Hop Stunt Decline: A Disease or Disorder of Unknown Aetiology in Australian Hop Yards

Abstract

Hop stunt decline was first observed in commercial hop yards in northeastern Tasmania in 1991. Over the next seven years, the incidence of hop stunt decline increased and reductions in cone yield were estimated to be approximately 30%. Symptoms of hop stunt decline include retarded spring growth, reduced burr production in summer, prolific lateral branching, and progressively shorter internodes on the main bine, and lateral branches which give the plant a “pine-tree” appearance. Final height of affected plants was between one-half to two-thirds of normal growth. Despite extensive investigations over 10 years, the cause of this problem has not been elucidated. However, the role of herbicides, soil physical properties, all described viruses and viroids affecting hop, phytoplasmas, deficiencies of molybdenum, manganese, boron and zinc, plant-parasitic nematodes, and soil-borne fungal diseases have been excluded. Planting with resistant (or tolerant) cultivars was successful at alleviating hop stunt decline. Accepted for publication 3 October 2008. Published 16 January 2009.