gardens in Bavaria

To assess the extent of aphid and spider mite infestations for the purpose of disseminating cultivation advice and control strategies, surveys and exact examinations of such infestations in commercial hop gardens are a necessity. For this purpose, investigations were conducted on location, on 12 dates in weekly intervals, in 33 representative hop gardens (including 3 organic hop gardens), between May 25 and August 9, 2021. The hop gardens were in the Hallertau (23), in Spalt (7), and in Hersbruck (3). Assessments covered infestations with hop aphids (a count) and common spider mites (according to an infestation index). These served as the basis for formulating advice and control strategies. As an example, Figure 4.21 shows an overview of the evolution of the spider mite infestation index. Because of the cool spring in 2021, spider mites were first detected relatively late and the infestation progressed much more slowly than it did in the two previous years. However, by calendar week 26, a sudden increase in spider mite infestations in numerous areas triggered the control threshold, just as it did in previous years. Following the control measures, the infestation index decreased.

Figure 4.21: The spider mite infestation index as an average across all 33 monitoring locations