Influence of Training System on Management of Eutypa Lata in a Cabernet
There were no symptoms of Eutypa dieback in minimally-pruned treatment while vines trained to bilateral cordon and Sylvoz with hand pruning displayed greater incidence and severity than head trained vines with hand pruning or machine-pruned vines either with or without hand follow-up. Light penetration into the fruiting zone was greatest with minimal pruning, followed by mechanical pruning with or without hand follow-up and head training with hand pruning. Vines trained to bilateral cordon and Sylvoz with hand pruning had the least amount. Mechanically pruned vines produced less clusters than minimally pruned vines but more clusters than head training, Sylvoz, or bilateral cordon training with hand pruning. Minimal pruning and mechanical pruning produced higher yield and smaller clusters than that of other training/pruning systems. Bilateral cordon trained vines had the greatest pruning weight and the least number of shoots, followed by head and Sylvoz trained vines with hand pruning. Mechanical pruning with or without hand follow-up had much less pruning weight but more shoots per vine. Training system had significant influence on fruit Brix and pH but not TA. Fruit from mechanically pruned vines harvested 10 days later than vines pruned by hand reached desirable level of fruit composition. However, minimal pruning displayed not only a delay in fruit maturation but also a lower level of Brix. Vines grown on Columbia silt loam (a high capacity soil) had greater incidence and severity of Eutypa dieback, lower level of light penetration into the fruiting zone from the top and south side of the canopy, and lower TA at harvest than San Joaquin loam (a low capacity soil). Soil fertility and training/pruning did not interact to affect the incidence and severity of Eutypa dieback. The effect of training/pruning systems on the light penetration into the fruiting zone from the south side of the canopy was dependent on the soil capacity. Eutypa dieback has not caused significant reduction in number of shoots, number of clusters, and yield per vine 4 years after symptoms appeared for the first time in 1996 in vines trained to bilateral cordon with hand pruning. Pruning weight was greater on vines showing Eutypa dieback symptoms, suggesting the possibility of more vigorous vines having greater infection of Eutypa dieback. Only 7 out of 187 samples (3.7%) tested positive using PCR technology. The reasons for this low detection rate remains unknown. We are at the early stages of using £w(ypa-specific PCR primers to identify Eutypa lata infection of grapevines in the field. Wine chemistry and wine sensory characteristics will be reported upon the completion of wine making and sample analysis in late March or early April.