Effects of an Ascophyllum nodosum (L.) Le Jol. extract on grapevine yield and berry composition of a Merlot vineyard

Few publications in the scientific literature document effects of seaweed extracts on winegrape varieties. A 2-year field experiment was conducted to evaluate effects of foliar applications of an Ascophyllum nodosum (L.) Le Jol. extract on vine yield components, canopy chlorophyll content, berry composition and phenolic indices. The split plot experiment allowed for the investigation of extract effects with and without in-season N fertilization in a Merlot vineyard in 2015 and 2016. Great differences in vine productivity and berry composition between years were attributed to hail damage in 2015. Vines were not affected by N supply in any single year other than a decline of some berry quality parameters in 2016. Effects of seaweed extract application were evident in the absence of hail damage in 2016. The greatest vine responses were obtained with 1% extract concentration under in-season N supply by a 26% increase in yield, 35% increase in the number of berries and 21% increase in anthocyanin extractability of berry skins. These beneficial effects came about without a negative impact on other parameters of berry composition or phenolic indices and, in part, appear to be caused by direct effects on berry physiology and grapevine nitrogen status. The lower extract concentration (0.2%) also increased number of berries and anthocyanin extractability, but these were accompanied by a reduction of berry phenols and an increase of seed tannins. The results demonstrate the potential of this extract to increase production and improve wine quality in red winegrape vineyards.