Products containing different gibberellic acids (GA) and GA inhibitors were applied to grapevines during the 2009/10 and 2010/11 growing seasons to evaluate possible effects on bunch architecture and subsequent botrytis bunch rot (BBR) severity In the 2010/11 season the timing formulation and dose responses of the GA inhibitors in association with a biological control agent were also evaluated for their effects on BBR In both seasons the effects on yield and fruit quality and quantity were also measured to determine whether the treatments might affect commercial production There were no significant differences in either BBR incidence or severity in either season between any treatments including the standard fungicide programme Bunch openness was significantly modified by treatments but with no consistent pattern

Botrytis bunch rot is a disease that requires management under New Zealand conditions in order to prevent financial losses for wine grape producers A survey was conducted to investigate the potential spore production of tendrils in 16 vineyards from the Marlborough and Hawkes Bay wine growing regions Significant differences in spore production potential of tendrils were detected between sampling before flowering and after fruit set Significant regional differences were also detected with tendrils from Marlborough producing fewer spores Under ideal laboratory conditions for incubation of the fungus spore production by tendrils was low at the start of the season and was reduced further following application of the industry standard fungicide programme Based on these experiments and a review of other data it is recommended that tendril removal is not required at pruning as part of vineyard disease management

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Current management options for grapevine trunk diseases are focused on ameliorating symptoms once they have occurred In grapevines and other crops plant stress has been observed to increase symptom expression for different pathogens depending on timing and type of stress This research aimed to establish whether stress to vines at the time of wounding enhances colonisation by fungi associated with trunk disease Potted plants were wounded and inoculated with two grapevine trunk fungi Eutypa lata and Botryosphaeria lutea Stress treatments (leaf removal and girdling) were applied to the vines immediately prior to inoculation Lesion size at the wound site and infection confirmed by reisolation of the pathogen were measured In these experiments stress did not induce greater infection incidence or larger lesions at the site of wounding Some difficulties in using potted plants to simulate responses of mature vines in the field are discussed