BIOLOGY, EPIDEMIOLOGY, AND MANAGEMENT OF HOP DISEASES

Dr David H. Gent, Research Plant Pathologist, U.S. Department of Agriculture-ARS Forage Seed and Cereal Research Unit, Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon

The research project is focused on developing effective, economical, and sustainable pest management strategies for powdery mildew (caused by Podosphaera macularis) and downy mildew (Pseudoperonospora humuli) of hop, and integration of disease and arthropod pest management practices on this crop. Outbreaks of these diseases occur annually in most hop production regions in the western U.S., and are estimated to cost the U.S. hop industry greater than $10 million annually in additional production expenses and crop loss. Research in my lab seeks to understand aspects of the epidemiology, ecology, and population biology of these pathogens and their diseases that will lead to new disease management approaches at the farm level. These objectives are achieved through integration of fundamental and applied research, strong collaborations with other researchers in the U.S. and abroad, and technology transfer to stakeholders.

Current efforts are centered on identifying and quantifying the interactions of environmental, biological, and production factors associated with the occurrence and severity of hop downy mildew. The long-term goal of the research is to develop predictive systems and sampling plans to detect and forecast disease appearance and infection risk, and optimize pest control strategies. Preliminary models developed indicate the role of dew wetness, discounted in past research, is an important factor in epidemic development. In collaboration with other Hop Research Council researchers, robust and sensitive PCR assays and novel methods for detection airborne inoculum of P. humuli have been developed and are being validated under field conditions. Monitoring for airborne inoculum will complement weather-driven decision aids and sequential sampling plans that are being developed.

Research efforts with powdery mildew are focused on quantifying the effects of fungicide programs on arthropod pests and natural enemies, and developing IPM approaches to disease management that enhance conservation biocontrol. My program interfaces with and helps to coordinate a team of entomologists and plant pathologists in the Pacific Northwest that are working to identify mechanisms responsible for spider mite outbreaks in response to sulfur applications, and develop system approaches to manage both pests. Research on grower cultural practices and their association with the cone infection phase of powdery mildew are ongoing. New research is underway to quantify the relations among incidence of powdery mildew on cones, disease incidence on leaves, weather factors during flowering and cone development, and grower practices (i.e., pesticide applications and pruning quality). The objective of this work is to develop a model and management-action thresholds to assist growers in deciding when late- season fungicide applications are warranted.