Control of grey mould by application of gibberellin acid inhibitor (Regalis®)and management practices in Vitis vinifera (cv. Riesling)

Abstract: Grapevine varieties with tight clusters are extremely susceptible to infection by greymould (Botrytis cinerea). Severe pathogen attack leads to reduced yield and affects wine quality. Acouple of management practices can reduce tightness of berry clusters, among them moderatedefoliation and the use of plant growth regulators. Prohexadione-Calcium (trademark Regalis®) is agibberellin acid biosynthesis inhibitor with low toxicity and persistence in the plant. Over a periodof three consecutive years the effect of prohexadione-Ca on grape cluster architecture was tested incv. Riesling and combined with anti-Botrytis fungicide applications and leaf removal measures.While prohexadione-Ca treatments significantly increased the flexibility of grape clusters in 2007,no significant effects were evident in 2008 and 2009. However, even a minor reduction of indexvalues of 0.2 – 0.3 may have an influence on the tightness of clusters and thus on the susceptibilityto B. cinerea infections. In all three years severity of B. cinerea was significantly reduced inRiesling grapes when the following measures were combined: application of Regalis®, fungicidetreatments and moderate defoliation. Therefore, future strategies to control grey mould should aimat a combination of different management strategies.