Effect of pre-bloom leaf defoliation on cluster morphology and disease pressure

Mestrado Vinifera Euromaster - Instituto Superior de Agronomia - UL

Defoliation of grapevines have been shown to impact fruit set and fruit development, although the extent to and timing of which defoliation impacts fruit set and development is still being investigated. This is useful for the purpose of managing crop load and can be a useful tool for disease management. Currently, the understanding is that removal of leaves from the fruiting zone alters the source-sink balance, forcing the grapevine to down-prioritize flowering resulting in reduced fruit set, smaller clusters and less rot (Incidence x Severity). The purpose of this project is to investigate how pre-bloom removal of the six basal leaves on Riesling (clone 49) grapevines alters fruit set, cluster morphology and berry composition. The experiment was conducted in 2014 at Michigan State University’s Southwest Michigan research and Extension Center in Benton Harbor, MI (lat. 42005’10.55” N, long. 86021’03.68”W). Our experiments show that there is a significant impact on fruit set as a consequence of defoliation, where defoliated vines showed a lower percentage of fruit set compared to control (43% vs. 63.4%) and the lower fruit set percentage also yielded less rot within the clusters (21.3% vs. 31.5%). Differences were noted in the rachis development (rachis were heavier and thicker with longer lateral branches in the control), but no significant changes were observed in berry composition and the proportions of successfully to unsuccessfully seeded berries as a result of the treatment