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P.A. Bowen and W.M. Kliewer

Two-dimensional partitioning of variation was used to determine the sources of relationships between the yield and vegetative characteristics of three `Cabernet Sauvignon' grape (Vitis vinifera L.) clones. Clonal differences were found in shoot growth rate, but not in duration or total growth. A weak positive relationship between total shoot growth and yield resulted from a positive relationship between fruit set and growth duration. Relationships between cluster number and foliar characteristics indicated that light exposure in the previous year may have influenced both vegetative and reproductive development. The mean number of clusters per bud was positively related to the mean area, dry weight, and nitrogen content of leaves.

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G.H. Neilsen, E.J. Hogue, D. Neilsen and P. Bowen

Zinc supplied as a fulvic-based Zn compound was absorbed and retranslocated to unsprayed new growth as effectively as zinc sulphate in apple seedlings of low Zn status grown hydroponically in the greenhouse. Similarly, fulvic- and humic-based compounds were as effective as zinc sulphate at improving short-term growth and Zn uptake into new tissues in Zn-deficient apple seedlings, with the best growth occurring at spray concentrations of Zn at 500 mg·L-1. Under field conditions, Zn concentration of peeled and washed `Jonagold' apples at harvest was increased, without phytotoxicity, by two or four postbloom sprays of fulvic Zn. It is therefore possible to use this material safely as an effective Zn-source after bloom. However the mobility of the foliar-applied Zn is limited and any yield response by treated apple orchards of marginal Zn nutrition is unlikely to occur in the short term (within two growing seasons).

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Imed E. Dami, Shouxin Li, Patricia A. Bowen, Carl P. Bogdanoff, Krista C. Shellie and Jim Willwerth

Economic loss due to cold weather events is a major constraint to winegrape (Vitis vinifera) production and wine-related industries where extreme and/or fluctuating winter temperatures induce injury and require remedial retraining and replanting increases production costs and lowers yield and fruit quality. The purpose of this study was to determine whether a foliar application of abscisic acid (ABA) could increase the freezing tolerance (FT) of field-grown, ‘Chardonnay’ winegrape and whether its effectiveness can be influenced by the phenological timing of the application. Mature ‘Chardonnay’ grapevines were treated with a foliar application of ABA at a concentration of 500 mg·L−1 at vine phenological stages corresponding to 50% véraison, postvéraison, and postharvest. Results from field trial sites located in four distinct winegrape production regions in the United States (Idaho and Ohio) and Canada (British Columbia and Ontario) showed that foliar application of ABA increased bud FT, primarily during autumn cold acclimation. Foliar ABA application had no consistent influence on bud FT in midwinter or during spring deacclimation, or on percent budburst in spring. Vine phenological stage at the time of ABA foliar application influenced ABA effectiveness, although results were inconsistent among locations. At most locations, applications made at véraison or postvéraison were more effective than applications made postharvest. No phytotoxic response or adverse changes in yield or berry composition were detected in response to ABA application. The consistent increase in bud FT during autumn cold acclimation observed at all trial locations in this study indicates that foliar ABA, applied at véraison or postvéraison, can reduce the risk of economic loss due to cold injury in production regions with frequent early autumn cold weather events.