STUDIES ON ASCOSPORE DISCHARGE IN PSEUDOP EZICULA-TRACHEIPHILA (MULL-THURG) KORF AND ZHUANG, THE CAUSE OF ROTBRENNER OF GRAPE

In the last years, the rotbrenner, a foliar disease on grape, is stead ily increasing in European vineyards. The development of a forecasting system for an integrated control of rotbrenner requires a thorough kn owledge of the epidemiology of Pseudopezicula tracheiphila. Investigat ions on the ascospore discharge in Pseudopezicula tracheiphila showed that the induction of apothecia does not depend on cool periods. Rainf all and larger periods of wetness favored the development and the matu ration of apothecia on overwintered leaves and caused the maturation o f ascospores. The quantity of rainfall which is needed to release the ascospores depends on the wetness of the leaves containing apothecia. Infections in later summer are caused by late development of apothecia on the overwintered infected leaves as well as by apothecia formed on infected and fallen leaves from the same year. The release of ascospo res is not influenced by daylight. It always occurs after and sometime s during rainfall events. The quantity as well as the severity of rain fall influence ascospore discharge whereas temperature does nor seem t o play an important role. Graduated application of fungicides showed c har the vine is susceptible after the fifth leave is unfolded. Losses in yield are possible if early infections result in severe defoliation during blossom-time. Application of fungicides are recommended after a rainfall event. when ES 15 is reached. The following treatment depen ds on plant growth and another rainfall period. Locosystemic and syste mic fungicides allows treatments until 2 days after a rain event. Afte r bloom, the control can be combined with sprays against downy mildew Plasmopara viticola. It is further known that at this stage of plant g rowth high levels of infection are not possible and that the vine plan t is able to compensate defoliation.