Wisconsin Hop Diseases & Their Management
Michelle Marks, Postdoctoral Research AssociateHop Production for the Wisconsin Craft Brew Industry
10th Annual SeminarFebruary 16, 2019
Hop Downy Mildew
• Caused by obligate, oomycete pathogen Pseudoperonospora humuli
• Infects shoots, leaves, stems, cones, roots
• Most significant hop disease issue here in Wisconsin
Disease Cycle
V. Brewster, Compendium of Hop Diseases and Pests
“basal spikes”
>43°F>90% humidity
60-70°F>1.5 h leaf wetness
Disease Management
• Resistant varieties
• Cultural practices
– Pruning basal foliage
– Bine stripping
– Sucker removal
• Fungicide applications
Resistant Varieties
Resistant
• Hallertauer Gold
• Hallertauer Magnum
• Hallertauer Tradition
• Newport
• Perle
• Spalter
Moderately Resistant
• Columbia
• Fuggle
• Sterling
• Teamaker
• Tettnanger (U.S.)
• Willamette
Source: http://msue.anr.msu.edu/uploads/234/71503/Hop_Field_Guide_Third_Edition.pdf
However…
Spring Pruning
• In spring, emerging shoots should be pruned to crown– Timing varies based on
variety & season
– Mechanical or chemical methods
– Reduction of initial inoculum
• Remove as much green tissue as possible
• Consider timing– May not be feasible in all
locations
Bine Stripping & Sucker Removal
• Bine stripping = removal of foliage on lowest 4 ft. of bine
• Sucker removal = removal of new growth @ plant base
• Decreasing humidity and increasing airflow
• Help prevent upward movement of spores
Hop Powdery Mildew
• Caused by biotrophic fungus Podosphaera macularis
• Primarily infects leaves and cones
• Persistent issue in PNW, emerging on east coast & Midwest
– Marathon County 2017
– Dodge County 2018
HPM Disease Cycle D. Gent
Powdery Mildew Management
• Early season
– Crowning (very few practicing here in WI) or,
– Completely removing green tissue during spring prune
– Fungicide application to base of plants before hill closure
– Periodic removal of basal growth (similar to downy management)
• Especially just before flowering
• Chemical control – be careful around burring
• Avoid excessive nitrogen/water applications
Mahaffee, W. F., Engelhard, B., Gent, D. H., and Grove, G. G. (2009)
Hop Viruses
• Several have been identified in Wisconsin– Apple mosaic virus
– Carlaviruses (Hop latent virus, Hop mosaic virus)
• Viroids?
• Widespread throughout the state
• Impacts on yields/quality not well understood– Variety dependent
https://www.ipmimages.org/browse/detail.cfm?imgnum=5393341
ApMV
Phoma Wilt
• Grayish, circular lesions on leaves, reddish-brown discoloration on cones, plants may wilt
• Pathogen likely survives in debris or decaying organic matter
• No specific management recommendations, fungicides for PM control may have activity against Phoma
Radisek et al. (2008)
Cone Browning Diseases
Alternaria cone disorder (Alternariaalternata)
Fusarium tip blight
(Fusarium spp.)
http://www.omafra.gov.on.ca/english/crops/hort/news/hortmatt/2014/21hrt14a1.htm
Cone Browning Diseases
Alternaria cone disorder (Alternaria alternata)
• Very common fungus found on decaying plant matter
• Weak pathogen that often invades wounds– Mechanical injury for hops
• Disease minimized by avoiding damage– Wind abrasion, arthropod pests, other
pathogens
• No fungicides registered for Alternaria, but may be suppressed by some fungicides applied for PM/DM control
Fusarium tip blight(Fusarium spp.)
• Little known about disease cycle
• Some evidence that disease is favored by high humidity, dew, rainfall during bloom/cone development
• Varieties with closed-cone architecture may be more susceptible– Eg. Nugget, Sorachi Ace
• Control seldom warranted
Fungicide Principles
• Know your disease targets
– Products that work for downy mildew may not work for powdery mildew, and vice versa
• Keep an eye on the weather
– High pressure = 5-7 day spray schedule
– Low pressure = 10-14 day spray schedule
• Alternate modes of action
– Helps prevent development of fungicide resistance
Resources
• Field guide
• ‘Hop’ section in A3422
– In print and online
– All registered fungicides
• Hop Disease Compendium
– Published through APS
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