Downy Mildew: Identification, Lifecycle , and Management

David H . Gent Forage Seed and Cereal Research UitUSDAUnit USDA-ARS Corvallis, Oregon Available at shopapspress.org Download free of charge from:

USAhops. org Disease and Pest Overview • Get a Positive ID before implementing any controls

Zinc

Iron Nitrogen

Average number of sprays made per season in Northwest Downy mildew Powdery Aphids and other Mites mildew insects 5.7 8.3 2 1.75 Things to Know 1. Disease status of planting materials – Don’t buy a perennial problem: obtain materials from Clean Plant Network or otherwise ensure disease-free 2. What you are controlling – Get an accurate ID before treating 3. Market – Quality standards – Organic vs. conventional: may dictate variety Disease and Pest Overview Susceptibility DownyDowny mildewMildew

Brewer’s Gold High Columbus Columbus CdCascade GlGalena Glaci er Centennial Chinook Galena Chinook Glacier Chinook Columbus Mt. Hood Brewer’s Gold Fuggle Centennial Golding Galena Golding Perle Glacier Brewer’s Gold Sterling U.S. Golding Centennial Mt. HdHood Nugget Willamette Nugget Intermediate Sterling Fuggle Perle Willamette Cascade Sterling Fuggle Mt. Hood Willamette Low Perle Nugget Downy Mildew • Caused by a fungus -like pathogen related to the downy mildew pathogen

• May survive in infected plants, perhaps sexual spores in soil BEB. Eng lhlehard

• SdSpreads easil ilbiby by airborne spores, infected planting materials, ppypotentially soil/crop debris

• 100% crop loss potential due to plant death, loss of all trained shoots and/or cone infection Downy Mildew “Spikes” on Nugget Glacier Lateral Branch Infection Severe Late Spring Downy Mildew Columbus

M. Nelson

Leaf Infections Spores produced on undersides of leaves Mahaffee et al. 2009 Survival in Systemically Infected Roots and Plants

Johnson et al. 2009 “PrimaryPrimary Infection ” “SecondarySecondary Infection ” Downy Mildew Lifecycle

Mahaffee et al, 2009 Compendium of Hop Diseases and Pests Disease Cycle BiBegins Shortly After Emergence 1.0 A Emergence of 0.8 Spikes Related to 0.6

Probability 0.4 Winter/Spring

0.2 Temperature and Simple average (base 6.5C) Sine function (base 6C) 000.0 Disease Last Year -200 -100 0 100 200 300 400 Observed - threshold degree-days 1.0 B • On average in OR, first spikes Current season 0.8 Previous season emer ge 27 March

0.6

PC • Association between how early DD spikes emerge and di sease RAU 0.4 severity the previous season

0.2

0.0 100 150 200 250 300 Spike emergence (degree-days)

Examples of Quality Association of Pruning Quality and Downy M ildew Sever ity

0.35

0.30 ress curve ress

0.25

0.20 isease prog dd

0.15

0.10 a under the ee 0.05

0.00 Relative ar Relative Excellent Moderate Poor Pruning quality

110 hop yards in Oregon; 2005 -2010 2014 Season: Grand Rapids • Predicted first spikes emerge iltAilin late April; widespread by late May

Date DDs Event 1% probability of 4-24-14 174 spike emergence 50% probability of 4-30-14 221 spike emergence 95% probability of 5-22-14 528 spike emergence Favored by Moderate Temperatures and Wetness • Leaves: – Range of 41-86F 24-15h1.5 hr wet ness – Most rapid at 60- 76 (1 .5 -2wethr)2 wet hr) • Shoots: –Range 48-74F 3-6 hr wetness – Mid70Most rapid near 70 (3 hr wetness) Derived from data reported by Royle (1970) 2014 Season: Hudsonville

6000 90 Downy mildew risk index

Average temperature 80 5000 70

4000 60 e rr

50 3000 40 isk Points age temperatu RR rr Ave 2000 30

owny Mildew 20 DD 1000 10

0 0 2/3/2014 3/3/2014 4/3/2014 5/3/2014 6/3/2014 7/3/2014 8/3/2014 9/3/2014 Basal Foliage Removal and Stri ppi ng of L ower Leaves

4 2010 Downy

3 Mildew Control with 2 ity rr 1

w seve Management ee 0 burn noburn burn noburn • Factors that bare cover

ny mild 300 2011 increase ww 250

Do duration of 200 leaf wetness 150 may increase 100 severity of 50

0 downy mildew Burn Noburn Burn Noburn bare Cover

Downy Mildew Fungicides (in PNW) plant-disease.ippc.orst.edu Fungicide Efficacy Notes Aliette Good-Excellent Resistance problems in Oregon Copper* Moderate Various formulations; organic Curzate* Good-Excellent Timing critical; pH sensitive Flint Moderate Suppression only Folpan Moderate Side effects on powdery mildew Forum/Acrobat* Excellent Phosphorous acid* Good Manyyp products; cross resistance with Aliette, high rates effective Pristine Moderate Suppression only Ranman Excellent Revus Excellent Ridomil Excellent Various formulations; resistance widespread in PNW Tanos* Excellent Zampro Excellent * Used extensively in PNW Fungicide Timing is Important

100

90

80

70 48 hr pre

ing area 24 hr pre tt 60 6 hr post 50 12 hr post 40 sporula 24 hr post tt 48 hr post 30 72 hr post 20 Percen

10

0 Aliette Curzate Flint Forum Kocide Downy Mildew Management • Early control measures key – Thorough pruning in well establish yards, timely first spray • Plant disease-free – National Clean Plant Network (www.usahops.org) • Avoid highly susceptible varieties – Susceptible: Columbus, Galena, Centennial, Northern Brewer – Tolerant: Perle, Magnum, Fuggle, Newport • If disease is not widespread, remove severely diseased plants • Canopy management to reduce wetness/humidity – Remove basal growth, , careful use of cover crops, irrigation • Fungicide applications during disease conducive weather, particularly wet weather > about 42-46F David Gent USDA-ARS Corvallis, Oregon