Controlling microbial infection by managing grapevine canopy

Pinots (Vitis vinifera L.) are known as tight-clustered grape varieties, where the mechanical pressure of adjacent berries may disrupt cuticle waxes, thus predisposing these sites to greater incidences of infection. One of the main causes of crop quality degradation is grape rot due to the development of various microorganisms (bacteria, yeasts or other fungi). Among them Botrytis cinerea is one of the most frequent problems. Because mold spores are ubiquitous, the control of germination and growth in the vineyard by use of fungicides may only be part of the solution. Therefore, carefully selected cultural practices may play a significant role toward encouraging or discouraging mold and other microbial infections. A field trial was established in Pinot Noir vineyard of Vipava Valley for two consecutive years. Preliminary results based on visual examination of microbial compromised grapes indicated that earlier leaf removal treatments reduced the extent of microbe damage on grape. Therefore in the following harvest three different treatments of leaf removal (at pre-flowering, berry-set and veraison phase of grape development) were performed, using untreated vines as a control. Temperature and humidity data were collected in the grape area of all treatments. Microbial population on grapes was followed using standard cultivation methods during ripening and at harvest time as well as visual inspection of damaged / sound grapes was performed at both times. At harvest time compactness of grapes was also evaluated. Parallel trial with excluding last Switch® application was done to evaluate the effect in different treatments. In general we observed the change in species composition on the surface of grapes with early predominance by the basidiomycetous yeasts and species Aureobasidium pullulans, and at harvest time with the prevalence of the ascomycetous yeasts, lactic / acetic acid bacteria and molds. Leaf removal was much more effective against Botrytis Cinerea compering to additional Switch® application, especially at leaf removals at earlier stages. Pre-flowering leaf removal also showed significant reduction of grape compactness. The results suggesting early leaf removals as successful tool for reducing the risk of microbial infections.