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