Responding to an Introduced Pathogen: <i>Podosphaera macularis</i> (Hop Powdery Mildew) in the Pacific Northwest

Abstract

Powdery mildew of hop (Humulus lupus L.), which is caused by Podosphaera macularis (formerly Sphaerotheca macularis) was found in the Yakima Valley, WA in 1996 and subsequently spread to the growing regions in Oregon and northern and southern Idaho. To rapidly assist growers in reducing the cost associated with the preventive fungicide program, the Gubler/Thomas grape powdery mildew risk infection model was adapted for hops. In addition, field surveys were utilized to identify other management practices that impacted disease development. Weather networks were established and utilized to deliver daily regional maps indicating the risk index. These maps were posted to the web for daily access. Lessons learned from this experience will be useful in addressing future pathogen introductions. Accepted for publication 28 March 2003. Published 13 November 2003.