This press release is available in Spanish.
Scientists at the Basque Institute of Agricultural Research and Development, NEIKER-Tecnalia, and the National Institute of Agricultural Research in Bordeaux (INRA) have come to the conclusion that alleged symptoms of 'black dead arm' (BDA) on grapevine leaves are, in fact, those of esca disease in its initial phase. Esca and BDA are diseases that affect the trunk of vines and cause serious losses to the wine-making and grape-growing sectors every year.
The symptoms produced by esca and BDA in vine leaves are reminiscent of those of drought. In the case of esca, the tissue between the veins dries up and appears surrounded by a red pigmentation and then another yellow discoloration before reaching the green, fresh tissue (tiger stripe pattern). The leaves which to date were believed to be affected by ''black dead arm" (BDA) only showed the red pigmentation beside the green tissue. This difference led some researchers to believe that two different diseases were involved.
With the goal of studying these signs more deeply, NEIKER-Tecnalia and INRA researchers undertook a fortnightly monitoring of affected vines over a period of three years, at a number of vineyards in the Rioja Alavesa (Spain), Bordeaux (France), the Rhine area (Germany) and the Bekaa Valley (Lebanon). The experts observed that the leaves progressed from the so-called BDA symptoms to those of esca, and even that both symptoms could be detected at the same time in many of the plants studied.
If two different, independent diseases were involved, most of the vines would show external signs of either BDA or esca; but not of both succesively.
Thus, the specialists concluded, both the leaves showing red markings and yellow ones beside the green tissue, as well as the ones showing red markings only, were affected by esca. Moreover, NEIKER-Tecnalia researchers have undertaken glasshouse trials in which they have inoculated botryosphaeriaceous fungi - which cause BDA - into vines and have never managed to reproduce the alleged foliar BDA symptoms.
Research published in Plant Disease
The results of the NEIKER-Tecnalia and INRA research were published last July in the prestigious scientific journal Plant Disease, which shows one of the highest impact factors in this discipline. The study was financed by the Aquitaine-Euskadi euro-regional platform, with the collaboration of grape growers in the Famers Union of Araba/Álava (UAGA)
Widespread throughout Europe
The esca disease is widespread throughout Europe. In order to understand its importance, it can be stated that 70% of French vineyards showed symptoms of esca/BDA during the 2003-2008 period, according to nationwide survey data. The affected vineyards had between 1% and 3% diseased plants, a very similar percentage to the one found in Rioja Alavesa.
To control this disease, sodium arsenite has been traditionally used, a chemical banned since 2003 given its extreme toxicity. Although there exist several alternative treatments on the market, they are not as effective against the fungi as the mentioned sodium arsenite. NEIKER-Tecnalia is currently testing chemical and biological treatments intended to be used on pruning wounds, which are the entry point for this disease.
Esca is a complex disease involving a succession of several fungi and affecting grapevine and other woody plants. It is one of the so-called grapevine trunk diseases since the fungi causing them grow within the wood of the trunk and branches. As the wood decays, from the inside towards the outside, the vascular tissues become affected and the normal flow of sap is impaired, to such an extent of inducing partial drying of leaves or even total wilting of canes.