Esca in Austria

Abstract

Esca, known from Austria since it was reported by Zweigelt (1933), has increased in importance in the last ten years. Investigations on the incidence of esca were therefore undertaken to assess its impact on Austrian viticulture. A visual assessment of 14,000 vines showed that about 1.3 percent of plants exhibited external esca symptoms. This incidence was correlated with vineyard age, but not with the cultivar grown. The spatial dispersal of esca, investigated by monitoring contaminated vineyards, seemed to be random. Investigations on the temporal incidence of infestation revealed that the number of diseased plants increased dramatically within the time span studied. The average annual increase of plants with external esca symptoms in monitored vineyards was approximately 2.7 percent. Further studies focused on certain phytopathological aspects, such as the effect of white-rot fungi and Phaeoacremonium chlamydosporum on disease incidence, and the control of Stereum hirsutum in vitro. The occurrence of basidiocarps of S. hirsutum, Trametes hirsuta and T. versicolor on diseased vines and the isolation of Phaeoacremonium spp. were documented in Austria for the first time. Inoculations of grapevines with S. hirsutum and P. chlamydosporum, either separately or in combination, failed to produce symptoms on leaves or berries. On the other hand, cross-sections of woody tissues showed a decayed zone in the pith when they had been inoculated with S. hirsutum, and P. chlamydosporum induced dark-brown necrosis in the wood. A combination of these two fungi caused only dark-brown necrosis, without wood decay, even though re-isolation corroborated the presence of both fungi. Various fungicides were evaluated for their efficacy against S. hirsutum in vitro. The most effective fungicide for inhibition of mycelial growth was the EBI fungicide fenarimol with an EC50 value of 0.002 mg a.i. ml-1. The dicarboximide fungicide procymidone was less effective, with an EC50 value of 80 mg a.i. ml-1. The effects of benomyl and hydroxychinolin did not differ significantly when compared with the control.