Grapevine leaf stripe disease symptoms (esca complex) are reduced by a nutrients and seaweed mixture

Summary. Grapevine leaf stripe disease (GLSD) seriously reduces the quality and quantity of grape production, and results in a shorter lifespan of vineyards. Recent research has shown that foliar applications of nutrients influence the development of GLSD foliar symptoms. Based on this knowledge the effect of foliar applications of a mixture of calcium chloride, magnesium nitrate and Fucales seaweed extract on the development of leaf symptoms was evaluated over a 3-year period from 2010 to 2012. Nine foliar applications of the full mixture and its individual mineral components, also in different combinations, were tested in three different vineyards, one of cv. Trebbiano d’Abruzzo and two of cv. Montepulciano d’Abruzzo in the Teramo province (Abruzzo, Italy). Treatments were applied every 10 days from the beginning of vegetative growth to pre-bunch closure. The final results were similar in all the three vineyards and in the three years leading to a significant reduction of symptom development in the vines treated with the full mixture, while lower effects were obtained by applying partial combinations or single components. Both quantity and quality of grapes from the treated vines increased, while no phytotoxic or other unwanted effects on grape growth were detected. Vines treated with the full mixture showed an increase in trans-resveratrol and flavonoids content, and a higher accumulation of calcium oxalate in crystal druses in the leaf mesophyll. These data can be a useful base to set up a control strategy against GLSD and give some input for better understanding the mechanisms involved in foliar symptom expression in GLSD.