Plant Disease Management Handbook

By K. Eastwell, D. H. Gent, and C. M. Ocamb

Image related to Hop (Humulus lupulus)-Viroid Diseases

Plants of the hop cultivar Glacier in the center of the photo showing reductions in vigor due to infection by Hop Stunt viroid, compared to the vigorous plant on the left.

Photo by Ken Eastwell, 2006.

Lime-green leaves symptomatic of Hop Stunt viroid infection during early June in a 'Glacier' hop plant.

Photo by Ken Eastwell, 2007.

Generalized speckling on 'Sterling' leaf due to HpSVd.

Photo by C. M. Ocamb, 2007

'Willamette' leaves that were infected with HpSVd showing light green coloration.

Photo by Ocamb lab, 2007

'Perle' leaves infected with HpSVd showing speckling concentrated along leaf veins.

Photo by Ocamb lab, 2007

By C. M. Ocamb and D. H. Gent

Image related to Hop (Humulus lupulus)-Verticillium Wilt

An infected plant showing wilt symptoms.

Photo by Darrell Smith.

Note the brown discoloration of the woody tissue under the bark.

Photo by Darrell Smith.

Cause A fungus, Phomopsis tuberivora (syn. Phacidiopycnis tuberivora), that can survive in plant debris, on hop plants, or in soil as sclerotia. The fungus needs injured hop tissue for infection to occur. This disease was first reported in Australia in 1981 and recently confirmed in a hop yard in the Pacific Northwest in 2013.

Image related to Hop (Humulus lupulus)-Red Crown Rot

Melodie Putnam 2007, Oregon State University

By C. M. Ocamb and D. H. Gent

Image related to Hop (Humulus lupulus)-Powdery Mildew

Hop cones affected by powdery mildew. Cone development is stunted, and malformations may be evident.

Photo by Cynthia M. Ocamb, 1998.

Note the white, circular colonies.

Photo by Cynthia M. Ocamb, 1998.

A new shoot covered with powdery mildew.

Photo by Cynthia M. Ocamb, 1998.

Flag shoots, such as the one above, are typical in the spring. The white colonies can be difficult to detect.

Photo by Cynthia M. Ocamb, 1999

Conidia of the powdery mildew fungus are borne in chains.

Photo by Cynthia M. Ocamb, 1999.

Cause Heterodera humuli. Cyst nematodes are sedentary endoparasites. Surveys in 1961-1962 determined the presence of this nematode in hop yards near Independence and Salem, OR. Movement of hop roots from yard to yard and area to area, combined with annual flooding, probably has widely distributed the pest.

Symptoms White to brown protuberances (cysts) on roots.

Cause The fungus, Fusarium sambucinum (teleomorph: Gibberella pulicaris), survives in soil and diseased plants and has been found in OR, WA, and ID. Confirmed by OSU in 'Chinook', 'Fuggles', 'Galena', 'Glacier', 'Mt. Hood', 'Nugget', 'Sterling', 'Willamette', and 'Zeus' varieties in the Pacific Northwest. The incidence of hop canker in the field is sporadic, not every bine on a hill is affected.

Image related to Hop (Humulus lupulus)-Fusarium Canker (Wilt)

Splitting of cankered bine.

Photo by Cynthia M. Ocamb, 2006

Bine at top shows Fusarium canker symptoms while the lower two bines show vascular discoloration due to Verticillium wilt.

Photo by Cynthia M. Ocamb, 2006

Hop bine with hop canker. Note the swollen base as well as the narrow point of attachment at the base of the bine.

Photo by Cynthia M. Ocamb, 2006

By D. H. Gent and C. M. Ocamb

Cause The fungus-like microorganism, Pseudoperonospora humuli, persists from year to year in infected hop crowns or plant debris in soil. It is an obligate parasite specific to hop. Disease is promoted by wet or foggy weather.

Image related to Hop (Humulus lupulus)-Downy Mildew

Aerial spike present on hop bine.

Photo by David H. Gent, 2006

Hop cone with downy mildew infection.

Photo by Cynthia M. Ocamb, 2002

Note the shoots with shortened internodes, characteristic of hop downy mildew.

Photo by Cynthia M. Ocamb, 2004

Cause Two fungal species, Fusarium avenaceum and F. sambucinum, cause cone tip blight and the disease has been found in OR, WA, and ID. These two fungi can survive in soil or plant debris. Field observations suggest that the onset of disease appears to be more severe in sites with more humid conditions during cone development, especially with overhead irrigation.

Image related to Hop (Humulus lupulus)-Cone Tip Blight

Affected tissue dies and turns browning, starting at the tip and moving up toward the stem. Some bracts have been removed from the cone on the left and discoloration of strig potions are visible.

Photo by Cynthia M. Ocamb, 1998.

Characteristic cone tip blight symptoms of 'Willamette' cones growing in a commercial hop yard.

Photo by Cynthia M. Ocamb, 2006

Discoloration of strigs from 'Nugget' cones growing in an experimental hop yard.

Photo by John C. Bienapfl, 2002

Cause A fungus-like microorganism, Phytophthora citricola, that survives in soil by long-lived oospores. It also may survive in infected plant parts but not in dead tissue except as oospores. The disease requires abnormally wet soils and is most often observed in areas of fields with soil or irrigation conditions that cause water to pool.

By C. M. Ocamb and D. H. Gent

Image related to Hop (Humulus lupulus)-Abiotic Wilt

The epidermis of affected vines cracks and oozes plant sap.

Photo by C. B. Skotland

The stems of affected plants (lower stem above) look rough and corky, particularly at the soil line and extending up the vine.

Photo by C. B. Skotland