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ARS Home » Pacific West Area » Corvallis, Oregon » Forage Seed and Cereal Research Unit » Research » Publications at this Location » Publication #406640
Research Project: Developing Decision Support Tools to Incorporate Hemp into Existing Farming Enterprises

Location: Forage Seed and Cereal Research Unit

Title: Characterization of powdery mildew fungi affecting hemp in the Pacific Northwest

Author
item Rivedal, Hannah
item WISEMAN, MICHELE - Oregon State University
item RICHARDSON, BRIANA - Oregon State University
item MASSIE, STEPHEN - Washington Hop Commission
item GARFINKEL, ANDREA - Oregon Cbd Seeds
item OCAMB, CYNTHIA - Oregon State University
item Gent, David - Dave

Submitted to: PhytoFrontiers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/24/2023
Publication Date: 1/24/2024
Citation: Rivedal, H.M., Wiseman, M.S., Richardson, B.J., Massie, S.T., Garfinkel, A.R., Ocamb, C.M., Gent, D.H. 2024. Characterization of powdery mildew fungi affecting hemp in the Pacific Northwest. PhytoFrontiers. 4(2):205-212. https://doi.org/10.1094/PHYTOFR-07-23-0099-R.
DOI: https://doi.org/10.1094/PHYTOFR-07-23-0099-R

Interpretive Summary: Hemp (Cannabis sativa) is a new crop for the Pacific Northwest (PNW) states of Oregon and Washington. This region is also where most of the country’s hop (Humulus lupulus) production is centered. These plants have overlapping host ranges for certain pathogens of interest including powdery mildew species. Surveys of hemp fields in the 2021 and 2022 season indicate that powdery mildew fungi are more prevalent late (August/September) in the season. Two powdery mildew species, Golovinomyces ambrosiae and Podosphaera macularis, were detected on hemp in Oregon and Washington. The presence of both pathogens on hemp has possible ramifications for hop producers in the PNW, including disruption of established management systems and quarantine policy.

Technical Abstract: Hemp (Cannabis sativa) is a new crop for the Pacific Northwest (PNW) states of Oregon and Washington. These states are also home to 90% of the country’s hop (Humulus lupulus) production. Powdery mildew is a common disease that affects both hemp and hop. There are at least two species of powdery mildew fungi that may occur on hemp, including Golovinomyces ambrosiae and Podosphaera macularis. Surveys were conducted throughout Oregon and Washington in 2021 and 2022 to determine the incidence and powdery mildew fungi associated with hemp. Seventy-four fields were evaluated at three time points during June to October. In Oregon, powdery mildew was not detected in either year at the early time point but was detected in 4.6 to 6.5% of fields at the mid-season time point, and 36.8 to 41.4% at the late time point. Powdery mildew was not detected in Washington at any time point in either year. We collected 204 powdery mildew samples from surveyed fields. Both P. macularis and G. ambrosiae were detected on hemp based on diagnostic PCR assays, comprising approximately 17 and 96% of assayed survey samples, respectively. Samples identified as P. macularis were all mating type MAT1-1, consistent with the population on hop. Thirty-nine convenience samples were collected outside of surveyed fields and include the first detections of both G. ambrosiae and P. macularis on hemp in Washington. The presence of P. macularis on hemp has possible ramifications for hop producers in the PNW including disruption of established management systems and quarantine policy.