Forecasting climate suitability of Australian hop growing regions for establishment of hop powdery and downy mildews

Comparisons of climate were made between the hop-production areas in Australia and those in the USA and UK to assess the suitability of the climate in Australia to support the exotic diseases, powdery mildew (caused by Podosphaera macularis) and downy mildew (caused by Pseudoperonospora humuli). Comparisons were based on long-term average data from the last 30 years using the climate-matching function of the CLIMEX computer program. Further assessments of the potential impact of downy mildew on the Australian hop industry were made by determining the number of infection periods throughout the growing season at two locations in Tasmania, and one in Victoria through the hop downy mildew model of the Adcon Telemetry System. Climate matching suggested that both diseases would survive in conditions found in areas where hops are commercially produced in Victoria and Tasmania. Match indices were greater between these areas in Australia and where disease intensity of downy mildew overseas is consistently higher than that of powdery mildew. The hop downy mildew forecasting model suggested that the environmental conditions were conducive for infection at all locations with up to nine infection periods predicted. Changes in the cultivation of hops in Australia necessary to manage these diseases effectively are also discussed.