Implementing best-grower practices are important for reducing damages due to cold injury.

Crop load management practices serve to enhance fruit quality and vine health through optimizing balances between photosynthetic source tissues (leaves) and sink tissues (fruit).  Traditionally, winter pruning, shoot and cluster thinning have acted as the primary means for regulating crop load.  Recently, the practice of early leaf removal during trace bloom and fruit set has shown promise as an effective tool in regulating yield while reducing cluster compactness.  However, few studies demonstrating the effects of early leaf removal have been performed in cold climate regions, where source-sink manipulations may impact carbohydrate assimilation for winter cold hardiness.  Using two over-cropping varieties, hybrid ‘Chancellor’ and vinifera ‘Grüner Veltliner’, we are comparing ways that intensity and timing of early leaf removal impact crop production, cold hardiness, and carbohydrate assimilation relative to an un-thinned and cluster thinning treatments.

Vine varieties differ greatly in phenology and cold hardiness, characteristics, which can determine vine success in sites that frequently experience cold stress events. Frost events during active growth can result in loss-of-function of water conducting vessels (xylem) through air embolism formation.  Vines, however, can cope and recover lost functionality through repair mechanisms.  To evaluate vine susceptibility to frost injury and recovery, hybrid and vinifera varieties are subjected to damaging minimum temperatures with recovery monitored through metrics of vine growth performance, including shoot growth, gas exchange, and plant-water relations.  The ability for the vine to withstand subsequent winter cold temperatures will be evaluated through measuring bud cold hardiness.