First Report of Powdery Mildew Caused by Podosphaera macularis on Hemp in Oregon

In Oregon, hemp (Cannabis sativa) production has increased substantially after cultivation was legalized in the 2014 and 2018 Farm Bills. Both hemp and hop (Humulus lupulus), two agriculturally important crops in the Pacific Northwest, are affected by powdery mildew diseases. Golovinomyces spp. have been reported to cause hemp powdery mildew in Canada (Pépin et al. 2018) and the United States (Farinas and Peduto Hand 2020; Szarka et al. 2019; Weldon et al. 2020), including Oregon (Wiseman et al. 2021). More recently, Podosphaera macularis was found to colonize hemp following inoculations under controlled conditions (Weldon et al. 2020) and has been reported to be naturally occurring in a hemp field in British Columbia, Canada (Z. K. Punja, personal communication). P. macularis has been a problem on hop in the Pacific Northwest since the 1990s, when the fungus was introduced into the region; however, this species has not been widely considered as a concern for hemp growers © 2021 The American Phytopathological Society