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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?
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