Greenhouse evaluation of post-infectional activity of cyazofamid, fosetyl-Al, metalaxyl-M, and carboxylic acid amides (CAA) fungicides on grape downy mildew (Plasmopara viticola).

Downy mildew caused by the oomycete Plasmopara viticola (Berk. & Curt) Berl. & de Toni, is a serious disease affecting grapevine (Vitis vinifera L.) in humid regions worldwide [1]. The pathogen attacks both leaves and berries but leaf infection is considered to be most important as leaves are commonly the source of inoculum for both berry and systemic buds infections [2]. The disease is mainly controlled by the use chemical fungicides. Besides protectant fungicides (multi-site) there are many fungicides (single-site) belonging to several classes as phenylamides, carboxylic acid amides (CAA), QoIs, QiIs and phosphonates [3] able to exert a curative/eradicative activity. These fungicides are able to act on the pathogen even after the beginning of the infectious process by interfering during the incubation period. Although the use of curative fungicides is discouraged in practice, to not facilitate the selection of resistance pathogen populations, an effective application of curative fungicides must be carried out by considering the different possible action of the products on the pathogen biology both in terms of blocking the infection process and of preventing sporulation. In previous experiments performed in greenhouse conditions [4], several fungicides were applied against P. viticola. It emerged for some of them (based on iprovalicarb, benthiavalicarb, and cyazofamid) a high capacity to prevent sporulation of downy mildew when applied within 24-36 hours (h) after inoculation. On the other hand a variable, poor, ability to control the development of oil spots symptoms was observed. The aim of this work was to investigate the different post-infectional activity of several fungicides by trials in greenhouse conditions in order to better understand their physical action on the pathogen during the incubation period.............................................