Investigation on Zweigelt disease in Austrian viticulture

摘要

A new grapevine disease has appeared in Austrian vineyards from 1995. Named after its main host, it is called Zweigelt disease (or bunch decline). Mostly red wine varieties (Zweigelt, St. Laurent, Blauburger) but also white wine varieties (e.g. Neuburger) are affected. Once the disease appears in a vineyard the whole vineyard is usually affected. Therefore severe economic losses can be expected as a result of lower quality and reduced yield. At ripening insufficient colouring and small berry size are characteristic symptoms for Zweigelt disease. Another typical decline symptom is the sudden loss of vigour of the berries most shortly before harvesting. Unlike other disorders like bunch-stem necrosis, berries suffering from bunch decline do not stayattached to the bunch stem but are dropped as the disease develops. Necrosis on the bunch stem is not correlated with the disease incidence but can be found after the berries have lost vigour. The leaves show necrosis with red margins which is typical of red wine berries as opposed to the yellow margins of white wine berries. Affected berries show a lower must density but a higher concentration of acidities than non-affected berries. Results of laboratory tests could exclude fungal pathogens as the cause of the decline. Several treatments with a selection of fungicides, leaf-fertilizers and minerals were tested. Most effective were MgCl_2 and CaCl_2 singly, if they were sprayed three times beginning at fruit set. The sugar content in affected grapes had been significantly reduced before visible symptoms appeared. The extension of the reduction depended on the bunch position on the fruiting cane. Bunches on the first position were strongly and frequently affected. It is assumed that Zweigelt disease is a physiological disorder.