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Development and testing of a Forecasting model for powdery mildew With the introduction of cultivars susceptible to Hop Powdery Mildew (HPM) in the Hallertau, this disease became gradually unpredictable in the growing region. As hitherto no prediction on the epidemiology of HPM was possible, there was no alternative to preventive fungicide applications even if the risks of infection were low. Infestation and damage by HPM are very variable from year to year, most likely due to varying weather conditions. We compared weather parameters in varying sequences with the actual situation of HPM infection in the years 1997 to 2004, and empirically deduced a preliminary forecasting model for HPM in Bavarian hop growing regions. Introduction Infection and economic damage of Hallertau hops by Hop Powdery Mildew Sphaerotheca humuli (De Candolle) Burrill (HPM) are varying from year to year clearly recognizable (Figs 1 and 2).
Fig. 1. - Fig. 2. In the years 2000, 2003 and 2004 an enormous amount of fungicides was applied, although many sprayings would not have been necessary from a later point of view. The differences between 1999 and 2000 were especially grave: Although in a trial in 1999 all HPM-infested hop plants had been chopped and left in the field, in 2000 the plants of the same field showed no infection at all. This was the starting point for the consideration that the key for a control strategy had to be searched in the differing weather parameters of those two years. |
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