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Epidemiology of Eyespot, Stripe Rustand Soilborne Wheat Mosaic

Tim MurrayPlant Pathologist

Goals for Today

Discuss basic principles of plant disease epidemiology

Describe three important wheat diseases with different epidemiological characteristics

Discuss control options for each disease relative to their epidemiology

better understand why we do what we do to control diseases

Epidemiology

Epidemiology

= the study of disease in populations 

Epidemic

= increase in disease intensity in a host population over time and space

Vanderplank (1963)

Survival:  overwintering/oversummering

Formation ofsurvival structures

Colonization/Growth and Reproduction

The Generalized Disease Cycle

Primary inoculum

Dissemination

Inoculation

Penetration

Infection

Primary Cycle

Secondary Cycle

Types of disease cycles:

Principles of Epidemiology

Single‐cycle (Monocyclic) diseases  

‐ primary inoculum only 

Multiple‐cycle (Polycyclic) diseases‐ primary & secondary inoculum 

Multiple‐cycle diseases have greater potential for rapid epidemic development than single‐cycle diseases

Modeling Epidemics

Logistic Model

Time

Log phase

Lag phase

Stationary phase

Disease Intensity

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Quantifying Disease

Disease progress curve= disease intensity over time

Disease intensity

Time

Quantifying Disease

Why use disease progress curves?

‐ Compare control measures

‐ Compare effect of environment on disease development

‐ Predict future disease development

Disease forecasting for improved control

X=XoRt Time

Rate of disease increaseInitial Inoculum

Modeling Monocyclic Epidemics

Time 

Disease

Slope = XoR

Amount of Disease

Simple interest diseases

X = X0ert

Modeling Polycyclic Epidemics

X = disease at time tX0= initial inoculumr = rate of disease 

increase t  = timee = base of natural log

money at time t

initial investmentinterest rate

X=Xoert Time

Rate of Disease IncreaseInitial Inoculum

Modeling Polycyclic Epidemics

Natural log

Compound interest diseases 

Time 

Disease

Inoculum increases within each season and disease builds‐up across years

monocyclic in one season and polycyclic across seasons

‐ typical of perennial plants, but not always

e.g. mistletoe, Dutch elm disease

Polyetic Epidemics

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Comparing Epidemic Types

Net blotch on barleySclerotium rolfsii on bean

Dutch elm disease Apple powdery mildew

Monocyclic:  X = X0Rt

Polycyclic: X = X0ert

Two ways to reduce X (disease):

•Reduce the initial inoculum X0•Reduce the rate of disease development 

(R or r)

Managing Epidemics

Effect of X0 on Epidemic Development

X0 depends upon:

• inoculum from previous crops within a field

• inoculum from crops in adjacent fields

X0 is affected by:

• destroying infested plant debris• removing diseased plants• chemical seed treatments• protective fungicides• race‐specific disease resistance• biological control agents targeted at initial inoculum

Effect of X0 on Epidemic Development

Time 

Disease X0

½X0T

Effect of X0 on Epidemic Development

delay onset and reduce the duration of the epidemic

Effect of r (R) on Epidemic Development

r depends upon:

• reproductive potential of the pathogen• virulence of the pathogen• susceptibility of the host• conduciveness of environment

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r is affected by:• non‐specific disease resistance• systemic fungicides• cultural practices that alter environment• removal of diseased plants

Effect of r (R) on Epidemic Development Effect of r on Epidemic Development

Time 

Disease

Large r

Small r

Slow the rate of spread of the epidemic

Disease Simulation

Plant Disease Development ‐Arneson, P.A. 2001 Plant Disease Epidemiology: Temporal Aspects. The Plant Health Instructor. DOI: 10.1094/PHI‐A‐2001‐0524‐01 (Revised 2011)

Disease Simulation

Scenarios:1. Compare the effect of rate of disease increase, r,with the same starting inoculum, X0r = 0.15 (polycyclic), 0.05 (monocyclic)X0 = 0.01 (1%)

Disease Simulation

Scenarios:2. Compare the effect of X0 with the same rr = 0.15X0 = 0.01 (1%), 0.001 (0.1%)

Disease Simulation

Scenarios:3. Compare the effect of reducing X0 when r is high r = 0.15X0 = 0.01 (1%), 0.001 (0.1%), 0.0001 (0.01%)

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Disease Simulation

Scenarios:4. Compare the effect of reducing X0 when r is lowr = 0.05X0 = 0.01 (1%), 0.001 (0.1%), 0.0001 (0.01%)

Disease Simulation

Scenarios:5. Compare the effect of reducing both r and X0 for a polycyclic diseaser = 0.15, 0.075 X0 = 0.01 (1%), 0.001 (0.1%)

Integrated Control

Time 

Disease

Reduce both X0 and r to delay onset (shorten the epidemic) and reduce rate of spread (less disease)

Eyespot or Strawbreaker Foot Rot

Eyespot Lodging Eyespot Pathogens 

O. yallundaeO. acuformis

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Sporulation on strawOct.

Eyespot Disease Cycle

Rain‐splash spreads spores

Infection and colonization of leaf sheaths 

Dec.

Colonization of true stems

May

Death ofinfectedstems June

Survival in straw Aug.

1°

2°

Factors Affecting Eyespot

Autumn temperatures

Rainfall

Snow cover

Stripe RustStripe Rust

Courtesy X. Chen

The Wheat Rusts

Stripe rust (yellow rust) ‐ cool season:  50‐64°F Puccinia striiformis f. sp. tritici 

Leaf rust (brown rust) ‐moderate:  68‐77°FPuccinia triticina

Stem rust (black rust) ‐ warm season:  75‐86°FPuccinia graminis f. sp. tritici

All require dew for spore germination & infection

Stripe Rust Disease Cycle

Cereal Disease LabT. Murray

T. MurrayAeciospores on barberry

Infection of grass host

Pycniosporeson barberry

Urediniospores

Basidiospores

Teliospores on wheat residue

Teliospores

Cereal Disease Lab

Infection of barberry

2°

1°

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Factors Affecting Stripe Rust

Favorable temps/moisture for infection‐ temps of 50‐64°F w/6 hrs of dew‐ cool temps best for disease development, but less important than infection

Fall infection‐ susceptible plants in fall

Winter survival‐ temperatures during Dec‐Feb

Stripe Rust Update – December 2015

1st update by Dr. Chen in January 2016 

What we know so far:Rust intensity during summer 2015 was relatively low and carryover inoculum was minimal

Dry fall conditions have not been favorable for rust development

Low potential for rust at this point

Going forward:Monitor temperatures through December and January

Soilborne Wheat MosaicSoilborne Wheat Mosaic Virus‐ SBWMV

Soilborne wheat mosaic (SBWM) discovered in 1919 in Illinois  Rosette disease

Polymyxa identified as the vector in 1960s

First identified in Walla Walla area in spring 2008, but reported in Umatilla Co. in 2005

‐ Reported in the Willamette valley in 1994

Localized in relatively small area ‐ unknown how widely distributed in county or state

A major problem in the Great Plains and NE US

SBWMV

SBWMV was identified at the Arlington, Virginia Experiment Farm in 1925

‐ Important site of much early research

‐ Now  the home of the Pentagon

apsnet.org

SBWM ‐ Symptoms

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SBWM ‐ Symptoms SBWM – Biology

Disease of fall‐sown wheat

Transmitted by Polymyxa graminis

acts like other soilborne diseases in terms of distribution within fields and spread

Infection occurs in the fall and symptoms appear in early spring

‐ symptoms fade and plants appear to recover as temperature increases in spring

Damage remains and yield is reduced

Polymyxa graminis

P. graminis infects root hairs and then invades root tissue forming resting spores

Wikipedia.orgJ. Deacon, Univ. Edinburgh

SBWM – Disease Cycle

Resting spores containing SBWMV 

virus in soil Resting spores germinate

Zoospores swim to nearby root

Zoospores encyst on root, penetrate 

& infectVirus replication in plant roots and stems

Plasmodium grows in cortical cells

Resting spores w/SBWMV in 

dead plant roots

Systemic spread in xylem

2°

1°

Disease Comparison

InoculumDisease Primary Secondary Type

Eyespot

Stripe rust

SBWMV

Yes

Yes

Yes

Not important

Yes

Not important

Monocyclic

Polycyclic

Polyetic

Eyespot Control Options

Cultural practices

→seeding date

Resistant varieties

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Resistance to Eyespot, Pullman, WA 2015

Variety/LineDisease Index

Yieldbu/A

Test wtlb/bu

Lodging % Variety/Line

Disease Index

Yield bu/A

Test wtlb/bu

Lodging%

WA 8177 46.4 140.0 58.4 30 MT1257 64.1 113.4 59.0 48OR2080637 47.2 127.6 57.6 20 ARS010669‐2C 64.8 104.3 58.0 13WA8212 49.3 126.0 58.1 18 IDO1209DH 65.0 118.6 60.3 13DAS003 50.7 127.2 58.9 20 WA8232 65.4 136.0 59.5 18

ARS06135‐9C 51.0 107.9 61.1 75 IDO1005 68.4 126.0 58.4 23

WA8234 52.0 135.1 60.0 45 UI Silver 68.9 115.6 59.0 45OR2100081H 52.6 118.0 59.4 13 A060126‐35C 70.3 99.8 59.5 82SY62‐21 52.7 147.4 60.8 15 WA8206 70.5 120.2 61.2 58Madsen 54.5 126.5 58.9 3 MTCS1204 71.3 100.9 60.3 40WA 8187 56.0 134.0 59.0 10 WA8169 71.4 128.2 56.7 53SY96‐2 57.6 129.1 60.0 25 WA8233 72.4 124.0 57.6 52OR2080641 57.9 163.5 59.2 15 SY71‐4 72.6 149.6 57.9 18SY13#38 58.0 110.7 60.5 30 MT1265 73.6 110.2 59.1 50

OR2101043 59.3 119.3 58.0 13 Eltan 74.2 94.7 56.6 78

DAS004 59.4 135.7 57.6 33 UI SRG 74.8 85.1 56.4 904J071366‐1 60.4 121.7 55.4 80 010263‐10‐3C 74.8 135.9 57.9 70OR2090473 60.8 143.1 57.9 10 MT1078 76.3 134.3 59.3 25OR2100940 60.8 154.4 58.4 23 MT1286 78.0 111.0 60.4 50IDO1101 60.8 122.3 59.5 85 MTS1224 80.0 113.1 59.6 62IDO1108DH 63.3 133.9 56.7 25 Mean 63.3 124.1 58.8ARS060123‐31C 64.0 118.9 59.7 78 LSD 0.05 13.2 20.5 1.4

Eyespot Resistant Winter VarietiesWSCIA 2015‐16 Winter Portfolio

• AP700CL• AP Legacy• ARS Chrystal• ARS Selbu• Brundage 96• Cara• Chukar• Coda• Jasper• LCS‐Azimut• Madsen

• Masami• Norwest 553 • ORCF‐102• Otto• Puma• Rosalyn • Tubbs 06 • WB 456 • WB 523 • WB 528• WB 1066CL

Soft white, Hard red, Club

Eyespot Control Options

Cultural practices

seeding date

Resistant varieties

Foliar fungicides

When to Spray?

“the 10% rule”

• Collect enough plants at spray time to give 50 stems

• Wash and separate into healthy and diseased

• Consider spraying when 5/50 are diseased

Sporulation on strawOct.

Eyespot Disease Cycle

Rain‐splash spreads spores

Infection and colonization of leaf sheaths 

Dec.

Colonization of true stems

May

Death ofinfectedstems June

Survival in straw Aug.

Spray Time 

What  to Spray?

Tilt + Topsin‐M (4 oz + 10 oz)(propiconazole + thiophanate‐methyl)

Alto + Topsin‐M (3.0‐5.5 oz + 10 oz)(cyproconazole + thiophanate‐methyl)

Priaxor (6 oz)(pyraclostrobin + fluxapyroxad)

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Fungicides for Eyespot Control, Knodel Farms, Ralston, WA 2015

TreatmentRate 

prod/ac

Lesion severity0 ‐ 4

% infected stems0 – 100

Disease index0 ‐ 100

Yieldbu/ac

Test weight lbs/bu

Priaxor 8 fl oz. 1.9 64.8 31.0 47.2 56.6

Tilt + Topsin‐M

4 fl oz + 20 fl oz

2.1 79.4 41.6 50.7 56.8

Alto 5.5 fl oz. 2.1 81.4 42.6 48.4 56.6

Untreated control

‐ 2.2 87.5 48.3 46.3 56.3

LSD NS 12.0 10.5 NS NS

P‐value 0.16 0.01 0.02 0.42 0.896

Fungicides for Eyespot Control, Warren Farms, Dayton, WA 2015

TreatmentRate 

prod/ac

Lesion severity0 ‐ 4

% infected stems0 ‐ 100

Disease index0 ‐ 100

Yieldbu/ac

Test weight lbs/bu

Priaxor 8 fl oz 1.7 65.2 27.5 74.6 54.9

Tilt + Topsin‐M

4 fl oz + 20 fl oz

2.0 90.4 44.3 69.5 54.7

Alto 5.5 fl oz. 1.8 89.6 39.9 67.4 55.0

Untreated control

‐ 1.9 85.3 41.1 72.8 55.2

LSD NS 15.9 12.4 NS NS

P‐value 0.32 0.01 0.05 0.65 0.96

Stripe Rust Control Options

Plant disease resistant varieties preferably those with HTAP resistanceCulturalGreen bridge management‐ reduce volunteer & grassy weeds 

Avoid early plantingAvoid excessive irrigation‐ furrow better than sprinkler

Balanced fertility; don’t over fertilize with NMonitor rust forecast, scout fields, spray fungicides when necessary

Stripe Rust Reactions

striperustalert.wsu.edu

Stripe Rust Resistant Winter Varieties, WSCIA 2015‐16 Portfolio

Rating Varieties

R (1,2) Amber, AP700CL, Bobtail, Bruneau, Cara, Chukar, Farnum, LCS Azimut, Legion, Madsen, Norwest 553, Otto, Rosalyn, Selbu, Skiles, Sprinter, SY Ovation, WB1066CL, WB1070CL

MR (3,4) Bitterroot, Bruehl, Chrystal, Coda, Crescent, Curiosity CL+, Finley, Jasper, Keldin, Kaseberg, LCS Artdeco, LCS Colonia, Mary, Masami, ORCF 102, Puma, Stephens, SY 107, UICF Brundage, WB456, WB523, WB528, WB Junction, Whetstone, SY Clearstone CL2

M (5) AP Badger, AP503 CL2, Boundary, Eltan, Ladd, Mela CL+, Xerpha, 

MS (6,7) AP Legacy, Bauermeister, Brundage 96, ORCF 103, WB Rimrock, Tubbs 06, WB Arrowhead,

S (8,9) Goetze

Soft white, Hard red, Club

Stripe Rust Resistant Spring VarietiesWSCIA 2015‐16 Portfolio

Rating Varieties

R (1,2) Seahawk, Dayn, JD, SY Basalt, WB6121, WB9518, 

MR (3,4) Alum, Chet, Diva, Glee, Louise, SY Steelhead, UI Platinum, Whit 

M (5) Bullseye, UI Stone, WB6341

MS (6,7) Cabernet, Kelse, Snow Crest, UI Pettit, WB1035 CL+, WB Hartline, WB Paloma

S (8,9) Babe, SY605CL2, WB Fuzion

Soft white, Hard red, Hard white

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Fungicides

Monitor forecasts and development of rust Scout, Scout, Scout!

Spray when necessary:Spray when susceptible varieties have 1 to 5% active rust

What Does 5% Rust Look Like?

15S

25S

10M/S2-5R

40S90S 50S

5S

Fungicides – NCERA‐184Class Active ingredient Product

Rate/A  

(fl. oz)Stripe rust Leaf rust Stem rust

Harvest Restriction

Strobilu

rin Picoxystrobin Aproach SC 6.0 ‐ 12 E VG ‐‐

Feekes 10.5 and 45 days

Fluoxastrobin Evito 480 SC 2.0 – 4.0 ‐‐ VG ‐‐Feekes 10.5 and 40 days

Pyraclostrobin Headline SC 6.0 ‐ 9.0 E2 E G Feekes 10.5

Triazole

Metconazole Caramba 0.75 SL 10.0 ‐ 17.0 E E E 30 days

Propiconazole Tilt 3.6 EC3 4.0 VG VG VG Feekes 10.5

Prothioconazole Proline 480 SC 5.0 ‐ 5.7 ‐‐ VG VG 30 days

Tebuconazole Folicur 3.6 F3 4.0 E E E 30 days

ProthioconazoleTebuconazole

Prosaro 421 SC 6.5 ‐ 8.2 E E E 30 days

Mixed

 modes of action4

MetconazolePyraclostrobin

TwinLine 1.75 EC 7.0 – 9.0 E E VG Feekes 10.5

FluxapyroxadPyraclostrobin

Priaxor 4.0 ‐ 8.0 E2 E VG Feekes 10.5

PropiconazoleAzoxystrobin

Quilt 200 SC3 10.5 ‐ 14.0 E E VG Feekes 10.5

PropiconazoleAzoxystrobin

Quilt Xcel 2.2 SE 10.5 ‐ 14.0 E E VG Feekes 10.5

ProthioconazoleTrifloxystrobin

Stratego YLD 4.0 VG VG VG 35 days

TebuconazoleTrifloxystrobin

Absolute 500 SC 5.0 VG E VG 35 days

SBWM – Management

Disease resistance – only practical option

Soil fumigation partially effective, but not cost‐effective

SBWM Variety Trial, Umatilla, OR 2011

Collaborative project with Phil Hamm, Mike Flowers, & Arron Carter

Irrigated circle on sandy soil with severe SBWM symptoms in 2010

SBWM Variety Trial, Umatilla, OR 2011

Aerial photos 31 May 2011

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SBWM Variety Trials, Hermiston 

Plot ratings taken in May on a 0 to 10 scale:

1 = no symptoms; 10 = 100% disease with discoloration and stunting

WB1066CL0

Coda 9

SBWM Variety Trial, Umatilla, OR 2011

Soft wheattrial

Hard wheattrial

Ladd borderGenesisWB-ArrrowheadWhetstoneAP503CL2

Ladd border

Ladd border

Skiles

LaddORCF-103

SY Ovation

Cara

WB-528

SBWMV Variety Trial, 2013Hermiston, OR

SBWM Variety Trial 2011‐15 Summary

Resistant:

AP Paladin ORCF‐101Altigo ORCF‐103AP503 CL2 PumaEsperia SY OvationGenesis UI/WSU HuffmanKeldin WB‐ArrowheadLadd WB‐JunctionLCS Aymeric Whetstone

Soft white, Hard red

SBWMV Conclusions

Very uniform plots with heavy disease pressure Reliable ratings of variety reaction and yield  for SBWM 

Most PNW‐adapted varieties with inadequate resistance if disease is severeVarieties rated 4.0 or less should do wellSeveral promising lines are in development in PNW breeding programs

Molecular marker is available and being used in WA to select lines with resistance

Questions?