Halo Blight of Hop Caused by <i>Diaporthe humulicola</i> : A Diagnostic Guide

Diaporthe humulicola, causing halo blight of hop, is one of the most impactful pathogens of hop in eastern North America. The pathogen, when left untreated, can cause approximately 50% yield loss due to shatter upon harvesting. The disease has a wide variety of symptoms on the cones, leaves, and bines that are not consistent between infections. The pathogen is slow growing on artificial media and can take up to 3 weeks for the development of pycnidia. This diagnostic guide outlines the current list of symptoms and signs for halo blight, offers information on the identification of the pathogen using both morphology and molecular tools, and provides information on pathogenicity testing for D. humulicola.